Spatial Variability of Wet Troposphere Delays Over Inland Water Bodies

NASA Astrophysics Data System (ADS)

Mehran, Ali; Clark, Elizabeth A.; Lettenmaier, Dennis P.

2017-11-01

Satellite radar altimetry has enabled the study of water levels in large lakes and reservoirs at a global scale. The upcoming Surface Water and Ocean Topography (SWOT) satellite mission (scheduled launch 2020) will simultaneously measure water surface extent and elevation at an unprecedented accuracy and resolution. However, SWOT retrieval accuracy will be affected by a number of factors, including wet tropospheric delay—the delay in the signal's passage through the atmosphere due to atmospheric water content. In past applications, the wet tropospheric delay over large inland water bodies has been corrected using atmospheric moisture profiles based on atmospheric reanalysis data at relatively coarse (tens to hundreds of kilometers) spatial resolution. These products cannot resolve subgrid variations in wet tropospheric delays at the spatial resolutions (of 1 km and finer) that SWOT is intended to resolve. We calculate zenith wet tropospheric delays (ZWDs) and their spatial variability from Weather Research and Forecasting (WRF) numerical weather prediction model simulations at 2.33 km spatial resolution over the southwestern U.S., with attention in particular to Sam Rayburn, Ray Hubbard, and Elephant Butte Reservoirs which have width and length dimensions that are of order or larger than the WRF spatial resolution. We find that spatiotemporal variability of ZWD over the inland reservoirs depends on climatic conditions at the reservoir location, as well as distance from ocean, elevation, and surface area of the reservoir, but that the magnitude of subgrid variability (relative to analysis and reanalysis products) is generally less than 10 mm.

Real-Time Tropospheric Delay Estimation using IGS Products

NASA Astrophysics Data System (ADS)

Stürze, Andrea; Liu, Sha; Söhne, Wolfgang

2014-05-01

The Federal Agency for Cartography and Geodesy (BKG) routinely provides zenith tropospheric delay (ZTD) parameter for the assimilation in numerical weather models since more than 10 years. Up to now the results flowing into the EUREF Permanent Network (EPN) or E-GVAP (EUMETNET EIG GNSS water vapour programme) analysis are based on batch processing of GPS+GLONASS observations in differential network mode. For the recently started COST Action ES1206 about "Advanced Global Navigation Satellite Systems tropospheric products for monitoring severe weather events and climate" (GNSS4SWEC), however, rapid updates in the analysis of the atmospheric state for nowcasting applications require changing the processing strategy towards real-time. In the RTCM SC104 (Radio Technical Commission for Maritime Services, Special Committee 104) a format combining the advantages of Precise Point Positioning (PPP) and Real-Time Kinematic (RTK) is under development. The so-called State Space Representation approach is defining corrections, which will be transferred in real-time to the user e.g. via NTRIP (Network Transport of RTCM via Internet Protocol). Meanwhile messages for precise orbits, satellite clocks and code biases compatible to the basic PPP mode using IGS products are defined. Consequently, the IGS Real-Time Service (RTS) was launched in 2013 in order to extend the well-known precise orbit and clock products by a real-time component. Further messages e.g. with respect to ionosphere or phase biases are foreseen. Depending on the level of refinement, so different accuracies up to the RTK level shall be reachable. In co-operation of BKG and the Technical University of Darmstadt the real-time software GEMon (GREF EUREF Monitoring) is under development. GEMon is able to process GPS and GLONASS observation and RTS product data streams in PPP mode. Furthermore, several state-of-the-art troposphere models, for example based on numerical weather prediction data, are implemented. Hence, it

Seasonal Variability Study of the Tropospheric Zenithal Delay in the South America using regional Numerical Weather Prediction model

NASA Astrophysics Data System (ADS)

Sapucci, L. F.; Monico, J. G.; Machado, L. T.

2007-05-01

In 2010 a new navigation and administration system of the air traffic, denominated CNS-ATM (Communication Navigation Surveillance - Air Traffic Management) should be running operationally in South America. This new system will basically employ the positioning techniques by satellites to the management and air traffic control. However, the efficiency of this new system demands the knowledge of the behavior of the atmosphere, consequently, an appropriated Zenithal Tropospheric Delay (ZTD) modeling in a regional scale. The predictions of ZTD values from Numeric Weather Prediction (NWP), denominated here dynamic modeling, is an alternative to model the atmospheric gases effects in the radio-frequency signals in real time. Brazilian Center for Weather Forecasting and Climate Studies (CPTEC) of the National Institute for Space Research (INPE), jointly with researchers from UNESP (Sao Paulo State University), has generated operationally prediction of ZTD values to South America Continent (available in the electronic address http:satelite.cptec.inpe.br/htmldocs/ztd/zenithal.htm). The available regional version is obtained using ETA model (NWP model with horizontal resolution of 20 km and 42 levels in the vertical). The application of NWP permit assess the temporal and spatial variation of ZTD values, which is an important characteristic of this techniques. The aim of the present paper is to investigate the ZTD seasonal variability over South America continent. A variability analysis of the ZTD components [hydrostatic(ZHD) and wet(ZWD)] is also presented, as such as discussion of main factors that influence this variation in this region. The hydrostatic component variation is related with atmospheric pressure oscillation, which is influenced by relief and high pressure centers that prevail over different region of the South America continent. The wet component oscillation is due to the temperature and humidity variability, which is also influenced by relief and by synoptic

Utilization of GPS Tropospheric Delays for Climate Research

NASA Astrophysics Data System (ADS)

Suparta, Wayan

2017-05-01

The tropospheric delay is one of the main error sources in Global Positioning Systems (GPS) and its impact plays a crucial role in near real-time weather forecasting. Accessibility and accurate estimation of this parameter are essential for weather and climate research. Advances in GPS application has allowed the measurements of zenith tropospheric delay (ZTD) in all weather conditions and on a global scale with fine temporal and spatial resolution. In addition to the rapid advancement of GPS technology and informatics and the development of research in the field of Earth and Planetary Sciences, the GPS data has been available free of charge. Now only required sophisticated processing techniques but user friendly. On the other hand, the ZTD parameter obtained from the models or measurements needs to be converted into precipitable water vapor (PWV) to make it more useful as a component of weather forecasting and analysis atmospheric hazards such as tropical storms, flash floods, landslide, pollution, and earthquake as well as for climate change studies. This paper addresses the determination of ZTD as a signal error or delay source during the propagation from the satellite to a receiver on the ground and is a key driving force behind the atmospheric events. Some results in terms of ZTD and PWV will be highlighted in this paper.

InSAR tropospheric delay mitigation by GPS observations: A case study in Tokyo area

NASA Astrophysics Data System (ADS)

Xu, Caijun; Wang, Hua; Ge, Linlin; Yonezawa, Chinatsu; Cheng, Pu

2006-03-01

Like other space geodetic techniques, interferometric synthetic aperture radar (InSAR) is limited by the variations of tropospheric delay noise. In this paper, we analyze the double-difference (DD) feature of tropospheric delay noise in SAR interferogram. By processing the ERS-2 radar pair, we find some tropospheric delay fringes, which have similar patterns with the GMS-5 visible-channel images acquired at almost the same epoch. Thirty-five continuous GPS (CGPS) stations are distributed in the radar scene. We analyze the GPS data by GIPSY-OASIS (II) software and extract the wet zenith delay (WZD) parameters at each station at the same epoch with the master and the slave image, respectively. A cosine mapping function is applied to transform the WZD to wet slant delay (WSD) in line-of-sight direction. Based on the DD WSD parameters, we establish a two-dimensional (2D) semi-variogram model, with the parameters 35.2, 3.6 and 0.88. Then we predict the DD WSD parameters by the kriging algorithm for each pixel of the interferogram, and subtract it from the unwrapped phase. Comparisons between CGPS and InSAR range changes in LOS direction show that the root of mean squares (RMS) decreased from 1.33 cm before correction to 0.87 cm after correction. From the result, we can conclude that GPS WZD parameters can be effectively used to identify and mitigate the large-scale InSAR tropospheric delay noise if the spatial resolution of GPS stations is dense enough.

Performance Assessment of a Gnss-Based Troposphere Path Delay Estimation Software

NASA Astrophysics Data System (ADS)

Mariotti, Gilles; Avanzi, Alessandro; Graziani, Alberto; Tortora, Paolo

2013-04-01

Error budgets of Deep Space Radio Science experiments are heavily affected by interplanetary and Earth transmission media, that corrupt, due to their non-unitary refraction index, the radiometric information of signals coming from the spacecraft. An effective removal of these noise sources is crucial to achieve the accuracy and signal stability levels required by radio science applications. Depending on the nature of these refractions, transmission media are divided into dispersive (that consists of ionized particles, i.e. Solar Wind and Ionosphere) and non-dispersive ones (the refraction is caused by neutral particles: Earth Troposphere). While dispersive noises are successfully removed by multifrequency combinations (as for GPS with the well-known ionofree combination), the most accurate estimation of tropospheric noise is obtained using microwave radiometers (MWR). As the use of MWRs suffers from strong operational limitations (rain and heavy clouds conditions), the GNSS-based processing is still widely adopted to provide a cost-effective, all-weather condition estimation of the troposphere path delay. This work describes the development process and reports the results of a GNSS analysis code specifically aimed to the estimation of the path delays introduced by the troposphere above deep space complexes, to be used for the calibration of Range and Doppler radiometric data. The code has been developed by the Radio Science Laboratory of the University of Bologna in Forlì, and is currently in the testing phase. To this aim, the preliminary output is compared to MWR measurements and IGS TropoSINEX products in order to assess the reliability of the estimate. The software works using ionofree carrier-phase observables and is based upon a double-difference approach, in which the GNSS receiver placed nearby the Deep Space receiver acts as the rover station. Several baselines are then created with various IGS and EUREF stations (master or reference stations) in order to

ITG: A New Global GNSS Tropospheric Correction Model

PubMed Central

Yao, Yibin; Xu, Chaoqian; Shi, Junbo; Cao, Na; Zhang, Bao; Yang, Junjian

2015-01-01

Tropospheric correction models are receiving increasing attentions, as they play a crucial role in Global Navigation Satellite System (GNSS). Most commonly used models to date include the GPT2 series and the TropGrid2. In this study, we analyzed the advantages and disadvantages of existing models and developed a new model called the Improved Tropospheric Grid (ITG). ITG considers annual, semi-annual and diurnal variations, and includes multiple tropospheric parameters. The amplitude and initial phase of diurnal variation are estimated as a periodic function. ITG provides temperature, pressure, the weighted mean temperature (Tm) and Zenith Wet Delay (ZWD). We conducted a performance comparison among the proposed ITG model and previous ones, in terms of meteorological measurements from 698 observation stations, Zenith Total Delay (ZTD) products from 280 International GNSS Service (IGS) station and Tm from Global Geodetic Observing System (GGOS) products. Results indicate that ITG offers the best performance on the whole. PMID:26196963

Integrity modelling of tropospheric delay models

NASA Astrophysics Data System (ADS)

Rózsa, Szabolcs; Bastiaan Ober, Pieter; Mile, Máté; Ambrus, Bence; Juni, Ildikó

2017-04-01

The effect of the neutral atmosphere on signal propagation is routinely estimated by various tropospheric delay models in satellite navigation. Although numerous studies can be found in the literature investigating the accuracy of these models, for safety-of-life applications it is crucial to study and model the worst case performance of these models using very low recurrence frequencies. The main objective of the INTegrity of TROpospheric models (INTRO) project funded by the ESA PECS programme is to establish a model (or models) of the residual error of existing tropospheric delay models for safety-of-life applications. Such models are required to overbound rare tropospheric delays and should thus include the tails of the error distributions. Their use should lead to safe error bounds on the user position and should allow computation of protection levels for the horizontal and vertical position errors. The current tropospheric model from the RTCA SBAS Minimal Operational Standards has an associated residual error that equals 0.12 meters in the vertical direction. This value is derived by simply extrapolating the observed distribution of the residuals into the tail (where no data is present) and then taking the point where the cumulative distribution has an exceedance level would be 10-7.While the resulting standard deviation is much higher than the estimated standard variance that best fits the data (0.05 meters), it surely is conservative for most applications. In the context of the INTRO project some widely used and newly developed tropospheric delay models (e.g. RTCA MOPS, ESA GALTROPO and GPT2W) were tested using 16 years of daily ERA-INTERIM Reanalysis numerical weather model data and the raytracing technique. The results showed that the performance of some of the widely applied models have a clear seasonal dependency and it is also affected by a geographical position. In order to provide a more realistic, but still conservative estimation of the residual

The New Tropospheric Product of the International GNSS Service

NASA Technical Reports Server (NTRS)

Byun, Sung H.; Bar-Sever, Yoaz E.; Gendt, Gerd

2005-01-01

We compare this new approach for generating the IGS tropospheric products with the previous approach, which was based on explicit combination of total zenith delay contributions from the IGS ACs. The new approach enables the IGS to rapidly generate highly accurate and highly reliable total zenith delay time series for many hundreds of sites, thus increasing the utility of the products to weather modelers, climatologists, and GPS analysts. In this paper we describe this new method, and discuss issues of accuracy, quality control, utility of the new products and assess its benefits.

Tropospheric Delay Raytracing Applied in VLBI Analysis

NASA Astrophysics Data System (ADS)

MacMillan, D. S.; Eriksson, D.; Gipson, J. M.

2013-12-01

Tropospheric delay modeling error continues to be one of the largest sources of error in VLBI analysis. For standard operational solutions, we use the VMF1 elevation-dependent mapping functions derived from ECMWF data. These mapping functions assume that tropospheric delay at a site is azimuthally symmetric. As this assumption does not reflect reality, we have determined the raytrace delay along the signal path through the troposphere for each VLBI quasar observation. We determined the troposphere refractivity fields from the pressure, temperature, specific humidity and geopotential height fields of the NASA GSFC GEOS-5 numerical weather model. We discuss results from analysis of the CONT11 R&D and the weekly operational R1+R4 experiment sessions. When applied in VLBI analysis, baseline length repeatabilities were better for 66-72% of baselines with raytraced delays than with VMF1 mapping functions. Vertical repeatabilities were better for 65% of sites.

Troposphere Delay Raytracing Applied in VLBI Analysis

NASA Astrophysics Data System (ADS)

Eriksson, David; MacMillan, Daniel; Gipson, John

2014-12-01

Tropospheric delay modeling error is one of the largest sources of error in VLBI analysis. For standard operational solutions, we use the VMF1 elevation-dependent mapping functions derived from European Centre for Medium Range Forecasting (ECMWF) data. These mapping functions assume that tropospheric delay at a site is azimuthally symmetric. As this assumption does not reflect reality, we have instead determined the raytrace delay along the signal path through the three-dimensional troposphere refractivity field for each VLBI quasar observation. We calculated the troposphere refractivity fields from the pressure, temperature, specific humidity, and geopotential height fields of the NASA GSFC GEOS-5 numerical weather model. We discuss results using raytrace delay in the analysis of the CONT11 R&D sessions. When applied in VLBI analysis, baseline length repeatabilities were better for 70% of baselines with raytraced delays than with VMF1 mapping functions. Vertical repeatabilities were better for 2/3 of all stations. The reference frame scale bias error was 0.02 ppb for raytracing versus 0.08 ppb and 0.06 ppb for VMF1 and NMF, respectively.

Latitudinal dependence of diurnal and seasonal variations in the tropospheric zenith delay observed from GPS measurements within the longitudinal sector of 50oE to 130oE.

NASA Astrophysics Data System (ADS)

Raju, Suresh; Saha, Korak; Anupama, K.; Parameswaran, Krishnaswamy

Ground based GPS finds potential applications in many atmospheric studies such as the spatial distribution of columnar water vapor as well as tidal oscillations in the atmosphere. As the zenith tropospheric delay (ZTD) derived from GPS data is a function of atmospheric pressure, temperature and watervapor, the effect of atmospheric oscillations could reflect more promi-nently in its temporal variations. The GPS data with very high temporal resolution (5 min.) from thirteen IGS stations in the longitudinal sector of 50o-130oE are used to establish its potential for studying the atmospheric tidal, intra-seasonal and planetary oscillations. Very prominent tidal (diurnal and semi-diurnal) oscillations observed at all these stations, with am-plitude of the diurnal variation as ˜0.5-12+0.5 mm and that of the semi-diurnal variation in the range ˜0.1-5+0.2 mm. Although 90% of the delay is contributed by the dry atmospheric pressure (which shows prominent semi-diurnal oscillations) the tidal oscillations in the ZTD is dominated by the diurnal component. This effect could be attributed to the temporal variations of atmospheric water vapor in a diurnal scale. The amplitude of these variations in general is largest near the equator and decreases with increase in latitude. Interestingly, this latitudinal trend matches very well with the latitude variation of the precipitable water vapor (as well as the actual precipitation) in this longitudinal region. Though the values of ZTD at stations very close to equator stations do not show any prominent seasonal variation, as the latitude increases the annual variation in ZTD becomes more distinct. A prominent peak in ZTD is observed during the July-August period, which matches well with the annual variation of atmospheric water vapor. This shows that the diurnal and seasonal variation of ZTD is mainly governed by the corresponding variations in atmospheric water vapor, even though its contribution to the total delay is around 10

Applying Kalman filtering to investigate tropospheric effects in VLBI

NASA Astrophysics Data System (ADS)

Soja, Benedikt; Nilsson, Tobias; Karbon, Maria; Heinkelmann, Robert; Liu, Li; Lu, Cuixian; Andres Mora-Diaz, Julian; Raposo-Pulido, Virginia; Xu, Minghui; Schuh, Harald

2014-05-01

Very Long Baseline Interferometry (VLBI) currently provides results, e.g., estimates of the tropospheric delays, with a delay of more than two weeks. In the future, with the coming VLBI2010 Global Observing System (VGOS) and increased usage of electronic data transfer, it is planned that the time between observations and results is decreased. This may, for instance, allow the integration of VLBI-derived tropospheric delays into numerical weather prediction models. Therefore, future VLBI analysis software packages need to be able to process the observational data autonomously in near real-time. For this purpose, we have extended the Vienna VLBI Software (VieVS) by a Kalman filter module. This presentation describes the filter and discusses its application for tropospheric studies. Instead of estimating zenith wet delays as piece-wise linear functions in a least-squares adjustment, the Kalman filter allows for more sophisticated stochastic modeling. We start with a random walk process to model the time-dependent behavior of the zenith wet delays. Other possible approaches include the stochastic model described by turbulence theory, e.g. the model by Treuhaft and Lanyi (1987). Different variance-covariance matrices of the prediction error, depending on the time of the year and the geographic latitude, have been tested. In winter and closer to the poles, lower variances and covariances are appropriate. The horizontal variations in tropospheric delays have been investigated by comparing three different strategies: assumption of a horizontally stratified troposphere, using north and south gradients modeled, e.g., as Gauss-Markov processes, and applying a turbulence model assuming correlations between observations in different azimuths. By conducting Monte-Carlo simulations of current standard VLBI networks and of future VGOS networks, the different tropospheric modeling strategies are investigated. For this purpose, we use the simulator module of VieVS which takes into

Impact of selected troposphere models on Precise Point Positioning convergence

NASA Astrophysics Data System (ADS)

Kalita, Jakub; Rzepecka, Zofia

2016-04-01

The Precise Point Positioning (PPP) absolute method is currently intensively investigated in order to reach fast convergence time. Among various sources that influence the convergence of the PPP, the tropospheric delay is one of the most important. Numerous models of tropospheric delay are developed and applied to PPP processing. However, with rare exceptions, the quality of those models does not allow fixing the zenith path delay tropospheric parameter, leaving difference between nominal and final value to the estimation process. Here we present comparison of several PPP result sets, each of which based on different troposphere model. The respective nominal values are adopted from models: VMF1, GPT2w, MOPS and ZERO-WET. The PPP solution admitted as reference is based on the final troposphere product from the International GNSS Service (IGS). The VMF1 mapping function was used for all processing variants in order to provide capability to compare impact of applied nominal values. The worst case initiates zenith wet delay with zero value (ZERO-WET). Impact from all possible models for tropospheric nominal values should fit inside both IGS and ZERO-WET border variants. The analysis is based on data from seven IGS stations located in mid-latitude European region from year 2014. For the purpose of this study several days with the most active troposphere were selected for each of the station. All the PPP solutions were determined using gLAB open-source software, with the Kalman filter implemented independently by the authors of this work. The processing was performed on 1 hour slices of observation data. In addition to the analysis of the output processing files, the presented study contains detailed analysis of the tropospheric conditions for the selected data. The overall results show that for the height component the VMF1 model outperforms GPT2w and MOPS by 35-40% and ZERO-WET variant by 150%. In most of the cases all solutions converge to the same values during first

A directional model of tropospheric horizontal gradients in Global Positioning System and its application for particular weather scenarios

NASA Astrophysics Data System (ADS)

Masoumi, Salim; McClusky, Simon; Koulali, Achraf; Tregoning, Paul

2017-04-01

Improper modeling of horizontal tropospheric gradients in GPS analysis induces errors in estimated parameters, with the largest impact on heights and tropospheric zenith delays. The conventional two-axis tilted plane model of horizontal gradients fails to provide an accurate representation of tropospheric gradients under weather conditions with asymmetric horizontal changes of refractivity. A new parametrization of tropospheric gradients whereby an arbitrary number of gradients are estimated as discrete directional wedges is shown via simulations to significantly improve the accuracy of recovered tropospheric zenith delays in asymmetric gradient scenarios. In a case study of an extreme rain event that occurred in September 2002 in southern France, the new directional parametrization is able to isolate the strong gradients in particular azimuths around the GPS stations consistent with the "V" shape spatial pattern of the observed precipitation. In another study of a network of GPS stations in the Sierra Nevada region where highly asymmetric tropospheric gradients are known to exist, the new directional model significantly improves the repeatabilities of the stations in asymmetric gradient situations while causing slightly degraded repeatabilities for the stations in normal symmetric gradient conditions. The average improvement over the entire network is ˜31%, while the improvement for one of the worst affected sites P631 is ˜49% (from 8.5 mm to 4.3 mm) in terms of weighted root-mean-square (WRMS) error and ˜82% (from -1.1 to -0.2) in terms of skewness. At the same station, the use of the directional model changes the estimates of zenith wet delay by 15 mm (˜25%).

Tropospheric nitrogen dioxide column retrieval from ground-based zenith-sky DOAS observations

NASA Astrophysics Data System (ADS)

Tack, F.; Hendrick, F.; Goutail, F.; Fayt, C.; Merlaud, A.; Pinardi, G.; Hermans, C.; Pommereau, J.-P.; Van Roozendael, M.

2015-01-01

We present an algorithm for retrieving tropospheric nitrogen dioxide (NO2) vertical column densities (VCDs) from ground-based zenith-sky (ZS) measurements of scattered sunlight. The method is based on a four-step approach consisting of (1) the Differential Optical Absorption Spectroscopy (DOAS) analysis of ZS radiance spectra using a fixed reference spectrum corresponding to low NO2 absorption, (2) the determination of the residual amount in the reference spectrum using a Langley-plot-type method, (3) the removal of the stratospheric content from the daytime total measured slant column based on stratospheric VCDs measured at sunrise and sunset, and simulation of the rapid NO2 diurnal variation, (4) the retrieval of tropospheric VCDs by dividing the resulting tropospheric slant columns by appropriate air mass factors (AMFs). These steps are fully characterized and recommendations are given for each of them. The retrieval algorithm is applied on a ZS dataset acquired with a Multi-AXis (MAX-) DOAS instrument during the Cabauw (51.97° N, 4.93° E, sea level) Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI) held from the 10 June to the 21 July 2009 in the Netherlands. A median value of 7.9 × 1015 molec cm-2 is found for the retrieved tropospheric NO2 VCDs, with maxima up to 6.0 × 1016 molec cm-2. The error budget assessment indicates that the overall error σTVCD on the column values is less than 28%. In case of low tropospheric contribution, σTVCD is estimated to be around 39% and is dominated by uncertainties in the determination of the residual amount in the reference spectrum. For strong tropospheric pollution events, σTVCD drops to approximately 22% with the largest uncertainties on the determination of the stratospheric NO2 abundance and tropospheric AMFs. The tropospheric VCD amounts derived from ZS observations are compared to VCDs retrieved from off-axis and direct-sun measurements of the same MAX-DOAS instrument as well as to

Tropospheric nitrogen dioxide column retrieval from ground-based zenith-sky DOAS observations

NASA Astrophysics Data System (ADS)

Tack, F.; Hendrick, F.; Goutail, F.; Fayt, C.; Merlaud, A.; Pinardi, G.; Hermans, C.; Pommereau, J.-P.; Van Roozendael, M.

2015-06-01

We present an algorithm for retrieving tropospheric nitrogen dioxide (NO2) vertical column densities (VCDs) from ground-based zenith-sky (ZS) measurements of scattered sunlight. The method is based on a four-step approach consisting of (1) the differential optical absorption spectroscopy (DOAS) analysis of ZS radiance spectra using a fixed reference spectrum corresponding to low NO2 absorption, (2) the determination of the residual amount in the reference spectrum using a Langley-plot-type method, (3) the removal of the stratospheric content from the daytime total measured slant column based on stratospheric VCDs measured at sunrise and sunset, and simulation of the rapid NO2 diurnal variation, (4) the retrieval of tropospheric VCDs by dividing the resulting tropospheric slant columns by appropriate air mass factors (AMFs). These steps are fully characterized and recommendations are given for each of them. The retrieval algorithm is applied on a ZS data set acquired with a multi-axis (MAX-) DOAS instrument during the Cabauw (51.97° N, 4.93° E, sea level) Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI) held from 10 June to 21 July 2009 in the Netherlands. A median value of 7.9 × 1015 molec cm-2 is found for the retrieved tropospheric NO2 VCDs, with maxima up to 6.0 × 1016 molec cm-2. The error budget assessment indicates that the overall error σTVCD on the column values is less than 28%. In the case of low tropospheric contribution, σTVCD is estimated to be around 39% and is dominated by uncertainties in the determination of the residual amount in the reference spectrum. For strong tropospheric pollution events, σTVCD drops to approximately 22% with the largest uncertainties on the determination of the stratospheric NO2 abundance and tropospheric AMFs. The tropospheric VCD amounts derived from ZS observations are compared to VCDs retrieved from off-axis and direct-sun measurements of the same MAX-DOAS instrument as well as to data

Tropospheric delays derived from Kalman-filtered VLBI observations

NASA Astrophysics Data System (ADS)

Soja, Benedikt; Nilsson, Tobias; Karbon, Maria; Balidakis, Kyriakos; Lu, Cuixian; Anderson, James; Glaser, Susanne; Liu, Li; Mora-Diaz, Julian A.; Raposo-Pulido, Virginia; Xu, Minghui; Heinkelmann, Robert; Schuh, Harald

2015-04-01

One of the most important error sources in the products of space geodetic techniques is the troposphere. Currently, it is not possible to model the rapid variations in the path delay caused by water vapor with sufficient accuracy, thus it is necessary to estimate these delays in the data analysis. Very long baseline interferometry (VLBI) is well suited to determine wet delays with high accuracy and precision. Compared to GNSS, the analysis does not need to deal with effects related to code biases, multipath, satellite orbit mismodeling, or antenna phase center variations that are inherent in GNSS processing. VLBI data are usually analyzed by estimating geodetic parameters in a least squares adjustment. However, once the VLBI Global Observing System (VGOS) will have become operational, algorithms providing real-time capability, for instance a Kalman filter, should be preferable for data analysis. Even today, certain advantages of such a filter, for example, allowing stochastic modeling of geodetic parameters, warrant its application. The estimation of tropospheric wet delays, in particular, greatly benefits from the stochastic approach of the filter. In this work we have investigated the benefits of applying a Kalman filter in the VLBI data analysis for the determination of tropospheric parameters. The VLBI datasets considered are the CONT campaigns, which demonstrate state-of-the-art capabilities of the VLBI system. They are unique in following a continuous observation schedule over 15 days and in having data recorded at higher bandwidth than usual. The large amount of observations leads to a very high quality of geodetic products. CONT campaigns are held every three years; we have analyzed all CONT campaigns between 2002 and 2014 for this study. In our implementation of a Kalman filter in the VLBI software VieVS@GFZ, the zenith wet delays (ZWD) are modeled as random walk processes. We have compared the resulting time series to corresponding ones obtained from

The Tropospheric Products of the International VLBI Service for Geodesy and Astrometry

NASA Technical Reports Server (NTRS)

Heinkelmann, Robert; Schwatke, Christian

2010-01-01

The IVS runs two tropospheric products: The IVS tropospheric parameter rapid combination monitors the zenith wet delay (ZWD) and zenith total delay (ZTD) of the rapid turnaround sessions R1 and R4. Goal of the combination is the identification and the exclusion of outliers by comparison and the assessment of the precision of current VLBI solutions in terms of tropospheric parameters. The rapid combination is done on a weekly basis four weeks after the observation files are released on IVS Data Centers. Since tropospheric and geodetic parameters, such as vertical station components, can significantly correlate, the consistency of the ZTD can be a measure of the consistency of the corresponding TRF as well. The ZWD mainly rely on accurate atmospheric pressure data. Thus, besides estimation techniques, modeling and analyst s noise, ZWD reflects differences in the atmospheric pressure data applied to the VLBI analysis. The second product, called tropospheric parameter long-term combination, aims for an accurate determination of climatological signals, such as trends of the atmospheric water vapor observed by VLBI. Therefore, the long-term homogeneity of atmospheric pressure data plays a crucial role for this product. The paper reviews the methods applied and results achieved so far and describes the new maintenance through DGFI.

The estimation of the propagation delay through the troposphere from microwave radiometer data. [very long base interferometry

NASA Technical Reports Server (NTRS)

Moran, J. M.; Rosen, B. R.

1980-01-01

The uncertainity in propagation delay estimates is due primarily to tropospheric water, the total amount and vertical distribution of which is variable. Because water vapor both delays and attenuates microwave signals, the propagation delay, or wet path length, can be estimated from the microwave brightness temperature near the 22.235 GHz transition of water vapor. The data from a total of 240 radiosonde launches taken simultaneously were analyzed. Estimates of brightness temperature at 19 and 22 GHz and wet path length were made from these data. The wet path length in the zenith direction could be estimated from the surface water vapor density to an accuracy of 5 cm for the summer data and 2 cm for winter data. Using the brightness temperatures, the wet path could be estimated to an accuracy of 0.3 cm. Two dual frequency radiometers were refurbished in order to test these techniques. These radiometers were capable of measuring the difference in the brightness temperature at 30 deg elevation angle and at the zenith to an accuracy of about 1 K. In August 1975, 45 radiosondes were launched over an 11 day period. Brightness temperature measurements were made simultaneously at 19 and 22 GHz with the radiometers. The rms error for the estimation of wet path length from surface meteorological parameters was 3.2 cm, and from the radiometer brightness temperatures, 1.5 cm.

Analysis of Zenith Tropospheric Delay above Europe based on long time series derived from the EPN data

NASA Astrophysics Data System (ADS)

Baldysz, Zofia; Nykiel, Grzegorz; Figurski, Mariusz; Szafranek, Karolina; Kroszczynski, Krzysztof; Araszkiewicz, Andrzej

2015-04-01

In recent years, the GNSS system began to play an increasingly important role in the research related to the climate monitoring. Based on the GPS system, which has the longest operational capability in comparison with other systems, and a common computational strategy applied to all observations, long and homogeneous ZTD (Zenith Tropospheric Delay) time series were derived. This paper presents results of analysis of 16-year ZTD time series obtained from the EPN (EUREF Permanent Network) reprocessing performed by the Military University of Technology. To maintain the uniformity of data, analyzed period of time (1998-2013) is exactly the same for all stations - observations carried out before 1998 were removed from time series and observations processed using different strategy were recalculated according to the MUT LAC approach. For all 16-year time series (59 stations) Lomb-Scargle periodograms were created to obtain information about the oscillations in ZTD time series. Due to strong annual oscillations which disturb the character of oscillations with smaller amplitude and thus hinder their investigation, Lomb-Scargle periodograms for time series with the deleted annual oscillations were created in order to verify presence of semi-annual, ter-annual and quarto-annual oscillations. Linear trend and seasonal components were estimated using LSE (Least Square Estimation) and Mann-Kendall trend test were used to confirm the presence of linear trend designated by LSE method. In order to verify the effect of the length of time series on the estimated size of the linear trend, comparison between two different length of ZTD time series was performed. To carry out a comparative analysis, 30 stations which have been operating since 1996 were selected. For these stations two periods of time were analyzed: shortened 16-year (1998-2013) and full 18-year (1996-2013). For some stations an additional two years of observations have significant impact on changing the size of linear

IVS Tropospheric Parameters: Comparison with DORIS and GPS for CONT02

NASA Technical Reports Server (NTRS)

Schuh, Harald; Snajdrova, Kristyna; Boehm, Johannes; Willis, Pascal; Engelhardt, Gerald; Lanotte, Roberto; Tomasi, Paolo; Negusini, Monia; MacMillan, Daniel; Vereshchagina, Iraida

2004-01-01

In April 2002 the IVS (International VLBI Service for Geodesy and Astrometry) set up the Pilot Project - Tropospheric Parameters, and the Institute of Geodesy and Geophysics (IGG), Vienna, was put in charge of coordinating the project. Seven IVS Analysis Centers have joined the project and regularly submitted their estimates of tropospheric parameters (wet and total zenith delays, horizontal gradients) for all IVS-R1 mid IVS-R4 sessions since January 1st, 2002. The individual submissions are combined by a two-step procedure to obtain stable, robust and highly accurate tropospheric parameter time series with one hour resolution (internal accuracy: 2-4 ram). Starting with July 2003, the combined tropospheric estimates became operational IVS products. In the second half of October 2002 the VLBI campaign CONT02 was observed with 8 stations participating around the globe. At four of them (Gilmore Creek, U.S.A.; Hartebeesthoek, South Africa; Kokee Park, U.S.A.; Ny-Alesund, Norway) also total zenith delays from DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) are available and these estimates are compared with those from the IGS (International GPS Service) and the IVS. The distance from the DORIS beacons to the co-located GPS and VLBI stations is around 2 km or less for the four sites mentioned above.

Evaluation of Empirical Tropospheric Models Using Satellite-Tracking Tropospheric Wet Delays with Water Vapor Radiometer at Tongji, China

PubMed Central

Wang, Miaomiao; Li, Bofeng

2016-01-01

An empirical tropospheric delay model, together with a mapping function, is commonly used to correct the tropospheric errors in global navigation satellite system (GNSS) processing. As is well-known, the accuracy of tropospheric delay models relies mainly on the correction efficiency for tropospheric wet delays. In this paper, we evaluate the accuracy of three tropospheric delay models, together with five mapping functions in wet delays calculation. The evaluations are conducted by comparing their slant wet delays with those measured by water vapor radiometer based on its satellite-tracking function (collected data with large liquid water path is removed). For all 15 combinations of three tropospheric models and five mapping functions, their accuracies as a function of elevation are statistically analyzed by using nine-day data in two scenarios, with and without meteorological data. The results show that (1) no matter with or without meteorological data, there is no practical difference between mapping functions, i.e., Chao, Ifadis, Vienna Mapping Function 1 (VMF1), Niell Mapping Function (NMF), and MTT Mapping Function (MTT); (2) without meteorological data, the UNB3 is much better than Saastamoinen and Hopfield models, while the Saastamoinen model performed slightly better than the Hopfield model; (3) with meteorological data, the accuracies of all three tropospheric delay models are improved to be comparable, especially for lower elevations. In addition, the kinematic precise point positioning where no parameter is set up for tropospheric delay modification is conducted to further evaluate the performance of tropospheric delay models in positioning accuracy. It is shown that the UNB3 model is best and can achieve about 10 cm accuracy for the N and E coordinate component while 20 cm accuracy for the U coordinate component no matter the meteorological data is available or not. This accuracy can be obtained by the Saastamoinen model only when meteorological data is

Extracting Independent Local Oscillatory Geophysical Signals by Geodetic Tropospheric Delay

NASA Technical Reports Server (NTRS)

Botai, O. J.; Combrinck, L.; Sivakumar, V.; Schuh, H.; Bohm, J.

2010-01-01

Zenith Tropospheric Delay (ZTD) due to water vapor derived from space geodetic techniques and numerical weather prediction simulated-reanalysis data exhibits non-linear and non-stationary properties akin to those in the crucial geophysical signals of interest to the research community. These time series, once decomposed into additive (and stochastic) components, have information about the long term global change (the trend) and other interpretable (quasi-) periodic components such as seasonal cycles and noise. Such stochastic component(s) could be a function that exhibits at most one extremum within a data span or a monotonic function within a certain temporal span. In this contribution, we examine the use of the combined Ensemble Empirical Mode Decomposition (EEMD) and Independent Component Analysis (ICA): the EEMD-ICA algorithm to extract the independent local oscillatory stochastic components in the tropospheric delay derived from the European Centre for Medium-Range Weather Forecasts (ECMWF) over six geodetic sites (HartRAO, Hobart26, Wettzell, Gilcreek, Westford, and Tsukub32). The proposed methodology allows independent geophysical processes to be extracted and assessed. Analysis of the quality index of the Independent Components (ICs) derived for each cluster of local oscillatory components (also called the Intrinsic Mode Functions (IMFs)) for all the geodetic stations considered in the study demonstrate that they are strongly site dependent. Such strong dependency seems to suggest that the localized geophysical signals embedded in the ZTD over the geodetic sites are not correlated. Further, from the viewpoint of non-linear dynamical systems, four geophysical signals the Quasi-Biennial Oscillation (QBO) index derived from the NCEP/NCAR reanalysis, the Southern Oscillation Index (SOI) anomaly from NCEP, the SIDC monthly Sun Spot Number (SSN), and the Length of Day (LoD) are linked to the extracted signal components from ZTD. Results from the synchronization

The effect of tropospheric fluctuations on the accuracy of water vapor radiometry

NASA Technical Reports Server (NTRS)

Wilcox, J. Z.

1992-01-01

Line-of-sight path delay calibration accuracies of 1 mm are needed to improve both angular and Doppler tracking capabilities. Fluctuations in the refractivity of tropospheric water vapor limit the present accuracies to about 1 nrad for the angular position and to a delay rate of 3x10(exp -13) sec/sec over a 100-sec time interval for Doppler tracking. This article describes progress in evaluating the limitations of the technique of water vapor radiometry at the 1-mm level. The two effects evaluated here are: (1) errors arising from tip-curve calibration of WVR's in the presence of tropospheric fluctuations and (2) errors due to the use of nonzero beamwidths for water vapor radiometer (WVR) horns. The error caused by tropospheric water vapor fluctuations during instrument calibration from a single tip curve is 0.26 percent in the estimated gain for a tip-curve duration of several minutes or less. This gain error causes a 3-mm bias and a 1-mm scale factor error in the estimated path delay at a 10-deg elevation per 1 g/cm(sup 2) of zenith water vapor column density present in the troposphere during the astrometric observation. The error caused by WVR beam averaging of tropospheric fluctuations is 3 mm at a 10-deg elevation per 1 g/cm(sup 2) of zenith water vapor (and is proportionally higher for higher water vapor content) for current WVR beamwidths (full width at half maximum of approximately 6 deg). This is a stochastic error (which cannot be calibrated) and which can be reduced to about half of its instantaneous value by time averaging the radio signal over several minutes. The results presented here suggest two improvements to WVR design: first, the gain of the instruments should be stabilized to 4 parts in 10(exp 4) over a calibration period lasting 5 hours, and second, the WVR antenna beamwidth should be reduced to about 0.2 deg. This will reduce the error induced by water vapor fluctuations in the estimated path delays to less than 1 mm for the elevation range

Comparison of Kalman filter estimates of zenith atmospheric path delays using the global positioning system and very long baseline interferometry

NASA Technical Reports Server (NTRS)

Tralli, David M.; Lichten, Stephen M.; Herring, Thomas A.

1992-01-01

Kalman filter estimates of zenith nondispersive atmospheric path delays at Westford, Massachusetts, Fort Davis, Texas, and Mojave, California, were obtained from independent analyses of data collected during January and February 1988 using the GPS and VLBI. The apparent accuracy of the path delays is inferred by examining the estimates and covariances from both sets of data. The ability of the geodetic data to resolve zenith path delay fluctuations is determined by comparing further the GPS Kalman filter estimates with corresponding wet path delays derived from water vapor radiometric data available at Mojave over two 8-hour data spans within the comparison period. GPS and VLBI zenith path delay estimates agree well within one standard deviation formal uncertainties (from 10-20 mm for GPS and 3-15 mm for VLBI) in four out of the five possible comparisons, with maximum differences of 5 and 21 mm over 8- to 12-hour data spans.

Tropospheric delay ray tracing applied in VLBI analysis

NASA Astrophysics Data System (ADS)

Eriksson, David; MacMillan, D. S.; Gipson, John M.

2014-12-01

Tropospheric delay modeling error continues to be one of the largest sources of error in VLBI (very long baseline interferometry) analysis. For standard operational solutions, we use the VMF1 elevation-dependent mapping functions derived from European Centre for Medium-Range Weather Forecasts data. These mapping functions assume that tropospheric delay at a site is azimuthally symmetric. As this assumption is not true, we have instead determined the ray trace delay along the signal path through the troposphere for each VLBI quasar observation. We determined the troposphere refractivity fields from the pressure, temperature, specific humidity, and geopotential height fields of the NASA Goddard Space Flight Center Goddard Earth Observing System version 5 numerical weather model. When applied in VLBI analysis, baseline length repeatabilities were improved compared with using the VMF1 mapping function model for 72% of the baselines and site vertical repeatabilities were better for 11 of 13 sites during the 2 week CONT11 observing period in September 2011. When applied to a larger data set (2011-2013), we see a similar improvement in baseline length and also in site position repeatabilities for about two thirds of the stations in each of the site topocentric components.

Effect of densifying the GNSS GBAS network on monitoring the troposphere zenith total delay and precipitable water vapour content during severe weather events

NASA Astrophysics Data System (ADS)

Kapłon, Jan; Stankunavicius, Gintautas

2016-04-01

The dense ground based augmentation networks can provide the important information for monitoring the state of neutral atmosphere. The GNSS&METEO research group at Wroclaw University of Environmental and Life Sciences (WUELS) is operating the self-developed near real-time service estimating the troposphere parameters from GNSS data for the area of Poland. The service is operational since December 2012 and it's results calculated from ASG-EUPOS GBAS network (120 stations) data are supporting the EGVAP (http://egvap.dmi.dk) project. At first the zenith troposphere delays (ZTD) were calculated in hourly intervals, but since September 2015 the service was upgraded to include SmartNet GBAS network (Leica Geosystems Polska - 150 stations). The upgrade included as well: increasing the result interval to 30 minutes, upgrade from Bernese GPS Software v. 5.0 to Bernese GNSS Software v. 5.2 and estimation of the ZTD and it's horizontal gradients. Processing includes nowadays 270 stations. The densification of network from 70 km of mean distance between stations to 40 km created the opportunity to investigate on it's impact on resolution of estimated ZTD and integrated water vapour content (IWV) fields during the weather events of high intensity. Increase in density of ZTD measurements allows to define better the meso-scale features within different synoptic systems (e.g. frontal waves, meso-scale convective systems, squall lines etc). These meso-scale structures, as a rule are short living but fast developing and hardly predictable by numerical models. Even so, such limited size systems can produce very hazardous phenomena - like widespread squalls and thunderstorms, tornadoes, heavy rains, snowfalls, hail etc. because of prevalence of Cb clouds with high concentration of IWV. Study deals with two meteorological events: 2015-09-01 with the devastating squalls and rainfall bringing 2M Euro loss of property in northern Poland and 2015-10-12 with the very active front bringing

GPS Water Vapor Tomography Based on Accurate Estimations of the GPS Tropospheric Parameters

NASA Astrophysics Data System (ADS)

Champollion, C.; Masson, F.; Bock, O.; Bouin, M.; Walpersdorf, A.; Doerflinger, E.; van Baelen, J.; Brenot, H.

2003-12-01

The Global Positioning System (GPS) is now a common technique for the retrieval of zenithal integrated water vapor (IWV). Further applications in meteorology need also slant integrated water vapor (SIWV) which allow to precisely define the high variability of tropospheric water vapor at different temporal and spatial scales. Only precise estimations of IWV and horizontal gradients allow the estimation of accurate SIWV. We present studies developed to improve the estimation of tropospheric water vapor from GPS data. Results are obtained from several field experiments (MAP, ESCOMPTE, OHM-CV, IHOP, .). First IWV are estimated using different GPS processing strategies and results are compared to radiosondes. The role of the reference frame and the a priori constraints on the coordinates of the fiducial and local stations is generally underestimated. It seems to be of first order in the estimation of the IWV. Second we validate the estimated horizontal gradients comparing zenith delay gradients and single site gradients. IWV, gradients and post-fit residuals are used to construct slant integrated water delays. Validation of the SIWV is under progress comparing GPS SIWV, Lidar measurements and high resolution meteorological models (Meso-NH). A careful analysis of the post-fit residuals is needed to separate tropospheric signal from multipaths. The slant tropospheric delays are used to study the 3D heterogeneity of the troposphere. We develop a tomographic software to model the three-dimensional distribution of the tropospheric water vapor from GPS data. The software is applied to the ESCOMPTE field experiment, a dense network of 17 dual frequency GPS receivers operated in southern France. Three inversions have been successfully compared to three successive radiosonde launches. Good resolution is obtained up to heights of 3000 m.

Tropospheric Delay from VLBI and GNSS Measurements

NASA Astrophysics Data System (ADS)

Gubanov, V. S.

2018-02-01

Using an updated version of the QUASAR software package developed at the Institute of Applied Astronomy of the Russian Academy of Sciences, we have processed the VLBI observations within the international CONT14 program (May 6-20, 2014), in which a global network of 17 stations was involved (a total of 250 000 observations). The package update concerned the optimization of data structure and the refinement of stochastic models for the random variations in wet tropospheric delay and atomic clock difference. The main goal of this paper is to compare the VLBI determinations of the tropospheric delay with its independent determinations using global navigation satellite systems (GNSS). We show that both these determinations agree well between themselves only in the case of a global analysis of the VLBI observations, where the VLBI station coordinates are also refined, along with the tropospheric delay and the clock synchronization and Earth orientation parameters. If, alternatively, the station coordinates are insufficiently accurate and are not refined from VLBI observations, then it is appropriate not to determine the tropospheric delay from these observations, but to take it from the publicly accessible independent GNSS data. However, this requires that the VLBI and GNSS techniques operate simultaneously at a common observing site. We have established the shortcomings of the universally accepted method of stabilizing the global solution associated with the absence of a criterion for choosing reference stations and radio sources. Two ways of their elimination are proposed: (i) introducing a coordinated list of weight factors for the errors in the coordinates of such stations and sources into the stabilization algorithm and (ii) adopting a coordinated list of stations and sources the refinement of whose coordinates is not required at all for a certain time.

On the Impact of Multi-GNSS Observations on Real-Time Precise Point Positioning Zenith Total Delay Estimates

NASA Astrophysics Data System (ADS)

Ding, Wenwu; Teferle, Norman; Kaźmierski, Kamil; Laurichesse, Denis; Yuan, Yunbin

2017-04-01

Observations from multiple Global Navigation Satellite System (GNSS) can improve the performance of real-time (RT) GNSS meteorology, in particular of the Zenith Total Delay (ZTD) estimates. RT ZTD estimates in combination with derived precipitable water vapour estimates can be used for weather now-casting and the tracking of severe weather events. While a number of published literature has already highlighted this positive development, in this study we describe an operational RT system for extracting ZTD using a modified version of the PPP-wizard (with PPP denoting Precise Point Positioning). Multi-GNSS, including GPS, GLONASS and Galileo, observation streams are processed using a RT PPP strategy based on RT satellite orbit and clock products from the Centre National d'Etudes Spatiales (CNES). A continuous experiment for 30 days was conducted, in which the RT observation streams of 20 globally distributed stations were processed. The initialization time and accuracy of the RT troposphere products using single and/or multi-system observations were evaluated. The effect of RT PPP ambiguity resolution was also evaluated. The results revealed that the RT troposphere products based on single system observations can fulfill the requirements of the meteorological application in now-casting systems. We noted that the GPS-only solution is better than the GLONASS-only solution in both initialization and accuracy. While the ZTD performance can be improved by applying RT PPP ambiguity resolution, the inclusion of observations from multiple GNSS has a more profound effect. Specifically, we saw that the ambiguity resolution is more effective in improving the accuracy, whereas the initialization process can be better accelerated by multi-GNSS observations. Combining all systems, RT troposphere products with an average accuracy of about 8 mm in ZTD were achieved after an initialization process of approximately 9 minutes, which supports the application of multi-GNSS observations

A Demonstration of Precise Calibration of Tropospheric Delay Fluctuations with Water Vapor Radiometers

NASA Technical Reports Server (NTRS)

Teitelbaum, L. P.; Keihm, S. J.; Linfield, R. P.; Mahoney, M. J.; Resch, G. M.

1996-01-01

The ability of water vapor radiometers (WVRs) to calibrate changes in tropospheric delay was demonstrated during very long baseline radio interferometer (VLBI) observations at Goldstone, California. WVR measurements reduced the observed VLBI delay variations over a 13 hr period by a factor of approx. = 2.5. When applied to shorter time scales, a approx. = 50% reduction in 100-700 s delay variations was achieved during conditions of high tropospheric activity. Thermal WVR noise precluded calibration of short time scale delay fluctuations during quiet tropospheric conditions.

Ray-traced tropospheric total slant delays for GNSS processing

NASA Astrophysics Data System (ADS)

Hobiger, T.; Ichikawa, R.; Hatanaka, Y.; Yutsudo, T.; Iwashita, C.; Miyahara, B.; Koyama, Y.; Kondo, T.

2007-12-01

Numerical weather models have undergone an improvement of spatial and temporal resolution in the recent years, which made their use for GNSS applications feasible. Ray-tracing through such models permits the computation of total troposphere delays and ray-bending angles. At the National Institute of Information and Communications Technology (NICT), Japan the so-called KAshima RAy-tracing Tools (KARAT) have been developed which allow to obtain troposphere delay corrections in real-time. Together with fine-mesh weather models from the Japanese Meteorological Agency (JMA) huge parts of the East Asian region, including Japan, Korea, Taiwan and East China, can be covered. The Japanese GEONET with its more than 1300 GNSS receivers represent an ideal test-bed for the evaluation of the performance of KARAT. In cooperation with the Geographical Survey Institute (GSI), Japan more than 1.6 billion observations, covering measurements from July 1st until August 31st, 2006, were processed and the corresponding troposphere delays were used to modify the original RINEX files by subtraction of code- and phase delays. These modified observations were processed by a dedicated analysis run of the GEONET operation center, taking advantage of the computer cluster at GSI. First results from this study, together with an in-depth discussion about the assets and drawbacks of the reduction of troposphere total slant delays will be given in this presentation. Additionally an overview about KARAT, the treatment of observational data and the impact of future refined numerical weather models on GNSS analysis will be included in this contribution.

Heterogeneity of residuals from comparison of GNSS and raytracing based troposphere slant total delays, as an indicator of hydrometeors

NASA Astrophysics Data System (ADS)

Hordyniec, Paweł; Rohm, Witold; Kapłon, Jan

2017-04-01

Post-fit residuals from Precise Point Positioning (PPP) carry the troposphere information except of multipath and residual antenna Phase Centre Variations (PCVs), when precise satellite orbits and clocks were introduced. Slant total delay (STD) of GNSS signal is a sum of a priori slant hydrostatic delay, estimated wet delay, asymetry introduced by the estimated zenith total delay (ZTD) horizontal gradients and a post-fit residual reduced by the systematic (site-dependant) effect. It was revealed, that application of reduced post-fit residuls to the slant total delays obtained from GNSS data processing increases the discrepancy with slant delays from raytracing (RT) through the Numerical Weather Model (NWM). One of the possible sources of that effect is neglected influence of hydrometeors in raytracing procedures. If the assumption of hydrometeor information existence in the PPP post-fit residuals is correct, we expect the diversity of slant delay discrepancies for satellite-receiver rays pointing or not the hydrometeors. Paper presents the spatial and temporal correlation analysis of the slant delay residuals (GNSS - RT) with hydrometeor phenomena recorded during the COST ES1206 GNSS4SWEC benchmark period (May 5th - June 29th, 2013). It presents the discussion of the results from different GNSS PPP slant delay estimation approaches including coordinates unconstraining or heavy constraining, and the calculation of slant delays with and without ZTD horizontal gradients estimation.

VLBI-derived troposphere parameters during CONT08

NASA Astrophysics Data System (ADS)

Heinkelmann, R.; Böhm, J.; Bolotin, S.; Engelhardt, G.; Haas, R.; Lanotte, R.; MacMillan, D. S.; Negusini, M.; Skurikhina, E.; Titov, O.; Schuh, H.

2011-07-01

Time-series of zenith wet and total troposphere delays as well as north and east gradients are compared, and zenith total delays ( ZTD) are combined on the level of parameter estimates. Input data sets are provided by ten Analysis Centers (ACs) of the International VLBI Service for Geodesy and Astrometry (IVS) for the CONT08 campaign (12-26 August 2008). The inconsistent usage of meteorological data and models, such as mapping functions, causes systematics among the ACs, and differing parameterizations and constraints add noise to the troposphere parameter estimates. The empirical standard deviation of ZTD among the ACs with regard to an unweighted mean is 4.6 mm. The ratio of the analysis noise to the observation noise assessed by the operator/software impact (OSI) model is about 2.5. These and other effects have to be accounted for to improve the intra-technique combination of VLBI-derived troposphere parameters. While the largest systematics caused by inconsistent usage of meteorological data can be avoided and the application of different mapping functions can be considered by applying empirical corrections, the noise has to be modeled in the stochastic model of intra-technique combination. The application of different stochastic models shows no significant effects on the combined parameters but results in different mean formal errors: the mean formal errors of the combined ZTD are 2.3 mm (unweighted), 4.4 mm (diagonal), 8.6 mm [variance component (VC) estimation], and 8.6 mm (operator/software impact, OSI). On the one hand, the OSI model, i.e. the inclusion of off-diagonal elements in the cofactor-matrix, considers the reapplication of observations yielding a factor of about two for mean formal errors as compared to the diagonal approach. On the other hand, the combination based on VC estimation shows large differences among the VCs and exhibits a comparable scaling of formal errors. Thus, for the combination of troposphere parameters a combination of the two

Performance Analysis of BDS Medium-Long Baseline RTK Positioning Using an Empirical Troposphere Model.

PubMed

Shu, Bao; Liu, Hui; Xu, Longwei; Qian, Chuang; Gong, Xiaopeng; An, Xiangdong

2018-04-14

For GPS medium-long baseline real-time kinematic (RTK) positioning, the troposphere parameter is introduced along with coordinates, and the model is ill-conditioned due to its strong correlation with the height parameter. For BeiDou Navigation Satellite System (BDS), additional difficulties occur due to its special satellite constellation. In fact, relative zenith troposphere delay (RZTD) derived from high-precision empirical zenith troposphere models can be introduced. Thus, the model strength can be improved, which is also called the RZTD-constrained RTK model. In this contribution, we first analyze the factors affecting the precision of BDS medium-long baseline RTK; thereafter, 15 baselines ranging from 38 km to 167 km in different troposphere conditions are processed to assess the performance of RZTD-constrained RTK. Results show that the troposphere parameter is difficult to distinguish from the height component, even with long time filtering for BDS-only RTK. Due to the lack of variation in geometry for the BDS geostationary Earth orbit satellite, the long convergence time of ambiguity parameters may reduce the height precision of GPS/BDS-combined RTK in the initial period. When the RZTD-constrained model was used in BDS and GPS/BDS-combined situations compared with the traditional RTK, the standard deviation of the height component for the fixed solution was reduced by 52.4% and 34.0%, respectively.

Performance Analysis of BDS Medium-Long Baseline RTK Positioning Using an Empirical Troposphere Model

PubMed Central

Liu, Hui; Xu, Longwei; Qian, Chuang; Gong, Xiaopeng; An, Xiangdong

2018-01-01

For GPS medium-long baseline real-time kinematic (RTK) positioning, the troposphere parameter is introduced along with coordinates, and the model is ill-conditioned due to its strong correlation with the height parameter. For BeiDou Navigation Satellite System (BDS), additional difficulties occur due to its special satellite constellation. In fact, relative zenith troposphere delay (RZTD) derived from high-precision empirical zenith troposphere models can be introduced. Thus, the model strength can be improved, which is also called the RZTD-constrained RTK model. In this contribution, we first analyze the factors affecting the precision of BDS medium-long baseline RTK; thereafter, 15 baselines ranging from 38 km to 167 km in different troposphere conditions are processed to assess the performance of RZTD-constrained RTK. Results show that the troposphere parameter is difficult to distinguish from the height component, even with long time filtering for BDS-only RTK. Due to the lack of variation in geometry for the BDS geostationary Earth orbit satellite, the long convergence time of ambiguity parameters may reduce the height precision of GPS/BDS-combined RTK in the initial period. When the RZTD-constrained model was used in BDS and GPS/BDS-combined situations compared with the traditional RTK, the standard deviation of the height component for the fixed solution was reduced by 52.4% and 34.0%, respectively. PMID:29661999

Application of troposphere model from NWP and GNSS data into real-time precise positioning

NASA Astrophysics Data System (ADS)

Wilgan, Karina; Hadas, Tomasz; Kazmierski, Kamil; Rohm, Witold; Bosy, Jaroslaw

2016-04-01

The tropospheric delay empirical models are usually functions of meteorological parameters (temperature, pressure and humidity). The application of standard atmosphere parameters or global models, such as GPT (global pressure/temperature) model or UNB3 (University of New Brunswick, version 3) model, may not be sufficient, especially for positioning in non-standard weather conditions. The possible solution is to use regional troposphere models based on real-time or near-real time measurements. We implement a regional troposphere model into the PPP (Precise Point Positioning) software GNSS-WARP (Wroclaw Algorithms for Real-time Positioning) developed at Wroclaw University of Environmental and Life Sciences. The software is capable of processing static and kinematic multi-GNSS data in real-time and post-processing mode and takes advantage of final IGS (International GNSS Service) products as well as IGS RTS (Real-Time Service) products. A shortcoming of PPP technique is the time required for the solution to converge. One of the reasons is the high correlation among the estimated parameters: troposphere delay, receiver clock offset and receiver height. To efficiently decorrelate these parameters, a significant change in satellite geometry is required. Alternative solution is to introduce the external high-quality regional troposphere delay model to constrain troposphere estimates. The proposed model consists of zenith total delays (ZTD) and mapping functions calculated from meteorological parameters from Numerical Weather Prediction model WRF (Weather Research and Forecasting) and ZTDs from ground-based GNSS stations using the least-squares collocation software COMEDIE (Collocation of Meteorological Data for Interpretation and Estimation of Tropospheric Pathdelays) developed at ETH Zurich.

Wet tropospheric delays forecast based on Vienna Mapping Function time series analysis

NASA Astrophysics Data System (ADS)

Rzepecka, Zofia; Kalita, Jakub

2016-04-01

It is well known that the dry part of the zenith tropospheric delay (ZTD) is much easier to model than the wet part (ZTW). The aim of the research is applying stochastic modeling and prediction of ZTW using time series analysis tools. Application of time series analysis enables closer understanding of ZTW behavior as well as short-term prediction of future ZTW values. The ZTW data used for the studies were obtained from the GGOS service hold by Vienna technical University. The resolution of the data is six hours. ZTW for the years 2010 -2013 were adopted for the study. The International GNSS Service (IGS) permanent stations LAMA and GOPE, located in mid-latitudes, were admitted for the investigations. Initially the seasonal part was separated and modeled using periodic signals and frequency analysis. The prominent annual and semi-annual signals were removed using sines and consines functions. The autocorrelation of the resulting signal is significant for several days (20-30 samples). The residuals of this fitting were further analyzed and modeled with ARIMA processes. For both the stations optimal ARMA processes based on several criterions were obtained. On this basis predicted ZTW values were computed for one day ahead, leaving the white process residuals. Accuracy of the prediction can be estimated at about 3 cm.

(abstract) A VLBI Test of Tropospheric Delay Calibration with WVRs

NASA Technical Reports Server (NTRS)

Linfield, R. P.; Teitelbaum, L. P.; Keihm, S. J.; Resch, G. M.; Mahoney, M. J.; Treuhaft, R. N.

1994-01-01

Dual frequency (S/X band) very long baseline interferometry (VLBI) observations were used to test troposphere calibration by water vapor radiometers (WVRs). Comparison of the VLBI and WVR measurements show a statistical agreement (specifically, their structure functions agree) on time scales less than 700 seconds. On longer time scales, VLBI instrumental errors become important. The improvement in VLBI residual delays from WVR calibration was consistent with the measured level of tropospheric fluctuations.

Measurements of tropospheric NO2 in Romania using a zenith-sky mobile DOAS system and comparisons with satellite observations.

PubMed

Constantin, Daniel-Eduard; Merlaud, Alexis; Van Roozendael, Michel; Voiculescu, Mirela; Fayt, Caroline; Hendrick, François; Pinardi, Gaia; Georgescu, Lucian

2013-03-20

In this paper we present a new method for retrieving tropospheric NO2 Vertical Column Density (VCD) from zenith-sky Differential Optical Absorption Spectroscopy (DOAS) measurements using mobile observations. This method was used during three days in the summer of 2011 in Romania, being to our knowledge the first mobile DOAS measurements peformed in this country. The measurements were carried out over large and different areas using a mobile DOAS system installed in a car. We present here a step-by-step retrieval of tropospheric VCD using complementary observations from ground and space which take into account the stratospheric contribution, which is a step forward compared to other similar studies. The detailed error budget indicates that the typical uncertainty on the retrieved NO2tropospheric VCD is less than 25%. The resulting ground-based data set is compared to satellite measurements from the Ozone Monitoring Instrument (OMI) and the Global Ozone Monitoring Experiment-2 (GOME-2). For instance, on 18 July 2011, in an industrial area located at 47.03°N, 22.45°E, GOME-2 observes a tropospheric VCD value of (3.4 ± 1.9) × 1015 molec./cm2, while average mobile measurements in the same area give a value of (3.4 ± 0.7) × 10(15) molec./cm2. On 22 August 2011, around Ploiesti city (44.99°N, 26.1°E), the tropospheric VCD observed by satellites is (3.3 ± 1.9) × 10(15) molec./cm2 (GOME-2) and (3.2 ± 3.2) × 10(15) molec./cm2 (OMI), while average mobile measurements give (3.8 ± 0.8) × 10(15) molec./cm2. Average ground measurements over "clean areas", on 18 July 2011, give (2.5 ± 0.6) × 10(15) molec./cm2 while the satellite observes a value of (1.8 ± 1.3) × 10(15) molec./cm2.

Measurements of Tropospheric NO2 in Romania Using a Zenith-Sky Mobile DOAS System and Comparisons with Satellite Observations

PubMed Central

Constantin, Daniel-Eduard; Merlaud, Alexis; Van Roozendael, Michel; Voiculescu, Mirela; Fayt, Caroline; Hendrick, François; Pinardi, Gaia; Georgescu, Lucian

2013-01-01

In this paper we present a new method for retrieving tropospheric NO2 Vertical Column Density (VCD) from zenith-sky Differential Optical Absorption Spectroscopy (DOAS) measurements using mobile observations. This method was used during three days in the summer of 2011 in Romania, being to our knowledge the first mobile DOAS measurements peformed in this country. The measurements were carried out over large and different areas using a mobile DOAS system installed in a car. We present here a step-by-step retrieval of tropospheric VCD using complementary observations from ground and space which take into account the stratospheric contribution, which is a step forward compared to other similar studies. The detailed error budget indicates that the typical uncertainty on the retrieved NO2tropospheric VCD is less than 25%. The resulting ground-based data set is compared to satellite measurements from the Ozone Monitoring Instrument (OMI) and the Global Ozone Monitoring Experiment-2 (GOME-2). For instance, on 18 July 2011, in an industrial area located at 47.03°N, 22.45°E, GOME-2 observes a tropospheric VCD value of (3.4 ± 1.9) × 1015 molec./cm2, while average mobile measurements in the same area give a value of (3.4 ± 0.7) × 1015 molec./cm2. On 22 August 2011, around Ploiesti city (44.99°N, 26.1°E), the tropospheric VCD observed by satellites is (3.3 ± 1.9) × 1015 molec./cm2 (GOME-2) and (3.2 ± 3.2) × 1015 molec./cm2 (OMI), while average mobile measurements give (3.8 ± 0.8) × 1015 molec./cm2. Average ground measurements over “clean areas”, on 18 July 2011, give (2.5 ± 0.6) × 1015 molec./cm2 while the satellite observes a value of (1.8 ± 1.3) × 1015 molec./cm2. PMID:23519349

Tropospheric products of the second GOP European GNSS reprocessing (1996-2014)

NASA Astrophysics Data System (ADS)

Dousa, Jan; Vaclavovic, Pavel; Elias, Michal

2017-09-01

In this paper, we present results of the second reprocessing of all data from 1996 to 2014 from all stations in International Association of Geodesy (IAG) Reference Frame Sub-Commission for Europe (EUREF) Permanent Network (EPN) as performed at the Geodetic Observatory Pecný (GOP). While the original goal of this research was to ultimately contribute to the realization of a new European Terrestrial Reference System (ETRS), we also aim to provide a new set of GNSS (Global Navigation Satellite System) tropospheric parameter time series with possible applications to climate research. To achieve these goals, we improved a strategy to guarantee the continuity of these tropospheric parameters and we prepared several variants of troposphere modelling. We then assessed all solutions in terms of the repeatability of coordinates as an internal evaluation of applied models and strategies and in terms of zenith tropospheric delays (ZTDs) and horizontal gradients with those of the ERA-Interim numerical weather model (NWM) reanalysis. When compared to the GOP Repro1 (first EUREF reprocessing) solution, the results of the GOP Repro2 (second EUREF reprocessing) yielded improvements of approximately 50 and 25 % in the repeatability of the horizontal and vertical components, respectively, and of approximately 9 % in tropospheric parameters. Vertical repeatability was reduced from 4.14 to 3.73 mm when using the VMF1 mapping function, a priori ZHD (zenith hydrostatic delay), and non-tidal atmospheric loading corrections from actual weather data. Raising the elevation cut-off angle from 3 to 7° and then to 10° increased RMS from coordinates' repeatability, which was then confirmed by independently comparing GNSS tropospheric parameters with the NWM reanalysis. The assessment of tropospheric horizontal gradients with respect to the ERA-Interim revealed a strong sensitivity of estimated gradients to the quality of GNSS antenna tracking performance. This impact was demonstrated at the

A Robust and Multi-Weighted Approach to Estimating Topographically Correlated Tropospheric Delays in Radar Interferograms

PubMed Central

Zhu, Bangyan; Li, Jiancheng; Chu, Zhengwei; Tang, Wei; Wang, Bin; Li, Dawei

2016-01-01

Spatial and temporal variations in the vertical stratification of the troposphere introduce significant propagation delays in interferometric synthetic aperture radar (InSAR) observations. Observations of small amplitude surface deformations and regional subsidence rates are plagued by tropospheric delays, and strongly correlated with topographic height variations. Phase-based tropospheric correction techniques assuming a linear relationship between interferometric phase and topography have been exploited and developed, with mixed success. Producing robust estimates of tropospheric phase delay however plays a critical role in increasing the accuracy of InSAR measurements. Meanwhile, few phase-based correction methods account for the spatially variable tropospheric delay over lager study regions. Here, we present a robust and multi-weighted approach to estimate the correlation between phase and topography that is relatively insensitive to confounding processes such as regional subsidence over larger regions as well as under varying tropospheric conditions. An expanded form of robust least squares is introduced to estimate the spatially variable correlation between phase and topography by splitting the interferograms into multiple blocks. Within each block, correlation is robustly estimated from the band-filtered phase and topography. Phase-elevation ratios are multiply- weighted and extrapolated to each persistent scatter (PS) pixel. We applied the proposed method to Envisat ASAR images over the Southern California area, USA, and found that our method mitigated the atmospheric noise better than the conventional phase-based method. The corrected ground surface deformation agreed better with those measured from GPS. PMID:27420066

A Robust and Multi-Weighted Approach to Estimating Topographically Correlated Tropospheric Delays in Radar Interferograms.

PubMed

Zhu, Bangyan; Li, Jiancheng; Chu, Zhengwei; Tang, Wei; Wang, Bin; Li, Dawei

2016-07-12

Spatial and temporal variations in the vertical stratification of the troposphere introduce significant propagation delays in interferometric synthetic aperture radar (InSAR) observations. Observations of small amplitude surface deformations and regional subsidence rates are plagued by tropospheric delays, and strongly correlated with topographic height variations. Phase-based tropospheric correction techniques assuming a linear relationship between interferometric phase and topography have been exploited and developed, with mixed success. Producing robust estimates of tropospheric phase delay however plays a critical role in increasing the accuracy of InSAR measurements. Meanwhile, few phase-based correction methods account for the spatially variable tropospheric delay over lager study regions. Here, we present a robust and multi-weighted approach to estimate the correlation between phase and topography that is relatively insensitive to confounding processes such as regional subsidence over larger regions as well as under varying tropospheric conditions. An expanded form of robust least squares is introduced to estimate the spatially variable correlation between phase and topography by splitting the interferograms into multiple blocks. Within each block, correlation is robustly estimated from the band-filtered phase and topography. Phase-elevation ratios are multiply- weighted and extrapolated to each persistent scatter (PS) pixel. We applied the proposed method to Envisat ASAR images over the Southern California area, USA, and found that our method mitigated the atmospheric noise better than the conventional phase-based method. The corrected ground surface deformation agreed better with those measured from GPS.

The Potential of Tropospheric Gradients for Regional Precipitation Prediction

NASA Astrophysics Data System (ADS)

Boisits, Janina; Möller, Gregor; Wittmann, Christoph; Weber, Robert

2017-04-01

Changes of temperature and humidity in the neutral atmosphere cause variations in tropospheric path delays and tropospheric gradients. By estimating zenith wet delays (ZWD) and gradients using a GNSS reference station network the obtained time series provide information about spatial and temporal variations of water vapour in the atmosphere. Thus, GNSS-based tropospheric parameters can contribute to the forecast of regional precipitation events. In a recently finalized master thesis at TU Wien the potential of tropospheric gradients for weather prediction was investigated. Therefore, ZWD and gradient time series at selected GNSS reference stations were compared to precipitation data over a period of six months (April to September 2014). The selected GNSS stations form two test areas within Austria. All required meteorological data was provided by the Central Institution for Meteorology and Geodynamics (ZAMG). Two characteristics in ZWD and gradient time series can be anticipated in case of an approaching weather front. First, an induced asymmetry in tropospheric delays results in both, an increased magnitude of the gradient and in gradients pointing towards the weather front. Second, an increase in ZWD reflects the increased water vapour concentration right before a precipitation event. To investigate these characteristics exemplary test events were processed. On the one hand, the sequence of the anticipated increase in ZWD at each GNSS station obtained by cross correlation of the time series indicates the direction of the approaching weather front. On the other hand, the corresponding peak in gradient time series allows the deduction of the direction of movement as well. To verify the results precipitation data from ZAMG was used. It can be deduced, that tropospheric gradients show high potential for predicting precipitation events. While ZWD time series rather indicate the orientation of the air mass boundary, gradients rather indicate the direction of movement

The effect of aperture averaging upon tropospheric delay fluctuations seen with a DSN antenna

NASA Technical Reports Server (NTRS)

Linfield, R.

1996-01-01

The spectrum of tropospheric delay fluctuations expected for a DSN antenna at time scales less than 100 s has been calculated. A new feature included in these calculations is the effect of aperture averaging, which causes a reduction in delay fluctuations on time scales less than the antenna wind speed crossing time, approximately equal to 5-10 s. On time scales less than a few seconds, the Allan deviation sigma(sub y)(Delta(t)) varies as (Delta(t))(sup +1), rather than sigma(sub y)(Delta(t)) varies as (Delta(t))(exp -1/6) without aperture averaging. Due to thermal radiometer noise, calibration of tropospheric delay fluctuations with water vapor radiometers will not be possible on time scales less than approximately 10 s. However, the tropospheric fluctuation level will be small enough that radio science measurements with a spacecraft on time scales less than a few seconds will be limited by the stability of frequency standards and/or other nontropospheric effects.

Generation of real-time mode high-resolution water vapor fields from GPS observations

NASA Astrophysics Data System (ADS)

Yu, Chen; Penna, Nigel T.; Li, Zhenhong

2017-02-01

Pointwise GPS measurements of tropospheric zenith total delay can be interpolated to provide high-resolution water vapor maps which may be used for correcting synthetic aperture radar images, for numeral weather prediction, and for correcting Network Real-time Kinematic GPS observations. Several previous studies have addressed the importance of the elevation dependency of water vapor, but it is often a challenge to separate elevation-dependent tropospheric delays from turbulent components. In this paper, we present an iterative tropospheric decomposition interpolation model that decouples the elevation and turbulent tropospheric delay components. For a 150 km × 150 km California study region, we estimate real-time mode zenith total delays at 41 GPS stations over 1 year by using the precise point positioning technique and demonstrate that the decoupled interpolation model generates improved high-resolution tropospheric delay maps compared with previous tropospheric turbulence- and elevation-dependent models. Cross validation of the GPS zenith total delays yields an RMS error of 4.6 mm with the decoupled interpolation model, compared with 8.4 mm with the previous model. On converting the GPS zenith wet delays to precipitable water vapor and interpolating to 1 km grid cells across the region, validations with the Moderate Resolution Imaging Spectroradiometer near-IR water vapor product show 1.7 mm RMS differences by using the decoupled model, compared with 2.0 mm for the previous interpolation model. Such results are obtained without differencing the tropospheric delays or water vapor estimates in time or space, while the errors are similar over flat and mountainous terrains, as well as for both inland and coastal areas.

Data analysis of a dense GPS network operated during the ESCOMPTE campaign: first results

NASA Astrophysics Data System (ADS)

Walpersdorf, A.; Bock, O.; Doerflinger, E.; Masson, F.; van Baelen, J.; Somieski, A.; Bürki, B.

The experiment GPS/H 2O involving 17 GPS receivers has been operated for two weeks in June 2001 in a dense network around Marseille. This project was integrated into the ESCOMPTE campaign. This paper will focus on the GPS analysis in preparation of the tomographic inversion of GPS slant delays. As first results, GPS tropospheric parameters zenith delays and horizontal gradients have been extracted. For a first visualization of the humidity field overlying the network, zenith delays have been transformed into precipitable water. Successive humidity fields are presented for a period of sudden drop in humidity, indicating some spatial resolution in the small network. The time series of horizontal gradients evaluated at individual sites are compared to correlated zenith delay variations over the whole network (horizontal gradient of zenith delays), showing that in the small size network horizontal atmospheric structure is reflected by both types of parameters. To compare these two quantities, scaling of zenith delays due to different station altitudes was necessary. In this way, a GPS internal validation of the individual gradients by comparison with the horizontal gradient of zenith delays has been established. Differential features along transects across the network indicate a good spatial resolution of tropospheric phenomena, encouraging for the further tomographic exploitation of the data. Moreover, individual and zenith delay gradients weight differently atmospheric horizontal gradients occurring at different heights. This different sensitivity has been used for a first identification of a vertical atmospheric structure from GPS tropospheric delays, by observing an inclined frontal zone crossing the network.

Scanning Raman lidar for tropospheric water vapor profiling and GPS path delay correction

NASA Astrophysics Data System (ADS)

Tarniewicz, Jerome; Bock, Olivier; Pelon, Jacques R.; Thom, Christian

2002-01-01

The design of a ground based and transportable combined Raman elastic-backscatter lidar for the remote sensing of lower tropospheric water vapor and nitrogen concentration is described. This lidar is intended to be used for an external calibration of the wet path delay of GPS signals. A description of the method used to derive water vapor and nitrogen profiles in the lower troposphere is given. The instrument has been tested during the ESCOMPTE campaign in June 2001 and first measurements are presented.

Estimating tropospheric phase delay in SAR interferograms using Global Atmospheric Models

NASA Astrophysics Data System (ADS)

Doin, M.; Lasserre, C.; Peltzer, G.; Cavalie, O.; Doubre, C.

2008-12-01

The main limiting factor on the accuracy of Interferometric SAR (InSAR) measurements comes from phase propagation delays through the Earth's troposphere. The delay can be divided into a stratified component, which correlates with the topography and often dominates the tropospheric signal in InSAR data, and a turbulent component. The stratified delay can be expressed as a function of atmospheric pressure P, temperature T, and water vapor partial pressure e vertical profiles. We compare the stratified delay computed using results from global atmospheric models with the topography-dependent signal observed in interferograms covering three test areas in different geographic and climatic environments: Lake Mead, Nevada, USA, the Haiyuan fault area, Gansu, China, and Afar, Republic of Djibouti. For each site we compute a multi-year series of interferograms. The phase-elevation ratio is estimated for each interferogram and the series is inverted to form a timeline of delay-elevation ratios characterizing each epoch of data acquisition. InSAR derived ratios are in good agreement with the ratios computed from global atmospheric models. This agreement shows that both estimations of the delay-elevation ratio can be used to perform a first order correction of the InSAR phase. Seasonal variations of the atmosphere significantly affect the phase delay throughout the year, aliasing the results of time series inversions using temporal smoothing or data stacking when the acquisitions are not evenly distributed in time. This is particularly critical when the spatial shape of the signal of interest correlates with topography. In the Lake Mead area, the irregular temporal sampling of our SAR data results in an interannual bias of amplitude ~2~cm on range change estimates. In the Haiyuan Fault area, the coarse and uneven data sampling results in a bias of up to ~0.5~cm/yr on the line of sight velocity across the fault. In the Afar area, the seasonal signal exceeds the deformation

A grid-based tropospheric product for China using a GNSS network

NASA Astrophysics Data System (ADS)

Zhang, Hongxing; Yuan, Yunbin; Li, Wei; Zhang, Baocheng; Ou, Jikun

2017-11-01

Tropospheric delay accounts for one source of error in global navigation satellite systems (GNSS). To better characterize the tropospheric delays in the temporal and spatial domain and facilitate the safety-critical use of GNSS across China, a method is proposed to generate a grid-based tropospheric product (GTP) using the GNSS network with an empirical tropospheric model, known as IGGtrop. The prototype system generates the GTPs in post-processing and real-time modes and is based on the undifferenced and uncombined precise point positioning (UU-PPP) technique. GTPs are constructed for a grid form (2.0{°}× 2.5{°} latitude-longitude) over China with a time resolution of 5 min. The real-time GTP messages are encoded in a self-defined RTCM3 format and broadcast to users using NTRIP (networked transport of RTCM via internet protocol), which enables efficient and safe transmission to real-time users. Our approach for GTP generation consists of three sequential steps. In the first step, GNSS-derived zenith tropospheric delays (ZTDs) for a network of GNSS stations are estimated using UU-PPP. In the second step, vertical adjustments for the GNSS-derived ZTDs are applied to address the height differences between the GNSS stations and grid points. The ZTD height corrections are provided by the IGGtrop model. Finally, an inverse distance weighting method is used to interpolate the GNSS-derived ZTDs from the surrounding GNSS stations to the location of the grid point. A total of 210 global positioning system (GPS) stations from the crustal movement observation network of China are used to generate the GTPs in both post-processing and real-time modes. The accuracies of the GTPs are assessed against with ERA-Interim-derived ZTDs and the GPS-derived ZTDs at 12 test GPS stations, respectively. The results show that the post-processing and real-time GTPs can provide the ZTDs with accuracies of 1.4 and 1.8 cm, respectively. We also apply the GTPs in real-time kinematic GPS PPP

Q Conversion Factor Models for Estimating Precipitable Water Vapor for Turkey

NASA Astrophysics Data System (ADS)

Deniz, Ilke; Mekik, Cetin; Gurbuz, Gokhan

2015-04-01

Global Navigation Satellite Systems (GNSS) have recently proved to be one of the crucial tools for determining continuous and precise precipitable water vapor (GNSS-MET networks). GNSS, especially CORS networks such as CORS-TR (the Turkish Network-RTK), provide high temporal and spatial accuracy for the wet tropospheric zenith delays which are then converted to the precipitable water vapor due to the fact that they can operate in all weather conditions continuously and economically. The accuracy of wet tropospheric zenith delay highly depends on the accuracy of precipitable water vapor content in the troposphere. Therefore, the precipitable water vapor is an important element of the tropospheric zenith delay. A number of studies can be found in the literature on the determination of the precipitable water vapor from the tropospheric zenith delay. Studies of Hogg showed that when the precipitable water vapor is known, the tropospheric zenith delay can be computed. Askne and Nodius have developed fundamental equations between the wet tropospheric zenith delay and the precipitable water vapor from the equation of the index of refraction in the troposphere. Furthermore, Bevis have developed a linear regression model to determine the weighted mean temperature (Tm) depending on the surface temperature (Ts) in Askne and Nodius studies. For this reason, nearly 9000 radiosonde profiles in USA were analyzed and the coefficients calculated. Similarly, there are other studies on the calculation of those coefficients for different regions: Solbrig for Germany, Liou for Taiwan, Jihyun for South Korea, Dongseob for North Korea, Suresh Raju for India, Boutiouta and Lahcene for Algeria, Bokoye for Canada, Baltink for Netherlands and Baltic, Bock for Africa. It is stated that the weighted mean temperature can be found with a root mean square error of ±2-5 K. In addition, there are studies on the calculation of the coefficients globally. Another model for the determination of

Consistency of different tropospheric models and mapping functions for precise GNSS processing

NASA Astrophysics Data System (ADS)

Graffigna, Victoria; Hernández-Pajares, Manuel; García-Rigo, Alberto; Gende, Mauricio

2017-04-01

The TOmographic Model of the IONospheric electron content (TOMION) software implements a simultaneous precise geodetic and ionospheric modeling, which can be used to test new approaches for real-time precise GNSS modeling (positioning, ionospheric and tropospheric delays, clock errors, among others). In this work, the software is used to estimate the Zenith Tropospheric Delay (ZTD) emulating real time and its performance is evaluated through a comparative analysis with a built-in GIPSY estimation and IGS final troposphere product, exemplified in a two-day experiment performed in East Australia. Furthermore, the troposphere mapping function was upgraded from Niell to Vienna approach. On a first scenario, only forward processing was activated and the coordinates of the Wide Area GNSS network were loosely constrained, without fixing the carrier phase ambiguities, for both reference and rover receivers. On a second one, precise point positioning (PPP) was implemented, iterating for a fixed coordinates set for the second day. Comparisons between TOMION, IGS and GIPSY estimates have been performed and for the first one, IGS clocks and orbits were considered. The agreement with GIPSY results seems to be 10 times better than with the IGS final ZTD product, despite having considered IGS products for the computations. Hence, the subsequent analysis was carried out with respect to the GIPSY computations. The estimates show a typical bias of 2cm for the first strategy and of 7mm for PPP, in the worst cases. Moreover, Vienna mapping function showed in general a fairly better agreement than Niell one for both strategies. The RMS values' were found to be around 1cm for all studied situations, with a slightly fitter performance for the Niell one. Further improvement could be achieved for such estimations with coefficients for the Vienna mapping function calculated from raytracing as well as integrating meteorological comparative parameters.

Temporal and spatial characterization of zenith total delay (ZTD) in North Europe

NASA Astrophysics Data System (ADS)

Stoew, B.; Elgered, G.

2003-04-01

The estimates of ZTD are often treated as realizations of random walk stochastic processes. We derive the corresponding process parameters for 34 different locations in North Europe using two measurement techniques - Global Positioning System (GPS) and Water Vapor Radiometer (WVR). GPS-estimated ZTD is an excellent candidate for data assimilation in numerical weather prediction (NWP) models in terms of both spatial and temporal resolution. We characterize the long term behavior of the ZTD as a function of site latitude and height. The spatial characteristics of the ZTD are studied as a function of site separation and season. We investigate the influence of the time-interpolated atmospheric pressure data used for the estimation of zenith wet delay (ZWD) from ZTD. Characterization of extreme atmospheric events can aid the development of an early warning system. We consider two types of extreme meteorological phenomena with regard to their spatial scales. The first type concerns larger regions (including several GPS sites); the extreme weather is characterized by intense precipitation which may result in a flood. The second type is related to local variations in the ZWD/ZTD and can be used for detection/monitoring of passing atmospheric fronts.

Corrections of stratified tropospheric delays in SAR interferometry: Validation with global atmospheric models

NASA Astrophysics Data System (ADS)

Doin, Marie-Pierre; Lasserre, Cécile; Peltzer, Gilles; Cavalié, Olivier; Doubre, Cécile

2010-05-01

The main limiting factor on the accuracy of Interferometric SAR measurements (InSAR) comes from phase propagation delays through the troposphere. The delay can be divided into a stratified component, which correlates with the topography and often dominates the tropospheric signal, and a turbulent component. We use Global Atmospheric Models (GAM) to estimate the stratified phase delay and delay-elevation ratio at epochs of SAR acquisitions, and compare them to observed phase delay derived from SAR interferograms. Three test areas are selected with different geographic and climatic environments and with large SAR archive available. The Lake Mead, Nevada, USA is covered by 79 ERS1/2 and ENVISAT acquisitions, the Haiyuan Fault area, Gansu, China, by 24 ERS1/2 acquisitions, and the Afar region, Republic of Djibouti, by 91 Radarsat acquisitions. The hydrostatic and wet stratified delays are computed from GAM as a function of atmospheric pressure P, temperature T, and water vapor partial pressure e vertical profiles. The hydrostatic delay, which depends on ratio P/T, varies significantly at low elevation and cannot be neglected. The wet component of the delay depends mostly on the near surface specific humidity. GAM predicted delay-elevation ratios are in good agreement with the ratios derived from InSAR data away from deforming zones. Both estimations of the delay-elevation ratio can thus be used to perform a first order correction of the observed interferometric phase to retrieve a ground motion signal of low amplitude. We also demonstrate that aliasing of daily and seasonal variations in the stratified delay due to uneven sampling of SAR data significantly bias InSAR data stacks or time series produced after temporal smoothing. In all three test cases, the InSAR data stacks or smoothed time series present a residual stratified delay of the order of the expected deformation signal. In all cases, correcting interferograms from the stratified delay removes all these

Corrections of stratified tropospheric delays in SAR interferometry: Validation with global atmospheric models

NASA Astrophysics Data System (ADS)

Doin, M.-P.; Lasserre, C.; Peltzer, G.; Cavalié, O.; Doubre, C.

2009-09-01

The main limiting factor on the accuracy of Interferometric SAR measurements (InSAR) comes from phase propagation delays through the troposphere. The delay can be divided into a stratified component, which correlates with the topography and often dominates the tropospheric signal, and a turbulent component. We use Global Atmospheric Models (GAM) to estimate the stratified phase delay and delay-elevation ratio at epochs of SAR acquisitions, and compare them to observed phase delay derived from SAR interferograms. Three test areas are selected with different geographic and climatic environments and with large SAR archive available. The Lake Mead, Nevada, USA is covered by 79 ERS1/2 and ENVISAT acquisitions, the Haiyuan Fault area, Gansu, China, by 24 ERS1/2 acquisitions, and the Afar region, Republic of Djibouti, by 91 Radarsat acquisitions. The hydrostatic and wet stratified delays are computed from GAM as a function of atmospheric pressure P, temperature T, and water vapor partial pressure e vertical profiles. The hydrostatic delay, which depends on ratio P/ T, varies significantly at low elevation and cannot be neglected. The wet component of the delay depends mostly on the near surface specific humidity. GAM predicted delay-elevation ratios are in good agreement with the ratios derived from InSAR data away from deforming zones. Both estimations of the delay-elevation ratio can thus be used to perform a first order correction of the observed interferometric phase to retrieve a ground motion signal of low amplitude. We also demonstrate that aliasing of daily and seasonal variations in the stratified delay due to uneven sampling of SAR data significantly bias InSAR data stacks or time series produced after temporal smoothing. In all three test cases, the InSAR data stacks or smoothed time series present a residual stratified delay of the order of the expected deformation signal. In all cases, correcting interferograms from the stratified delay removes all these

Accuracy Assessment of the Precise Point Positioning for Different Troposphere Models

NASA Astrophysics Data System (ADS)

Oguz Selbesoglu, Mahmut; Gurturk, Mert; Soycan, Metin

2016-04-01

This study investigates the accuracy and repeatability of PPP technique at different latitudes by using different troposphere delay models. Nine IGS stations were selected between 00-800 latitudes at northern hemisphere and southern hemisphere. Coordinates were obtained for 7 days at 1 hour intervals in summer and winter. At first, the coordinates were estimated by using Niell troposphere delay model with and without including north and east gradients in order to investigate the contribution of troposphere delay gradients to the positioning . Secondly, Saastamoinen model was used to eliminate troposphere path delays by using standart atmosphere parameters were extrapolated for all station levels. Finally, coordinates were estimated by using RTCA-MOPS empirical troposphere delay model. Results demonstrate that Niell troposphere delay model with horizontal gradients has better mean values of rms errors 0.09 % and 65 % than the Niell troposphere model without horizontal gradients and RTCA-MOPS model, respectively. Saastamoinen model mean values of rms errors were obtained approximately 4 times bigger than the Niell troposphere delay model with horizontal gradients.

Data assimilation of GNSS zenith total delays from a Nordic processing centre

NASA Astrophysics Data System (ADS)

Lindskog, Magnus; Ridal, Martin; Thorsteinsson, Sigurdur; Ning, Tong

2017-11-01

Atmospheric moisture-related information estimated from Global Navigation Satellite System (GNSS) ground-based receiver stations by the Nordic GNSS Analysis Centre (NGAA) have been used within a state-of-the-art kilometre-scale numerical weather prediction system. Different processing techniques have been implemented to derive the moisture-related GNSS information in the form of zenith total delays (ZTDs) and these are described and compared. In addition full-scale data assimilation and modelling experiments have been carried out to investigate the impact of utilizing moisture-related GNSS data from the NGAA processing centre on a numerical weather prediction (NWP) model initial state and on the ensuing forecast quality. The sensitivity of results to aspects of the data processing, station density, bias-correction and data assimilation have been investigated. Results show benefits to forecast quality when using GNSS ZTD as an additional observation type. The results also show a sensitivity to thinning distance applied for GNSS ZTD observations but not to modifications to the number of predictors used in the variational bias correction applied. In addition, it is demonstrated that the assimilation of GNSS ZTD can benefit from more general data assimilation enhancements and that there is an interaction of GNSS ZTD with other types of observations used in the data assimilation. Future plans include further investigation of optimal thinning distances and application of more advanced data assimilation techniques.

Evaluation of current tropospheric mapping functions by Deep Space Network very long baseline interferometry

NASA Technical Reports Server (NTRS)

Sovers, O. J.; Lanyi, G. E.

1994-01-01

To compare the validity of current algorithms that map zenith tropospheric delay to arbitrary elevation angles, 10 different tropospheric mapping functions are used to analyze the current data base of Deep Space Network Mark 3 intercontinental very long baseline interferometric (VLBI) data. This analysis serves as a stringent test because of the high proportion of low-elevation observations necessitated by the extremely long baselines. Postfit delay and delay-rate residuals are examined, as well as the scatter of baseline lengths about the time-linear model that characterizes tectonic motion. Among the functions that utilize surface meteorological data as input parameters, the Lanyi 1984 mapping shows the best performance both for residuals and baselines, through the 1985 Davis function is statistically nearly identical. The next best performance is shown by the recent function of Niell, which is based on an examination of global atmospheric characteristics as a function of season and uses no weather data at the time of the measurements. The Niell function shows a slight improvement in residuals relative to Lanyi, but also an increase in baseline scatter that is significant for the California-Spain baseline. Two variants of the Chao mapping function, as well as the Chao tables used with the interpolation algorithm employed in the Orbit Determination Program software, show substandard behavior for both VLBI residuals and baseline scatter. The length of the California-Australia baseline (10,600 km) in the VLBI solution can vary by as much as 5 to 10 cm for the 10 mapping functions.

VMF3/GPT3: refined discrete and empirical troposphere mapping functions

NASA Astrophysics Data System (ADS)

Landskron, Daniel; Böhm, Johannes

2018-04-01

Incorrect modeling of troposphere delays is one of the major error sources for space geodetic techniques such as Global Navigation Satellite Systems (GNSS) or Very Long Baseline Interferometry (VLBI). Over the years, many approaches have been devised which aim at mapping the delay of radio waves from zenith direction down to the observed elevation angle, so-called mapping functions. This paper contains a new approach intended to refine the currently most important discrete mapping function, the Vienna Mapping Functions 1 (VMF1), which is successively referred to as Vienna Mapping Functions 3 (VMF3). It is designed in such a way as to eliminate shortcomings in the empirical coefficients b and c and in the tuning for the specific elevation angle of 3°. Ray-traced delays of the ray-tracer RADIATE serve as the basis for the calculation of new mapping function coefficients. Comparisons of modeled slant delays demonstrate the ability of VMF3 to approximate the underlying ray-traced delays more accurately than VMF1 does, in particular at low elevation angles. In other words, when requiring highest precision, VMF3 is to be preferable to VMF1. Aside from revising the discrete form of mapping functions, we also present a new empirical model named Global Pressure and Temperature 3 (GPT3) on a 5°× 5° as well as a 1°× 1° global grid, which is generally based on the same data. Its main components are hydrostatic and wet empirical mapping function coefficients derived from special averaging techniques of the respective (discrete) VMF3 data. In addition, GPT3 also contains a set of meteorological quantities which are adopted as they stand from their predecessor, Global Pressure and Temperature 2 wet. Thus, GPT3 represents a very comprehensive troposphere model which can be used for a series of geodetic as well as meteorological and climatological purposes and is fully consistent with VMF3.

What is the impact of different VLBI analysis setups of the tropospheric delay on precipitable water vapor trends?

NASA Astrophysics Data System (ADS)

Balidakis, Kyriakos; Nilsson, Tobias; Heinkelmann, Robert; Glaser, Susanne; Zus, Florian; Deng, Zhiguo; Schuh, Harald

2017-04-01

The quality of the parameters estimated by global navigation satellite systems (GNSS) and very long baseline interferometry (VLBI) are distorted by erroneous meteorological observations applied to model the propagation delay in the electrically neutral atmosphere. For early VLBI sessions with poor geometry, unsuitable constraints imposed on the a priori tropospheric gradients is a source of additional hassle of VLBI analysis. Therefore, climate change indicators deduced from the geodetic analysis, such as the long-term precipitable water vapor (PWV) trends, are strongly affected. In this contribution we investigate the impact of different modeling and parameterization of the propagation delay in the troposphere on the estimates of long-term PWV trends from geodetic VLBI analysis results. We address the influence of the meteorological data source, and of the a priori non-hydrostatic delays and gradients employed in the VLBI processing, on the estimated PWV trends. In particular, we assess the effect of employing temperature and pressure from (i) homogenized in situ observations, (ii) the model levels of the ERA Interim reanalysis numerical weather model and (iii) our own blind model in the style of GPT2w with enhanced parameterization, calculated using the latter data set. Furthermore, we utilize non-hydrostatic delays and gradients estimated from (i) a GNSS reprocessing at GeoForschungsZentrum Potsdam, rigorously considering tropospheric ties, and (ii)) direct ray-tracing through ERA Interim, as additional observations. To evaluate the above, the least-squares module of the VieVS@GFZ VLBI software was appropriately modified. Additionally, we study the noise characteristics of the non-hydrostatic delays and gradients estimated from our VLBI and GNSS analyses as well as from ray-tracing. We have modified the Theil-Sen estimator appropriately to robustly deduce PWV trends from VLBI, GNSS, ray-tracing and direct numerical integration in ERA Interim. We disseminate all

Mark 3 VLBI system: Tropospheric calibration subsystems

NASA Technical Reports Server (NTRS)

Resch, G. M.

1980-01-01

Tropospheric delay calibrations are implemented in the Mark 3 system with two subsystems. Estimates of the dry component of tropospheric delay are provided by accurate barometric data from a subsystem of surface meteorological sensors (SMS). An estimate of the wet component of tropospheric delay is provided by a water vapor radiometer (WVR). Both subsystems interface directly to the ASCII Transceiver bus of the Mark 3 system and are operated by the control computer. Seven WVR's under construction are designed to operate in proximity to a radio telescope and can be commanded to point along the line-of-sight to a radio source. They should provide a delay estimate that is accurate to the + or - 2 cm level.

Use of Global Meteorological Model to Correct for Stratified Tropospheric Delays in SAR Data: Application to Active Mexican Stratovolcanoes.

NASA Astrophysics Data System (ADS)

Pinel, V. M.; Doin, M.; de La Cruz-Reyna, S.; Hooper, A.

2008-12-01

Artefacts induced by temporal changes of water content within the tropospheric layer have long been recognised as the main limitation for the use of InSAR data in order to detect magma movement at depth beneath stratovolcanoes (Delacourt, 1998). Difficulty in discriminating between tropospheric artefacts and deformation induced by magma accumulation or withdrawal at depth is mainly due to the similarity of the expected signal centred on the volcanic edifice. However it is of prime importance to be able to detect magma storage which is the most reliable precursor for volcanic eruptions. We processed time series of InSAR data acquired by ENVISAT from December 2002 to August 2006 at Popocatépetl and Colima Volcano (Mexico) using both the Stanford method for persistent scatterers and a derived small baseline approach (Hooper, 2008). Tropospheric delays are estimated for each interferogram using temperature, pressure and water content profiles from the North American Regional Reanalysis (NARR), a global atmospheric model provided by the National Centers for Environmental Prediction. A strong seasonal effect is observed leading to maximum value for delays of 10 rad/km corresponding to 4 fringes on the volcano slopes. These delays are validated using the correlation between the wrapped phase and the elevation as well as spectrometer data acquired by the Medium Resolution Imaging System (MERIS) onboard on the ENVISAT platform. The tropospheric effect is removed from the wrapped phase which improves the unwrapping process. On Popocatépetl no significant deformations were observed. We could not detect any deep magma storage zone beneath Colima volcano, but its summit area exhibits a constant and almost linear subsidence of more than 1.5 cm/year mainly related to recent volcanic deposits loading. References: Delacourt, P. Briole and J. Achache, Tropospheric corrections of SAR interferograms with strong topography. Application to Etna. Geophys. Res. Lett., 25, 2849- 2852

Studies on Instabilities in Long-Baseline Two-Way Satellite Time and Frequency Transfer (TWSTFT) Including a Troposphere Delay Model

DTIC Science & Technology

2007-11-01

TRANSFER ( TWSTFT ) INCLUDING A TROPOSPHERE DELAY MODEL D. Piester, A. Bauch Physikalisch-Technische Bundesanstalt (PTB) Bundesallee 100...Abstract Two-way satellite time and frequency transfer ( TWSTFT ) is one of the leading techniques for remote comparisons of atomic frequency standards...nanosecond level. These achievements are due to the fact that many delay variations of the transmitted signals cancel out in TWSTFT because of the

Impacts of ionospheric electric fields on the GPS tropospheric delays during geomagnetic storms in Antarctica

NASA Astrophysics Data System (ADS)

Suparta, W.

2017-05-01

This paper aimed to overview the interaction of the thunderstorm with the ionospheric electric fields during major geomagnetic storms in Antarctica through the GPS tropospheric delays. For the purpose of study, geomagnetic activity and electric fields data for the period from 13 to 21 March 2015 representing the St. Patrick’s Day storm is analyzed. To strengthen the analysis, data for the period of 27 October to 1st November 2003 representing for the Halloween storm is also compared. Our analysis showed that both geomagnetic storms were severe (Ap ≥ 100 nT), where the intensity of Halloween storm is double compared to St. Patrick’s Day storm. For the ionospheric electric field, the peaks were dropped to -1.63 mV/m and -2.564 mV/m for St. Patrick and Halloween storms, respectively. At this time, the interplanetary magnetic field Bz component was significantly dropped to -17.31 nT with Ap > 150 nT (17 March 2015 at 19:20 UT) and -26.51 nT with Ap = 300 nT (29 October 2003 at 19:40 UT). For both geomagnetic storms, the electric field was correlated well with the ionospheric activity where tropospheric delays show a different characteristic.

A direct evaluation of the Geosat altimeter wet atmospheric range delay using very long baseline interferometry observations

NASA Technical Reports Server (NTRS)

Koblinsky, C. J.; Ryan, J.; Braatz, L.; Klosko, S. M.

1993-01-01

The overall accuracy of the U.S. Navy Geosat altimeter wet atmospheric range delay caused by refraction through the atmosphere is directly assessed by comparing the estimates made from the DMSP Special Sensor Microwave/Imager and the U.S. Navy Fleet Numerical Ocean Center forecast model for Geosat with measurements of total zenith columnar water vapor content from four VLBI sites. The assessment is made by comparing time series of range delay from various methods at each location. To determine the importance of diurnal variation in water vapor content in noncoincident estimates, the VLBI measurements were made at 15-min intervals over a few days. The VLBI measurements showed strong diurnal variations in columnar water vapor at several sites, causing errors of the order 3 cm rms in any noncoincident measurement of the wet troposphere range delay. These errors have an effect on studies of annual and interannual changes in sea level with Geosat data.

Fan tomography of the tropospheric water vapor for the calibration of the Ka band tracking of the Bepi-Colombo spacecraft (MORE experiment).

NASA Astrophysics Data System (ADS)

Barriot, Jean-Pierre; Serafini, Jonathan; Sichoix, Lydie

2012-07-01

The radiosciences Bepi-Colombo MORE experiment will use X/X, X/Ka and Ka/Ka band radio links to make accurate measurements of the spacecraft range and range rate. Tropospheric zenith wet delays range from 1.5 cm to 10 cm, with high variability (less than 1000 s) and will impair these accurate measurements. Conditions vary from summer (worse) to winter (better), from day (worse) to night (better). These wet delays cannot be estimated from ground weather measurements and alternative calibration methods should be used in order to cope with the MORE requirements (no more than 3 mm at 1000 s). Due to the Mercury orbit, MORE measurements will be performed by daylight and more frequently in summer than in winter (from Northern hemisphere). Two systems have been considered to calibrate this wet delay: Water Vapour Radiometers (WVRs) and GPS receivers. The Jet Propulsion Laboratory has developed a new class of WVRs reaching a 5 percent accuracy for the wet delay calibration (0.75 mm to 5 mm), but these WVRs are expensive to build and operate. GPS receivers are also routinely used for the calibration of data from NASA Deep Space probes, but several studies have shown that GPS receivers can give good calibration (through wet delay mapping functions) for long time variations, but are not accurate enough for short time variations (100 to 1000 s), and that WVRs must be used to efficiently calibrate the wet troposphere delays over such time spans. We think that such a calibration could be done by assimilating data from all the GNSS constellations (GPS, GLONASS, Galileo, Beidou and IRNSS) that will be available at the time of the Bepi-Colombo arrival at Mercury (2021), provided that the underlying physics of the turbulent atmosphere and evapotranspiration processes are properly taken into account at such time scales. This implies to do a tomographic image of the troposphere overlying each Deep Space tracking station at time scales of less than 1000 s. For this purpose, we have

Benchmark Campaign of the COST Action GNSS4SWEC: Main Goals and Achievements

NASA Astrophysics Data System (ADS)

Dick, G.; Dousa, J.; Kacmarik, M.; Pottiaux, E.; Zus, F.; Brenot, H. H.; Moeller, G.; Kaplon, J.; Morel, L.; Hordyniec, P.

2016-12-01

This talk will give an overview of achievements of the Benchmark campaign, one of the central activities in the framework of the COST Action ES 1206 GNSS4SWEC. The main goal of the campaign is supporting the development and validation of advanced Global Navigation Satellite System (GNSS) tropospheric products, in particular high-resolution and ultra-fast/real-time zenith total delays (ZTD) and asymmetry products in terms of tropospheric horizontal gradients and slant delays.For the Benchmark campaign a complex data set of GNSS observations and various meteorological data were collected for a two-month period in 2013 (May-June) which included severe weather events in central Europe. An initial processing of data sets from GNSS and numerical weather models (NWM) provided independently estimated tropospheric reference products - ZTDs, tropospheric horizontal gradients and others. The comparison of horizontal tropospheric gradients from GNSS and NWM data demonstrated a very good agreement among independent solutions with negligible biases and an accuracy of about 0.5 mm. Visual comparisons of maps of zenith wet delays and tropospheric horizontal gradients showed very promising results for future exploitations of advanced GNSS tropospheric products in meteorological applications such as severe weather event monitoring and weather nowcasting.The benchmark data set is also used for an extensive validation of line-of-sight tropospheric Slant Total Delays (STD) from GNSS, NWM-raytracing and Water Vapour Radiometer (WVR) solutions. Six institutions delivered their STDs based on GNSS observations processed using different software and strategies. STDs from NWM ray-tracing came from three institutions using three different NWM models. Results show generally a very good mutual agreement among all solutions from all techniques. Among all an influence of adding not cleaned as well as cleaned GNSS post-fit residuals, i.e. residuals with eliminated and not eliminated non-tropospheric

Atmospheric oscillations comparison on long term tropospheric delay time series derived from ray-tracing and GPS

NASA Astrophysics Data System (ADS)

Nikolaidou, Thalia; Santos, Marcelo

2017-04-01

The caused time delay induced by the atmosphere on the GNSS signals (NAD), depends primarily on the amount of atmosphere the signal traverses till it reaches to the Earth's surface and can exceed t 20 m for low elevation angles (around 3 degrees). For a particular ray i.e. satellite/quasar-antenna link, the delay depends on the atmospheric parameters of total pressure, temperature, and the partial pressure of water vapor. Because of that, numerical weather models (NWM) have already proven beneficial for atmospheric modelling and geodesy. By direct raytracing, inside NWM, the VMF1 and the University of New Brunswick VMF1 (UNB-VMF1) (Urquhart et al. 2011), access the 3D variation of the meteorological parameters that determine the delay thus being the state-the-art mapping functions used today. The raytracing procedure is capable of providing NADs delays for any point on the Earth's surface. In this study we study the impact of regional numerical weather models, with high spatial and temporal resolution, namely 25km and 6h. These models outweigh the currently used NWM by having about 2.6 times better spatial resolution. Raytracing through such NWM, using the independent raytracing algorithm develop at UNB (Nievinski, 2009), we acquire superior quality NADs with regional application. We ray-trace for the International GNSS service (IGS) network stations for a time span of 11 years. Benchmarking against the IGS troposphere product is performed to access the accuracy of our results. A periodicity analysis is conducted to examine the signature of atmospheric oscillations on the NAD time series. In order to recognize the NAD periodicities, we compared our product against the GPS-derived IGS troposphere product. Systematic effects within each single technique are identified and long-term NAD stability is accessed.

Investigation of the Air Quality Change Effect on Gnss Signals

NASA Astrophysics Data System (ADS)

Gurbuz, G.; Gormus, K. S.; Altan, U.

2017-11-01

Air pollution is the most important environmental problem in Zonguldak city center. Since bituminous coal is used for domestic heating in houses and generating electricity in thermal power plants, particulate matter (PM10) is the leading air pollutant. Previous studies have shown that the water vapor in the troposphere is responsible for the tropospheric zenith delay in Global Navigation Satellite System (GNSS) measurements. In this study, data obtained from the ZONG GNSS station from Türkiye Ulusal Sabit GNSS Ağı (TUSAGA-Active network) in the central district of Zonguldak province, processed with GIPSY-OASIS II and GAMIT/GlobK software using the VMF1 mapping function, which is developed previously and considered to be the most accurate model. The resulting values were examined separately in terms of software. The meteorological parameters obtained from the Turkish State Meteorological Service and the air pollution values obtained from the Ministry of Environment and Urban Planning were analyzed and the zenith delay values were compared. When wet zenith delays of different days with different amounts of PM10 concentrations were examined in succession and under the same meteorological conditions, differences in the range of 20-40 mm on ZTD were observed.

Vertical distribution of aerosol extinction cross section and inference of aerosol imaginary index in the troposphere by lidar technique

NASA Technical Reports Server (NTRS)

Spinhirne, J. D.; Reagan, J. A.; Herman, B. M.

1980-01-01

The paper reports on vertical profiles of aerosol extinction and backscatter in the troposphere which were obtained from multi zenith angle lidar measurements. It is reported that a direct slant path solution was found to be not possible due to horizontal inhomogeneity of the atmosphere. Attention is given to the use of a regression analysis with respect to zenith angle for a layer integration of the angle dependent lidar equation in order to determine the optical thickness and aerosol extinction-to-backscatter ratio for defined atmospheric layers and the subsequent evaluation of cross-section profiles.

Employing Tropospheric Numerical Weather Prediction Model for High-Precision GNSS Positioning

NASA Astrophysics Data System (ADS)

Alves, Daniele; Gouveia, Tayna; Abreu, Pedro; Magário, Jackes

2014-05-01

In the past few years is increasing the necessity of realizing high accuracy positioning. In this sense, the spatial technologies have being widely used. The GNSS (Global Navigation Satellite System) has revolutionized the geodetic positioning activities. Among the existent methods one can emphasize the Precise Point Positioning (PPP) and network-based positioning. But, to get high accuracy employing these methods, mainly in real time, is indispensable to realize the atmospheric modeling (ionosphere and troposphere) accordingly. Related to troposphere, there are the empirical models (for example Saastamoinen and Hopfield). But when highly accuracy results (error of few centimeters) are desired, maybe these models are not appropriated to the Brazilian reality. In order to minimize this limitation arises the NWP (Numerical Weather Prediction) models. In Brazil the CPTEC/INPE (Center for Weather Prediction and Climate Studies / Brazilian Institute for Spatial Researches) provides a regional NWP model, currently used to produce Zenithal Tropospheric Delay (ZTD) predictions (http://satelite.cptec.inpe.br/zenital/). The actual version, called eta15km model, has a spatial resolution of 15 km and temporal resolution of 3 hours. In this paper the main goal is to accomplish experiments and analysis concerning the use of troposphere NWP model (eta15km model) in PPP and network-based positioning. Concerning PPP it was used data from dozens of stations over the Brazilian territory, including Amazon forest. The results obtained with NWP model were compared with Hopfield one. NWP model presented the best results in all experiments. Related to network-based positioning it was used data from GNSS/SP Network in São Paulo State, Brazil. This network presents the best configuration in the country to realize this kind of positioning. Actually the network is composed by twenty stations (http://www.fct.unesp.br/#!/pesquisa/grupos-de-estudo-e-pesquisa/gege//gnss-sp-network2789/). The

Characteristics of skylight at the zenith during twilight as indicators of atmospheric turbidity. 2: Intensity and color ratio.

PubMed

Coulson, K L

1981-05-01

This is the second of two papers based on an extensive series of measurements of the intensity and polarization of light from the zenith sky during periods of twilight made at an altitude of 3400 m on the island of Hawaii. Part 1 dealt with the skylight polarization; part 2 is on the measured intensity and quantities derived from the intensity. The principal results are that (1) the polarization and intensity of light from the zenith during twilight are sensitive indicators of the existence of turbid layers in the stratosphere and upper troposphere, and (2) at least at Mauna Loa primary scattering of the sunlight incident on the upper atmosphere during twilight is strongly dominant over secondary or multiple scattering at wavelengths beyond ~0.60microm, whereas this is much less true at shorter wavelengths. It is suggested that the development and general use of a simple twilight polarimeter would greatly facilitate determinations of turbidity in the upper layers of the atmosphere.

Generation of High Resolution Water Vapour Fields from GPS Observations and Integration With ECMWF and MODIS

NASA Astrophysics Data System (ADS)

Yu, C.; Li, Z.; Penna, N. T.

2016-12-01

Precipitable water vapour (PWV) can be routinely retrieved from ground-based GPS arrays in all-weather conditions and also in real-time. But to provide dense spatial coverage maps, for example for calibrating SAR images, for correcting atmospheric effects in Network RTK GPS positioning and which may be used for numerical weather prediction, the pointwise GPS PWV measurements must be interpolated. Several previous interpolation studies have addressed the importance of the elevation dependency of water vapour, but it is often a challenge to separate elevation-dependent tropospheric delays from turbulent components. We present a tropospheric turbulence iterative decomposition model that decouples the total PWV into (i) a stratified component highly correlated with topography which therefore delineates the vertical troposphere profile, and (ii) a turbulent component resulting from disturbance processes (e.g., severe weather) in the troposphere which trigger uncertain patterns in space and time. We will demonstrate that the iterative decoupled interpolation model generates improved dense tropospheric water vapour fields compared with elevation dependent models, with similar accuracies obtained over both flat and mountainous terrain, as well as for both inland and coastal areas. We will also show that our GPS-based model may be enhanced with ECMWF zenith tropospheric delay and MODIS PWV, producing multi-data sources high temporal-spatial resolution PWV fields. These fields were applied to Sentinel-1 SAR interferograms over the Los Angeles region, for which a maximum noise reduction due to atmosphere artifacts reached 85%. The results reveal that the turbulent troposphere noise, especially those in a SAR image, often occupy more than 50% of the total zenith tropospheric delay and exert systematic, rather than random patterns.

Estimates of Zenith Total Delay trends from GPS reprocessing with autoregressive process

NASA Astrophysics Data System (ADS)

Klos, Anna; Hunegnaw, Addisu; Teferle, Felix Norman; Ebuy Abraha, Kibrom; Ahmed, Furqan; Bogusz, Janusz

2017-04-01

Nowadays, near real-time Zenith Total Delay (ZTD) estimates from Global Positioning System (GPS) observations are routinely assimilated into numerical weather prediction (NWP) models to improve the reliability of forecasts. On the other hand, ZTD time series derived from homogeneously re-processed GPS observations over long periods have the potential to improve our understanding of climate change on various temporal and spatial scales. With such time series only recently reaching somewhat adequate time spans, the application of GPS-derived ZTD estimates to climate monitoring is still to be developed further. In this research, we examine the character of noise in ZTD time series for 1995-2015 in order to estimate more realistic magnitudes of trend and its uncertainty than would be the case if the stochastic properties are not taken into account. Furthermore, the hourly sampled, homogeneously re-processed and carefully homogenized ZTD time series from over 700 globally distributed stations were classified into five major climate zones. We found that the amplitudes of annual signals reach values of 10-150 mm with minimum values for the polar and Alpine zones. The amplitudes of daily signals were estimated to be 0-12 mm with maximum values found for the dry zone. We examined seven different noise models for the residual ZTD time series after modelling all known periodicities. This identified a combination of white plus autoregressive process of fourth order to be optimal to match all changes in power of the ZTD data. When the stochastic properties are neglected, ie. a pure white noise model is employed, only 11 from 120 trends were insignificant. Using the optimum noise model more than half of the 120 examined trends became insignificant. We show that the uncertainty of ZTD trends is underestimated by a factor of 3-12 when the stochastic properties of the ZTD time series are ignored and we conclude that it is essential to properly model the noise characteristics of

Real-Time Tropospheric Product Establishment and Accuracy Assessment in China

NASA Astrophysics Data System (ADS)

Chen, M.; Guo, J.; Wu, J.; Song, W.; Zhang, D.

2018-04-01

Tropospheric delay has always been an important issue in Global Navigation Satellite System (GNSS) processing. Empirical tropospheric delay models are difficult to simulate complex and volatile atmospheric environments, resulting in poor accuracy of the empirical model and difficulty in meeting precise positioning demand. In recent years, some scholars proposed to establish real-time tropospheric product by using real-time or near-real-time GNSS observations in a small region, and achieved some good results. This paper uses real-time observing data of 210 Chinese national GNSS reference stations to estimate the tropospheric delay, and establishes ZWD grid model in the country wide. In order to analyze the influence of tropospheric grid product on wide-area real-time PPP, this paper compares the method of taking ZWD grid product as a constraint with the model correction method. The results show that the ZWD grid product estimated based on the national reference stations can improve PPP accuracy and convergence speed. The accuracy in the north (N), east (E) and up (U) direction increase by 31.8 %,15.6 % and 38.3 %, respectively. As with the convergence speed, the accuracy of U direction experiences the most improvement.

Radicals and Aerosols in the Troposphere and Lower Stratosphere

NASA Astrophysics Data System (ADS)

Volkamer, Rainer; Koenig, Theodore; Dix, Barbara

2016-06-01

The remote tropical free troposphere (FT) is one of the most relevant atmospheric environments on Earth. About 75% of the global tropospheric O3 and CH4 loss occurs at tropical latitudes. Tropospheric bromine and iodine catalytically destroy tropospheric O3, oxidize atmospheric mercury, and modify oxidative capacity, and aerosols. Oxygenated VOCs (OVOC) modify HOx (= OH + HO2), NOx (= NO + NO2), tropospheric O3, aerosols, and are a sink for BrOx (= Br + BrO). Until recently, atmospheric models were untested for lack of vertically resolved measurements of BrO and IO radicals in the tropical troposphere. BrO and IO are highly reactive trace gases. Even very low concentrations (parts per trillion; 1 pptv = 10-12 volume mixing ratio) can significantly modify the lifetime of climate active gases, and determine (bromine) the rate limiting step of mercury oxidation in air (that is washed out, and subsequently bio-accumulates in fish). Analytical challenges arise when these radicals modify in sampling lines. Sensitive yet robust, portable, and inherently calibrated measurements directly in the open atmosphere have recently been demonstrated by means of limb-measurements of scattered solar photons by the University of Colorado Airborne Multi-AXis DOAS instrument (CU AMAX-DOAS) from research aircraft. The CU AMAX-DOAS instrument is optimized to (1) locate BrO, IO and glyoxal (a short lived OVOC) in the troposphere, (2) decouple stratospheric absorbers, (3) maximize sensitivity at instrument altitude, (4) facilitate altitude control and (5) enable observations over a wide range of solar zenith angles. Further, (6) the filling-in of Fraunhofer lines (Ring-effect) by Raman Scattering offers interesting opportunities for radiative closure studies to assess the effects of aerosols on Climate.

Development of a System to Generate Near Real Time Tropospheric Delay and Precipitable Water Vapor in situ at Geodetic GPS Stations, to Improve Forecasting of Severe Weather Events

NASA Astrophysics Data System (ADS)

Moore, A. W.; Bock, Y.; Geng, J.; Gutman, S. I.; Laber, J. L.; Morris, T.; Offield, D. G.; Small, I.; Squibb, M. B.

2012-12-01

We describe a system under development for generating ultra-low latency tropospheric delay and precipitable water vapor (PWV) estimates in situ at a prototype network of geodetic GPS sites in southern California, and demonstrating their utility in forecasting severe storms commonly associated with flooding and debris flow events along the west coast of North America through infusion of this meteorological data at NOAA National Weather Service (NWS) Forecast Offices and the NOAA Earth System Research Laboratory (ESRL). The first continuous geodetic GPS network was established in southern California in the early 1990s and much of it was converted to real-time (latency <1s) high-rate (1Hz) mode over the following decades. GPS stations are multi-purpose and can also provide estimates of tropospheric zenith delays, which can be converted into mm-accuracy PWV using collocated pressure and temperature measurements, the basis for GPS meteorology (Bevis et al. 1992, 1994; Duan et al. 1996) as implemented by NOAA with a nationwide distribution of about 300 GPS-Met stations providing PW estimates at subhourly resolution currently used in operational weather forecasting in the U.S. We improve upon the current paradigm of transmitting large quantities of raw data back to a central facility for processing into higher-order products. By operating semi-autonomously, each station will provide low-latency, high-fidelity and compact data products within the constraints of the narrow communications bandwidth that often occurs in the aftermath of natural disasters. The onsite ambiguity-resolved precise point positioning solutions are enabled by a power-efficient, low-cost, plug-in Geodetic Module for fusion of data from in situ sensors including GPS and a low-cost MEMS meteorological sensor package. The decreased latency (~5 minutes) PW estimates will provide the detailed knowledge of the distribution and magnitude of PW that NWS forecasters require to monitor and predict severe winter

Effective recombination coefficient and solar zenith angle effects on low-latitude D-region ionosphere evaluated from VLF signal amplitude and its time delay during X-ray solar flares

NASA Astrophysics Data System (ADS)

Basak, Tamal; Chakrabarti, Sandip Kumar

Excess solar X-ray radiation during solar flares causes an enhancement of ionization in the ionospheric D-region and hence affects sub-ionospherically propagating VLF signal amplitude and phase. VLF signal amplitude perturbation (DeltaA) and amplitude time delay (Deltat) (vis- ´a-vis corresponding X-ray light curve as measured by GOES-15) of NWC/19.8 kHz signal have been computed for solar flares which is detected by us during Jan-Sep 2011. The signal is recorded by SoftPAL facility of IERC/ICSP, Sitapur (22(°) 27'N, 87(°) 45'E), West Bengal, India. In first part of the work, using the well known LWPC technique, we simulated the flare induced excess lower ionospheric electron density by amplitude perturbation method. Unperturbed D-region electron density is also obtained from simulation and compared with IRI-model results. Using these simulation results and time delay as key parameters, we calculate the effective electron recombination coefficient (alpha_{eff}) at solar flare peak region. Our results match with the same obtained by other established models. In the second part, we dealt with the solar zenith angle effect on D-region during flares. We relate this VLF data with the solar X-ray data. We find that the peak of the VLF amplitude occurs later than the time of the X-ray peak for each flare. We investigate this so-called time delay (Deltat). For the C-class flares we find that there is a direct correspondence between Deltat of a solar flare and the average solar zenith angle Z over the signal propagation path at flare occurrence time. Now for deeper analysis, we compute the Deltat for different local diurnal time slots DT. We find that while the time delay is anti-correlated with the flare peak energy flux phi_{max} independent of these time slots, the goodness of fit, as measured by reduced-chi(2) , actually worsens as the day progresses. The variation of the Z dependence of reduced-chi(2) seems to follow the variation of standard deviation of Z along

Satellite laser ranging as a tool for the recovery of tropospheric gradients

NASA Astrophysics Data System (ADS)

Drożdżewski, M.; Sośnica, K.

2018-11-01

Space geodetic techniques, such as Global Navigation Satellite Systems (GNSS) and Very Long Baseline Interferometry (VLBI) have been extensively used for the recovery of the tropospheric parameters. Both techniques employ microwave observations, for which the troposphere is a non-dispersive medium and which are very sensitive to the water vapor content. Satellite laser ranging (SLR) is the only space geodetic technique used for the definition of the terrestrial reference frames which employs optical - laser observations. The SLR sensitivity to the hydrostatic part of the troposphere delay is similar to that of microwave observations, whereas the sensitivity of laser observations to non-hydrostatic part of the delay is about two orders of magnitude smaller than in the case of microwave observations. Troposphere is a dispersive medium for optical wavelengths, which means that the SLR tropospheric delay depends on the laser wavelength. This paper presents the sensitivity and capability of the SLR observations for the recovery of azimuthal asymmetry over the SLR stations, which can be described as horizontal gradients of the troposphere delay. For the first time, the horizontal gradients are estimated, together with other parameters typically estimated from the SLR observations to spherical LAGEOS satellites, i.e., station coordinates, earth rotation parameters, and satellite orbits. Most of the SLR stations are co-located with GNSS receivers, thus, a cross-correlation between both techniques is possible. We compare our SLR horizontal gradients to GNSS results and to the horizontal gradients derived from the numerical weather models (NWM). Due to a small number of the SLR observations, SLR is not capable of reconstructing short-period phenomena occurring in the atmosphere. However, the long-term analysis allows for the recovery of the atmosphere asymmetry using SLR. As a result, the mean offsets of the SLR-derived horizontal gradients agree to the level of 47%, 74%, 54

The Altimetric Wet Tropospheric Correction: Progress Since The ERS-1 Mission

NASA Astrophysics Data System (ADS)

Eymard, L.; Obligis, E.

2006-07-01

To correct for the path delay due to humidity in the troposphere, dedicated microwave radiometers have been added to altimeters on ESA and NASA/CNES missions. This paper presents the major issues with calibration and retrieval of the wet tropospheric path d elay s ince E RS1, a s w ell a s n ew developments for in-flight monitoring, retrieval of the path delay over the open ocean and in coastal regions.

Establishment of a Site-Specific Tropospheric Model Based on Ground Meteorological Parameters over the China Region.

PubMed

Zhou, Chongchong; Peng, Bibo; Li, Wei; Zhong, Shiming; Ou, Jikun; Chen, Runjing; Zhao, Xinglong

2017-07-27

China is a country of vast territory with complicated geographical environment and climate conditions. With the rapid progress of the Chinese BeiDou satellite navigation system (BDS); more accurate tropospheric models must be applied to improve the accuracy of navigation and positioning. Based on the formula of the Saastamoinen and Callahan models; this study develops two single-site tropospheric models (named SAAS_S and CH_S models) for the Chinese region using radiosonde data from 2005 to 2012. We assess the two single-site tropospheric models with radiosonde data for 2013 and zenith tropospheric delay (ZTD) data from four International GNSS Service (IGS) stations and compare them to the results of the Saastamoinen and Callahan models. The experimental results show that: the mean accuracy of the SAAS_S model (bias: 0.19 cm; RMS: 3.19 cm) at all radiosonde stations is superior to those of the Saastamoinen (bias: 0.62 cm; RMS: 3.62 cm) and CH_S (bias: -0.05 cm; RMS: 3.38 cm) models. In most Chinese regions; the RMS values of the SAAS_S and CH_S models are about 0.51~2.12 cm smaller than those of their corresponding source models. The SAAS_S model exhibits a clear improvement in the accuracy over the Saastamoinen model in low latitude regions. When the SAAS_S model is replaced by the SAAS model in the positioning of GNSS; the mean accuracy of vertical direction in the China region can be improved by 1.12~1.55 cm and the accuracy of vertical direction in low latitude areas can be improved by 1.33~7.63 cm. The residuals of the SAAS_S model are closer to a normal distribution compared to those of the Saastamoinen model. Single-site tropospheric models based on the short period of the most recent data (for example 2 years) can also achieve a satisfactory accuracy. The average performance of the SAAS_S model (bias: 0.83 cm; RMS: 3.24 cm) at four IGS stations is superior to that of the Saastamoinen (bias: -0.86 cm; RMS: 3.59 cm) and CH_S (bias: 0.45 cm; RMS: 3.38 cm

Establishment of a Site-Specific Tropospheric Model Based on Ground Meteorological Parameters over the China Region

PubMed Central

Zhou, Chongchong; Peng, Bibo; Li, Wei; Zhong, Shiming; Ou, Jikun; Chen, Runjing; Zhao, Xinglong

2017-01-01

China is a country of vast territory with complicated geographical environment and climate conditions. With the rapid progress of the Chinese BeiDou satellite navigation system (BDS); more accurate tropospheric models must be applied to improve the accuracy of navigation and positioning. Based on the formula of the Saastamoinen and Callahan models; this study develops two single-site tropospheric models (named SAAS_S and CH_S models) for the Chinese region using radiosonde data from 2005 to 2012. We assess the two single-site tropospheric models with radiosonde data for 2013 and zenith tropospheric delay (ZTD) data from four International GNSS Service (IGS) stations and compare them to the results of the Saastamoinen and Callahan models. The experimental results show that: the mean accuracy of the SAAS_S model (bias: 0.19 cm; RMS: 3.19 cm) at all radiosonde stations is superior to those of the Saastamoinen (bias: 0.62 cm; RMS: 3.62 cm) and CH_S (bias: −0.05 cm; RMS: 3.38 cm) models. In most Chinese regions; the RMS values of the SAAS_S and CH_S models are about 0.51~2.12 cm smaller than those of their corresponding source models. The SAAS_S model exhibits a clear improvement in the accuracy over the Saastamoinen model in low latitude regions. When the SAAS_S model is replaced by the SAAS model in the positioning of GNSS; the mean accuracy of vertical direction in the China region can be improved by 1.12~1.55 cm and the accuracy of vertical direction in low latitude areas can be improved by 1.33~7.63 cm. The residuals of the SAAS_S model are closer to a normal distribution compared to those of the Saastamoinen model. Single-site tropospheric models based on the short period of the most recent data (for example 2 years) can also achieve a satisfactory accuracy. The average performance of the SAAS_S model (bias: 0.83 cm; RMS: 3.24 cm) at four IGS stations is superior to that of the Saastamoinen (bias: −0.86 cm; RMS: 3.59 cm) and CH_S (bias: 0.45 cm; RMS: 3.38 cm

Atmospheric Phase Delay in Sentinel SAR Interferometry

NASA Astrophysics Data System (ADS)

Krishnakumar, V.; Monserrat, O.; Crosetto, M.; Crippa, B.

2018-04-01

The repeat-pass Synthetic Aperture Radio Detection and Ranging (RADAR) Interferometry (InSAR) has been a widely used geodetic technique for observing the Earth's surface, especially for mapping the Earth's topography and deformations. However, InSAR measurements are prone to atmospheric errors. RADAR waves traverse the Earth's atmosphere twice and experience a delay due to atmospheric refraction. The two major layers of the atmosphere (troposphere and ionosphere) are mainly responsible for this delay in the propagating RADAR wave. Previous studies have shown that water vapour and clouds present in the troposphere and the Total Electron Content (TEC) of the ionosphere are responsible for the additional path delay in the RADAR wave. The tropospheric refractivity is mainly dependent on pressure, temperature and partial pressure of water vapour. The tropospheric refractivity leads to an increase in the observed range. These induced propagation delays affect the quality of phase measurement and introduce errors in the topography and deformation fields. The effect of this delay was studied on a differential interferogram (DInSAR). To calculate the amount of tropospheric delay occurred, the meteorological data collected from the Spanish Agencia Estatal de Meteorología (AEMET) and MODIS were used. The interferograms generated from Sentinel-1 carrying C-band Synthetic Aperture RADAR Single Look Complex (SLC) images acquired on the study area are used. The study area consists of different types of scatterers exhibiting different coherence. The existing Saastamoinen model was used to perform a quantitative evaluation of the phase changes caused by pressure, temperature and humidity of the troposphere during the study. Unless the phase values due to atmospheric disturbances are not corrected, it is difficult to obtain accurate measurements. Thus, the atmospheric error correction is essential for all practical applications of DInSAR to avoid inaccurate height and deformation

Effective recombination coefficient and solar zenith angle effects on low-latitude D-region ionosphere evaluated from VLF signal amplitude and its time delay during X-ray solar flares

NASA Astrophysics Data System (ADS)

Basak, Tamal; Chakrabarti, Sandip K.

2013-12-01

Excess solar X-ray radiation during solar flares causes an enhancement of ionization in the ionospheric D-region and hence affects sub-ionospherically propagating VLF signal amplitude and phase. VLF signal amplitude perturbation (Δ A) and amplitude time delay (Δ t) (vis-á-vis corresponding X-ray light curve as measured by GOES-15) of NWC/19.8 kHz signal have been computed for solar flares which is detected by us during Jan-Sep 2011. The signal is recorded by SoftPAL facility of IERC/ICSP, Sitapur (22∘ 27'N, 87∘ 45'E), West Bengal, India. In first part of the work, using the well known LWPC technique, we simulated the flare induced excess lower ionospheric electron density by amplitude perturbation method. Unperturbed D-region electron density is also obtained from simulation and compared with IRI-model results. Using these simulation results and time delay as key parameters, we calculate the effective electron recombination coefficient ( α eff ) at solar flare peak region. Our results match with the same obtained by other established models. In the second part, we dealt with the solar zenith angle effect on D-region during flares. We relate this VLF data with the solar X-ray data. We find that the peak of the VLF amplitude occurs later than the time of the X-ray peak for each flare. We investigate this so-called time delay (Δ t). For the C-class flares we find that there is a direct correspondence between Δ t of a solar flare and the average solar zenith angle Z over the signal propagation path at flare occurrence time. Now for deeper analysis, we compute the Δ t for different local diurnal time slots DT. We find that while the time delay is anti-correlated with the flare peak energy flux ϕ max independent of these time slots, the goodness of fit, as measured by reduced- χ 2, actually worsens as the day progresses. The variation of the Z dependence of reduced- χ 2 seems to follow the variation of standard deviation of Z along the T x - R x propagation

Ground-Based GPS Sensing of Azimuthal Variations in Precipitable Water Vapor

NASA Technical Reports Server (NTRS)

Kroger, P. M.; Bar-Sever, Y. E.

1997-01-01

Current models for troposphere delay employed by GPS software packages map the total zenith delay to the line-of-sight delay of the individual satellite-receiver link under the assumption of azimuthal homogeneity. This could be a poor approximation for many sites, in particular, those located at an ocean front or next to a mountain range. We have modified the GIPSY-OASIS II software package to include a simple non-symmetric mapping function (MacMillan, 1995) which introduces two new parameters.

Sensitivity of airborne radio occultation to tropospheric properties over ocean and land

NASA Astrophysics Data System (ADS)

Xie, Feiqin; Adhikari, Loknath; Haase, Jennifer S.; Murphy, Brian; Wang, Kuo-Nung; Garrison, James L.

2018-02-01

Airborne radio occultation (ARO) measurements collected during a ferry flight at the end of the PRE-Depression Investigation of Cloud-systems in the Tropics (PREDICT) field campaign from the Virgin Islands to Colorado are analyzed. The large contrast in atmospheric conditions along the flight path from the warm and moist Caribbean Sea to the much drier and cooler continental conditions provides a unique opportunity to address the sensitivity of ARO measurements to the tropospheric temperature and moisture changes. This long flight at nearly constant altitude (˜ 13 km) provided an optimal configuration for simultaneous high-quality ARO measurements from two high-gain side-looking antennas, as well as one relatively lower gain zenith (top) antenna. The omnidirectional top antenna has the advantage of tracking robustly more occulting satellites in all direction as compared to the limited-azimuth tracking of the side-looking antennas. Two well-adapted radio-holographic bending angle retrieval methods, full-spectrum inversion (FSI) and phase matching (PM), were compared with the standard geometric-optics (GO) retrieval method. Comparison of the ARO retrievals from the top antenna with the near-coincident ECMWF reanalysis-interim (ERA-I) profiles shows only a small root-mean-square (RMS) refractivity difference of ˜ 0.3 % in the drier upper troposphere from ˜ 5 to ˜ 11.5 km over both land and ocean. Both the FSI and PM methods improve the ARO retrievals in the moist lower troposphere and reduce the negative bias found in the GO retrieval due to atmospheric multipath. In the lowest layer of the troposphere, the ARO refractivity derived using FSI shows a negative bias of about -2 %. The increase of the refractivity bias occurs below 5 km over the ocean and below 3.5 km over land, corresponding to the approximate altitude of large vertical moisture gradients above the ocean and land surface, respectively. In comparisons to radiosondes, the FSI ARO soundings capture well

Performance analysis of a GPS equipment by general linear models approach

NASA Astrophysics Data System (ADS)

Teodoro, M. Filomena; Gonçalves, Fernando M.; Correia, Anacleto

2017-06-01

One of the major challenges in processing high-accurate long baselines is the presence of un-modelled ionospheric and tropospheric delays. There are effective mitigation strategies for ionospheric biases, such as the ionosphere-free linear combination of L1 and L2 carrier-phase, which can remove about 98% of the first-order ionospheric biases. With few exceptions this was the solution found by LGO for the 11760 baselines processed in this research. Therefore, for successful results, the appropriated approach to the mitigation of biases due to tropospheric delays is vital. The main aim of the investigations presented in this work was to evaluate the improvements, or not, of the rate of baselines successfully produced by adopting an advanced tropospheric bias mitigation strategy as opposed to a sample tropospheric bias mitigation approach. In both cases LGO uses as a priori tropospheric model the simplified Hopfield model, improved in the first case with a zenith tropospheric scale factor per station. Being aware that 1D and 2D present different behaviors, both cases are analyzed individually with each strategy.

Some tests of wet tropospheric calibration for the CASA Uno Global Positioning System experiment

NASA Technical Reports Server (NTRS)

Dixon, T. H.; Wolf, S. Kornreich

1990-01-01

Wet tropospheric path delay can be a major error source for Global Positioning System (GPS) geodetic experiments. Strategies for minimizing this error are investigted using data from CASA Uno, the first major GPS experiment in Central and South America, where wet path delays may be both high and variable. Wet path delay calibration using water vapor radiometers (WVRs) and residual delay estimation is compared with strategies where the entire wet path delay is estimated stochastically without prior calibration, using data from a 270-km test baseline in Costa Rica. Both approaches yield centimeter-level baseline repeatability and similar tropospheric estimates, suggesting that WVR calibration is not critical for obtaining high precision results with GPS in the CASA region.

Software for Generating Troposphere Corrections for InSAR Using GPS and Weather Model Data

NASA Technical Reports Server (NTRS)

Moore, Angelyn W.; Webb, Frank H.; Fishbein, Evan F.; Fielding, Eric J.; Owen, Susan E.; Granger, Stephanie L.; Bjoerndahl, Fredrik; Loefgren, Johan; Fang, Peng; Means, James D.;

Analysis of Satellite-Derived Arctic Tropospheric BrO Columns in Conjunction with Aircraft Measurements During ARCTAS and ARCPAC

NASA Technical Reports Server (NTRS)

Choi, S.; Wang, Y.; Salawitch, R. J.; Canty, T.; Joiner, J.; Zeng, T.; Kurosu, T. P.; Chance, K.; Richter, A.; Huey, L. G.;

Variability of wet troposphere delays over inland reservoirs as simulated by a high-resolution regional climate model

NASA Astrophysics Data System (ADS)

Clark, E.; Lettenmaier, D. P.

2014-12-01

Satellite radar altimetry is widely used for measuring global sea level variations and, increasingly, water height variations of inland water bodies. Existing satellite radar altimeters measure water surfaces directly below the spacecraft (approximately at nadir). Over the ocean, most of these satellites use radiometry to measure the delay of radar signals caused by water vapor in the atmosphere (also known as the wet troposphere delay (WTD)). However, radiometry can only be used to estimate this delay over the largest inland water bodies, such as the Great Lakes, due to spatial resolution issues. As a result, atmospheric models are typically used to simulate and correct for the WTD at the time of observations. The resolutions of these models are quite coarse, at best about 5000 km2 at 30˚N. The upcoming NASA- and CNES-led Surface Water and Ocean Topography (SWOT) mission, on the other hand, will use interferometric synthetic aperture radar (InSAR) techniques to measure a 120-km-wide swath of the Earth's surface. SWOT is expected to make useful measurements of water surface elevation and extent (and storage change) for inland water bodies at spatial scales as small as 250 m, which is much smaller than current altimetry targets and several orders of magnitude smaller than the models used for wet troposphere corrections. Here, we calculate WTD from very high-resolution (4/3-km to 4-km) simulations of the Weather Research and Forecasting (WRF) regional climate model, and use the results to evaluate spatial variations in WTD. We focus on six U.S. reservoirs: Lake Elwell (MT), Lake Pend Oreille (ID), Upper Klamath Lake (OR), Elephant Butte (NM), Ray Hubbard (TX), and Sam Rayburn (TX). The reservoirs vary in climate, shape, use, and size. Because evaporation from open water impacts local water vapor content, we compare time series of WTD over land and water in the vicinity of each reservoir. To account for resolution effects, we examine the difference in WRF

Forecast Vienna Mapping Functions 1 for real-time analysis of space geodetic observations

NASA Astrophysics Data System (ADS)

Boehm, J.; Kouba, J.; Schuh, H.

2009-05-01

The Vienna Mapping Functions 1 (VMF1) as provided by the Institute of Geodesy and Geophysics (IGG) at the Vienna University of Technology are the most accurate mapping functions for the troposphere delays that are available globally and for the entire history of space geodetic observations. So far, the VMF1 coefficients have been released with a time delay of almost two days; however, many scientific applications require their availability in near real-time, e.g. the Ultra Rapid solutions of the International GNSS Service (IGS) or the analysis of the Intensive sessions of the International VLBI Service (IVS). Here we present coefficients of the VMF1 as well as the hydrostatic and wet zenith delays that have been determined from forecasting data of the European Centre for Medium-Range Weather Forecasts (ECMWF) and provided on global grids. The comparison with parameters derived from ECMWF analysis data shows that the agreement is at the 1 mm level in terms of station height, and that the differences are larger for the wet mapping functions than for the hydrostatic mapping functions and the hydrostatic zenith delays. These new products (VMF1-FC and hydrostatic zenith delays from forecast data) can be used in real-time analysis of geodetic data without significant loss of accuracy.

The Algorithm Theoretical Basis Document for the Atmospheric Delay Correction to GLAS Laser Altimeter Ranges. Volume 8

NASA Technical Reports Server (NTRS)

Herring, Thomas A.; Quinn, Katherine J.

2012-01-01

NASA s Ice, Cloud, and Land Elevation Satellite (ICESat) mission will be launched late 2001. It s primary instrument is the Geoscience Laser Altimeter System (GLAS) instrument. The main purpose of this instrument is to measure elevation changes of the Greenland and Antarctic icesheets. To accurately measure the ranges it is necessary to correct for the atmospheric delay of the laser pulses. The atmospheric delay depends on the integral of the refractive index along the path that the laser pulse travels through the atmosphere. The refractive index of air at optical wavelengths is a function of density and molecular composition. For ray paths near zenith and closed form equations for the refractivity, the atmospheric delay can be shown to be directly related to surface pressure and total column precipitable water vapor. For ray paths off zenith a mapping function relates the delay to the zenith delay. The closed form equations for refractivity recommended by the International Union of Geodesy and Geophysics (IUGG) are optimized for ground based geodesy techniques and in the next section we will consider whether these equations are suitable for satellite laser altimetry.

Constraints on a Broadcast Innovation: Zenith's Phonevision System, 1931-1972.

ERIC Educational Resources Information Center

Bellamy, Robert V., Jr.

1988-01-01

Demonstrates that the reason for Zenith's Phonevision's failure was the interweaving of such individual factors as the actions of the regulatory system and the opposition of the broadcast and film industries, along with the internal activities of Zenith and prevailing market conditions. (MS)

Meteoroid stream flux densities and the zenith exponent

NASA Astrophysics Data System (ADS)

Molau, Sirko; Barentsen, Geert

2013-01-01

The MetRec software was recently extended to measure the limiting magnitude in real-time, and to determine meteoroid stream flux densities. This paper gives a short overview of the applied algorithms. We introduce the MetRec Flux Viewer, a web tool to visualize activity profiles on- line. Starting from the Lyrids 2011, high-quality flux density profiles were derived from IMO Video Network observations for every major meteor shower. They are often in good agreement with visual data. Analyzing the 2011 Perseids, we found systematic daily variations in the flux density profile, which can be attributed to a zenith exponent gamma > 1.0. We analyzed a number of meteor showers in detail and found zenith exponent variations from shower to shower in the range between 1.55 and 2.0. The average value over all analyzed showers is gamma = 1.75. In order to determine the zenith exponent precisely, the observations must cover a large altitude range (at least 45 degrees).

Thromboembolic Complications after Zenith{sup ®} Low Profile Endovascular Graft for Infrarenal Abdominal Aneurysms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Urlings, T. A. J., E-mail: t-urlings@hotmail.com; Vries, A. C. de, E-mail: a.de.vries@mchaaglanden.nl; Mol van Otterloo, J. C. A. de, E-mail: a.de.molvanotterloo@mchaaglanden.nl

2015-06-15

PurposeThe purpose of this study was to objectify and evaluate risk factors for thromboembolic complications after treatment with a Zenith{sup ®} Low Profile Endovascular Graft (Zenith LP). Results were compared with those in the recent literature on endovascular aortic repair (EVAR) and with the thromboembolic complications in the patient group treated with a Zenith Flex Endovascular Graft in our institute in the period before the use of the Zenith LP.Materials and MethodsAll consecutive patients who were suitable for treatment with a Zenith LP endograft between October 2010 and December 2011 were included. The preprocedural computed tomography scan (CT), procedural angiographicmore » images, and the postprocedural CT scans were evaluated for risk factors for and signs of thromboembolic complications. All patients treated between December 2007 and November 2012 with a Zenith Flex endograft were retrospectively evaluated for thromboembolic complications.ResultsIn the study period 17 patients were treated with a LP Zenith endograft. Limb occlusion occurred in 35 % of the patients. Limb occlusions occurred in 24 % of the limbs at risk (one limb occluded twice). In one patient two risk factors for limb occlusion were identified. Between December 2007 and November 2012, a total of 43 patients were treated with a Zenith Flex endograft. No limb occlusion or distal embolization occurred.ConclusionDespite that this was a small retrospective study, the Zenith LP endograft seems to be associated with more frequent thromboembolic complications compared with the known limb occlusion rates in the literature and those of the patients treated with a Zenith Flex endograft in our institute.« less

A test of water vapor radiometer-based troposphere calibration using VLBI observations on a 21-kilometer baseline

NASA Technical Reports Server (NTRS)

Linfield, R. P.; Teitelbaum, L. P.; Skjerve, L. J.; Keihm, S. J.; Walter, S. J.; Mahoney, M. J.; Treuhaft, R. N.

1995-01-01

Simultaneous very long baseline interferometry (VLBI) and water vapor radiometer (WVR) measurements on a 21 km baseline showed that calibration by WVRs removed a significant fraction of the effect of tropospheric delay fluctuations for these experiments. From comparison of the residual delay variations within scans and between scans, the total tropospheric contribution t the delay residuals for each of the three 5 to 20 hour sessions was estimated as 1, 17, and 10%, with the first value being uncertain. The observed improvement in rms residual delay from WVR calibration during these three sessions was 4, 16, and 2%, respectively. The improvement is consistent with the estimated 2 to 3 mm path delay precision of current WVRs. The VLBI measurements, of natural radio sources, were conducted in April and May 1993 at Goldstone, California. Dual-frequency (2.3 and 8.4 GHz) observations were employed to remove the effects of charged particles from the data. Measurements with co-pointed WVRs, located within 50 m of the axis of each antenna, were performed to test the ability of the WVRs to calibrate line-of-sight path delays. Factors that made WVR performance assessment difficult included (1) the fact that the level of tropospheric fluctuations was smaller than is typical for Goldstone during these experiments and (2) VLBI delay variations on longer time scales (i.e., over multiple scans) contained uncalibrated instrumental effects (probably a result of slow temperature variations in the VLBI hardware) that were larger than the tropospheric effects.

The prediction of zenith range refraction from surface measurements of meteorological parameters. [mathematical models of atmospheric refraction used to improve spacecraft tracking space navigation

NASA Technical Reports Server (NTRS)

Berman, A. L.

1976-01-01

In the last two decades, increasingly sophisticated deep space missions have placed correspondingly stringent requirements on navigational accuracy. As part of the effort to increase navigational accuracy, and hence the quality of radiometric data, much effort has been expended in an attempt to understand and compute the tropospheric effect on range (and hence range rate) data. The general approach adopted has been that of computing a zenith range refraction, and then mapping this refraction to any arbitrary elevation angle via an empirically derived function of elevation. The prediction of zenith range refraction derived from surface measurements of meteorological parameters is presented. Refractivity is separated into wet (water vapor pressure) and dry (atmospheric pressure) components. The integration of dry refractivity is shown to be exact. Attempts to integrate wet refractivity directly prove ineffective; however, several empirical models developed by the author and other researchers at JPL are discussed. The best current wet refraction model is here considered to be a separate day/night model, which is proportional to surface water vapor pressure and inversely proportional to surface temperature. Methods are suggested that might improve the accuracy of the wet range refraction model.

The Parallax of the Red Hypergiant VX Sgr with Accurate Tropospheric Delay Calibration

NASA Astrophysics Data System (ADS)

Xu, Shuangjing; Zhang, Bo; Reid, Mark J.; Menten, Karl M.; Zheng, Xingwu; Wang, Guangli

2018-05-01

We report astrometric results of VLBI phase-referencing observations of 22 GHz H2O masers emission toward the red hypergiant VX Sgr, one of most massive and luminous red hypergiant stars in our Galaxy, using the Very Long Baseline Array. A background source, J1820‑2528, projected 4.°4 from the target VX Sgr, was used as the phase reference. For the low decl. of these sources, such a large separation normally would seriously degrade the relative astrometry. We use a two-step method of tropospheric delay calibration, which combines the VLBI geodetic-block (or Global Positioning System) calibration with an image-optimization calibration, to obtain a trigonometric parallax of 0.64 ± 0.04 mas, corresponding to a distance of {1.56}-0.10+0.11 kpc. The measured proper motion of VX Sgr is 0.36 ± 0.76 and ‑2.92 ± 0.78 mas yr‑1 in the eastward and northward directions. The parallax and proper motion confirms that VX Sgr belong to the Sgr OB1 association. Rescaling bolometric luminosities in the literature to our parallax distance, we find that the luminosity of VX Sgr is (1.95 ± 0.62) × 105 L ⊙, where the uncertainty is dominated by differing photometry measurements.

The effect of the dynamic wet troposphere on VLBI measurements

NASA Technical Reports Server (NTRS)

Treuhaft, R. N.; Lanyi, G. E.

1986-01-01

Calculations using a statistical model of water vapor fluctuations yield the effect of the dynamic wet troposphere on Very Long Baseline Interferometry (VLBI) measurements. The statistical model arises from two primary assumptions: (1) the spatial structure of refractivity fluctuations can be closely approximated by elementary (Kolmogorov) turbulence theory, and (2) temporal fluctuations are caused by spatial patterns which are moved over a site by the wind. The consequences of these assumptions are outlined for the VLBI delay and delay rate observables. For example, wet troposphere induced rms delays for Deep Space Network (DSN) VLBI at 20-deg elevation are about 3 cm of delay per observation, which is smaller, on the average, than other known error sources in the current DSN VLBI data set. At 20-deg elevation for 200-s time intervals, water vapor induces approximately 1.5 x 10 to the minus 13th power s/s in the Allan standard deviation of interferometric delay, which is a measure of the delay rate observable error. In contrast to the delay error, the delay rate measurement error is dominated by water vapor fluctuations. Water vapor induced VLBI parameter errors and correlations are calculated. For the DSN, baseline length parameter errors due to water vapor fluctuations are in the range of 3 to 5 cm. The above physical assumptions also lead to a method for including the water vapor fluctuations in the parameter estimation procedure, which is used to extract baseline and source information from the VLBI observables.

Global Characterization of Tropospheric Noise for InSAR Analysis Using MODIS Data

NASA Astrophysics Data System (ADS)

Yun, S.; Hensley, S.; Chaubell, M.; Fielding, E. J.; Pan, L.; Rosen, P. A.

2013-12-01

Radio wave's differential phase delay variation through the troposphere is one of the largest error sources in Interferometric Synthetic Aperture Radar (InSAR) measurements, and water vapor variability in the troposphere is known to be the dominant factor. We use the precipitable water vapor products from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) sensors mounted on Terra and Aqua satellites to produce tropospheric noise maps of InSAR. Then we extract a small set of characteristic parameters of its power spectral density curve and 1-D covariance function, and calculate the structure function to estimate the expected tropospheric noise level as a function of distance. The results serve two purposes: 1) to provide guidance on the expected covariance matrix for geophysical modeling, 2) to provide quantitative basis of the measurement requirements for the planned US L-band SAR mission. We build over a decade span (2000-2013) of a lookup table of the parameters derived from 2-by-2 degree tiles at 1-by-1 degree posting of global coverage, representing 10 days of each season in each year. The MODIS data were retrieved from OSCAR (Online Services for Correcting Atmosphere in Radar) server. MODIS images with 5 percent or more cloud cover were discarded. Cloud mask and sensor scanning artifacts were removed with interpolation and spectral filtering, respectively. We also mitigate topography dependent stratified tropospheric delay variation using the European Centre for Medium-Range Weather Forecasts (ECMWF) and Shuttle Radar Topography Mission Digital Elevation Models (SRTM DEMs).

An Inequality Constrained Least-Squares Approach as an Alternative Estimation Procedure for Atmospheric Parameters from VLBI Observations

NASA Astrophysics Data System (ADS)

Halsig, Sebastian; Artz, Thomas; Iddink, Andreas; Nothnagel, Axel

2016-12-01

On its way through the atmosphere, radio signals are delayed and affected by bending and attenuation effects relative to a theoretical path in vacuum. In particular, the neutral part of the atmosphere contributes considerably to the error budget of space-geodetic observations. At the same time, space-geodetic techniques become more and more important in the understanding of the Earth's atmosphere, because atmospheric parameters can be linked to the water vapor content in the atmosphere. The tropospheric delay is usually taken into account by applying an adequate model for the hydrostatic component and by additionally estimating zenith wet delays for the highly variable wet component. Sometimes, the Ordinary Least Squares (OLS) approach leads to negative estimates, which would be equivalent to negative water vapor in the atmosphere and does, of course, not reflect meteorological and physical conditions in a plausible way. To cope with this phenomenon, we introduce an Inequality Constrained Least Squares (ICLS) method from the field of convex optimization and use inequality constraints to force the tropospheric parameters to be non-negative allowing for a more realistic tropospheric parameter estimation in a meteorological sense. Because deficiencies in the a priori hydrostatic modeling are almost fully compensated by the tropospheric estimates, the ICLS approach urgently requires suitable a priori hydrostatic delays. In this paper, we briefly describe the ICLS method and validate its impact with regard to station positions.

Determination of zenith hydrostatic delay and its impact on GNSS-derived integrated water vapor

NASA Astrophysics Data System (ADS)

Wang, Xiaoming; Zhang, Kefei; Wu, Suqin; He, Changyong; Cheng, Yingyan; Li, Xingxing

2017-08-01

Surface pressure is a necessary meteorological variable for the accurate determination of integrated water vapor (IWV) using Global Navigation Satellite System (GNSS). The lack of pressure observations is a big issue for the conversion of historical GNSS observations, which is a relatively new area of GNSS applications in climatology. Hence the use of the surface pressure derived from either a blind model (e.g., Global Pressure and Temperature 2 wet, GPT2w) or a global atmospheric reanalysis (e.g., ERA-Interim) becomes an important alternative solution. In this study, pressure derived from these two methods is compared against the pressure observed at 108 global GNSS stations at four epochs (00:00, 06:00, 12:00 and 18:00 UTC) each day for the period 2000-2013. Results show that a good accuracy is achieved from the GPT2w-derived pressure in the latitude band between -30 and 30° and the average value of 6 h root-mean-square errors (RMSEs) across all the stations in this region is 2.5 hPa. Correspondingly, an error of 5.8 mm and 0.9 kg m-2 in its resultant zenith hydrostatic delay (ZHD) and IWV is expected. However, for the stations located in the mid-latitude bands between -30 and -60° and between 30 and 60°, the mean value of the RMSEs is 7.3 hPa, and for the stations located in the high-latitude bands from -60 to -90° and from 60 to 90°, the mean value of the RMSEs is 9.9 hPa. The mean of the RMSEs of the ERA-Interim-derived pressure across at the selected 100 stations is 0.9 hPa, which will lead to an equivalent error of 2.1 mm and 0.3 kg m-2 in the ZHD and IWV, respectively, determined from this ERA-Interim-derived pressure. Results also show that the monthly IWV determined using pressure from ERA-Interim has a good accuracy - with a relative error of better than 3 % on a global scale; thus, the monthly IWV resulting from ERA-Interim-derived pressure has the potential to be used for climate studies, whilst the monthly IWV resulting from GPT2w

GNSS-derived Path Delay Plus (GPD+): a methodology for the computation of improved wet tropospheric corrections for coastal altimetry

NASA Astrophysics Data System (ADS)

Fernandes, Joana; Lázaro, Clara; Ambrózio, Américo; Restano, Marco; Benveniste, Jérôme

2017-04-01

Satellite altimetry missions provide the sea surface height above a reference ellipsoid with centimetric accuracy as long as all terms involved in the altimeter measurement system (satellite orbit, altimeter range between the satellite and the sea surface, and instrumental, range and geophysical corrections) are known with the same accuracy. The wet tropospheric correction (WTC), the range correction that accounts for the delay induced by the presence of water vapour and liquid water in the troposphere, has an absolute value less than 50 cm but large space-time variability, being therefore difficult to model. Despite the progress observed in WTC modelling from numerical weather models (NWM), the accuracy of present NWM-derived WTC is still deficient for most altimetry applications such as e.g. sea level variation. Actually, accurate WTC at time and location of the altimetric measurements can only be achieved through observations of the atmospheric water vapour content, acquired by on-board microwave radiometers (MWR). In open ocean, MWR-derived WTC are centimeter-level accurate; in coastal regions, WTC degrades due to several reasons, among which is the contamination, from the surrounding land surfaces, of the signal measured by the MWR. Also the presence of ice and rain contaminates the MWR observations. Therefore, MWR-derived WTC are generally incorrect or invalid in coastal, rainy and high-latitude regions, and altimeter measurements cannot benefit from MWR corrections. The GNSS-derived Path Delay (GPD) algorithm was developed by the University of Porto (UPorto) aiming at computing the WTC for coastal regions where MWR observations are invalid, envisaging the recovery of the altimeter data in these regions. The GPD-derived WTC is based on a space-time optimal interpolation that combines path delays measured by MWR and computed at more than 800 coastal/island GNSS stations. Its most recent version, the GPD Plus (GPD+) estimates the WTC globally relying also on

Evaluation of Real-Time Ground-Based GPS Meteorology

NASA Astrophysics Data System (ADS)

Fang, P.; Bock, Y.; Gutman, S.

2003-04-01

We demonstrate and evaluate a system to estimate zenith tropospheric delays in real time (5-10 minute latency) based on the technique of instantaneous GPS positioning as described by Bock et al. [2000] using data from the Orange County Real Time GPS Network. OCRTN is an upgrade of a sub-network of SCIGN sites in southern California to low latency (1-2 sec), high-rate (1 Hz) data streaming. Currently, ten sites are streaming data (Ashtech binary MBEN format) by means of dedicated, point-to-point radio modems to a network hub that translates the asynchronous serial data to TCP/IP and onto a PC workstation residing on a local area network. Software residing on the PC allows multiple clients to access the raw data simultaneously though TCP/IP. One of the clients is a Geodetics RTD server that receives and archives (1) the raw 1 Hz network data, (2) estimates of instantaneous positions and zenith tropospheric delays, and (3) RINEX data to decimated to 30 seconds. The network is composed of ten sites. The distribution of nine of the sites approximates a right triangle with two 60 km legs, and a tenth site on Catalina Island a distance of about 50 km (over water) from the hypotenuse of the triangle. Relative zenith delays are estimated every second with a latency less than a second. Median values are computed at a user-specified interval (e.g., 10 minutes) with outliers greater than 4 times the interquartile range rejected. We describe the results with those generated by our operational system using the GAMIT software, with a latency of 30-60 minutes. Earlier results (from a similar network) comparing 30-minute median RTD values to GAMIT 30-minute estimates indicate that the two solutions differ by about 1 cm. We also describe our approach to determining absolute zenith delays. If an Internet connection is available we will present a real-time demonstration. [Bock, Y., R. Nikolaidis, P. J. de Jonge, and M. Bevis, Instantaneous resolution of crustal motion at medium

Assessment of satellite retrieval algorithms for chlorophyll-a concentration under high solar zenith angle

NASA Astrophysics Data System (ADS)

Li, Hao; He, Xianqiang; Bai, Yan; Chen, Xiaoyan; Gong, Fang; Zhu, Qiankun; Hu, Zifeng

2016-10-01

Numerous empirical algorithms have been operationally used to retrieve the global ocean chlorophyll-a concentration (Chla) from ocean color satellite data, e.g., the OC4V4 algorithm for SeaWiFS and OC3M for MODIS. However, the algorithms have been established and validated based on the in situ data mainly measured under low to moderate solar zenith angle (<70°). Currently, with the development of the geostationary satellite ocean color remote sensing which observes from early morning to later afternoon, it is necessary to know whether the empirical Chla algorithms could be applied to high solar zenith angle. In this study, the performances of seven widely-used Chla algorithms under high solar zenith angles, i.e., OC2, OC3M, OC3V, OC4V4, CLARK, OCI, and YOC algorithms, were evaluated using the NOMAD global in situ ocean color dataset. The results showed that the performances of all the seven algorithms decreased significantly under high solar zenith angles as compared to those under low-moderate solar zenith angles. For instance, for the OC4V4 algorithm, the relative percent difference (RPD) and root-mean-square error (RMSE) were 13.78% and 1.66 μg/l for the whole dataset, and 3.95% and 1.49 μg/l for the solar zenith angles ranged from 30° to 40°, respectively. However, the RPD and RMSE increased to 30.45% and 6.10μg/l for solar zenith angle larger than 70°.

An investigation of the solar zenith angle variation of D-region ionization

NASA Technical Reports Server (NTRS)

Ratnasiri, P. A. J.; Sechrist, C. F., Jr.

1975-01-01

Model calculations are carried out with a view to interpreting the solar zenith angle variation of D-region ionization. A model is developed for the neutral chemistry including the transport terms relating to molecular and eddy diffusion. The diurnal behavior is described of the minor neutral constituents formed in an oxygen-hydrogen-nitrogen atmosphere, in the height interval between 30 and 120 km. Computations carried out for two cases of the eddy diffusion coefficients models indicate that the constituents which are important for the D-region positive-ion chemistry do not show a significant variation with zenith angle for values up to 75 deg over the D-region heights. In the ion chemistry model, ion-pair production rates are calculated for solar X-rays between 1 A and 100 A, EUV radiations from 100 A up to the Lyman-alpha line, precipitating electrons, and galactic cosmic rays. The solar zenith angle variation of the positive-ion composition, negative-ion composition, and the electron densities are described up to 75 deg zenith angle, in the height interval between 60 and 100 km.

Atmospheric effects on radiometry from zenith of a plane with dark vertical protrusions

NASA Technical Reports Server (NTRS)

Otterman, J.

1983-01-01

Effects of an optically thin plane-parallel scattering atmosphere on radiometric imaging from the zenith of a specific surface-type are analyzed. The surface model was previously developed to describe arid steppe, where the sparse vegetation forms dark vertical protrusions from the bright soil-plane. The analysis is in terms of the surface reflectivity to the zenith r sub p for the direct beam, which is formulated as r sub p = r sub i exp (-s tan theta sub 0), where v sub i is the Lambert law reflectivity of the soil, the protrusions parameters s is the projection on a vertical plane of protrusions per unit area and theta sub 0 is the zenith angle. The surface reflectivity r sub p is approximately equal to that for the global irradiance (which is directly measured in the field) only for a narrow range of the solar zenith angles. The effects of the atmosphere when imaging large uniform areas of this type are comparable to those in imaging a Lambert surface with a reflectivity r sub p. Thus, the effects can be approximated by those in the case of a dark Lambert surface (analyzed previously), inasmuch as r sub p is smaller than the soil reflectivity r sub i for any off-zenith illumination. The surface becomes effectively darker with increasing solar zenith angle. Adjacency effects of a reflection from one area and scattering in the instantaneous field of view (object pixel) are analyzed as cross radiance and cross irradiance.

Tropospheric Chemistry

NASA Technical Reports Server (NTRS)

Mohnen, V.

1984-01-01

The fundamental processes that control the chemical composition and cycles of the global troposphere and how these processes and properties affect the physical behavior of the atmosphere are examined. The long-term information needs for tropospheric chemistry are: to be able to predict tropospheric responses to perturbations, both natural and anthropogenic, of these cycles, and to provide the information required for the maintenance and effective future management of the atmospheric component of our global life support system. The processes controlling global tropospheric biogeochemical cycles include: the input of trace species into the troposphere, their long-range transport and distribution as affected by the mean wind and vertical venting, their chemical transformations, including gas to particle conversion, leading to the appearance of aerosols or aqueous phase reactions inside cloud droplets, and their removal from the troposphere via wet (precipitation) and dry deposition.

Global Tropospheric Noise Maps for InSAR Observations

NASA Astrophysics Data System (ADS)

Yun, S. H.; Hensley, S.; Agram, P. S.; Chaubell, M.; Fielding, E. J.; Pan, L.

2014-12-01

Radio wave's differential phase delay variation through the troposphere is the largest error sources in Interferometric Synthetic Aperture Radar (InSAR) measurements, and water vapor variability in the troposphere is known to be the dominant factor. We use the precipitable water vapor (PWV) products from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) sensors mounted on Terra and Aqua satellites to produce tropospheric noise maps of InSAR. We estimate the slope and y-intercept of power spectral density curve of MODIS PWV and calculate the structure function to estimate the expected tropospheric noise level as a function of distance. The results serve two purposes: 1) to provide guidance on the expected covariance matrix for geophysical modeling, 2) to provide quantitative basis for the science Level-1 requirements of the planned NASA-ISRO L-band SAR mission (NISAR mission). We populate lookup tables of such power spectrum parameters derived from each 1-by-1 degree tile of global coverage. The MODIS data were retrieved from OSCAR (Online Services for Correcting Atmosphere in Radar) server. Users will be able to use the lookup tables and calculate expected tropospheric noise level of any date of MODIS data at any distance scale. Such calculation results can be used for constructing covariance matrix for geophysical modeling, or building statistics to support InSAR missions' requirements. For example, about 74% of the world had InSAR tropospheric noise level (along a radar line-of-sight for an incidence angle of 40 degrees) of 2 cm or less at 50 km distance scale during the time period of 2010/01/01 - 2010/01/09.

Simultaneous Ka-Band Site Characterization: Goldstone, CA, White Sands, NM, and Guam, USA

NASA Technical Reports Server (NTRS)

Acosta, Roberto; Morse, Jacquelynne; Zemba, Michael; Nessel, James; Morabito, David; Caroglanian, Armen

2011-01-01

To statistically characterize atmospheric effects on Ka-band links at NASA operational sites, NASA has constructed site test interferometers (STI s) which directly measure the tropospheric phase stability and rain attenuation. These instruments observe an unmodulated beacon signal broadcast from a geostationary satellite (e.g., Anik F2) and measure the phase difference between the signals received by the two antennas and its signal attenuation. Three STI s have been deployed so far: the first one at the NASA Deep Space Network Tracking Complex in Goldstone, California (May 2007); the second at the NASA White Sands Complex, in Las Cruses, New Mexico (February 2009); and the third at the NASA Tracking and Data Relay Satellite (TDRS) Remote Ground Terminal (GRGT) complex in Guam (May 2010). Two station-years of simultaneous atmospheric phase fluctuation data have been collected at Goldstone and White Sands, while one year of data has been collected in Guam. With identical instruments operating simultaneously, we can directly compare the phase stability and rain attenuation at the three sites. Phase stability is analyzed statistically in terms of the root-mean-square (rms) of the tropospheric induced time delay fluctuations over 10 minute blocks. For two years, the time delay fluctuations at the DSN site in Goldstone, CA, have been better than 2.5 picoseconds (ps) for 90% of the time (with reference to zenith), meanwhile at the White Sands, New Mexico site, the time delay fluctuations have been better than 2.2 ps with reference to zenith) for 90% of time. For Guam, the time delay fluctuations have been better than 12 ps (reference to zenith) at 90% of the time, the higher fluctuations are as expected from a high humidity tropical rain zone. This type of data analysis, as well as many other site quality characteristics (e.g., rain attenuation, infrastructure, etc.) will be used to determine the suitability of all the sites for NASA s future communication services at Ka-band.

VLBI Analysis with the Multi-Technique Software GEOSAT

NASA Technical Reports Server (NTRS)

Kierulf, Halfdan Pascal; Andersen, Per-Helge; Boeckmann, Sarah; Kristiansen, Oddgeir

2010-01-01

GEOSAT is a multi-technique geodetic analysis software developed at Forsvarets Forsknings Institutt (Norwegian defense research establishment). The Norwegian Mapping Authority has now installed the software and has, together with Forsvarets Forsknings Institutt, adapted the software to deliver datum-free normal equation systems in SINEX format. The goal is to be accepted as an IVS Associate Analysis Center and to provide contributions to the IVS EOP combination on a routine basis. GEOSAT is based on an upper diagonal factorized Kalman filter which allows estimation of time variable parameters like the troposphere and clocks as stochastic parameters. The tropospheric delays in various directions are mapped to tropospheric zenith delay using ray-tracing. Meteorological data from ECMWF with a resolution of six hours is used to perform the ray-tracing which depends both on elevation and azimuth. Other models are following the IERS and IVS conventions. The Norwegian Mapping Authority has submitted test SINEX files produced with GEOSAT to IVS. The results have been compared with the existing IVS combined products. In this paper the outcome of these comparisons is presented.

Asronomical refraction: Computational methods for all zenith angles

NASA Technical Reports Server (NTRS)

Auer, L. H.; Standish, E. M.

2000-01-01

It is shown that the problem of computing astronomical refraction for any value of the zenith angle may be reduced to a simple, nonsingular, numerical quadrature when the proper choice is made for the independent variable of integration.

First Zenith Total Delay and Integrated Water Vapour Estimates from the Near Real-Time GNSS Data Processing Systems at the University of Luxembourg

NASA Astrophysics Data System (ADS)

Ahmed, F.; Teferle, F. N.; Bingley, R. M.

2012-04-01

Since September 2011 the University of Luxembourg in collaboration with the University of Nottingham has been setting up two near real-time processing systems for ground-based GNSS data for the provision of zenith total delay (ZTD) and integrated water vapour (IWV) estimates. Both systems are based on Bernese v5.0, use the double-differenced network processing strategy and operate with a 1-hour (NRT1h) and 15-minutes (NRT15m) update cycle. Furthermore, the systems follow the approach of the E-GVAP METO and IES2 systems in that the normal equations for the latest data are combined with those from the previous four updates during the estimation of the ZTDs. NRT1h currently takes the hourly data from over 130 GNSS stations in Europe whereas NRT15m is primarily using the real-time streams of EUREF-IP. Both networks include additional GNSS stations in Luxembourg, Belgium and France. The a priori station coordinates for all of these stem from a moving average computed over the last 20 to 50 days and are based on the precise point positioning processing strategy. In this study we present the first ZTD and IWV estimates obtained from the NRT1h and NRT15m systems in development at the University of Luxembourg. In a preliminary evaluation we compare their performance to the IES2 system at the University of Nottingham and find the IWV estimates to agree at the sub-millimetre level.

Simulation and mitigation of higher-order ionospheric errors in PPP

NASA Astrophysics Data System (ADS)

Zus, Florian; Deng, Zhiguo; Wickert, Jens

2017-04-01

We developed a rapid and precise algorithm to compute ionospheric phase advances in a realistic electron density field. The electron density field is derived from a plasmaspheric extension of the International Reference Ionosphere (Gulyaeva and Bilitza, 2012) and the magnetic field stems from the International Geomagnetic Reference Field. For specific station locations, elevation and azimuth angles the ionospheric phase advances are stored in a look-up table. The higher-order ionospheric residuals are computed by forming the standard linear combination of the ionospheric phase advances. In a simulation study we examine how the higher-order ionospheric residuals leak into estimated station coordinates, clocks, zenith delays and tropospheric gradients in precise point positioning. The simulation study includes a few hundred globally distributed stations and covers the time period 1990-2015. We take a close look on the estimated zenith delays and tropospheric gradients as they are considered a data source for meteorological and climate related research. We also show how the by product of this simulation study, the look-up tables, can be used to mitigate higher-order ionospheric errors in practise. Gulyaeva, T.L., and Bilitza, D. Towards ISO Standard Earth Ionosphere and Plasmasphere Model. In: New Developments in the Standard Model, edited by R.J. Larsen, pp. 1-39, NOVA, Hauppauge, New York, 2012, available at https://www.novapublishers.com/catalog/product_info.php?products_id=35812

Algorithm Estimates Microwave Water-Vapor Delay

NASA Technical Reports Server (NTRS)

Robinson, Steven E.

1989-01-01

Accuracy equals or exceeds conventional linear algorithms. "Profile" algorithm improved algorithm using water-vapor-radiometer data to produce estimates of microwave delays caused by water vapor in troposphere. Does not require site-specific and weather-dependent empirical parameters other than standard meteorological data, latitude, and altitude for use in conjunction with published standard atmospheric data. Basic premise of profile algorithm, wet-path delay approximated closely by solution to simplified version of nonlinear delay problem and generated numerically from each radiometer observation and simultaneous meteorological data.

Gingival zenith positions and levels of the maxillary anterior dentition.

PubMed

Chu, Stephen J; Tan, Jocelyn H-P; Stappert, Christian F J; Tarnow, Dennis P

2009-01-01

The location of the gingival zenith in a medial-lateral position relative to the vertical tooth axis of the maxillary anterior teeth remains to be clearly defined. In addition, the apex of the free gingival margin of the lateral incisor teeth relative to the gingival zeniths of the adjacent proximal teeth remains undetermined. Therefore, this investigation evaluated two clinical parameters: (1) the gingival zenith position (GZP) from the vertical bisected midline (VBM) along the long axis of each individual maxillary anterior tooth; and (2) the gingival zenith level (GZL) of the lateral incisors in an apical-coronal direction relative to the gingival line joining the tangents of the GZP of the adjacent central incisor and canine teeth under healthy conditions. A total of 240 sites in 20 healthy patients (13 females, 7 males) with an average age of 27.7 years were evaluated. The inclusion patient criteria were absence of periodontal disease, gingival recession, or gingival hypertrophy as well as teeth without loss of interdental papillae, spacing, crowding, existing restorations, and incisal attrition. GZP dimensions were measured with calibrated digital calipers for each individual tooth and within each tooth group in a medial-lateral direction from the VBM. GZLs were measured in an apical-coronal direction from a tangent line drawn on the diagnostic casts from the GZPs of the adjacent teeth. This study demonstrated that all central incisors displayed a distal GZP from the VBM, with a mean average of 1 mm. Lateral incisors showed a deviation of the gingival zenith by a mean of 0.4 mm. In 97.5% of the canine population, the GZP was centralized along the long axis of the canine. The mean distance of the contour of the gingival margin in an apical-coronal direction of the lateral incisors (GZL) relative to gingival line joining the tangent of the adjacent central and canine GZPs was approximately 1 mm. This investigation revealed a GZP mean value of 1 mm distal from

Retrieval and Validation of Zenith and Slant Path Delays From the Irish GPS Network

NASA Astrophysics Data System (ADS)

Hanafin, Jennifer; Jennings, S. Gerard; O'Dowd, Colin; McGrath, Ray; Whelan, Eoin

2010-05-01

Retrieval of atmospheric integrated water vapour (IWV) from ground-based GPS receivers and provision of this data product for meteorological applications has been the focus of a number of Europe-wide networks and projects, most recently the EUMETNET GPS water vapour programme. The results presented here are from a project to provide such information about the state of the atmosphere around Ireland for climate monitoring and improved numerical weather prediction. Two geodetic reference GPS receivers have been deployed at Valentia Observatory in Co. Kerry and Mace Head Atmospheric Research Station in Co. Galway, Ireland. These two receivers supplement the existing Ordnance Survey Ireland active network of 17 permanent ground-based receivers. A system to retrieve column-integrated atmospheric water vapour from the data provided by this network has been developed, based on the GPS Analysis at MIT (GAMIT) software package. The data quality of the zenith retrievals has been assessed using co-located radiosondes at the Valentia site and observations from a microwave profiling radiometer at the Mace Head site. Validation of the slant path retrievals requires a numerical weather prediction model and HIRLAM (High-Resolution Limited Area Model) version 7.2, the current operational forecast model in use at Met Éireann for the region, has been used for this validation work. Results from the data processing and comparisons with the independent observations and model will be presented.

Periodontics, Implantology, and Prosthodontics Integrated: The Zenith-Driven Rehabilitation

PubMed Central

Cabral, Guilherme

2017-01-01

A customized treatment plan is important to reach results that will satisfy the patient providing esthetics, function, and long-term stability. This type of oral rehabilitation requires professionals from different dental specialties where communication is a major key point. Digital Smile Design allows the practitioners to plan and discuss the patient's condition to establish the proper treatment plan, which must be driven by the desired zenith position. The ideal gingival position will guide the professionals and determine the need to perform surgical procedures or orthodontic movement before placing the final restorations. In this article, the zenith-driven concept is discussed and a challenging case is presented with 4-year follow-up where tooth extraction, immediate implant placement, bone regeneration, and a connective tissue graft were performed. PMID:28713600

Application of GPS Measurements for Ionospheric and Tropospheric Modelling

NASA Astrophysics Data System (ADS)

Rajendra Prasad, P.; Abdu, M. A.; Furlan, Benedito. M. P.; Koiti Kuga, Hélio

solar maximum period. In the equatorial region the irregularity structures are highly elongated in the north-south direction and are discrete in the east-west direction with dimensions of several hundred km. With such spatial distribution of irregularities needs to determine how often the GPS receivers fails to provide navigation aid with the available constellation. The effects of scintillation on the performance of GPS navigation systems in the equatorial region can be analyzed through commissioning few ground receivers. Incidentally there are few GPS receivers near these latitudes. Despite the recent advances in the ionosphere and tropospheric delay modeling for geodetic applications of GPS, the models currently used are not very precise. The conventional and operational ionosphere models viz. Klobuchar, Bent, and IRI models have certain limitations in providing very precise accuracies at all latitudes. The troposphere delay modeling also suffers in accuracy. The advances made in both computing power and knowledge of the atmosphere leads to make an effort to upgrade some of these models for improving delay corrections in GPS navigation. The ionospheric group delay corrections for orbit determination can be minimized using duel frequency. However in single frequency measurements the group delay correction is an involved task. In this paper an investigation is carried out to estimate the model coefficients of ionosphere along with precise orbit determination modeling using GPS measurements. The locations of the ground-based receivers near equator are known very exactly. Measurements from these ground stations to a precisely known satellite carrying duel receiver is used for orbit determination. The ionosphere model parameters can be refined corresponding to spatially distributed GPS receivers spread over Brazil. The tropospheric delay effects are not significant for the satellites by choosing appropriate elevation angle. However it needs to be analyzed for user like

Tropospheric wet refractivity tomography using multiplicative algebraic reconstruction technique

NASA Astrophysics Data System (ADS)

Xiaoying, Wang; Ziqiang, Dai; Enhong, Zhang; Fuyang, K. E.; Yunchang, Cao; Lianchun, Song

2014-01-01

Algebraic reconstruction techniques (ART) have been successfully used to reconstruct the total electron content (TEC) of the ionosphere and in recent years be tentatively used in tropospheric wet refractivity and water vapor tomography in the ground-based GNSS technology. The previous research on ART used in tropospheric water vapor tomography focused on the convergence and relaxation parameters for various algebraic reconstruction techniques and rarely discussed the impact of Gaussian constraints and initial field on the iteration results. The existing accuracy evaluation parameters calculated from slant wet delay can only evaluate the resultant precision of the voxels penetrated by slant paths and cannot evaluate that of the voxels not penetrated by any slant path. The paper proposes two new statistical parameters Bias and RMS, calculated from wet refractivity of the total voxels, to improve the deficiencies of existing evaluation parameters and then discusses the effect of the Gaussian constraints and initial field on the convergence and tomography results in multiplicative algebraic reconstruction technique (MART) to reconstruct the 4D tropospheric wet refractivity field using simulation method.

Performance verification of adaptive optics for satellite-to-ground coherent optical communications at large zenith angle.

PubMed

Chen, Mo; Liu, Chao; Rui, Daoman; Xian, Hao

2018-02-19

Although there is an urgent demand, it is still a tremendous challenge to use the coherent optical communication technology to the satellite-to-ground data transmission system especially at large zenith angle due to the influence of atmospheric turbulence. Adaptive optics (AO) is a considerable scheme to solve the problem. In this paper, we integrate the adaptive optics (AO) to the coherent laser communications and the performances of mixing efficiency as well as bit-error-rate (BER) at different zenith angles are studied. The analytical results show that the increasing of zenith angle can severely decrease the performances of the coherent detection, and increase the BER to higher than 10 -3 , which is unacceptable. The simulative results of coherent detection with AO compensation indicate that the larger mixing efficiency and lower BER can be performed by the coherent receiver with a high-mode AO compensation. The experiment of correcting the atmospheric turbulence wavefront distortion using a 249-element AO system at large zenith angles is carried out. The result demonstrates that the AO system has a significant improvement on satellite-to-ground coherent optical communication system at large zenith angle. It also indicates that the 249-element AO system can only meet the needs of coherent communication systems at zenith angle smaller than 65̊ for the 1.8m telescope under weak and moderate turbulence.

The effect of the dynamic wet troposphere on radio interferometric measurements

NASA Technical Reports Server (NTRS)

Treuhaft, R. N.; Lanyi, G. E.

1987-01-01

A statistical model of water vapor fluctuations is used to describe the effect of the dynamic wet troposphere on radio interferometric measurements. It is assumed that the spatial structure of refractivity is approximated by Kolmogorov turbulence theory, and that the temporal fluctuations are caused by spatial patterns moved over a site by the wind, and these assumptions are examined for the VLBI delay and delay rate observables. The results suggest that the delay rate measurement error is usually dominated by water vapor fluctuations, and water vapor induced VLBI parameter errors and correlations are determined as a function of the delay observable errors. A method is proposed for including the water vapor fluctuations in the parameter estimation method to obtain improved parameter estimates and parameter covariances.

Cirrus properties deduced from CO2 lidar observations of zenith-enhanced backscatter from oriented crystals

NASA Technical Reports Server (NTRS)

Eberhard, Wynn L.

1993-01-01

Many lidar researchers have occasionally observed zenith-enhanced backscatter (ZEB) from middle and high clouds. The ZEB signature consists of strong backscatter when the lidar is pointed directly at zenith and a dramatic decline in backscatter as the zenith angle dips slightly off zenith. Mirror-like reflection from horizontal facets of oriented crystals (especially plates) is generally accepted as the cause. It was found during a 3-year observation program that approximately 50 percent of ice clouds had ZEB, regardless of cloud height. The orientation of crystals and the ZEB they cause are important to study and understand for several reasons. First, radiative transfer in clouds with oriented crystals is different than if the same particles were randomly oriented. Second, crystal growth depends partly on the orientation of the particles. Third, ZEB measurements may provide useful information about cirrus microphysical and radiative properties. Finally, the remarkable effect of ZEB on lidar signals should be understood in order to properly interpret lidar data.

Monte Carlo simulations of the impact of troposphere, clock and measurement errors on the repeatability of VLBI positions

NASA Astrophysics Data System (ADS)

Pany, A.; Böhm, J.; MacMillan, D.; Schuh, H.; Nilsson, T.; Wresnik, J.

2011-01-01

Within the International VLBI Service for Geodesy and Astrometry (IVS) Monte Carlo simulations have been carried out to design the next generation VLBI system ("VLBI2010"). Simulated VLBI observables were generated taking into account the three most important stochastic error sources in VLBI, i.e. wet troposphere delay, station clock, and measurement error. Based on realistic physical properties of the troposphere and clocks we ran simulations to investigate the influence of the troposphere on VLBI analyses, and to gain information about the role of clock performance and measurement errors of the receiving system in the process of reaching VLBI2010's goal of mm position accuracy on a global scale. Our simulations confirm that the wet troposphere delay is the most important of these three error sources. We did not observe significant improvement of geodetic parameters if the clocks were simulated with an Allan standard deviation better than 1 × 10-14 at 50 min and found the impact of measurement errors to be relatively small compared with the impact of the troposphere. Along with simulations to test different network sizes, scheduling strategies, and antenna slew rates these studies were used as a basis for the definition and specification of VLBI2010 antennas and recording system and might also be an example for other space geodetic techniques.

Precision GPS orbit determination strategies for an earth orbiter and geodetic tracking system

NASA Technical Reports Server (NTRS)

Lichten, Stephen M.; Bertiger, Willy I.; Border, James S.

1988-01-01

Data from two 1985 GPS field tests were processed and precise GPS orbits were determined. With a combined carrier phase and pseudorange, the 1314-km repeatability improves substantially to 5 parts in 10 to the 9th (0.6 cm) in the north and 2 parts in 10 to the 8th (2-3 cm) in the other components. To achieve these levels of repeatability and accuracy, it is necessary to fine-tune the GPS solar radiation coefficients and ground station zenith tropospheric delays.

GPS Water Vapor Tomography: First results from the ESCOMPTE Field Experiment

NASA Astrophysics Data System (ADS)

Masson, F.; Champollion, C.; Bouin, M.-N.; Walpersdorf, A.; van Baelen, J.; Doerflinger, E.; Bock, O.

2003-04-01

We develop a tomographic software to model the spatial distribution of the tropospheric water vapor from GPS data. First we present simulations based on a real GPS station distribution and simple tropospheric models, which prove the potentiality of the method. Second we apply the software to the ESCOMPTE data. During the ESCOMPTE field experiment, a dense network of 17 dual frequency GPS receivers has been operated for two weeks within a 20 km x 20 km area around Marseille (Southern France). The network extends from the sea level to the top of the Etoile chain (~700 m high). The input data are the slant delay values obtained by combining the estimated zenith delay values with the horizontal gradients. The effect of the initial tropospheric water vapor model, the number and thickness of the layers of the model, the a priori model and data covariance and some other parameters will be discussed. Simultaneously water vapor radiometer, solar spectrometer, Raman lidar and radiosondes have been deployed to get a data set usable for comparison with the tomographic inversion results and validation of the method. Comparison with meteorological models (MesoNH - Meteo-France) will be shown.

Spectral Invariant Behavior of Zenith Radiance Around Cloud Edges Observed by ARM SWS

NASA Technical Reports Server (NTRS)

Marshak, A.; Knyazikhin, Y.; Chiu, J. C.; Wiscombe, W. J.

2009-01-01

The ARM Shortwave Spectrometer (SWS) measures zenith radiance at 418 wavelengths between 350 and 2170 nm. Because of its 1-sec sampling resolution, the SWS provides a unique capability to study the transition zone between cloudy and clear sky areas. A spectral invariant behavior is found between ratios of zenith radiance spectra during the transition from cloudy to cloud-free. This behavior suggests that the spectral signature of the transition zone is a linear mixture between the two extremes (definitely cloudy and definitely clear). The weighting function of the linear mixture is a wavelength-independent characteristic of the transition zone. It is shown that the transition zone spectrum is fully determined by this function and zenith radiance spectra of clear and cloudy regions. An important result of these discoveries is that high temporal resolution radiance measurements in the clear-to-cloud transition zone can be well approximated by lower temporal resolution measurements plus linear interpolation.

Overview of the MISSE 7 Polymers and Zenith Polymers Experiments After 1.5 Years of Space Exposure

NASA Technical Reports Server (NTRS)

Yi, Grace T.; de Groh, Kim K.; Banks, Bruce A.; Haloua, Athena; Imka, Emily C.; Mitchell, Gianna G.

2013-01-01

As part of the Materials International Space Station Experiment 7 (MISSE 7), two experiments called the Polymers Experiment and the Zenith Polymers Experiment were flown on the exterior of the International Space Station (ISS) and exposed to the low Earth orbit (LEO) space environment for 1.5 years. The Polymers Experiment contained 47 samples, which were flown in a ram or wake flight orientation. The objectives of the Polymers Experiment were to determine the LEO atomic oxygen erosion yield (Ey, volume loss per incident oxygen atoms, given in cu cm/atom) of the polymers, and to determine if atomic oxygen erosion of high and low ash containing polymers is dependent on fluence. The Zenith Polymers Experiment was flown in a zenith flight orientation. The primary objective of the Zenith Polymers Experiment was to determine the effect of solar exposure on the erosion of fluoropolymers. Kapton H (DuPont, Wilmington, DE) was flown in each experiment for atomic oxygen fluence determination. This paper provides an introduction to both the MISSE 7 Polymers Experiment and the MISSE 7 Zenith Polymers Experiment, and provides initial erosion yield results.

Strategies for high-precision Global Positioning System orbit determination

NASA Technical Reports Server (NTRS)

Lichten, Stephen M.; Border, James S.

1987-01-01

Various strategies for the high-precision orbit determination of the GPS satellites are explored using data from the 1985 GPS field test. Several refinements to the orbit determination strategies were found to be crucial for achieving high levels of repeatability and accuracy. These include the fine tuning of the GPS solar radiation coefficients and the ground station zenith tropospheric delays. Multiday arcs of 3-6 days provided better orbits and baselines than the 8-hr arcs from single-day passes. Highest-quality orbits and baselines were obtained with combined carrier phase and pseudorange solutions.

Multipurpose Spectroradiometer for Satellite Instrument Calibration and Zenith Sky Remote Sensing Measurements

NASA Technical Reports Server (NTRS)

Heath, Donald F.; Ahmad, Zia

2001-01-01

In the early 1990s a series of surface-based direct sun and zenith sky measurements of total column ozone were made with SBUV/2 flight models and the SSBUV Space Shuttle instrument in Boulder, Colorado which were compared with NOAA Dobson Instrument direct sun observations and TOMS instrument overpass observations of column ozone. These early measurements led to the investigation of the accuracy of derived total column ozone amounts and aerosol optical depths from zenith sky observations. Following the development and availability of radiometrically stable IAD narrow band interference filter and nitrided silicon photodiodes a simple compact multifilter spectroradiometer was developed which can be used as a calibration transfer standard spectroradiometer (CTSS) or as a surface based instrument remote sensing instruments for measurements of total column ozone and aerosol optical depths. The total column ozone derived from zenith sky observations agrees with Dobson direct sun AD double wavelength pair measurements and with TOMS overpass ozone amounts within uncertainties of about 1%. When used as a calibration transfer standard spectroradiometer the multifilter spectroradiometer appears to be capable of establishing instrument radiometric calibration uncertainties of the order of 1% or less relative to national standards laboratory radiometric standards.

Zenith: A Radiosonde Detector for Rapid-Response Ionizing Atmospheric Radiation Measurements During Solar Particle Events

NASA Astrophysics Data System (ADS)

Dyer, A. C. R.; Ryden, K. A.; Hands, A. D. P.; Dyer, C.; Burnett, C.; Gibbs, M.

2018-03-01

Solar energetic particle events create radiation risks for aircraft, notably single-event effects in microelectronics along with increased dose to crew and passengers. In response to this, some airlines modify their flight routes after automatic alerts are issued. At present these alerts are based on proton flux measurements from instruments onboard satellites, so it is important that contemporary atmospheric radiation measurements are made and compared. This paper presents the development of a rapid-response system built around the use of radiosondes equipped with a radiation detector, Zenith, which can be launched from a Met Office weather station after significant solar proton level alerts are issued. Zenith is a compact, battery-powered solid-state radiation monitor designed to be connected to a Vaisala RS-92 radiosonde, which transmits all data to a ground station as it ascends to an altitude of 33 km. Zenith can also be operated as a stand-alone detector when connected to a laptop, providing real-time count rates. It can also be adapted for use on unmanned aerial vehicles. Zenith has been flown on the Met Office Civil Contingency Aircraft, taken to the European Organization for Nuclear Research-EU high energy Reference Field facility for calibration and launched on a meteorological balloon at the Met Office's weather station in Camborne, Cornwall, UK. During this sounding, Zenith measured the Pfotzer-Regener maximum to be at an altitude of 18-20 km where the count rate was measured to be 1.15 c s-1 cm-2 compared to 0.02 c s-1 cm-2 at ground level.

Evidence of L-mode electromagnetic wave pumping of ionospheric plasma near geomagnetic zenith

NASA Astrophysics Data System (ADS)

Leyser, Thomas B.; James, H. Gordon; Gustavsson, Björn; Rietveld, Michael T.

2018-02-01

The response of ionospheric plasma to pumping by powerful HF (high frequency) electromagnetic waves transmitted from the ground into the ionosphere is the strongest in the direction of geomagnetic zenith. We present experimental results from transmitting a left-handed circularly polarized HF beam from the EISCAT (European Incoherent SCATter association) Heating facility in magnetic zenith. The CASSIOPE (CAScade, Smallsat and IOnospheric Polar Explorer) spacecraft in the topside ionosphere above the F-region density peak detected transionospheric pump radiation, although the pump frequency was below the maximum ionospheric plasma frequency. The pump wave is deduced to arrive at CASSIOPE through L-mode propagation and associated double (O to Z, Z to O) conversion in pump-induced radio windows. L-mode propagation allows the pump wave to reach higher plasma densities and higher ionospheric altitudes than O-mode propagation so that a pump wave in the L-mode can facilitate excitation of upper hybrid phenomena localized in density depletions in a larger altitude range. L-mode propagation is therefore suggested to be important in explaining the magnetic zenith effect.

Spectral changes in the zenith skylight during total solar eclipses.

PubMed

Hall, W N

1971-06-01

The relative spectral intensity of the zenith sky was measured with an optical scanning spectrometer at Nantucket Island, Massachusetts, during the total solar eclipse of 7 March 1970. The spectral ratios I(5100 A)/I(4300 A) and I(5900 A)/I(5100 A) at Nantucket remained unchanged for 96% or less obscuration of the sun by the moon. The results are compared with other recent relative spectral intensity measurements made during total solar eclipses. Comparison with other eclipse measurements for solar elevation angle at totality less than 45 degrees shows a blue color shift consistent with rayleigh scattering. Eclipses with solar elevation angles at totality greater than 45 degrees do not show consistent color shifts. This inconsistency may be due to difficulty in establishing a suitable reference spectrum for comparison with the spectral distribution of the zenith sky at totality. Selection of a suitable reference spectrum is discussed.

InSAR Tropospheric Correction Methods: A Statistical Comparison over Different Regions

NASA Astrophysics Data System (ADS)

Bekaert, D. P.; Walters, R. J.; Wright, T. J.; Hooper, A. J.; Parker, D. J.

2015-12-01

Observing small magnitude surface displacements through InSAR is highly challenging, and requires advanced correction techniques to reduce noise. In fact, one of the largest obstacles facing the InSAR community is related to tropospheric noise correction. Spatial and temporal variations in temperature, pressure, and relative humidity result in a spatially-variable InSAR tropospheric signal, which masks smaller surface displacements due to tectonic or volcanic deformation. Correction methods applied today include those relying on weather model data, GNSS and/or spectrometer data. Unfortunately, these methods are often limited by the spatial and temporal resolution of the auxiliary data. Alternatively a correction can be estimated from the high-resolution interferometric phase by assuming a linear or a power-law relationship between the phase and topography. For these methods, the challenge lies in separating deformation from tropospheric signals. We will present results of a statistical comparison of the state-of-the-art tropospheric corrections estimated from spectrometer products (MERIS and MODIS), a low and high spatial-resolution weather model (ERA-I and WRF), and both the conventional linear and power-law empirical methods. We evaluate the correction capability over Southern Mexico, Italy, and El Hierro, and investigate the impact of increasing cloud cover on the accuracy of the tropospheric delay estimation. We find that each method has its strengths and weaknesses, and suggest that further developments should aim to combine different correction methods. All the presented methods are included into our new open source software package called TRAIN - Toolbox for Reducing Atmospheric InSAR Noise (Bekaert et al., in review), which is available to the community Bekaert, D., R. Walters, T. Wright, A. Hooper, and D. Parker (in review), Statistical comparison of InSAR tropospheric correction techniques, Remote Sensing of Environment

A New Technique for Retrieval of Tropospheric and Stratospheric Ozone Profiles using Sky Radiance Measurements at Multiple View Angles: Application to a Brewer Spectrometer

NASA Technical Reports Server (NTRS)

Tzortziou, Maria; Krotkov, Nickolay A.; Cede, Alexander; Herman, Jay R.; Vasilkov, Alexander

2008-01-01

This paper describes and applies a new technique for retrieving diurnal variability in tropospheric ozone vertical distribution using ground-based measurements of ultraviolet sky radiances. The measured radiances are obtained by a polarization-insensitive modified Brewer double spectrometer located at Goddard Space Flight Center, in Greenbelt, Maryland, USA. Results demonstrate that the Brewer angular (0-72deg viewing zenith angle) and spectral (303-320 nm) measurements of sky radiance in the solar principal plane provide sufficient information to derive tropospheric ozone diurnal variability. In addition, the Brewer measurements provide stratospheric ozone vertical distributions at least twice per day near sunrise and sunset. Frequent measurements of total column ozone amounts from direct-sun observations are used as constraints in the retrieval. The vertical ozone profile resolution is shown in terms of averaging kernels to yield at least four points in the troposphere-low stratosphere, including good information in Umkehr layer 0 (0-5 km). The focus of this paper is on the derivation of stratospheric and tropospheric ozone profiles using both simulated and measured radiances. We briefly discuss the necessary modifications of the Brewer spectrometer that were used to eliminate instrumental polarization sensitivity so that accurate sky radiances can be obtained in the presence of strong Rayleigh scattering and aerosols. The results demonstrate that including a site-specific and time-dependent aerosol correction, based on Brewer direct-sun observations of aerosol optical thickness, is critical to minimize the sky radiance residuals as a function of observing angle in the optimal estimation inversion algorithm and improve the accuracy of the retrieved ozone profile.

Chemistry and dynamics of the lower troposphere over North America and the North Atlantic Ocean in fall 1997 observed using an airborne UV DIAL system

NASA Technical Reports Server (NTRS)

Grant, William B.; Butler, Carolyn F.; Fenn, Marta A.; Kooi, Susan A.; Browell, Edward V.; Fuelberg, Henry

1998-01-01

The NASA Langley Research Center's airborne UV Differential Absorption Lidar (DIAL) system participated in the Subsonic Assessment, Ozone and Nitrogen Oxide Experiment (SONEX) mission from October 13 to November 12, 1997. The purpose of the mission was to study the upper troposphere/lower stratosphere in and near the North Atlantic flight corridor to better understand this region of the atmosphere and how civilian air travel in the corridor might be affecting the atmospheric chemistry. Bases of operations included NASA Ames, California (37.4 deg N, 122.1 deg W); Bangor, Maine (44.8 deg N, 68.8 deg W); Shannon, Ireland (52.7 deg N, 8.9 deg W); and Lajes, Terceira Island, Azores (38.8 deg N, 27.1 deg W). Since the UV DIAL system observes in the nadir as well as the zenith, aerosol and ozone data were obtained from near the Earth's surface to the lower stratosphere. A number of interesting features were noted relating to both chemistry and dynamics of the troposphere, which are reported here.

Comparative analysis of positioning and zenith total delay retrieval using GPS-, GLONASS-only, and GPS/GLONASS combined precise point positioning

NASA Astrophysics Data System (ADS)

Zhou, Feng; Li, Xingxing; Cai, Miaomiao; Chen, Wen; Dong, Danan; Schuh, Harald

2017-04-01

Since October 2011, the Russian GLONASS has been revitalized and is now fully operational with 24 satellites in orbit. It is critical to assess the benefits and problems of using GLONASS observations (i.e. GLONASS-only or combined GPS/GLONASS) for precise positioning and zenith total delay (ZTD) retrieval on a global scale using the precise point positioning (PPP) technique. In this contribution, extensive evaluations are conducted with GNSS data sets collected from 251 globally distributed stations of the International GNSS Service (IGS) network in July 2016. The stations are divided into 30 groups by antenna/radome types to investigate whether there are antenna/radome-dependent biases in position and ZTD results derived from GLONASS-only PPP. The positioning results do not show obvious antenna/radome-dependent biases except the stations with JAV_RINGANT_G3T/NONE. The averaged biases of the stations with JAV_RINGANT_G3T/NONE in horizontal component especially in north component can even achieve -9.0 mm. The standard deviation (STD) and root mean square (RMS) are used as indicators of positioning repeatability and accuracy, respectively. Compared with GPS-only PPP, smaller averaged STD and RMS values of GLONASS-only PPP are achieved in horizontal component, while larger ones in vertical component. Furthermore, the STD and RMS values of GPS/GLONASS combined PPP solutions are the smallest in horizontal and vertical components, indicating that adding GLONASS observations can achieve better positioning performance than GPS-only PPP. Meanwhile, better positioning repeatability and accuracy are found in north component than that in east component, which may be caused by the configuration of GNSS satellite orbit. With respect to GPS-only PPP-derived ZTD, the ZTD biases, accuracy, and correlation derived from GLONASS-only and GPS/GLONASS PPP solutions are antenna/radome-independent, while the biases and accuracy are slightly latitude- or Geometric Dilution of Precisions

Magnetic zenith effect in the ionospheric modification by an X-mode HF heater wave

NASA Astrophysics Data System (ADS)

Blagoveshchenskaya, N. F.; Borisova, T. D.; Haggstrom, I.; Rietveld, M. T.; Yeoman, T. K.

2013-12-01

We report experimental results aimed at an investigation of the magnetic zenith effect in the high latitude ionosphere F region from ionospheric modification by powerful HF heater wave with X-polarization. The ionospheric modification was produced by the HF heating facility at Tromsø (Norway) using the phased array with a narrow beam with of 6 degrees. Effective radiated power was varied between 450 and 1000 MW. The HF pump wave radiated in different directions relative to the magnetic field from 90 degrees (vertical) to 78 degrees (magnetic zenith) at frequencies near or above the ordinary-mode critical frequency. The response of the ionosphere plasma to the HF pump wave impact was checked by the UHF incoherent scatter radar located in the immediate vicinity of the HF heater. UHF radar was probing the plasma parameters, such as electron density and temperature (Ne and Te), HF-induced plasma and ion lines in the altitude range from 90 to 600 km. It was running in a scanning mode when UHF radar look angles were changed from 74 to 90 degrees by 1 or 2 degree step. It was clearly demonstrated that the strongest heater-induced effects took place in the magnetic field-aligned direction when HF pointing was also to the magnetic zenith. It was found that strong Ne enhancement of up to 80 % along magnetic field (artificial density ducts) were excited only under HF pumping towards magnetic zenith. The width of the artificial ducts comes to only 2 degrees. The Ne increases were accompanied by the Te enhancements of up to about 50 %. Less pronounced Te increases were also observed in the directions of 84 and 90 degrees. Strong Ne enhancements can be accompanied by excitation of strong HF-induced plasma and ion lines. Thus experimental results obtained points to the strong magnetic zenith effect due to self-focusing powerful HF radio wave with X-mode polarization.

Atmospheric Phase Delay Correction of D-Insar Based on SENTINEL-1A

NASA Astrophysics Data System (ADS)

Li, X.; Huang, G.; Kong, Q.

2018-04-01

In this paper, we used the Generic Atmospheric Correction Online Service for InSAR (GACOS) tropospheric delay maps to correct the atmospheric phase delay of the differential interferometric synthetic aperture radar (D-InSAR) monitoring, and we improved the accuracy of subsidence monitoring using D-InSAR technology. Atmospheric phase delay, as one of the most important errors that limit the monitoring accuracy of InSAR, would lead to the masking of true phase in subsidence monitoring. For the problem, this paper used the Sentinel-1A images and the tropospheric delay maps got from GACOS to monitor the subsidence of the Yellow River Delta in Shandong Province. The conventional D-InSAR processing was performed using the GAMMA software. The MATLAB codes were used to correct the atmospheric delay of the D-InSAR results. The results before and after the atmospheric phase delay correction were verified and analyzed in the main subsidence area. The experimental results show that atmospheric phase influences the deformation results to a certain extent. After the correction, the measurement error of vertical deformation is reduced by about 18 mm, which proves that the removal of atmospheric effects can improve the accuracy of the D-InSAR monitoring.

Effects of Tropospheric Spatio-Temporal Correlated Noise on the Analysis of Space Geodetic Data

NASA Technical Reports Server (NTRS)

Romero-Wolf, A. F.; Jacobs, C. S.

2011-01-01

The standard VLBI analysis models measurement noise as purely thermal errors modeled according to uncorrelated Gaussian distributions. As the price of recording bits steadily decreases, thermal errors will soon no longer dominate. It is therefore expected that troposphere and instrumentation/clock errors will increasingly become more dominant. Given that both of these errors have correlated spectra, properly modeling the error distributions will become more relevant for optimal analysis. This paper will discuss the advantages of including the correlations between tropospheric delays using a Kolmogorov spectrum and the frozen ow model pioneered by Treuhaft and Lanyi. We will show examples of applying these correlated noise spectra to the weighting of VLBI data analysis.

Characterizing the zenithal night sky brightness in large territories: how many samples per square kilometre are needed?

NASA Astrophysics Data System (ADS)

Bará, Salvador

2018-01-01

A recurring question arises when trying to characterize, by means of measurements or theoretical calculations, the zenithal night sky brightness throughout a large territory: how many samples per square kilometre are needed? The optimum sampling distance should allow reconstructing, with sufficient accuracy, the continuous zenithal brightness map across the whole region, whilst at the same time avoiding unnecessary and redundant oversampling. This paper attempts to provide some tentative answers to this issue, using two complementary tools: the luminance structure function and the Nyquist-Shannon spatial sampling theorem. The analysis of several regions of the world, based on the data from the New world atlas of artificial night sky brightness, suggests that, as a rule of thumb, about one measurement per square kilometre could be sufficient for determining the zenithal night sky brightness of artificial origin at any point in a region to within ±0.1 magV arcsec-2 (in the root-mean-square sense) of its true value in the Johnson-Cousins V band. The exact reconstruction of the zenithal night sky brightness maps from samples taken at the Nyquist rate seems to be considerably more demanding.

Retrieval of Total Ozone Amounts from Zenith-Sky Intensities in the Ultraviolet Region

NASA Technical Reports Server (NTRS)

Bojkov, B. R.; Bhartia, P. K.; Hilsenrath, E.; Labow, G. J.

2004-01-01

A new method to determine the total ozone column from zenith-sky intensities in the ultraviolet region has been developed for the Shuttle Solar Backscatter Ultraviolet Spectrometer (SSBUV) operating at the NASA Goddard Space Flight Center. The total ozone column amounts are derived by comparing the ratio of measured intensities from three wavelengths with the equivalent ratios calculated by a radiative transfer model. The differences between the retrieved ozone column amounts and the collocated Brewer double monochromator are within 2% for the measurement period beginning in April 2001. The methodology, as well as the influences of the ozone profiles, aerosols, surface albedo, and the solar zenith angle on the retrieved total ozone amounts will be presented.

Working Group 1 "Advanced GNSS Processing Techniques" of the COST Action GNSS4SWEC: Overview of main achievements

NASA Astrophysics Data System (ADS)

Douša, Jan; Dick, Galina; Kačmařík, Michal; Václavovic, Pavel; Pottiaux, Eric; Zus, Florian; Brenot, Hugues; Moeller, Gregor; Hinterberger, Fabian; Pacione, Rosa; Stuerze, Andrea; Eben, Kryštof; Teferle, Norman; Ding, Wenwu; Morel, Laurent; Kaplon, Jan; Hordyniec, Pavel; Rohm, Witold

2017-04-01

The COST Action ES1206 GNSS4SWEC addresses new exploitations of the synergy between developments in GNSS and meteorological communities. The Working Group 1 (Advanced GNSS processing techniques) deals with implementing and assessing new methods for GNSS tropospheric monitoring and precise positioning exploiting all modern GNSS constellations, signals, products etc. Besides other goals, WG1 coordinates development of advanced tropospheric products in support of weather numerical and non-numerical nowcasting. These are ultra-fast and high-resolution tropospheric products available in real time or in a sub-hourly fashion and parameters in support of monitoring an anisotropy of the troposphere, e.g. horizontal gradients and tropospheric slant path delays. This talk gives an overview of WG1 activities and, particularly, achievements in two activities, Benchmark and Real-time demonstration campaigns. For the Benchmark campaign a complex data set of GNSS observations and various meteorological data were collected for a two-month period in 2013 (May-June) which included severe weather events in central Europe. An initial processing of data sets from GNSS and numerical weather models (NWM) provided independently estimated reference parameters - ZTDs and tropospheric horizontal gradients. The comparison of horizontal tropospheric gradients from GNSS and NWM data demonstrated a very good agreement among independent solutions with negligible biases and an accuracy of about 0.5 mm. Visual comparisons of maps of zenith wet delays and tropospheric horizontal gradients showed very promising results for future exploitations of advanced GNSS tropospheric products in meteorological applications such as severe weather event monitoring and weather nowcasting. The Benchmark data set is also used for an extensive validation of line-of-sight tropospheric Slant Total Delays (STD) from GNSS, NWM-raytracing and Water Vapour Radiometer (WVR) solutions. Seven institutions delivered their STDs

Characteristics of skylight at the zenith during twilight as indicators of atmospheric turbidity. 1: Degree of polarization.

PubMed

Coulson, K L

1980-10-15

An extensive series of measurements of the intensity and polarization of the light from the zenith sky during periods of twilight was made at an altitude of 3400 m on the island of Hawaii during a 5-month period in 1977. This first of two papers is on the twilight polarization; the second will deal with intensity. The measurements were made in eight narrow spectral ranges between 0.32 and 0.90 microm under clear sky conditions. The data show that the degree of polarization at the zenith is a sensitive indicator of the existence of turbid layers at high levels in the atmosphere, and by monitoring the zenith skylight as a function of time during the twilight, it is possible to obtain qualitative information on both the altitude and relative density of the layers.

Zenith angle dependence of the geocoronal Lyman-alpha glow.

NASA Technical Reports Server (NTRS)

Paresce, F.; Kumar, S.; Bowyer, S.

1972-01-01

Review of the observations made on the zenith angle dependence and intensity of the geocoronal hydrogen Lyman-alpha glow by means of one of four extreme ultraviolet photometers flown to an altitude of 264 km on a Nike Tomahawk rocket launched from Thumba, India, in March 1970. The results obtained are compared with Meier and Mange's (1970) theoretical predictions. The possible causes for the discrepancies found are discussed.

Source attribution of tropospheric ozone

NASA Astrophysics Data System (ADS)

Butler, T. M.

2015-12-01

Tropospheric ozone is a harmful pollutant with adverse effects on human health and ecosystems. As well as these effects, tropospheric ozone is also a powerful greenhouse gas, with an anthropogenic radiative forcing one quarter of that of CO2. Along with methane and atmospheric aerosol, tropospheric ozone belongs to the so-called Short Lived Climate forcing Pollutants, or SLCP. Recent work has shown that efforts to reduce concentrations of SLCP in the atmosphere have the potential to slow the rate of near-term climate change, while simultaneously improving public health and reducing crop losses. Unlike many other SLCP, tropospehric ozone is not directly emitted, but is instead influenced by two distinct sources: transport of air from the ozone-rich stratosphere; and photochemical production in the troposphere from the emitted precursors NOx (oxides of nitrogen), CO (Carbon Monoxide), and VOC (volatile organic compounds, including methane). Better understanding of the relationship between ozone production and the emissions of its precursors is essential for the development of targeted emission reduction strategies. Several modeling methods have been employed to relate the production of tropospheric ozone to emissions of its precursors; emissions perturbation, tagging, and adjoint sensitivity methods all deliver complementary information about modelled ozone production. Most studies using tagging methods have focused on attribution of tropospheric ozone production to emissions of NOx, even though perturbation methods have suggested that tropospheric ozone is also sensitive to VOC, particularly methane. In this study we describe the implementation into a global chemistry-climate model of a scheme for tagging emissions of NOx and VOC with an arbitrary number of labels, which are followed through the chemical reactions of tropospheric ozone production in order to perform attribution of tropospehric ozone to its emitted precursors. Attribution is performed to both

Determination of coupling coefficients at various zenith angles of the basis of the cosmic ray azimuth effect

NASA Technical Reports Server (NTRS)

Belskiy, S. A.; Dmitriev, B. A.; Romanov, A. M.

1975-01-01

The value of EW asymmetry and coupling coefficients at different zenith angles were measured by means of a double coincidence crossed telescope which gives an opportunity to measure simultaneously the intensity of the cosmic ray hard component at zenith angles from 0 to 84 deg in opposite azimuths. The advantages of determining the coupling coefficients by the cosmic ray azimuth effect as compared to their measurement by the latitudinal effect are discussed.

Comparison of GPS tropospheric delays derived from two consecutive EPN reprocessing campaigns from the point of view of climate monitoring

NASA Astrophysics Data System (ADS)

Baldysz, Zofia; Nykiel, Grzegorz; Araszkiewicz, Andrzej; Figurski, Mariusz; Szafranek, Karolina

2016-09-01

The main purpose of this research was to acquire information about consistency of ZTD (zenith total delay) linear trends and seasonal components between two consecutive GPS reprocessing campaigns. The analysis concerned two sets of the ZTD time series which were estimated during EUREF (Reference Frame Sub-Commission for Europe) EPN (Permanent Network) reprocessing campaigns according to 2008 and 2015 MUT AC (Military University of Technology Analysis Centre) scenarios. Firstly, Lomb-Scargle periodograms were generated for 57 EPN stations to obtain a characterisation of oscillations occurring in the ZTD time series. Then, the values of seasonal components and linear trends were estimated using the LSE (least squares estimation) approach. The Mann-Kendall trend test was also carried out to verify the presence of linear long-term ZTD changes. Finally, differences in seasonal signals and linear trends between these two data sets were investigated. All these analyses were conducted for the ZTD time series of two lengths: a shortened 16-year series and a full 18-year one. In the case of spectral analysis, amplitudes of the annual and semi-annual periods were almost exactly the same for both reprocessing campaigns. Exceptions were found for only a few stations and they did not exceed 1 mm. The estimated trends were also similar. However, for the reprocessing performed in 2008, the trends values were usually higher. In general, shortening of the analysed time period by 2 years resulted in a decrease of the linear trends values of about 0.07 mm yr-1. This was confirmed by analyses based on two data sets.

Impact of geoengineered aerosols on the troposphere and stratosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tilmes, S.; Garcia, Rolando R.; Kinnison, Douglas E.

2009-06-27

A coupled chemistry climate model, the Whole Atmosphere Community Climate Model was used to perform a transient climate simulation to quantify the impact of geoengineered aerosols on atmospheric processes. In contrast to previous model studies, the impact on stratospheric chemistry, including heterogeneous chemistry in the polar regions, is considered in this simulation. In the geoengineering simulation, a constant stratospheric distribution of volcanic-sized, liquid sulfate aerosols is imposed in the period 2020–2050, corresponding to an injection of 2 Tg S/a. The aerosol cools the troposphere compared to a baseline simulation. Assuming an Intergovernmental Panel on Climate Change A1B emission scenario, globalmore » warming is delayed by about 40 years in the troposphere with respect to the baseline scenario. Large local changes of precipitation and temperatures may occur as a result of geoengineering. Comparison with simulations carried out with the Community Atmosphere Model indicates the importance of stratospheric processes for estimating the impact of stratospheric aerosols on the Earth’s climate. Changes in stratospheric dynamics and chemistry, especially faster heterogeneous reactions, reduce the recovery of the ozone layer in middle and high latitudes for the Southern Hemisphere. In the geoengineering case, the recovery of the Antarctic ozone hole is delayed by about 30 years on the basis of this model simulation. For the Northern Hemisphere, a onefold to twofold increase of the chemical ozone depletion occurs owing to a simulated stronger polar vortex and colder temperatures compared to the baseline simulation, in agreement with observational estimates.« less

Tropospheric Ozone Over North America

NASA Astrophysics Data System (ADS)

Oltmans, S. J.; Thompson, A. M.; Cooper, O. R.; Merrill, J. T.; Tarasick, D. W.; Newchurch, M. J.

2007-05-01

Ozone in the troposphere plays a significant role as an absorber of infrared radiation (greenhouse gas), in the cleansing capacity of the atmosphere as a precursor of hydroxol radical formation, and a regulated air pollutant capable of deleterious health and ecosystem effects. Knowledge of the ozone budget in the troposphere over North America (NA) is required to properly understand the various mechanisms that contribute to the measured distribution and to develop and test models capable of simulating and predicting this key player in atmospheric chemical and physical processes. Recent field campaigns including the 2004 and 2006 INTEX Ozone Network Studies (IONS) http:croc.gsfc.nasa.gov/intexb/ions06.html that have included intensive ozone profile measurements from ozonesondes provide a unique data set for describing tropospheric ozone over a significant portion of the North American continent. These campaigns have focused on the spring and summer seasons when tropospheric ozone over NA is particularly influenced by long-range transport processes, significant photochemical ozone production resulting from both anthropogenic and natural (lightning) precursor emissions, and exchange with the stratosphere. This study uses ozone profiles measured over NA in the latitude band from approximately 12-60N, extending from the tropics to the high mid latitudes, to describe the seasonal behavior of tropospheric ozone over NA with an emphasis on the spring and summer. This includes the variability within seasons at a particular site as well as the contrasts between the seasons. Emphasis is placed on the variations among the sites including latitudinal and longitudinal gradients and how these differ through the seasons and with altitude in the troposphere. Regional differences are most pronounced during the summer season likely reflecting the influence of a wider variation in processes influencing the tropospheric ozone distribution including lightning NOX production in the upper

Inclined Zenith Aurora over Kyoto on 17 September 1770: Graphical Evidence of Extreme Magnetic Storm

NASA Astrophysics Data System (ADS)

Kataoka, Ryuho; Iwahashi, Kiyomi

2017-10-01

Red auroras were observed in Japan during an extreme magnetic storm that occurred on 17 September 1770. We show new evidence that the red aurora extended toward the zenith of Kyoto around midnight. The basic appearance of the historical painting of the red aurora is geometrically reproduced based on the inclination of the local magnetic field and a detailed description in a newly discovered diary. The presence of the inclined zenith aurora over Kyoto suggests that the intensity of the September 1770 magnetic storm is comparable to, or slightly larger than that of the September 1859 Carrington storm.

Observing Tropospheric Ozone From Space

NASA Technical Reports Server (NTRS)

Fishman, Jack

2000-01-01

The importance of tropospheric ozone embraces a spectrum of relevant scientific issues ranging from local environmental concerns, such as damage to the biosphere and human health, to those that impact global change questions, Such is climate warming. From an observational perspective, the challenge is to determine the tropospheric ozone global distribution. Because its lifetime is short compared with other important greenhouse gases that have been monitored over the past several decades, the distribution of tropospheric ozone cannot be inferred from a relatively small set of monitoring stations. Therefore, the best way to obtain a true global picture is from the use of space-based instrumentation where important spatial gradients over vast ocean expanses and other uninhabited areas can be properly characterized. In this paper, the development of the capability to measure tropospheric ozone from space over the past 15 years is summarized. Research in the late 1980s successfully led to the determination of the climatology of tropospheric ozone as a function of season; more recently, the methodology has improved to the extent where regional air pollution episodes can be characterized. The most recent modifications now provide quasi-global (50 N) to 50 S) maps on a daily basis. Such a data set would allow for the study of long-range (intercontinental) transport of air pollution and the quantification of how regional emissions feed into the global tropospheric ozone budget. Future measurement capabilities within this decade promise to offer the ability to provide Concurrent maps of the precursors to the in situ formation of tropospheric ozone from which the scientific community will gain unprecedented insight into the processes that control global tropospheric chemistry

Satellite Observations of Tropospheric Chemistry

NASA Technical Reports Server (NTRS)

Singh, Hanwant B.; Jacob, Daniel J.; Hipskind, R. Stephen (Technical Monitor)

2001-01-01

The troposphere is an essential component of the earth's life support system as well as the gateway for the exchange of chemicals between different geochemical reservoirs of the earth. The chemistry of the troposphere is sensitive to perturbation from a wide range of natural phenomena and human activities. The societal concern has been greatly enhanced in recent decades due to ever increasing pressures of population growth and industrialization. Chemical changes within the troposphere control a vast array of processes that impact human health, the biosphere, and climate. A main goal of tropospheric chemistry research is to measure and understand the response of atmospheric composition to natural and anthropogenic perturbations, and to develop the capability to predict future change. Atmospheric chemistry measurements are extremely challenging due to the low concentrations of critical species and the vast scales over which the observations must be made. Available tropospheric data are mainly from surface sites and aircraft missions. Because of the limited temporal extent of aircraft observations, we have very limited information on tropospheric composition above the surface. This situation can be contrasted to the stratosphere, where satellites have provided critical and detailed chemical data on the global distribution of key trace gases.

Zenith 1 truss transfer ceremony

NASA Technical Reports Server (NTRS)

2000-01-01

The STS-92 astronaut team study the the Zenith-1 (Z-1) Truss during the Crew Equipment Interface Test. The Z-1 Truss was officially presented to NASA by The Boeing Co. on the Space Station Processing Facility floor on July 31. The truss is the cornerstone truss of the International Space Station and is scheduled to fly in Space Shuttle Discovery's payload pay on STS- 92 targeted for launch Oct. 5, 2000. The Z-1 is considered a cornerstone truss because it carries critical components of the Station's attitude, communications, thermal and power control systems as well as four control moment gyros, high and low gain antenna systems, and two plasma contactor units used to disperse electrical charge build-ups. The Z-1 truss and a Pressurized Mating Adapter (PMA-3), also flying to the Station on the same mission, will be the first major U.S. elements flown to the ISS aboard the Shuttle since the launch of the Unity element in December 1998.

Transition of NOAA's GPS-Met Data Acquisition and Processing System to the Commercial Sector

NASA Astrophysics Data System (ADS)

Jackson, M. E.; Holub, K.; Callahan, W.; Blatt, S.

2014-12-01

In April of 2014, NOAA/OAR/ESRL Global Systems Division (GSD) and Trimble, in collaboration with Earth Networks, Inc. (ENI) signed a Cooperative Research and Development Agreement (CRADA) to transfer the existing NOAA GPS-Met Data Acquisition and Processing System (GPS-Met DAPS) technology to a commercial Trimble/ENI partnership. NOAA's GPS-Met DAPS is currently operated in a pseudo-operational mode but has proven highly reliable and running at over 95% uptime. The DAPS uses the GAMIT software to ingest dual frequency carrier phase GPS/GNSS observations and ancillary information such as real-time satellite orbits to estimate the zenith-scaled tropospheric (ZTD) signal delays and, where surface MET data are available, retrieve integrated precipitable water vapor (PWV). The NOAA data and products are made available to end users in near real-time. The Trimble/ENI partnership will use the Trimble Pivot™ software with the Atmosphere App to calculate zenith tropospheric (ZTD), tropospheric slant delay, and integrated precipitable water vapor (PWV). Evaluation of the Trimble software is underway starting with a comparison of ZTD and PWV values determined from GPS stations located near NOAA Radiosonde Observation (Upper-Air Observation) launch sites. A success metric was established that requires Trimble's PWV estimates to match ESRL/GSD's to within 1.5 mm 95% of the time, which corresponds to a ZTD uncertainty of less than 10 mm 95% of the time. Initial results indicate that Trimble/ENI data meet and exceed the ZTD metric, but for some stations PWV estimates are out of specification. These discrepancies are primarily due to how offsets between MET and GPS stations are handled and are easily resolved. Additional test networks are proposed that include low terrain/high moisture variability stations, high terrain/low moisture variability stations, as well as high terrain/high moisture variability stations. We will present results from further testing along with a timeline

Chemistry in the Troposphere.

ERIC Educational Resources Information Center

Chameides, William L.; Davis, Douglas D.

1982-01-01

Topics addressed in this review of chemistry in the troposphere (layer of atmosphere extending from earth's surface to altitude of 10-16km) include: solar radiation/winds; earth/atmosphere interface; kinetic studies of atmospheric reactions; tropospheric free-radical photochemistry; instruments for nitric oxide detection; sampling…

Reactive Nitrogen, Ozone and Ozone Production in the Arctic Troposphere and the Impact of Stratosphere-Troposphere Exchange

NASA Technical Reports Server (NTRS)

Liang, Q.; Rodriquez, J. M.; Douglass, A. R.; Crawford, J. H.; Apel, E.; Bian, H.; Blake, D. R.; Brune, W.; Chin, M.; Colarco, P. R.;

Reactive nitrogen, ozone and ozone production in the Arctic troposphere and the impact of stratosphere-troposphere exchange

NASA Astrophysics Data System (ADS)

Liang, Q.; Rodriguez, J. M.; Douglass, A. R.; Crawford, J. H.; Olson, J. R.; Apel, E.; Bian, H.; Blake, D. R.; Brune, W.; Chin, M.; Colarco, P. R.; da Silva, A.; Diskin, G. S.; Duncan, B. N.; Huey, L. G.; Knapp, D. J.; Montzka, D. D.; Nielsen, J. E.; Pawson, S.; Riemer, D. D.; Weinheimer, A. J.; Wisthaler, A.

2011-12-01

We use aircraft observations obtained during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission to examine the distributions and source attributions of O3 and NOy in the Arctic and sub-Arctic region. Using a number of marker tracers, we distinguish various air masses from the background troposphere and examine their contributions to NOx, O3, and O3 production in the Arctic troposphere. The background Arctic troposphere has a mean O3 of ~60 ppbv and NOx of ~25 pptv throughout spring and summer with CO decreasing from ~145 ppbv in spring to ~100 ppbv in summer. These observed mixing ratios are not notably different from the values measured during the 1988 ABLE-3A and the 2002 TOPSE field campaigns despite the significant changes in emissions and stratospheric ozone layer in the past two decades that influence Arctic tropospheric composition. Air masses associated with stratosphere-troposphere exchange are present throughout the mid and upper troposphere during spring and summer. These air masses, with mean O3 concentrations of 140-160 ppbv, are significant direct sources of O3 in the Arctic troposphere. In addition, air of stratospheric origin displays net O3 formation in the Arctic due to its sustainable, high NOx (75 pptv in spring and 110 pptv in summer) and NOy (~800 pptv in spring and ~1100 pptv in summer). The air masses influenced by the stratosphere sampled during ARCTAS-B also show conversion of HNO3 to PAN. This active production of PAN is the result of increased degradation of ethane in the stratosphere-troposphere mixed air mass to form CH3CHO, followed by subsequent formation of PAN under high NOx conditions. These findings imply that an adequate representation of stratospheric NOy input, in addition to stratospheric O3 influx, is essential to accurately simulate tropospheric Arctic O3, NOx and PAN in chemistry transport models. Plumes influenced by recent anthropogenic and biomass burning emissions

CIMEL Measurements of Zenith Radiances at the ARM Site

NASA Technical Reports Server (NTRS)

Marshak, Alexander; Wiscombe, Warren; Lau, William K. M. (Technical Monitor)

2002-01-01

Starting from October 1, 2001, Cimel at the ARM Central Facility in Oklahoma has been switched to a new "cloud mode." This mode allows taking measurements of zenith radiance when the Sun in blocked by clouds. In this case, every 13 min. Cimel points straight up and takes 10 measurements with 9 sec. time interval. The new Cimel's mode has four filters at 440, 670, 870 and 1020 nm. For cloudy conditions, the spectral contrast in surface albedo dominates over Rayleigh and aerosol effects; this makes normalized zenith radiances at 440 and 670 as well as for 870 and 1020 almost indistinguishable. We compare Cimel measurements with other ARM cart site instruments: Multi-Filter Rotating Shadowband Radiometer (MFRSR), Narrow Field of View (NFOV) sensor, and MicroWave Radiometer(MWR). Based on Cimel and MFRSR 670 and 870 nm channels, we build a normalized difference cloud index (NDCI) for radiances and fluxes, respectively. Radiance NDCI from Cimel and flux NDCI from MFRSR are compared between themselves as well as with cloud Liquid Water Path (LWP) retrieved from MWR. Based on our theoretical calculations and preliminary data analysis,there is a good correlation between NDCIs and LWP for cloudy sky above green vegetation. Based on this correlation, an algorithm to retrieve cloud optical depth from NDCI is proposed.

Ozone, Tropospheric

NASA Technical Reports Server (NTRS)

Fishman, Jack

1995-01-01

In the early part of the 20th century, ground-based and balloon-borne measurements discovered that most of atmosphere's ozone is located in the stratosphere with highest concentrations located between 15 and 30 km (9,3 and 18.6 miles). For a long time, it was believed that tropospheric ozone originated from the stratosphere and that most of it was destroyed by contact with the earth's surface. Ozone, O3, was known to be produced by the photo-dissociation of molecular oxygen, O2, a process that can only occur at wavelengths shorter than 242 nm. Because such short-wave-length radiation is present only in the stratosphere, no tropospheric ozone production is possible by this mechanism. In the 1940s, however, it became obvious that production of ozone was also taking place in the troposphere. The overall reaction mechanism was eventually identified by Arie Haagen-Smit of the California Institute of Technology, in highly polluted southern California. The copious emissions from the numerous cars driven there as a result of the mass migration to Los Angeles after World War 2 created the new unpleasant phenomenon of photochemical smog, the primary component of which is ozone. These high levels of ozone were injuring vegetable crops, causing women's nylons to run, and generating increasing respiratory and eye-irritation problems for the populace. Our knowledge of tropospheric ozone increased dramatically in the early 1950s as monitoring stations and search centers were established throughout southern California to see what could be done to combat this threat to human health and the environment.

Derivation of Cloud Heating Rate Profiles using observations of Mixed-Phase Arctic Clouds: Impacts of Solar Zenith Angle

NASA Astrophysics Data System (ADS)

Zhang, G.; McFarquhar, G.; Poellot, M.; Verlinde, J.; Heymsfield, A.; Kok, G.

2005-12-01

Arctic stratus clouds play an important role in the energy balance of the Arctic region. Previous studies have suggested that Arctic stratus persist due to a balance among cloud top radiation cooling, latent heating, ice crystal fall out and large scale forcing. In this study, radiative heating profiles through Arctic stratus are computed using cloud, surface and thermodynamic observations obtained during the Mixed-Phase Arctic Cloud Experiment (M-PACE) as input to the radiative transfer model STREAMER. In particular, microphysical and macrophycial cloud properties such as phase, water content, effective particle size, particle shape, cloud height and cloud thickness were derived using data collected by in-situ sensors on the University of North Dakota (UND) Citation and ground-based remote sensors at Barrow and Oliktok Point. Temperature profiles were derived from radiosonde launches and a fresh snow surface was assumed. One series of sensitivity studies explored the dependence of the heating profile on the solar zenith angle. For smaller solar zenith angles, more incoming solar radiation is received at cloud top acting to counterbalance infrared cooling. As solar zenith angle in the Arctic is large compared to low latitudes, a large solar zenith angle may contribute to the longevity of these clouds.

Methane from the Tropospheric Emission Spectrometer (TES)

NASA Technical Reports Server (NTRS)

Payne, Vivienne; Worden, John; Kulawik, Susan; Frankenberg, Christian; Bowman, Kevin; Wecht, Kevin

2012-01-01

TES V5 CH4 captures latitudinal gradients, regional variability and interannual variation in the free troposphere. V5 joint retrievals offer improved sensitivity to lower troposphere. Time series extends from 2004 to present. V5 reprocessing in progress. Upper tropospheric bias. Mitigated by N2O correction. Appears largely spatially uniform, so can be corrected. How to relate free-tropospheric values to surface emissions.

Zenith 1 truss transfer ceremony

NASA Technical Reports Server (NTRS)

2000-01-01

The Zenith-1 (Z-1) Truss is officially presented to NASA by The Boeing Co. on the Space Station Processing Facility floor on July 31. STS-92 Commander Col. Brian Duffy, comments on the presentation. Pictured are The Boeing Co. processing team and STS-92 astronauts. The Z-1 Truss is the cornerstone truss of the International Space Station and is scheduled to fly in Space Shuttle Discovery's payload pay on STS-92 targeted for launch Oct. 5, 2000. The Z-1 is considered a cornerstone truss because it carries critical components of the Station's attitude, communications, thermal and power control systems as well as four control moment gyros, high and low gain antenna systems, and two plasma contactor units used to disperse electrical charge build- ups. The Z-1 truss and a Pressurized Mating Adapter (PMA-3), also flying to the Station on the same mission, will be the first major U.S. elements flown to the ISS aboard the Shuttle since the launch of the Unity element in December 1998.

Calibration and Testing of Digital Zenith Camera System Components

NASA Astrophysics Data System (ADS)

Ulug, Rasit; Halicioglu, Kerem; Tevfik Ozludemir, M.; Albayrak, Muge; Basoglu, Burak; Deniz, Rasim

2017-04-01

Starting from the beginning of the new millennium, thanks to the Charged-Coupled Device (CCD) technology, fully or partly automatic zenith camera systems are designed and used in order to determine astro-geodetic deflections of the vertical components in several countries, including Germany, Switzerland, Serbia, Latvia, Poland, Austria, China and Turkey. The Digital Zenith Camera System (DZCS) of Turkey performed successful observations yet it needs to be improved in terms of automating the system and increasing observation accuracy. In order to optimize the observation time and improve the system, some modifications have been implemented. Through the modification process that started at the beginning of 2016, some DZCS components have been replaced with the new ones and some new additional components have been installed. In this presentation, the ongoing calibration and testing process of the DZCS are summarized in general. In particular, one of the tested system components is the High Resolution Tiltmeter (HRTM), which enable orthogonal orientation of DZCS to the direction of plump line, is discussed. For the calibration of these components, two tiltmeters with different accuracies (1 nrad and 0.001 mrad) were observed nearly 30 days. The data recorded under different environmental conditions were divided into hourly, daily, and weekly subsets. In addition to the effects of temperature and humidity, interoperability of two tiltmeters were also investigated. Results show that with the integration of HRTM and the other implementations, the modified DZCS provides higher accuracy for the determination of vertical deflections.

Stratospheric NO2 vertical profile retrieved from ground-based Zenith-Sky DOAS observations at Kiruna, Sweden

NASA Astrophysics Data System (ADS)

Gu, Myojeong; Enell, Carl-Fredrik; Hendrick, François; Pukite, Janis; Van Roozendael, Michel; Platt, Ulrich; Raffalski, Uwe; Wagner, Thomas

2014-05-01

Stratospheric NO2 destroys ozone and acts as a buffer against halogen-catalyzed ozone loss through the formation of reservoir species (ClONO2, BrONO2). Since the importance of both mechanisms depends on the altitude, the investigation of stratospheric NO2 vertical distribution can provide more insight into the role of nitrogen compounds in the destruction of ozone. Here we present stratospheric NO2 vertical profiles retrieved from twilight ground-based zenith-sky DOAS observations at Kiruna, Sweden (68.84°N, 20.41°E) covering 1997 - 2013 periods. This instrument observes zenith scattered sunlight. The sensitivity for stratospheric trace gases is highest during twilight due to the maximum altitude of the scattering profile and the light path through the stratosphere, which vary with the solar zenith angle. The profiling algorithm, based on the Optimal Estimation Method, has been developed by IASB-BIRA and successfully applied at other stations (Hendrick et al., 2004). The basic principle behind this profiling approach is that during twilight, the mean Rayleigh scattering altitude scans the stratosphere rapidly, providing height-resolved information on the absorption by stratospheric NO2. In this study, the long-term evolution of the stratospheric NO2 profile at polar latitude will be investigated. Hendrick, F., B. Barret, M. Van Roozendael, H. Boesch, A. Butz, M. De Mazière, F. Goutail, C. Hermans, J.-C. Lambert, K. Pfeilsticker, and J.-P. Pommereau, Retrieval of nitrogen dioxide stratospheric profiles from ground-based zenith-sky UV-visible observations: Validation of the technique through correlative comparisons, Atmospheric Chemistry and Physics, 4, 2091-2106, 2004

Tropospheric ozone in east Asia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Phadnis, M.J.

1996-12-31

An analysis of the observed data for the tropospheric ozone at mid latitudes in east Asia is done. There are three ways by which the tropospheric ozone is calculated, namely: (1) Ozonesonde measurements, (2) Fishman`s method of Residual Ozone and (3) TOMS measurements - an indirect method of calculating tropospheric ozone. In addition the surface ozone values at the network sites in Japan is also considered. The analysis of data is carried out for a period of twelve years from 1979 to 1991. In general it is observed that the tropospheric ozone is more in summer than winter, obviously becausemore » of the larger tropopause height in summer. On an average for the period of the analysis, the ozone values are at a high of about 60 DU (dobson units). While in winter the values go down to around 30 DU. Also a time series analysis shows an increasing trend in the values over the years. The ozonesonde values are correlated more to the TOMS tropospheric ozone values. For the stations analyzed in Japan, the TOMS tropospheric ozone values are generally greater than the ozonesonde values. The analysis of the average monthly surface ozone in Japan shows highs in spring and lows in summer. This can be attributed to movement of pollutant laden fronts towards Japan during spring. The highs for surface ozone are about 50 DU while the lows are around 20 DU.« less

Investigation of the 16-year and 18-year ZTD Time Series Derived from GPS Data Processing

NASA Astrophysics Data System (ADS)

Bałdysz, Zofia; Nykiel, Grzegorz; Figurski, Mariusz; Szafranek, Karolina; KroszczyńSki, Krzysztof

2015-08-01

The GPS system can play an important role in activities related to the monitoring of climate. Long time series, coherent strategy, and very high quality of tropospheric parameter Zenith Tropospheric Delay (ZTD) estimated on the basis of GPS data analysis allows to investigate its usefulness for climate research as a direct GPS product. This paper presents results of analysis of 16-year time series derived from EUREF Permanent Network (EPN) reprocessing performed by the Military University of Technology. For 58 stations Lomb-Scargle periodograms were performed in order to obtain information about the oscillations in ZTD time series. Seasonal components and linear trend were estimated using Least Square Estimation (LSE) and Mann—Kendall trend test was used to confirm the presence of a linear trend designated by LSE method. In order to verify the impact of the length of time series on trend value, comparison between 16 and 18 years were performed.

Observed Spectral Invariant Behavior of Zenith Radiance in the Transition Zone Between Cloud-Free and Cloudy Regions

NASA Technical Reports Server (NTRS)

Marshak, A.; Knyazikhin, Y.; Chiu, C.; Wiscombe, W.

2010-01-01

The Atmospheric Radiation Measurement Program's (ARM) new Shortwave Spectrometer (SWS) looks straight up and measures zenith radiance at 418 wavelengths between 350 and 2200 nm. Because of its 1-sec sampling resolution, the SWS provides a unique capability to study the transition zone between cloudy and clear sky areas. A surprising spectral invariant behavior is found between ratios of zenith radiance spectra during the transition from cloudy to cloud-free atmosphere. This behavior suggests that the spectral signature of the transition zone is a linear mixture between the two extremes (definitely cloudy and definitely clear). The weighting function of the linear mixture is found to be a wavelength-independent characteristic of the transition zone. It is shown that the transition zone spectrum is fully determined by this function and zenith radiance spectra of clear and cloudy regions. This new finding may help us to better understand and quantify such physical phenomena as humidification of aerosols in the relatively moist cloud environment and evaporation and activation of cloud droplets.

Plan of Time Management of Satellite Positioning System using Quasi-zenith Satellite

NASA Astrophysics Data System (ADS)

Takahashi, Yasuhiro; Fujieda, Miho; Amagai, Jun; Yokota, Shoichiro; Kimura, Kazuhiro; Ito, Hiroyuki; Hama, Shin'ichi; Morikawa, Takao; Kawano, Isao; Kogure, Satoshi

The Quasi-Zenith satellites System (QZSS) is developed as an integrated satellite service system of communication, broadcasting and positioning for mobile users in specified regions of Japan from high elevation angle. Purposes of the satellite positioning system using Quasi-Zenith satellite (QZS) are to complement and augment the GPS. The national institutes concerned have been developing the positioning system using QZS since 2003 and will carry out experiments and researches in three years after the launch. In this system, National Institute of Information and Communications Technology (NICT) is mainly in charge of timing system for the satellite positioning system using QZS, such as onboard hydrogen maser atomic clock and precise time management system of the QZSS. We started to develop the engineering model of the time management system for the QZSS. The time management system for the QZSS will be used to compare time differences between QZS and earth station as well as to compare between three onboard atomic clocks. This paper introduces time management of satellite positioning system using the QZSS.

Modeling the effects of UV variability and the QBO on the troposphere-stratosphere system. Part II: The troposphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rind, D.; Balachandran, N.K.

1995-08-01

Results of experiments with a GCM involving changes in UV input ({plus_minus} 25%, {plus_minus}5% at wavelengths below 0.3 {mu}) and simulated equatorial QBO are presented, with emphasis on the tropospheric response. The QBO and UV changes alter the temperature in the lower stratosphere/upper troposphere warms, tropospheric eddy energy is reduced, leading to extratropical tropospheric cooling of some 0.5{degrees}C on the zonal average, and surface temperature changes up to {plus_minus}5{degrees}C locally. Opposite effects occur when the extratropical lower stratosphere/upper troposphere cools. Cooling or warming of the comparable region in the Tropics decreases/increases static stability, accelerating/decelerating the Hadley circulation. Tropospheric dynamical changesmore » are on the order of 5%. The combined UV/QBO effect in the troposphere results from its impact on the middle atmosphere; in the QBO east phase, more energy is refracted to higher latitudes, due to the increased horizontal shear of the zonal wind, but with increased UV, this energy propagates preferentially out of the polar lower stratosphere, in response to the increased vertical shear of the zonal winds; therefore, it is less effective in warming the polar lower stratosphere. Due to their impacts on planetary wave generation and propagation, all combinations of UV and QBO phases affect the longitudinal patterns of tropospheric temperatures and geopotential heights. The modeled perturbations often agree qualitatively with observations and are of generally similar orders of magnitude. The results are sensitive to the forcing employed. In particular, the nature of the tropospheric response depends upon the magnitude (and presumably wavelength) of the solar irradiance perturbation. The results of the smaller UV variations ({plus_minus}5%) are more in agreement with observations, showing clear differences between the UV impact in the east and west QBO phase. 34 refs., 15 figs., 3 tabs.« less

Space opportunities for tropospheric chemistry research

NASA Technical Reports Server (NTRS)

Levine, Joel S.; Hoell, James M.; Mcneal, Robert J.

1986-01-01

The use of the Space Shuttle to measure tropospheric trace species is examined. Factors which affect the measurement of tropospheric trace species are discussed. The Academy of Sciences 1985 report categorized the trace species into levels: first-level gases include water vapor, O3, CO, and CH4, and the second-level gases are N2O, NO2, NH3, SO2, chlorofluoromethanes, and HCl. The effects of first-level gases on the earth's climate, the photochemistry/chemistry of the troposphere, and the photochemical/chemical production and destruction of the hydroxyl radical are studied; the distribution and magnitude of the hydroxyl radical in the troposphere are analyzed in terms of water vapor, O3, CO, and CH4.

Tropospheric processes: Observations and interpretation

NASA Technical Reports Server (NTRS)

Isaksen, Ivar S. A.; Fuglestvedt, J. A.; Lee, Yuan-Pern; Johnson, Colin; Atkinson, Roger; Lelieveld, Joseph; Sidebottom, Howard; Thompson, Anne; Brune, William H.; Oppenheimer, Michael

1991-01-01

Three aspects of tropospheric chemical processes imposed by manmade emission of source gases will be discussed. First, the implications for the OH distribution and thereby for the lifetime of source gases which are controlled by reactions with OH in the troposphere (e.g., CH4 and HCFC) are investigated. This is of importance for stratosphere ozone and climate. Second, we will study the impact of source gas emission on tropospheric ozone and discuss the possibility to estimate indirect climate effects from the changes in ozone and other climate gases. Finally, the degradation of HFC and HCFC's is discussed.

Man's impact on the troposphere: Lectures in tropospheric chemistry

NASA Technical Reports Server (NTRS)

Levine, J. S. (Editor); Schryer, D. R. (Editor)

1978-01-01

Lectures covering a broad spectrum of current research in tropospheric chemistry with particular emphasis on the interaction of measurements, modeling, and understanding of fundamental processes are presented.

Tropospheric Ozone from the TOMS TDOT (TOMS-Direct-Ozone-in-Troposphere) Technique During SAFARI-2000

NASA Technical Reports Server (NTRS)

Stone, J. B.; Thompson, A. M.; Frolov, A. D.; Hudson, R. D.; Bhartia, P. K. (Technical Monitor)

2002-01-01

There are a number of published residual-type methods for deriving tropospheric ozone from TOMS (Total Ozone Mapping Spectrometer). The basic concept of these methods is that within a zone of constant stratospheric ozone, the tropospheric ozone column can be computed by subtracting stratospheric ozone from the TOMS Level 2 total ozone column, We used the modified-residual method for retrieving tropospheric ozone during SAFARI-2000 and found disagreements with in-situ ozone data over Africa in September 2000. Using the newly developed TDOT (TOMS-Direct-Ozone-in-Troposphere) method that uses TOMS radiances and a modified lookup table based on actual profiles during high ozone pollution periods, new maps were prepared and found to compare better to soundings over Lusaka, Zambia (15.5 S, 28 E), Nairobi and several African cities where MOZAIC aircraft operated in September 2000. The TDOT technique and comparisons are described in detail.

Spatio-Temporal Variability of Water Vapor in the Free Troposphere Investigated by Dial and Ftir Vertical Soundings

NASA Astrophysics Data System (ADS)

Vogelmann, H.; Sussmann, R.; Trickl, T.; Reichert, A.

2016-06-01

We report on the free tropospheric spatio-temporal variability of water vapor investigated by the analysis of a five-year period of water vapor vertical soundings above Mt. Zugspitze (2962 m a.s.l., Germany). Our results are obtained from a combination of measurements of vertically integrated water vapor (IWV), recorded with a solar Fourier Transform InfraRed (FTIR) spectrometer and of water vapor profiles recorded with the nearby differential absorption lidar (DIAL). The special geometrical arrangement of one zenith-viewing and one sun-pointing instrument and the temporal resolution of both optical instruments allow for an investigation of the spatio-temporal variability of IWV on a spatial scale of less than one kilometer and on a time scale of less than one hour. We investigated the short-term variability of both IWV and water vapor profiles from statistical analyses. The latter was also examined by case studies with a clear assignment to certain atmospheric processes as local convection or long-range transport. This study is described in great detail in our recent publication [1].

Free tropospheric observations of Carbonyl Sulfide from Aura Tropospheric Emission Spectrometer over ocean

NASA Astrophysics Data System (ADS)

Kuai, Le; Worden, John; Campbell, Ellitt; Kulawik, Susan; Montzka, Stephen; Liu, Jiabin

2014-05-01

Carbonyl sulfide (OCS) is the most abundant sulfur gas in the troposphere with a global averaging mixing ratio of about 500 part per trillion (ppt). The ocean is the primary source of OCS, emitting OCS directly or its precursors, carbon disulfide and dimethyl sulfide. The most important atmospheric sink of OCS is uptake by terrestrial plants via photosynthesis. Although the global budget of atmospheric OCS has been studied, the global integrated OCS fluxes have large uncertainties, e.g. the uncertainties of the ocean fluxes are as large as 100% or more and how the ocean sources are distributed is not well known. We developed a retrieval algorithm for free tropospheric carbonyl sulfide (OCS) observations above the ocean using radiance measurements from the Tropospheric Emission Spectrometer (TES). These first observations of the free tropospheric OCS provide global maps with information of OCS seasonal and spatial variability in the mid troposphere. These data will help to characterize ocean OCS fluxes. Evaluation of the biases and uncertainties in the TES OCS estimates against aircraft profiles from the HIPPO campaign and ground data from the NOAA Mauna Loa site suggests that the OCS retrievals (1) have less than 1.0 degree of freedom for signals (DOFs), (2) are sensitive in the mid-troposphere with a peak sensitivity typically between 300 to 500 hPa, (3) and have much smaller systematic errors from temperature, CO2 and H2O calibrations relative to random errors from measurement noise. Here we estimate the monthly means from TES measurements averaged over multiple years so that random errors are reduced and useful information about OCS seasonal and latitudinal variability can be derived. With this averaging, TES OCS data are found to be consistent (within the calculated uncertainties) with NOAA ground observations and HIPPO aircraft measurements and captures the seasonal and latitudinal variations observed by these in situ data within the estimated uncertainties

Tropospheric Ozone Lidar Network (TOLNet) Observations of Processes Controlling Spatio-Temporal Tropospheric-Ozone Distributions

NASA Astrophysics Data System (ADS)

Newchurch, M.; Johnson, M. S.; Leblanc, T.; Langford, A. O.; Senff, C. J.; Kuang, S.; Strawbridge, K. B.; McGee, T. J.; Berkoff, T.; Chen, G.

2017-12-01

The Tropospheric Ozone Lidar Network, TOLNet, has matured into a credible scientific group of six ozone lidars that are capable of accurate, high-spatio-temporal-resolution measurement of tropospheric ozone structures and morphology These lidars have demonstrated their 10% accuracy in several intercomparison campaigns and have participated in several scientific investigations both in small and large instrumentation groups. They have investigated many scientific phenomena including stratosphere-to-troposphere exchange, boundary-layer development, the interaction between the boundary layer and the free troposphere, Front-range-ozone morphology, urban outflow, land/sea interactions, et al. These processes determine the ozone distribution affecting large portions of the population. The TOLNet group is now making significant contributions to the innovation of ozone lidar instrumentation and retrieval techniques. The campaigns proposed over the next few years build on demonstrated capability to address more difficult scientific issues, especially the ozone production potential and distribution from wildfires and prescribed burns. Through scientific cooperation with other ground-based profiling instrumentation, TOLNet is also contributing to the validation of the new measurement capabilities of TEMPO.

High zenith angle observations of PKS 2155-304 with the MAGIC-I telescope

NASA Astrophysics Data System (ADS)

Aleksić, J.; Alvarez, E. A.; Antonelli, L. A.; Antoranz, P.; Asensio, M.; Backes, M.; Barres de Almeida, U.; Barrio, J. A.; Bastieri, D.; Becerra González, J.; Bednarek, W.; Berdyugin, A.; Berger, K.; Bernardini, E.; Biland, A.; Blanch, O.; Bock, R. K.; Boller, A.; Bonnoli, G.; Borla Tridon, D.; Braun, I.; Bretz, T.; Cañellas, A.; Carmona, E.; Carosi, A.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Cossio, L.; Covino, S.; Dazzi, F.; De Angelis, A.; De Caneva, G.; De Cea del Pozo, E.; De Lotto, B.; Delgado Mendez, C.; Diago Ortega, A.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Dorner, D.; Doro, M.; Eisenacher, D.; Elsaesser, D.; Ferenc, D.; Fonseca, M. V.; Font, L.; Fruck, C.; García López, R. J.; Garczarczyk, M.; Garrido, D.; Giavitto, G.; Godinović, N.; Gozzini, S. R.; Hadasch, D.; Häfner, D.; Herrero, A.; Hildebrand, D.; Höhne-Mönch, D.; Hose, J.; Hrupec, D.; Jogler, T.; Kellermann, H.; Klepser, S.; Krähenbühl, T.; Krause, J.; Kushida, J.; La Barbera, A.; Lelas, D.; Leonardo, E.; Lewandowska, N.; Lindfors, E.; Lombardi, S.; López, M.; López, R.; López-Oramas, A.; Lorenz, E.; Makariev, M.; Maneva, G.; Mankuzhiyil, N.; Mannheim, K.; Maraschi, L.; Marcote, B.; Mariotti, M.; Martínez, M.; Mazin, D.; Meucci, M.; Miranda, J. M.; Mirzoyan, R.; Moldón, J.; Moralejo, A.; Munar-Adrover, P.; Niedzwiecki, A.; Nieto, D.; Nilsson, K.; Nowak, N.; Orito, R.; Paiano, S.; Paneque, D.; Paoletti, R.; Pardo, S.; Paredes, J. M.; Partini, S.; Perez-Torres, M. A.; Persic, M.; Peruzzo, L.; Pilia, M.; Pochon, J.; Prada, F.; Prada Moroni, P. G.; Prandini, E.; Puerto Gimenez, I.; Puljak, I.; Reichardt, I.; Reinthal, R.; Rhode, W.; Ribó, M.; Rico, J.; Rügamer, S.; Saggion, A.; Saito, K.; Saito, T. Y.; Salvati, M.; Satalecka, K.; Scalzotto, V.; Scapin, V.; Schultz, C.; Schweizer, T.; Shayduk, M.; Shore, S. N.; Sillanpää, A.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Spanier, F.; Spiro, S.; Stamatescu, V.; Stamerra, A.; Steinke, B.; Storz, J.; Strah, N.; Sun, S.; Surić, T.; Takalo, L.; Takami, H.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Tescaro, D.; Teshima, M.; Tibolla, O.; Torres, D. F.; Treves, A.; Uellenbeck, M.; Vankov, H.; Vogler, P.; Wagner, R. M.; Weitzel, Q.; Zabalza, V.; Zandanel, F.; Zanin, R.

2012-08-01

Context. The high frequency peaked BL Lac PKS 2155-304 with a redshift of z = 0.116 was discovered in 1997 in the very high energy (VHE, E > 100 GeV) γ-ray range by the University of Durham Mark VI γ-ray Cherenkov telescope in Australia with a flux corresponding to 20% of the Crab Nebula flux. It was later observed and detected with high significance by the southern Cherenkov observatory H.E.S.S. establishing this source as the best studied southern TeV blazar. Detection from the northern hemisphere is difficult due to challenging observation conditions under large zenith angles. In July 2006, the H.E.S.S. collaboration reported an extraordinary outburst of VHE γ-emission. During the outburst, the VHE γ-ray emission was found to be variable on the time scales of minutes and with a mean flux of ~7 times the flux observed from the Crab Nebula. Follow-up observations with the MAGIC-I standalone Cherenkov telescope were triggered by this extraordinary outburst and PKS 2155-304 was observed between 28 July to 2 August 2006 for 15 h at large zenith angles. Aims: We studied the behavior of the source after its extraordinary flare. Furthermore, we developed an analysis method in order to analyze these data taken under large zenith angles. Methods: Here we present an enhanced analysis method for data taken at high zenith angles. We developed improved methods for event selection that led to a better background suppression. Results: The quality of the results presented here is superior to the results presented previously for this data set: detection of the source on a higher significance level and a lower analysis threshold. The averaged energy spectrum we derived has a spectral index of (-3.5 ± 0.2) above 400 GeV, which is in good agreement with the spectral shape measured by H.E.S.S. during the major flare on MJD 53 944. Furthermore, we present the spectral energy distribution modeling of PKS 2155-304. With our observations we increased the duty cycle of the source

Tropical tropospheric ozone and biomass burning.

PubMed

Thompson, A M; Witte, J C; Hudson, R D; Guo, H; Herman, J R; Fujiwara, M

2001-03-16

New methods for retrieving tropospheric ozone column depth and absorbing aerosol (smoke and dust) from the Earth Probe-Total Ozone Mapping Spectrometer (EP/TOMS) are used to follow pollution and to determine interannual variability and trends. During intense fires over Indonesia (August to November 1997), ozone plumes, decoupled from the smoke below, extended as far as India. This ozone overlay a regional ozone increase triggered by atmospheric responses to the El Niño and Indian Ocean Dipole. Tropospheric ozone and smoke aerosol measurements from the Nimbus 7 TOMS instrument show El Niño signals but no tropospheric ozone trend in the 1980s. Offsets between smoke and ozone seasonal maxima point to multiple factors determining tropical tropospheric ozone variability.

Zenith 1 truss transfer ceremony

NASA Technical Reports Server (NTRS)

2000-01-01

The Zenith-1 (Z-1) Truss is officially presented to NASA by The Boeing Co. on the Space Station Processing Facility floor on July 31. STS-92 Commander Col. Brian Duffy, comments on the presentation. At his side is Tip Talone, NASA director of International Space Station and Payload Processing at KSC. Talone and Col. Duffy received a symbolic key for the truss from John Elbon, Boeing director of ISS ground operations. The Z-1 Truss is the cornerstone truss of the International Space Station and is scheduled to fly in Space Shuttle Discovery's payload pay on STS- 92 targeted for launch Oct. 5, 2000. The Z-1 is considered a cornerstone truss because it carries critical components of the Station's attitude, communications, thermal and power control systems as well as four control moment gyros, high and low gain antenna systems, and two plasma contactor units used to disperse electrical charge build-ups. The Z-1 truss and a Pressurized Mating Adapter (PMA-3), also flying to the Station on the same mission, will be the first major U.S. elements flown to the ISS aboard the Shuttle since the launch of the Unity element in December 1998.

Effects of the gaseous and liquid water content of the atmosphere on range delay and Doppler frequency

NASA Technical Reports Server (NTRS)

Flock, W. L.

1981-01-01

When high precision is required for range measurement on Earth space paths, it is necessary to correct as accurately as possible for excess range delays due to the dry air, water vapor, and liquid water content of the atmosphere. Calculations based on representative values of atmospheric parameters are useful for illustrating the order of magnitude of the expected delays. Range delay, time delay, and phase delay are simply and directly related. Doppler frequency variations or noise are proportional to the time rate of change of excess range delay. Tropospheric effects were examined as part of an overall consideration of the capability of precision two way ranging and Doppler systems.

The sulfur budget of the troposphere

NASA Technical Reports Server (NTRS)

Tiwari, S. N.; Augustsson, T. R.

1981-01-01

A one dimensional photochemical tropospheric model was used to calculate the vertical profiles of tropospheric species. Particular attention is focused on the recent inclusion of the chemistry of the sulfur group, which consists of 13 species involving a total of 45 chemical reactions. It is found that the chemistry of the sulfur species, because it is largely anthropogenic, plays an increasingly important role in the distribution of tropospheric gases. The calculated vertical profiles were compared to available measurements and generally found to be in good agreement.

The Governing Processes and Timescales of Stratosphere-to-Troposphere Transport and its Contribution to Ozone in the Arctic Troposphere

NASA Technical Reports Server (NTRS)

Liang, Q.; Douglass, A. R.; Duncan, B. N.; Stolarski, R. S.; Witte, J. C.

2009-01-01

We used the seasonality of a combination of atmospheric trace gases and idealized tracers to examine stratosphere-to-troposphere transport and its influence on tropospheric composition in the Arctic. Maximum stratosphere-to-troposphere transport of CFCs and O3 occurs in April as driven by the Brewer-Dobson circulation. Stratosphere-troposphere exchange (STE) occurs predominantly between 40 deg N to 80 deg N with stratospheric influx in the mid-latitudes (30-70 deg N) accounting for 67.81 percent of the air of stratospheric origin in the Northern Hemisphere extratropical troposphere. Transport from the lower stratosphere to the lower troposphere (LT) takes three months on average, one month to cross the tropopause, the second month to travel from the upper troposphere (UT) to the middle troposphere (MT), and the third month to reach the LT. During downward transport, the seasonality of a trace gas can be greatly impacted by wet removal and chemistry. A comparison of idealized tracers with varying lifetimes suggests that when initialized with the same concentrations and seasonal cycles at the tropopause, trace gases that have shorter lifetimes display lower concentrations, smaller amplitudes, and earlier seasonal maxima during transport to the LT. STE contributes to O3 in the Arctic troposphere directly from the transport of O3 and indirectly from the transport of NOy . Direct transport of O3 from the stratosphere accounts for 78 percent of O3 in the Arctic UT with maximum contributions occurring from March to May. The stratospheric contribution decreases significantly in the MT/LT (20.25 percent of total O3) and shows a very weak March.April maximum. Our NOx budget analysis in the Arctic UT shows that during spring and summer, the stratospheric injection of NO y-rich air increases NOx concentrations above the 20 pptv threshold level, thereby shifting the Arctic UT from a regime of net photochemical ozone loss to one of net production with rates as high as +16 ppbv/month.

Using CFC-12 and HCl to quantify the annual cycle of the stratospheric contribution to ozone in the Arctic troposphere

NASA Astrophysics Data System (ADS)

Liang, Q.; Douglass, A. R.; Duncan, B. N.; Stolarski, R. S.; Witte, J. C.

2007-12-01

In this study, we use CFC-12 and hydrochloric acid (HCl) to quantify the annual cycle of stratosphere-to- troposphere transport of O3 to the Arctic troposphere. To do so, we analyze results from a 5-year stratosphere and troposphere simulation from the Global Modeling Initiative (GMI) Chemical Transport Model (CTM) for 1994- 1998 and a 10-year simulation using the GEOS Chemistry Climate Model (GEOS CCM) for 1995-2004. The later includes a tagged CFC-12 tracer to track the transport of aged stratospheric air into the troposphere. We compare the simulated CFC-12 with 10 years surface CFC-12 measurements at two NOAA-GMD sites, Alert and Barrow. We compare O3 with 10 years of ozonesondes at Alert, Eureka, and Resolute. CFC-12, HCl and O3 are all compared with satellite observations from the Advanced Composition Explorer (ACE) and several MkIV balloon measurements in the Arctic. The GEOS CCM and GMI CTM simulations capture well the observed magnitude and annual cycle of CFC-12, HCl, and O3 in the stratosphere and troposphere. Since CFC-12 is emitted at the surface and destroyed in the stratosphere while HCl and O3 are produced in the stratosphere, the stratospheric air shows strong correlation between HCl and O3 and anti-correlation between CFC-12 and O3. We use the CFC-12 tagged tracer to track the transport from the stratosphere to the troposphere and the subsequent transport into the lower troposphere in the Arctic. HCl is paired with O3 to quantify the stratospheric contribution to O3 in the troposphere by applying a scaling factor to the simulated HCl using the HCl-O3 regression ratio. O3 and its annual cycle in the upper troposphere are dominated by stratospheric influence, which peaks in spring. The stratospheric contribution decreases as altitude decreases, accompanied by a delay in the phase of maximum. In the middle troposphere (2-6km), the stratospheric contribution peaks during the summer and is comparable to that of net photochemistry. Due to inefficient

GPS-PWV Estimation and Analysis for CGPS Sites Operating in Mexico

NASA Astrophysics Data System (ADS)

Gutierrez, O.; Vazquez, G. E.; Bennett, R. A.; Adams, D. K.

2014-12-01

Eighty permanent Global Positioning System (GPS) tracking stations that belong to several networks spanning Mexico intended for diverse purposes and applications were used to estimate precipitable water vapor (PWV) using measurement series covering the period of 2000-2014. We extracted the GPS-PWV from the ionosphere-free double-difference carrier phase observations, processed using the GAMIT software. The GPS data were processed with a 30 s sampling rate, 15-degree cutoff angle, and precise GPS orbits disseminated by IGS. The time-varying part of the zenith wet delay was estimated using the Global Mapping Function (GMF), while the constant part is evaluated using the Neil tropospheric model. The data reduction to compute the zenith wet delay follows the step piecewise linear strategy, which is subsequently transformed to PWV estimated every 2-hr. Although there exist previous isolated studies for estimating PWV in Mexico, this study is an attempt to perform a more complete and comprehensive analysis of PWV estimation throughout the Mexican territory. Our resulting GPS-based PWV were compared to available PWV values for 30 stations that operate in Mexico and report the PWV to Suominet. This comparison revealed differences of 1 to 2 mm between the GPS-PWV solution and the PWV reported by Suominet. Accurate values of GPS-PWV will help enhance Mexico ability to investigate water vapor advection, convective and frontal rainfall and long-term climate variability.

Applying modeling Results in designing a global tropospheric experiment

NASA Technical Reports Server (NTRS)

1982-01-01

A set of field experiments and advanced modeling studies which provide a strategy for a program of global tropospheric experiments was identified. An expanded effort to develop space applications for trospheric air quality monitoring and studies was recommended. The tropospheric ozone, carbon, nitrogen, and sulfur cycles are addressed. Stratospheric-tropospheric exchange is discussed. Fast photochemical processes in the free troposphere are considered.

Interpreting vegetation reflectance measurements as a function of solar zenith angle

NASA Technical Reports Server (NTRS)

Kimes, D. S.; Smith, J. A.; Ranson, K. J.

1979-01-01

Spectral hemispherical-conical reflectances of a nadir looking sensor were taken throughout the day for a lodgepole pine and two grass canopies. Mathematical simulations of both spectral hemispherical-conical and bi-hemispherical reflectances were performed for two theoretical canopies of contrasting geometric structure. These results and comparisons with literature studies showed a great amount of variability of vegetation canopy reflectances as a function of solar zenith angle. Explanations for this variability are discussed and recommendations for further measurements are proposed.

Tropospheric Trace Gas Interactions with Aerosols

NASA Technical Reports Server (NTRS)

Penner, Joyce E.; Maddrea, George L., Jr. (Technical Monitor)

2002-01-01

Tropospheric aerosols are of considerable environmental importance. They modify the radiative budget of Earth by scattering and absorbing radiation, and by providing nuclei for cloud formation. Additionally, they provide surfaces for heterogeneous and multiphase reactions that affect tropospheric chemistry. For example, Dentener and Crutzen (1993) showed that reactions of N2O5 and NO3 with sulfate aerosols may significantly alter the tropospheric concentrations of NO(x), O3, and OH by converting NOx to HNO3 which is rapidly removed by precipitation. Zhang et al. (1994) assumed these same reactions would occur on dust aerosols and showed that dust outbreaks may reduce NO(x) levels by up to 50%. Dentener et al. (1996) studied the possible effect of reactions on dust on sulfate, nitrate, and O3 concentration. Heterogeneous and multiphase reactions on aerosols may also perturb the sulfur cycle the chlorine cycle and the bromine cycle. Because these reactions can release free chlorine and free bromine they might lead to the destruction of ozone in the marine boundary layer that may be important to include in models of tropospheric chemistry. The goal of our proposed work is to examine the role of heterogeneous and multiphase reactions in the tropospheric cycles of reactive nitrogen and sulfur.

An estimation of tropospheric corrections using GPS and synoptic data: Improving Urmia Lake water level time series from Jason-2 and SARAL/AltiKa satellite altimetry

NASA Astrophysics Data System (ADS)

Arabsahebi, Reza; Voosoghi, Behzad; Tourian, Mohammad J.

2018-05-01

Tropospheric correction is one of the most important corrections in satellite altimetry measurements. Tropospheric wet and dry path delays have strong dependence on temperature, pressure and humidity. Tropospheric layer has particularly high variability over coastal regions due to humidity, wind and temperature gradients. Depending on the extent of water body and wind conditions over an inland water, Wet Tropospheric Correction (WTC) is within the ranges from a few centimeters to tens of centimeters. Therefore, an extra care is needed to estimate tropospheric corrections on the altimetric measurements over inland waters. This study assesses the role of tropospheric correction on the altimetric measurements over the Urmia Lake in Iran. For this purpose, four types of tropospheric corrections have been used: (i) microwave radiometer (MWR) observations, (ii) tropospheric corrections computed from meteorological models, (iii) GPS observations and (iv) synoptic station data. They have been applied to Jason-2 track no. 133 and SARAL/AltiKa track no. 741 and 356 corresponding to 117-153 and the 23-34 cycles, respectively. In addition, the corresponding measurements of PISTACH and PEACHI, include new retracking method and an innovative wet tropospheric correction, have also been used. Our results show that GPS observation leads to the most accurate tropospheric correction. The results obtained from the PISTACH and PEACHI projects confirm those obtained with the standard SGDR, i.e., the role of GPS in improving the tropospheric corrections. It is inferred that the MWR data from Jason-2 mission is appropriate for the tropospheric corrections, however the SARAL/AltiKa one is not proper because Jason-2 possesses an enhanced WTC near the coast. Furthermore, virtual stations are defined for assessment of the results in terms of time series of Water Level Height (WLH). The results show that GPS tropospheric corrections lead to the most accurate WLH estimation for the selected

Midlatitude ionospheric D region: Height, sharpness, and solar zenith angle

NASA Astrophysics Data System (ADS)

Thomson, Neil R.; Clilverd, Mark A.; Rodger, Craig J.

2017-08-01

VLF radio amplitude and phase measurements are used to find the height and sharpness of the D region of the ionosphere at a mid to high geomagnetic dip latitude of 52.5°. The two paths used are both from the 23.4 kHz transmitter, DHO, in north Germany with the first path being northward and mainly over the sea along the west coast of Denmark over a range of 320-425 km, and the second, also mainly all-sea, to a single fixed recording receiver at Eskdalemuir in Scotland ( 750 km). From plots of the measured amplitudes and phases versus distance for the first of these paths compared with calculations using the U.S. Navy code, ModeFinder, the Wait height and sharpness parameters of the D region at midday in summer 2015 are found to be H' = 72.8 ± 0.2 km and β = 0.345 ± 0.015 km-1 at a solar zenith angle 33°. From phase and amplitude measurements at other times of day on the second path, the daytime changes in H' and β as functions of solar zenith angle are determined from shortly after dawn to shortly before dusk. Comparisons are also made between the modal ModeFinder calculations and wave hop calculations, with both giving similar results. The parameters found here should be useful in understanding energy inputs to the D region from the radiation belts, solar flares, or transient luminous events. The midday values may be sufficiently precise to be useful for monitoring climate change.

Halogens and the Chemistry of the Free Troposphere

NASA Technical Reports Server (NTRS)

Lary, David John

2004-01-01

The role of halogens in both the marine boundary layer and the stratosphere has long been recognized, while their role in the free troposphere is often not considered in global chemical models. However, a careful examination of free-tropospheric chemistry constrained by observations using a full chemical data assimilation system shows that halogens do play a significant role in the free troposphere. In particular, the chlorine initiation of methane oxidation in the free troposphere can contribute more than 10%, and in some regions up to 50%, of the total rate of initiation. The initiation of methane oxidation by chlorine is particularly important below the polar vortex and in northern mid-latitudes. Likewise, the hydrolysis of BrONO2 alone can contribute more than 35% of the HNO3 production rate in the free-troposphere.

The High Resolution Tropospheric Ozone Residual

NASA Technical Reports Server (NTRS)

Schoeberl, Mark R.

2006-01-01

The co-flight of the MLS stratospheric limb sounder and the Ozone Monitoring Instrument (OMI) provides the capability of computing the Tropospheric Ozone Residual (TOR) in much greater detail [Ziemke et al., 2006]. Using forward trajectory calculations of MLS ozone measurements combined with OMI column ozone we have developed a high horizontal resolution tropospheric ozone residual (HTOR) which can provide even more detail than the standard TOR product. HTOR is especially useful for extra-tropical studies of tropospheric ozone transport. We find that both the Pacific pollution corridor (East Asia to Alaska) and the Atlantic pollution corridor (North America east coast to Europe) are also preferred locations for strat-trop folds leading to systematic overestimates of pollution amounts. In fact, fold events appear to dominate extra-tropical Northern Hemisphere day-to-day maps of HTOR. Model estimates of the tropospheric column are in reasonable agreement with the HTOR amounts when offsets due to different tropopause height calculations are taken into consideration.

Correlative nature of ozone and carbon monoxide in the troposphere - Implications for the tropospheric ozone budget

NASA Technical Reports Server (NTRS)

Fishman, J.; Seiler, W.

1983-01-01

The small-scale vertical variability of troposheric O3 and CO is examined using a set of simultaneous measurements obtained in July and August 1974 between 55 deg S and 67 deg N. From this set of vertical profiles, it is found that many of the fluctuations are coincident in both species, and a method is presented that quantifies the correlation between the observed O3 and CO variability. A two-dimensional depiction of the distribution of these O3-CO correlations reveals that there are regions in the troposphere where these trace gases are positively correlated and that, at the same time, there are preferred locations where these two species are primarily anticorrelated. The regions of anticorrelation are found to be consistent with the traditional picture of the tropospheric ozone cycle, suggesting that this gas is chemically unreactive in the troposphere. On the other hand, the location and magnitude of the region in which these two species are positively correlated indicates that there is considerable in situ production of tropospheric ozone.

Microwave radiometry as a tool to calibrate tropospheric water-vapor delay

NASA Technical Reports Server (NTRS)

Resch, G. M.; Claflin, E. S.

1980-01-01

Microwave radiometers were used to measure the emission line due to the water vapor molecules of atmospheric emission. Four separate field tests were completed which compared radiometers to other techniques which measure water vapor. It is shown that water vapor induced delay can be estimated with an accuracy of plus or minus 2 cm for elevation angles above 17 degrees.

Tropospheric profiles of wet refractivity and humidity from the combination of remote sensing data sets and measurements on the ground

NASA Astrophysics Data System (ADS)

Hurter, F.; Maier, O.

2013-11-01

We reconstruct atmospheric wet refractivity profiles for the western part of Switzerland with a least-squares collocation approach from data sets of (a) zenith path delays that are a byproduct of the GPS (global positioning system) processing, (b) ground meteorological measurements, (c) wet refractivity profiles from radio occultations whose tangent points lie within the study area, and (d) radiosonde measurements. Wet refractivity is a parameter partly describing the propagation of electromagnetic waves and depends on the atmospheric parameters temperature and water vapour pressure. In addition, we have measurements of a lower V-band microwave radiometer at Payerne. It delivers temperature profiles at high temporal resolution, especially in the range from ground to 3000 m a.g.l., though vertical information content decreases with height. The temperature profiles together with the collocated wet refractivity profiles provide near-continuous dew point temperature or relative humidity profiles at Payerne for the study period from 2009 to 2011. In the validation of the humidity profiles, we adopt a two-step procedure. We first investigate the reconstruction quality of the wet refractivity profiles at the location of Payerne by comparing them to wet refractivity profiles computed from radiosonde profiles available for that location. We also assess the individual contributions of the data sets to the reconstruction quality and demonstrate a clear benefit from the data combination. Secondly, the accuracy of the conversion from wet refractivity to dew point temperature and relative humidity profiles with the radiometer temperature profiles is examined, comparing them also to radiosonde profiles. For the least-squares collocation solution combining GPS and ground meteorological measurements, we achieve the following error figures with respect to the radiosonde reference: maximum median offset of relative refractivity error is -16% and quartiles are 5% to 40% for the lower

Carbon monoxide measurements in the troposphere

NASA Technical Reports Server (NTRS)

Reichle, H. G., Jr.; Beck, S. M.; Haynes, R. E.; Hesketh, W. D.; Holland, J. A.; Hypes, W. D.; Orr, H. D., III; Sherrill, R. T.; Wallio, H. A.; Casas, J. C.

1982-01-01

Approximately 35 hours of radiometric measurements were obtained of the CO mixing ratio in the middle troposphere, upper troposphere, and lower stratosphere, by means of the Measurement of Air Pollution from Satellites (MAPS) experiment carried in the OSTA-1 payload of the second Space Shuttle flight. In view of gas filter radiometer data in the 4.67-micron band, gathered over the 38 N-38 S latitude region during both daytime and nighttime, the performance of MAPS was excellent. Significant gradients have been found in the middle tropospheric CO mixing ratio with both latitude and longitude over the North Atlantic, the Mediterranean Sea, and the Middle East.

Tropospheric Chemistry Studies using Observations from GOME and TOMS

NASA Technical Reports Server (NTRS)

Chance, Kelly; Spurr, Robert J. D.; Kurosu, Thomas P.; Jacob, Daniel J.; Gleason, James F.

2003-01-01

Studies to quantitatively determine trace gas and aerosol amounts from the Global Ozone Monitoring Experiment (GOME) and the Total Ozone Monitoring Experiment (TOMS) and to perform chemical modeling studies which utilize these results are given. This includes: 1. Analysis of measurements from the GOME and TOMS instruments for troposphere distributions of O3 and HCHO; troposphere enhancements of SO2, NO2 and aerosols associated with major sources; and springtime events of elevated BrO in the lower Arctic troposphere. 2. Application of a global 3-dimensional model of troposphere chemistry to interpret the GOME observations in terms of the factors controlling the abundances of troposphere ozone and OH.

Homepage for the Global Tropospheric Experiment

NASA Technical Reports Server (NTRS)

Ward, Eugene

1995-01-01

The objective of my NASA summer research project was to create a homepage to describe and present results from the NASA Global Tropospheric Experiment (GTE). The GTE is a major component of NASA's Tropospheric Chemistry Program and is managed in the Atmospheric Studies Branch, Atmospheric Sciences Division at the NASA Langley Research Center.

Calibration of the KA Band Tracking of the Bepi-Colombo Spacecraft (more Experiment)

NASA Astrophysics Data System (ADS)

Barriot, J.; Serafini, J.; Sichoix, L.

2013-12-01

The radiosciences Bepi-Colombo MORE experiment will use X/X, X/Ka and Ka/Ka band radio links to make accurate measurements of the spacecraft range and range rate. Tropospheric zenith wet delays range from 1.5 cm to 10 cm, with high variability (less than 1000 s) and will impair these accurate measurements. Conditions vary from summer (worse) to winter (better), from day (worse) to night (better). These wet delays cannot be estimated from ground weather measurements and alternative calibration methods should be used in order to cope with the MORE requirements (no more than 3 mm at 1000 s). Due to the Mercury orbit, MORE measurements will be performed by daylight and more frequently in summer than in winter (from Northern hemisphere). Two systems have been considered to calibrate this wet delay: Water Vapor Radiometers (WVRs) and GPS receivers. The Jet Propulsion Laboratory has developed a new class of WVRs reaching a 5 percent accuracy for the wet delay calibration (0.75 mm to 5 mm), but these WVRs are expensive to build and operate. GPS receivers are also routinely used for the calibration of data from NASA Deep Space probes, but several studies have shown that GPS receivers can give good calibration (through wet delay mapping functions) for long time variations, but are not accurate enough for short time variations (100 to 1000 s), and that WVRs must be used to efficiently calibrate the wet troposphere delays over such time spans. We think that such a calibration could be done by assimilating data from all the GNSS constellations (GPS, GLONASS, Galileo, Beidou and IRNSS) that will be available at the time of the Bepi-Colombo arrival at Mercury (2021), provided that the underlying physics of the turbulent atmosphere and evapotranspiration processes are properly taken into account at such time scales. This implies to do a tomographic image of the troposphere overlying each Deep Space tracking station at time scales of less than 1000 s. For this purpose, we have

Multi-year GNSS monitoring of atmospheric IWV over Central and South America for climate studies

NASA Astrophysics Data System (ADS)

Mendoza, Luciano; Bianchi, Clara; Fernández, Laura; Natali, María Paula; Meza, Amalia; Moirano, Juan

2017-04-01

Atmospheric water vapour has been acknowledged as an essential climate variable. Weather prediction and hazard assessment systems benefit from real-time observations, whereas long-term records contribute to climate studies. Nowadays, ground-based GNSS products have become widely employed, complementing satellite observations over the oceans. Although the past decade has seen a significant development of the GNSS infrastructure in Central and South America, its potential for atmospheric water vapour monitoring has not been fully exploited. With this in mind, we have performed a regional, seven-year long and homogeneous analysis, comprising 136 GNSS tracking stations, obtaining high-rate and continuous observations of column integrated water vapour and troposphere zenith total delay (Bianchi et al. 2016). As preliminary application for this data set, we have estimated local water vapour trends, their significance, and their relation with specific climate regimes. We have found evidence of drying at temperate regions in South America, at a rate of about 2% per decade, while a slow moistening of the troposphere over tropical regions is also weakly suggested by our results. Furthermore, we have assessed the regional performance of the empirical model GPT2w to blindly estimate troposphere delays. The model fairly reproduces the observed mean delays, including their annual and semi-annual variations. Nevertheless, a long-term evaluation has shown systematical biases, up to 20 mm, probably inherited form the underling atmospheric reanalysis. Additionally, the complete data set has been made openly available at a scientific repository (doi:10.1594/PANGAEA.858234). References: C. Bianchi, L. Mendoza, L. Fernandez, M. P. Natali, A. Meza, J. F. Moirano, Multi-year GNSS monitoring of atmospheric IWV over Central and South America for climate studies, Ann. Geophys., ISSN 0992-7689, eISSN 1432-0576, 34 (7), 623-639 (doi:10.5194/angeo-34-623-2016).

Effects of Tropospheric Spatio-Temporal Correlated Noise on the Analysis of Space Geodetic Data

NASA Technical Reports Server (NTRS)

Romero-Wolf, A.; Jacobs, C. S.; Ratcliff, J. T.

2012-01-01

The standard VLBI analysis models the distribution of measurement noise as Gaussian. Because the price of recording bits is steadily decreasing, thermal errors will soon no longer dominate. As a result, it is expected that troposphere and instrumentation/clock errors will increasingly become more dominant. Given that both of these errors have correlated spectra, properly modeling the error distributions will become increasingly relevant for optimal analysis. We discuss the advantages of modeling the correlations between tropospheric delays using a Kolmogorov spectrum and the frozen flow assumption pioneered by Treuhaft and Lanyi. We then apply these correlated noise spectra to the weighting of VLBI data analysis for two case studies: X/Ka-band global astrometry and Earth orientation. In both cases we see improved results when the analyses are weighted with correlated noise models vs. the standard uncorrelated models. The X/Ka astrometric scatter improved by approx.10% and the systematic Delta delta vs. delta slope decreased by approx. 50%. The TEMPO Earth orientation results improved by 17% in baseline transverse and 27% in baseline vertical.

Troposphere mapping functions for GPS and very long baseline interferometry from European Centre for Medium-Range Weather Forecasts operational analysis data

NASA Astrophysics Data System (ADS)

Boehm, Johannes; Werl, Birgit; Schuh, Harald

2006-02-01

In the analyses of geodetic very long baseline interferometry (VLBI) and GPS data the analytic form used for mapping of the atmosphere delay from zenith to the line of site is most often a three-parameter continued fraction in 1/sin(elevation). Using the 40 years reanalysis (ERA-40) data of the European Centre for Medium-Range Weather Forecasts for the year 2001, the b and c coefficients of the continued fraction form for the hydrostatic mapping functions have been redetermined. Unlike previous mapping functions based on data from numerical weather models (isobaric mapping functions (Niell, 2000) and Vienna mapping functions (VMF) (Boehm and Schuh, 2004)), the new c coefficients are dependent on the day of the year, and unlike the Niell mapping functions (Niell, 1996) they are no longer symmetric with respect to the equator (apart from the opposite phase for the two hemispheres). Compared to VMF, this causes an effect on the VLBI or GPS station heights that is constant and as large as 2 mm at the equator and that varies seasonally between 4 mm and 0 mm at the poles. The updated VMF, based on these new coefficients and called VMF1 hereinafter, yields slightly better baseline length repeatabilities for VLBI data. The hydrostatic and wet mapping functions are applied in various combinations with different kinds of a priori zenith delays in the analyses of all VLBI International VLBI Service for Geodesy and Astrometry (IVS)-R1 and IVS-R4 24-hour sessions of 2002 and 2003; the investigations concentrate on baseline length repeatabilities, as well as on absolute changes of station heights.

Evaluating a Priori Ozone Profile Information Used in TEMPO (Tropospheric Emissions: Monitoring of Pollution) Tropospheric Ozone Retrievals

NASA Technical Reports Server (NTRS)

Johnson, Matthew Stephen

2017-01-01

A primary objective for TOLNet is the evaluation and validation of space-based tropospheric O3 retrievals from future systems such as the Tropospheric Emissions: Monitoring of Pollution (TEMPO) satellite. This study is designed to evaluate the tropopause-based O3 climatology (TB-Clim) dataset which will be used as the a priori profile information in TEMPO O3 retrievals. This study also evaluates model simulated O3 profiles, which could potentially serve as a priori O3 profile information in TEMPO retrievals, from near-real-time (NRT) data assimilation model products (NASA Global Modeling and Assimilation Office (GMAO) Goddard Earth Observing System (GEOS-5) Forward Processing (FP) and Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA2)) and full chemical transport model (CTM), GEOS-Chem, simulations. The TB-Clim dataset and model products are evaluated with surface (0-2 km) and tropospheric (0-10 km) TOLNet observations to demonstrate the accuracy of the suggested a priori dataset and information which could potentially be used in TEMPO O3 algorithms. This study also presents the impact of individual a priori profile sources on the accuracy of theoretical TEMPO O3 retrievals in the troposphere and at the surface. Preliminary results indicate that while the TB-Clim climatological dataset can replicate seasonally-averaged tropospheric O3 profiles observed by TOLNet, model-simulated profiles from a full CTM (GEOS-Chem is used as a proxy for CTM O3 predictions) resulted in more accurate tropospheric and surface-level O3 retrievals from TEMPO when compared to hourly (diurnal cycle evaluation) and daily-averaged (daily variability evaluation) TOLNet observations. Furthermore, it was determined that when large daily-averaged surface O3 mixing ratios are observed (65 ppb), which are important for air quality purposes, TEMPO retrieval values at the surface display higher correlations and less bias when applying CTM a priori profile information

Impact of climate variability on tropospheric ozone.

PubMed

Grewe, Volker

2007-03-01

A simulation with the climate-chemistry model (CCM) E39/C is presented, which covers both the troposphere and stratosphere dynamics and chemistry during the period 1960 to 1999. Although the CCM, by its nature, is not exactly representing observed day-by-day meteorology, there is an overall model's tendency to correctly reproduce the variability pattern due to an inclusion of realistic external forcings, like observed sea surface temperatures (e.g. El Niño), major volcanic eruption, solar cycle, concentrations of greenhouse gases, and Quasi-Biennial Oscillation. Additionally, climate-chemistry interactions are included, like the impact of ozone, methane, and other species on radiation and dynamics, and the impact of dynamics on emissions (lightning). However, a number of important feedbacks are not yet included (e.g. feedbacks related to biogenic emissions and emissions due to biomass burning). The results show a good representation of the evolution of the stratospheric ozone layer, including the ozone hole, which plays an important role for the simulation of natural variability of tropospheric ozone. Anthropogenic NO(x) emissions are included with a step-wise linear trend for each sector, but no interannual variability is included. The application of a number of diagnostics (e.g. marked ozone tracers) allows the separation of the impact of various processes/emissions on tropospheric ozone and shows that the simulated Northern Hemisphere tropospheric ozone budget is not only dominated by nitrogen oxide emissions and other ozone pre-cursors, but also by changes of the stratospheric ozone budget and its flux into the troposphere, which tends to reduce the simulated positive trend in tropospheric ozone due to emissions from industry and traffic during the late 80s and early 90s. For tropical regions the variability in ozone is dominated by variability in lightning (related to ENSO) and stratosphere-troposphere exchange (related to Northern Hemisphere Stratospheric

Global tropospheric chemistry: A plan for action

NASA Astrophysics Data System (ADS)

1984-10-01

Prompted by an increasing awareness of the influence of human activity on the chemistry of the global troposphere, a panel was formed to (1) assess the requirement for a global study of the chemistry of the troposphere; (2) develop a scientific strategy for a comprehensive plan taking into account the existing and projected programs of the government; (3) assess the requirements of a global study in terms of theoretical knowledge, numerical modeling, instrumentation, observing platforms, ground-level observational techniques, and other related needs; and (4) outline the appropriate sequence and coordination required to achieve the most effective utilization of available resources. Part 1 presents a coordinated national blueprint for scientific investigations of biogeochemical cycles in the global troposphere. part 2 presents much of the background information of the present knowledge and gaps in the understanding of tropospheric chemical cycles and processes from which the proposed program was developed.

Global tropospheric chemistry: A plan for action

NASA Technical Reports Server (NTRS)

1984-01-01

Prompted by an increasing awareness of the influence of human activity on the chemistry of the global troposphere, a panel was formed to (1) assess the requirement for a global study of the chemistry of the troposphere; (2) develop a scientific strategy for a comprehensive plan taking into account the existing and projected programs of the government; (3) assess the requirements of a global study in terms of theoretical knowledge, numerical modeling, instrumentation, observing platforms, ground-level observational techniques, and other related needs; and (4) outline the appropriate sequence and coordination required to achieve the most effective utilization of available resources. Part 1 presents a coordinated national blueprint for scientific investigations of biogeochemical cycles in the global troposphere. part 2 presents much of the background information of the present knowledge and gaps in the understanding of tropospheric chemical cycles and processes from which the proposed program was developed.

Quantifying isentropic stratosphere-troposphere exchange of ozone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Huang; Chen, Gang; Tang, Qi

There is increased evidence that stratosphere-troposphere exchange (STE) of ozone has a significant impact on tropospheric chemistry and radiation. Traditional diagnostics of STE consider the ozone budget in the lowermost stratosphere (LMS) as a whole. However, this can only render the hemispherically integrated ozone flux and therefore does not distinguish the exchange of ozone into low latitudes from that into high latitudes. The exchange of ozone at different latitudes may have different tropospheric impacts. This present study extends the traditional approach from the entire LMS to individual isentropic layers in the LMS and therefore gives the meridional distribution of STEmore » by the latitudes where each isentropic surface intersects the tropopause. The specified dynamics version of the Whole Atmosphere Community Climate Model is used to estimate the STE ozone flux on each isentropic surface. It is found that net troposphere-to-stratosphere ozone transport occurs in low latitudes along the 350–380 K isentropic surfaces and that net stratosphere-to-troposphere ozone transport takes place in the extratropics along the 280–350 K isentropes. Particularly, the seasonal cycle of extratropical STE ozone flux in the Northern Hemisphere displays a maximum in late spring and early summer, following the seasonal migration of the upper tropospheric jet and associated isentropic mixing. Moreover, differential diabatic heating and isentropic mixing tend to induce STE ozone fluxes in opposite directions, but the net effect results in a spatiotemporal pattern similar to the STE ozone flux associated with isentropic mixing.« less

Quantifying isentropic stratosphere-troposphere exchange of ozone

DOE PAGES

Yang, Huang; Chen, Gang; Tang, Qi; ...

2016-03-25

There is increased evidence that stratosphere-troposphere exchange (STE) of ozone has a significant impact on tropospheric chemistry and radiation. Traditional diagnostics of STE consider the ozone budget in the lowermost stratosphere (LMS) as a whole. However, this can only render the hemispherically integrated ozone flux and therefore does not distinguish the exchange of ozone into low latitudes from that into high latitudes. The exchange of ozone at different latitudes may have different tropospheric impacts. This present study extends the traditional approach from the entire LMS to individual isentropic layers in the LMS and therefore gives the meridional distribution of STEmore » by the latitudes where each isentropic surface intersects the tropopause. The specified dynamics version of the Whole Atmosphere Community Climate Model is used to estimate the STE ozone flux on each isentropic surface. It is found that net troposphere-to-stratosphere ozone transport occurs in low latitudes along the 350–380 K isentropic surfaces and that net stratosphere-to-troposphere ozone transport takes place in the extratropics along the 280–350 K isentropes. Particularly, the seasonal cycle of extratropical STE ozone flux in the Northern Hemisphere displays a maximum in late spring and early summer, following the seasonal migration of the upper tropospheric jet and associated isentropic mixing. Moreover, differential diabatic heating and isentropic mixing tend to induce STE ozone fluxes in opposite directions, but the net effect results in a spatiotemporal pattern similar to the STE ozone flux associated with isentropic mixing.« less

Free-tropospheric BrO investigations based on GOME

NASA Astrophysics Data System (ADS)

Post, P.; van Roozendael, M.; Backman, L.; Damski, J.; Thölix, L.; Fayt, C.; Taalas, P.

2003-04-01

Bromine compounds contribute significantly to the stratospheric ozone depletion. However measurements of most bromine compounds are sparse or non-existent, and experimental studies essentially rely on BrO observations. The differences between balloon and ground based measurements of stratospheric BrO columns and satellite total column measurements are too large to be explained by measurement uncertainties. Therefore, it has been assumed that there is a concentration of BrO in the free troposphere of about 1-3 ppt. In a previous work, we have calculated the tropospheric BrO abundance as the difference between total BrO and stratospheric BrO columns. The total vertical column densities of BrO are extracted from GOME measurements using IASB-BIRA algorithms. The stratospheric amount has been calculated using chemical transport models (CTM). Results from SLIMCAT and FinROSE simulations are used for this purpose. SLIMCAT is a widely used 3D CTM that has been tested against balloon measurements. FinROSE is a 3D CTM developed at FMI. We have tried several different tropospheric BrO profiles. Our results show that a profile with high BrO concentrations in the boundary layer usually gives unrealistically high tropospheric column values over areas of low albedo (like oceans). This suggests that the tropospheric BrO would be predominantly distributed in the free troposphere. In this work, attempts are made to identify the signature of a free tropospheric BrO content when comparing cloudy and non-cloudy scenes. The possible impact of orography on measured BrO columns is also investigated.

Erosion Results of the MISSE 7 Polymers Experiment and Zenith Polymers Experiment After 1.5 Years of Space Exposure

NASA Technical Reports Server (NTRS)

De Groh, Kim K.; Banks, Bruce A.; Yi, Grace T.; Haloua, Athena; Imka, Emily C.; Mitchell, Gianna G.; Asmar, Olivia C.; Leneghan, Halle A.; Sechkar, Edward A.

2016-01-01

Polymers and other oxidizable materials on the exterior of spacecraft in the low Earth orbit (LEO) space environment can be eroded due to reaction with atomic oxygen (AO). Therefore, in order to design durable spacecraft it is important to know the LEO AO erosion yield (E(sub y), volume loss per incident oxygen atom) of materials susceptible to AO reaction. Two spaceflight experiments, the Polymers Experiment and the Zenith Polymers Experiment, were developed to determine the AO E(sub y) of various polymers flown in ram, wake or zenith orientations in LEO. These experiments were flown as part of the Materials International Space Station Experiment 7 (MISSE 7) mission for 1.5 years on the exterior of the International Space Station (ISS). The experiments included Kapton H(TradeMark) witness samples for AO fluence determination in ram and zenith orientations. The Polymers Experiment also included samples to determine whether AO erosion of high and low ash containing polymers is dependent on fluence. This paper provides an overview of the MISSE 7 mission, a description of the flight experiments with details on the polymers flown, the characterization techniques used, the AO fluence for each exposure orientation, and the LEO E(sub y) results. The E(sub y) values ranged from 7.99x10(exp -28)cu cm/atom for TiO2/Al2O3 coated Teflon(TradeMark) fluorinated ethylene propylene (FEP) flown in the ram orientation to 1.22x10(exp -23cu cm/atom for polyvinyl alcohol (PVOH) flown in the zenith orientation. The E(sub y) of similar samples flown in different orientations has been compared to help determine solar exposure and associated heating effects on AO erosion. The E(sub y) data from these ISS spaceflight experiments provides valuable information for LEO spacecraft design purposes.

Analytical Model for Estimating the Zenith Angle Dependence of Terrestrial Cosmic Ray Fluxes

PubMed Central

Sato, Tatsuhiko

2016-01-01

A new model called “PHITS-based Analytical Radiation Model in the Atmosphere (PARMA) version 4.0” was developed to facilitate instantaneous estimation of not only omnidirectional but also angular differential energy spectra of cosmic ray fluxes anywhere in Earth’s atmosphere at nearly any given time. It consists of its previous version, PARMA3.0, for calculating the omnidirectional fluxes and several mathematical functions proposed in this study for expressing their zenith-angle dependences. The numerical values of the parameters used in these functions were fitted to reproduce the results of the extensive air shower simulation performed by Particle and Heavy Ion Transport code System (PHITS). The angular distributions of ground-level muons at large zenith angles were specially determined by introducing an optional function developed on the basis of experimental data. The accuracy of PARMA4.0 was closely verified using multiple sets of experimental data obtained under various global conditions. This extension enlarges the model’s applicability to more areas of research, including design of cosmic-ray detectors, muon radiography, soil moisture monitoring, and cosmic-ray shielding calculation. PARMA4.0 is available freely and is easy to use, as implemented in the open-access EXcel-based Program for Calculating Atmospheric Cosmic-ray Spectrum (EXPACS). PMID:27490175

Analytical Model for Estimating the Zenith Angle Dependence of Terrestrial Cosmic Ray Fluxes.

PubMed

Sato, Tatsuhiko

2016-01-01

A new model called "PHITS-based Analytical Radiation Model in the Atmosphere (PARMA) version 4.0" was developed to facilitate instantaneous estimation of not only omnidirectional but also angular differential energy spectra of cosmic ray fluxes anywhere in Earth's atmosphere at nearly any given time. It consists of its previous version, PARMA3.0, for calculating the omnidirectional fluxes and several mathematical functions proposed in this study for expressing their zenith-angle dependences. The numerical values of the parameters used in these functions were fitted to reproduce the results of the extensive air shower simulation performed by Particle and Heavy Ion Transport code System (PHITS). The angular distributions of ground-level muons at large zenith angles were specially determined by introducing an optional function developed on the basis of experimental data. The accuracy of PARMA4.0 was closely verified using multiple sets of experimental data obtained under various global conditions. This extension enlarges the model's applicability to more areas of research, including design of cosmic-ray detectors, muon radiography, soil moisture monitoring, and cosmic-ray shielding calculation. PARMA4.0 is available freely and is easy to use, as implemented in the open-access EXcel-based Program for Calculating Atmospheric Cosmic-ray Spectrum (EXPACS).

WVR-GPS comparison measurements and calibration of the 20-32 GHz tropospheric water vapor absorption model.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keihm, S. J.; Bar-Server, Y.; Liljegren, J. C.

2002-06-01

Collocated measurements of opacity (from water vapor radiometer brightness temperatures) and wet path delay (from ground-based tracking of global positioning satellites) are used to constrain the model of atmospheric water vapor absorption in the 20-32 GHz band. A differential approach is presented in which the slope of opacity-versus-wet delay data is used as the absorption model constraint. This technique minimizes the effects of radiometric calibration errors and oxygen model uncertainties in the derivation of a best-fit vapor absorption model. A total of approximately five months of data was obtained from two experiment sites. At the Cloud and Radiation Testbed (CART)more » site near Lamont, Oklahoma, three independent water vapor radiometers (WVRs) provided near-continuous opacity measurements over the interval July-September 1998. At the NASA/Goldstone tracking station in the California desert two WVRs; obtained opacity data over the September-October 1997 interval. At both sites a Global Positioning Satellite (GPS) receiver and surface barometer obtained the data required for deriving the zenith wet delays over the same time frames. Measured values of the opacity-versus-wet delay slope parameter were obtained at four WVR frequencies (20.7, 22.2, 23.8, and 31.4 GHz) and compared with predictions of four candidate absorption models referenced in the literature. With one exception, all three models provide agreement within 5% of the opacity-versus-wet delay slope measurements at all WVR frequencies at both sites. One model provides agreement for all channels at both sites to the 2-3% level. This absorption model accuracy level represents a significant improvement over that attainable using radiosondes.« less

Software development and its description for Geoid determination based on Spherical-Cap-Harmonics Modelling using digital-zenith camera and gravimetric measurements hybrid data

NASA Astrophysics Data System (ADS)

Morozova, K.; Jaeger, R.; Balodis, J.; Kaminskis, J.

2017-10-01

Over several years the Institute of Geodesy and Geoinformatics (GGI) was engaged in the design and development of a digital zenith camera. At the moment the camera developments are finished and tests by field measurements are done. In order to check these data and to use them for geoid model determination DFHRS (Digital Finite element Height reference surface (HRS)) v4.3. software is used. It is based on parametric modelling of the HRS as a continous polynomial surface. The HRS, providing the local Geoid height N, is a necessary geodetic infrastructure for a GNSS-based determination of physcial heights H from ellipsoidal GNSS heights h, by H=h-N. The research and this publication is dealing with the inclusion of the data of observed vertical deflections from digital zenith camera into the mathematical model of the DFHRS approach and software v4.3. A first target was to test out and validate the mathematical model and software, using additionally real data of the above mentioned zenith camera observations of deflections of the vertical. A second concern of the research was to analyze the results and the improvement of the Latvian quasi-geoid computation compared to the previous version HRS computed without zenith camera based deflections of the vertical. The further development of the mathematical model and software concerns the use of spherical-cap-harmonics as the designed carrier function for the DFHRS v.5. It enables - in the sense of the strict integrated geodesy approach, holding also for geodetic network adjustment - both a full gravity field and a geoid and quasi-geoid determination. In addition, it allows the inclusion of gravimetric measurements, together with deflections of the vertical from digital-zenith cameras, and all other types of observations. The theoretical description of the updated version of DFHRS software and methods are discussed in this publication.

Zenith 1 truss transfer ceremony

NASA Technical Reports Server (NTRS)

2000-01-01

A wide-angle view of the floor of the Space Station Processing Facility. The floor is filled with racks and hardware for processing and testing the various components of the International Space Station (ISS). At center left is the Zenith-1 (Z-1) Truss, the cornerstone truss of the Space Station. The Z-1 Truss was officially turned over to NASA from The Boeing Co. on July 31. It is scheduled to fly in Space Shuttle Discovery's payload pay on STS-92 targeted for launch Oct. 5, 2000. The Z-1 is considered a cornerstone truss because it carries critical components of the Station's attitude, communications, thermal and power control systems as well as four control moment gyros, high and low gain antenna systems, and two plasma contactor units used to disperse electrical charge build-ups. The Z-1 truss and a Pressurized Mating Adapter (PMA-3), also flying to the Station on the same mission, will be the first major U.S. elements flown to the ISS aboard the Shuttle since the launch of the Unity element in December 1998. The large module in the upper right hand corner of the floor is the U.S. Lab, Destiny. Expected to be a major feature in future research, Destiny will provide facilities for biotechnology, fluid physics, combustion, and life sciences research. It is scheduled to be launched on mission STS-98 (no date determined yet for launch).

Ozone in the Pacific Troposphere from Ozonesonde Observations

NASA Technical Reports Server (NTRS)

Oltmans, S. J.; Johnson, B. J.; Harris, J. M.; Voemel, H.; Koshy, K.; Simon, P.; Bendura, R.; Thompson, A. M.; Logan, J. A.; Hasebe, F.;

Low to middle tropospheric profiles and biosphere/troposphere fluxes of acidic gases in the summertime Canadian taiga

NASA Technical Reports Server (NTRS)

Klemm, O.; Talbot, R. W.; Fitzgerald, D. R.; Klemm, K. I.; Lefer, B. L.

1994-01-01

We report features of acidic gases in the troposphere from 9 to 5000 m altitude above ground over the Canadian taiga in the summer of 1990. The measurements were conducted at a 30-m meteorological tower and from the NASA Wallops Electra aircraft as part of the joint U.S.-Canadian Arctic Boundary Layer Expedition (ABLE) 3B Northern Wetland Studies (NOWES). We sampled air for acidic gases using the mist chamber collector coupled with subsequent analysis using ion chromatography. At the tower we collected samples at two heights during a 13-day period, including diurnal studies. Using eddy flux and profile data, we estimated the biosphere/troposphere fluxes of nitric, formic, and acetic acids and sulfur dioxide. For the organic acids, emissions from the taiga in the afternoon hours and deposition during the predawn morning hours were observed. The flux intensities alone were however not high enough to explain the observed changes in mixing ratios. The measured deposition fluxes of nitric acid were high enough to have a significant influence on its mixing ratio in the boundary layer. On three days we measured vertical profiles of nitric, formic, and acetic acids through the lower to midtroposphere. We found that the chemical composition of the troposphere was extremely heterogenous. Pronounced layers of polluted air were readily apparent from our measurements. Local photochemical production and episodic long-range transport of trace components, originating from biomass burning and possibly industrial emissions, appear to have a strong influence on the composition of the troposphere and biosphere/troposphere fluxes of acidic gases at this site.

Beam-splitter switches based on zenithal bistable liquid-crystal gratings.

PubMed

Zografopoulos, Dimitrios C; Beccherelli, Romeo; Kriezis, Emmanouil E

2014-10-01

The tunable optical diffractive properties of zenithal bistable nematic liquid-crystal gratings are theoretically investigated. The liquid-crystal orientation is rigorously solved via a tensorial formulation of the Landau-de Gennes theory and the optical transmission properties of the gratings are investigated via full-wave finite-element frequency-domain simulations. It is demonstrated that by proper design the two stable states of the grating can provide nondiffracting and diffracting operation, the latter with equal power splitting among different diffraction orders. An electro-optic switching mechanism, based on dual-frequency nematic materials, and its temporal dynamics are further discussed. Such gratings provide a solution towards tunable beam-steering and beam-splitting components with extremely low power consumption.

Mid- and long-term device migration after endovascular abdominal aortic aneurysm repair: a comparison of AneuRx and Zenith endografts.

PubMed

Tonnessen, Britt H; Sternbergh, W Charles; Money, Samuel R

2005-09-01

Freedom from migration is key to the durability of endovascular aneurysm repair (EVAR). This study evaluates the mid- and long-term incidence of migration with two different endografts. Between September 1997 and June 2004, 235 patients were scheduled for EVAR with an AneuRx (Medtronic/AVE Inc.) or Zenith (Cook) endograft. Patients with fusiform, infrarenal aneurysms and a minimum 12 months of follow-up were analyzed, for a final cohort of 130 patients. Migration was assessed on axial computed tomography (CT) (2.5 to 3 mm cuts) as the distance from the most caudal renal artery to the first slice containing endograft (AneuRx) or to the top of the bare suprarenal stent (Zenith). Aortic neck diameters were measured at the most caudal renal artery. The initial postoperative CT scan was the baseline. Migration was defined by caudal movement of the endograft at two thresholds, > or =5 mm and > or =10 mm, or any migration with a related clinical event. Life-table analysis demonstrated AneuRx freedom from migration (> or =10 mm or clinical event) was 96.1%, 89.5%, 78.0%, and 72.0% at 1, 2, 3, and 4 years, respectively. Zenith freedom from migration was 100%, 97.6%, 97.6%, and 97.6% at 1, 2, 3, and 4 years, respectively (P = .01, log-rank test). The stricter 5-mm migration threshold found 67.4% of AneuRx and 90.1% of Zenith patients free from migration at 4 years of follow-up. Twelve out of 14 (85.7%) AneuRx patients (12/14) with migration (> or =10 mm or clinical event) underwent 14 related secondary procedures (13 endovascular, 1 open conversion). The single Zenith patient with migration (> or =10 mm) has not required adjuvant treatment. Mean follow-up was 39.0 +/- 2.3 months (AneuRx) and 30.8 +/- 1.9 months (Zenith, P = .01). Patients with and without migration did not differ in age, gender ratio, aneurysm diameter, and neck diameter. However, initial neck length was shorter in patients with migration (22.1 +/- 2.1 mm vs 31.2 +/- 1.2 mm, P = .02). A subset of patients

Atmospheric retrievals with the Tropospheric Emission Spectrometer (TES)

NASA Technical Reports Server (NTRS)

Bowman, K. W.

2003-01-01

The Tropospheric Emission Spectrometer (TES) on the EOS-Aura spacecraft will measure the global 3-dimensional distribution of ozone in the troposphere and many of the chemical species that are part of its formation and destruction.

Remote Sensing of Cloud Properties using Ground-based Measurements of Zenith Radiance

NASA Technical Reports Server (NTRS)

Chiu, J. Christine; Marshak, Alexander; Knyazikhin, Yuri; Wiscombe, Warren J.; Barker, Howard W.; Barnard, James C.; Luo, Yi

2006-01-01

An extensive verification of cloud property retrievals has been conducted for two algorithms using zenith radiances measured by the Atmospheric Radiation Measurement (ARM) Program ground-based passive two-channel (673 and 870 nm) Narrow Field-Of-View Radiometer. The underlying principle of these algorithms is that clouds have nearly identical optical properties at these wavelengths, but corresponding spectral surface reflectances (for vegetated surfaces) differ significantly. The first algorithm, the RED vs. NIR, works for a fully three-dimensional cloud situation. It retrieves not only cloud optical depth, but also an effective radiative cloud fraction. Importantly, due to one-second time resolution of radiance measurements, we are able, for the first time, to capture detailed changes in cloud structure at the natural time scale of cloud evolution. The cloud optical depths tau retrieved by this algorithm are comparable to those inferred from both downward fluxes in overcast situations and microwave brightness temperatures for broken clouds. Moreover, it can retrieve tau for thin patchy clouds, where flux and microwave observations fail to detect them. The second algorithm, referred to as COUPLED, couples zenith radiances with simultaneous fluxes to infer 2. In general, the COUPLED and RED vs. NIR algorithms retrieve consistent values of tau. However, the COUPLED algorithm is more sensitive to the accuracies of measured radiance, flux, and surface reflectance than the RED vs. NIR algorithm. This is especially true for thick overcast clouds where it may substantially overestimate z.

Project Zenith: Multicultural/Multimedia/Emphasis in Speech-Language Pathology, 1997-2001. Grant Performance Report--Final Report.

ERIC Educational Resources Information Center

San Jose State Univ., CA.

This report discusses the activities and outcomes of Project Zenith, which was designed to recruit two cohorts of bilingual graduate students to complete a graduate program with specialized skills in the diagnosis and treatment of communicative disorders in multicultural populations in the public schools. Included in the specialized training is…

Gingival Zenith Positions and Levels of Maxillary Anterior Dentition in Cases of Bimaxillary Protrusion: A Morphometric Analysis.

PubMed

Gowd, Snigdha; Shankar, T; Chatterjee, Suravi; Mohanty, Pritam; Sahoo, Nivedita; Baratam, Srinivas

2017-08-01

To investigate the two clinical parameters, such as gingival zenith positions (GZPs) and gingival zenith levels (GZLs), of maxillary anterior dentition in bimaxillary protrusion cases and collate it with severiety of crown inclination. Gingival zenith position and GZL in 40 healthy patients (29 females and 11 males) with an average age of 21.5 years were assessed. Inclusion criteria involved absence of periodontal diseases, Angle's class I molar relationship, and upper anterior proclination within 25 to 45° based on Steiner's analysis; exclusion criteria included spacing, crowding, anterior restoration and teeth with incisor attrition or rotation. The GZP was evaluated using digital calipers from voxel-based morphometry (VBM), and GZL was assessed from the tangent drawn from GZP of central incisor and canines to the linear vertical distance of GZP of lateral incisor. All the central incisors showed a GZP distal to VBM with a mean average of 1 mm. Severe proclination between 40 and 45° showed a statistically significant variation. Lateral incisors displayed a mean of 0.5 mm deviation of GZP from the vertically bisected midline. In 80% of canine population, GZP was centralized. We conclude that the degree of proclination of maxillary anterior dentition was correlated to the gingival contour in bimaxillary cases. The investigation revealed that there is a variation in the location of GZP as the severity of proclination increases. This study highlights the importance of microesthetics in fixed orthodontic treatment. The gingival contour should be unaltered while retraction during management of bimaxillary protrusion.

HALOE Algorithm Improvements for Upper Tropospheric Sounding

NASA Technical Reports Server (NTRS)

McHugh, Martin J.; Gordley, Larry L.; Russell, James M., III; Hervig, Mark E.

1999-01-01

This report details the ongoing efforts by GATS, Inc., in conjunction with Hampton University and University of Wyoming, in NASA's Mission to Planet Earth UARS Science Investigator Program entitled "HALOE Algorithm Improvements for Upper Tropospheric Soundings." The goal of this effort is to develop and implement major inversion and processing improvements that will extend HALOE measurements further into the troposphere. In particular, O3, H2O, and CH4 retrievals may be extended into the middle troposphere, and NO, HCl and possibly HF into the upper troposphere. Key areas of research being carried out to accomplish this include: pointing/tracking analysis; cloud identification and modeling; simultaneous multichannel retrieval capability; forward model improvements; high vertical-resolution gas filter channel retrievals; a refined temperature retrieval; robust error analyses; long-term trend reliability studies; and data validation. The current (first-year) effort concentrates on the pointer/tracker correction algorithms, cloud filtering and validation, and multi-channel retrieval development. However, these areas are all highly coupled, so progress in one area benefits from and sometimes depends on work in others.

HALOE Algorithm Improvements for Upper Tropospheric Sounding

NASA Technical Reports Server (NTRS)

Thompson, Robert Earl; McHugh, Martin J.; Gordley, Larry L.; Hervig, Mark E.; Russell, James M., III; Douglass, Anne (Technical Monitor)

2001-01-01

This report details the ongoing efforts by GATS, Inc., in conjunction with Hampton University and University of Wyoming, in NASA's Mission to Planet Earth Upper Atmospheric Research Satellite (UARS) Science Investigator Program entitled 'HALOE Algorithm Improvements for Upper Tropospheric Sounding.' The goal of this effort is to develop and implement major inversion and processing improvements that will extend Halogen Occultation Experiment (HALOE) measurements further into the troposphere. In particular, O3, H2O, and CH4 retrievals may be extended into the middle troposphere, and NO, HCl and possibly HF into the upper troposphere. Key areas of research being carried out to accomplish this include: pointing/tracking analysis; cloud identification and modeling; simultaneous multichannel retrieval capability; forward model improvements; high vertical-resolution gas filter channel retrievals; a refined temperature retrieval; robust error analyses; long-term trend reliability studies; and data validation. The current (first year) effort concentrates on the pointer/tracker correction algorithms, cloud filtering and validation, and multichannel retrieval development. However, these areas are all highly coupled, so progress in one area benefits from and sometimes depends on work in others.

Accurate Satellite-Derived Estimates of Tropospheric Ozone Radiative Forcing

NASA Technical Reports Server (NTRS)

Joiner, Joanna; Schoeberl, Mark R.; Vasilkov, Alexander P.; Oreopoulos, Lazaros; Platnick, Steven; Livesey, Nathaniel J.; Levelt, Pieternel F.

2008-01-01

Estimates of the radiative forcing due to anthropogenically-produced tropospheric O3 are derived primarily from models. Here, we use tropospheric ozone and cloud data from several instruments in the A-train constellation of satellites as well as information from the GEOS-5 Data Assimilation System to accurately estimate the instantaneous radiative forcing from tropospheric O3 for January and July 2005. We improve upon previous estimates of tropospheric ozone mixing ratios from a residual approach using the NASA Earth Observing System (EOS) Aura Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS) by incorporating cloud pressure information from OMI. Since we cannot distinguish between natural and anthropogenic sources with the satellite data, our estimates reflect the total forcing due to tropospheric O3. We focus specifically on the magnitude and spatial structure of the cloud effect on both the shortand long-wave radiative forcing. The estimates presented here can be used to validate present day O3 radiative forcing produced by models.

Extratropical Stratosphere-Troposphere Mass Exchange

NASA Technical Reports Server (NTRS)

Schoeberl, Mark R.

2004-01-01

Understanding the exchange of gases between the stratosphere and the troposphere is important for determining how pollutants enter the stratosphere and how they leave. This study does a global analysis of that the exchange of mass between the stratosphere and the troposphere. While the exchange of mass is not the same as the exchange of constituents, you can t get the constituent exchange right if you have the mass exchange wrong. Thus this kind of calculation is an important test for models which also compute trace gas transport. In this study I computed the mass exchange for two assimilated data sets and a GCM. The models all agree that amount of mass descending from the stratosphere to the troposphere in the Northern Hemisphere extra tropics is approx. 10(exp 10) kg/s averaged over a year. The value for the Southern Hemisphere by about a factor of two. ( 10(exp 10) kg of air is the amount of air in 100 km x 100 km area with a depth of 100 m - roughly the size of the D.C. metro area to a depth of 300 feet.) Most people have the idea that most of the mass enters the stratosphere through the tropics. But this study shows that almost 5 times more mass enters the stratosphere through the extra-tropics. This mass, however, is quickly recycled out again. Thus the lower most stratosphere is a mixture of upper stratospheric air and tropospheric air. This is an important result for understanding the chemistry of the lower stratosphere.

Comparison of stratospheric NO2 profiles above Kiruna, Sweden retrieved from ground-based zenith sky DOAS measurements, SAOZ balloon measurements and SCIAMACHY limb observations

NASA Astrophysics Data System (ADS)

Gu, Myojeong; Enell, Carl-Fredrik; Hendrick, François; Pukite, Janis; Van Roozendael, Michel; Platt, Ulrich; Raffalski, Uwe; Wagner, Thomas

2015-04-01

Stratospheric NO2 not only destroys ozone but acts as a buffer against halogen catalyzed ozone loss by converting halogen species into stable nitrates. These two roles of stratospheric NO2 depend on the altitude. Hence, the objective of this study is to investigate the vertical distribution of stratospheric NO2. We compare the NO2 profiles derived from the zenith sky DOAS with those obtained from, SAOZ balloon measurements and satellite limb observations. Vertical profiles of stratospheric NO2 are retrieved from ground-based zenith sky DOAS observations operated at Kiruna, Sweden (68.84°N, 20.41°E) since 1996. To determine the profile of stratospheric NO2 measured from ground-based zenith sky DOAS, we apply the Optimal Estimation Method (OEM) to retrieval of vertical profiles of stratospheric NO2 which has been developed by IASB-BIRA. The basic principle behind this profiling approach is the dependence of the mean scattering height on solar zenith angle (SZA). We compare the retrieved profiles to two additional datasets of stratospheric NO2 profile. The first one is derived from satellite limb observations by SCIAMACHY (Scanning Imaging Absorption spectrometer for Atmospheric CHartographY) on EnviSAT. The second is derived from the SAOZ balloon measurements (using a UV/Visible spectrometer) performed at Kiruna in Sweden.

Insights into Tropical Tropospheric Ozone from Satellite and Sonde Data

NASA Technical Reports Server (NTRS)

Thompson, Anne M.

2003-01-01

The first climatological overview of total, stratospheric and tropospheric ozone in the southern hemisphere tropical and subtropics is based on ozone sounding data from 10 sites comprising the Southern Hemisphere Additional OZonesondes (SHADOZ) network. Observations were made over: Ascension Island; Nairobi, Kenya; Irene, South Africa; Reunion Island; Watukosek, Java; Fiji; Tahiti; American Samoa; San Cristobal, Galapagos; Natal, Brazil. The data reside at: http://code916.gsfc.nasa.gov/Data_services/shadoz. SHADOZ ozone time-series and profiles give a perspective on tropical total, stratospheric and tropospheric ozone. Prominent features are highly variable tropospheric ozone and a zonal wave-one pattern in total (and tropospheric) column ozone. Dynamical and chemical influences appear to be of comparable magnitude though model studies are needed to quantify this. In addition to leading the SHADOZ network, we have been producing near-real tropical tropospheric ozone ('TTO') data from the Total Ozone Mapping Spectrometer (TOMS) since 1997 with Prof. Hudson and students at the University of Maryland: http://metosrv2.umd.edu/tropo. Further perspective on the complexity of tropospheric ozone variability is shown using satellite observations.

Volcanic Contribution to Decadal Changes in Tropospheric Temperature

NASA Technical Reports Server (NTRS)

Santer, Benjamin D.; Bonfils, Celine; Painter, Jeffrey F.; Zelinka, Mark D.; Mears, Carl; Solomon, Susan; Schmidt, Gavin A.; Fyfe, John C.; Cole, Jason N.S.; Nazarenko, Larissa;

Tropospheric Passive Remote Sensing

NASA Technical Reports Server (NTRS)

Keafer, L. S., Jr. (Editor)

1982-01-01

The long term role of airborne/spaceborne passive remote sensing systems for tropospheric air quality research and the identification of technology advances required to improve the performance of passive remote sensing systems were discussed.

Troc: a proposed tropospheric sounder for chemistry and climate

NASA Astrophysics Data System (ADS)

Camy-Peyret, C.

TROC has been submitted to ESA in the last call for proposals of the Earth Explorer Opportunity Missions and its focus is on tropospheric composition and chemistry-climate interactions. The mission objectives of TROC cover four research subjects. Global tropospheric chemistry: perform global measurements from space of tropospheric composition in order to improve our understanding and to constrain models of tropospheric chemistry with emphasis on tropospheric ozone. Pollution: establish the impact of mega cities of industrialised or developing countries by monitoring their pollution plumes. Biomass burning: monitor the chemical species and aerosols injected in the free troposphere during major burning episodes in the intertropical region as well as by major forest fires at other latitudes. Chemistry-climate interactions: quantify on a global scale the distributions and the sources of greenhouse gases like CO2, CH4, O3, N2O and the CFCs. Contribute to demonstration studies for monitoring from space how Montreal and Kyoto protocols are enforced as far as human impacts on atmospheric chemistry and climate are concerned. To fulfil these objectives, passive remote sensing of the troposphere has been selected as the best compromise between technical maturity and multi-species coverage. The main elements of TROC are a Fourier transform infrared (FTIR) instrument and an ultraviolet-visible (UV-vis) spectrometer, both operating in the downward-looking geometry with a 10 km diameter footprint at nadir. An ``intelligent'' pointing mirror coupled to an infrared imager is used to optimise day/night sounding down to the surface. The FTIR instrument covers at 0.1 cm-1 apodised spectral resolution 3 bands from 14 to 3.3 μ m in thermal emission and one band in solar reflected light around 2.3 μ m. The UV-vis instrument covers the regions 290-490 nm (1 nm resolution) and 520-1030 nm (2.5 nm resolution) with 43 array detectors (2 bands × 2 polarizations) in reflected

Global Troposphere Experiment Project

NASA Technical Reports Server (NTRS)

Bandy, Alan R.; Thornton, Donald C.

1997-01-01

For the Global Troposphere Experiment project Pacific Exploratory Measurements West B (PEM West B), we made determinations of sulfur dioxide (SO2) and dimethyl sulfide (DMS) using gas chromatography-mass spectrometry with isotopically labelled internal standards. This technique provides measurements with precision of 1 part-per-trillion by volume below 20 pptv and 1% above 20 pptv. Measurement of DMS and SO2 were performed with a time cycle of 5-6 minutes with intermittent zero checks. The detection limits were about 1 pptv for SO2 and 2 pptv for DMS. Over 700 measurements of each compound were made in flight. Volcanic impacts on the upper troposphere were again found as a result of deep convection in the tropics. Extensive emission of SO2 from the Pacific Rim land masses were primarily observed in the lower well-mixed part of the boundary layer but also in the upper part of the boundary layer. Analyses of the SO2 data with aerosol sulfate, beryllium-7, and lead-210 indicated that SO2, contributed to half or more of the observed total oxidized sulfur (SO2 plus aerosol sulfate) in free tropospheric air. Cloud processing and rain appeared to be responsible for lower SO2 levels between 3 and 8.5 km than above or below this region. During both phases of PEM-West, dimethyl sulfide did not appear to be a major source of sulfur dioxide in the upper free troposphere over the western Pacific Ocean. In 1991 the sources Of SO2 at high altitude appeared to be both anthropogenic and volcanic with an estimated 1% being solely from DMS. The primary difference for the increase in the DMS source was the very low concentration of SO2 at high altitude. In the midlatitude region near the Asian land masses, DMS in the mixed layer was lower than in the tropical region of the western Pacific. Convective cloud systems near volcanoes in the tropical convergence in the western Pacific troposphere were a major source of SO2 at high altitudes during PEM-West B. High levels of SO2 were

Improving BeiDou real-time precise point positioning with numerical weather models

NASA Astrophysics Data System (ADS)

Lu, Cuixian; Li, Xingxing; Zus, Florian; Heinkelmann, Robert; Dick, Galina; Ge, Maorong; Wickert, Jens; Schuh, Harald

2017-09-01

Precise positioning with the current Chinese BeiDou Navigation Satellite System is proven to be of comparable accuracy to the Global Positioning System, which is at centimeter level for the horizontal components and sub-decimeter level for the vertical component. But the BeiDou precise point positioning (PPP) shows its limitation in requiring a relatively long convergence time. In this study, we develop a numerical weather model (NWM) augmented PPP processing algorithm to improve BeiDou precise positioning. Tropospheric delay parameters, i.e., zenith delays, mapping functions, and horizontal delay gradients, derived from short-range forecasts from the Global Forecast System of the National Centers for Environmental Prediction (NCEP) are applied into BeiDou real-time PPP. Observational data from stations that are capable of tracking the BeiDou constellation from the International GNSS Service (IGS) Multi-GNSS Experiments network are processed, with the introduced NWM-augmented PPP and the standard PPP processing. The accuracy of tropospheric delays derived from NCEP is assessed against with the IGS final tropospheric delay products. The positioning results show that an improvement in convergence time up to 60.0 and 66.7% for the east and vertical components, respectively, can be achieved with the NWM-augmented PPP solution compared to the standard PPP solutions, while only slight improvement in the solution convergence can be found for the north component. A positioning accuracy of 5.7 and 5.9 cm for the east component is achieved with the standard PPP that estimates gradients and the one that estimates no gradients, respectively, in comparison to 3.5 cm of the NWM-augmented PPP, showing an improvement of 38.6 and 40.1%. Compared to the accuracy of 3.7 and 4.1 cm for the north component derived from the two standard PPP solutions, the one of the NWM-augmented PPP solution is improved to 2.0 cm, by about 45.9 and 51.2%. The positioning accuracy for the up component

Midterm outcomes of the Zenith Renu AAA Ancillary Graft.

PubMed

Jim, Jeffrey; Rubin, Brian G; Geraghty, Patrick J; Money, Samuel R; Sanchez, Luis A

2011-08-01

The Zenith Renu abdominal aortic aneurysm (AAA) Ancillary Graft (Cook Medical Inc, Bloomington, Ind) provides active proximal fixation for treatment of pre-existing endografts with failed or failing proximal fixation or seal. The purpose of this study was to evaluate the midterm outcomes of treatment with this device. From September 2005 to November 2006, a prospective, nonrandomized, multicenter, postmarket registry was utilized to collect physician experiences from 151 cases (89 converters and 62 main body extensions) at 95 institutions. Preoperative indications and procedural and postimplantation outcomes were collected and analyzed. Technical success and clinical success were determined as defined by the Society of Vascular Surgery reporting standards. Patients were predominantly male (87%) with a mean age of 77 years. The interval between the original endograft implantation to Renu treatment was 43.4 ± 18.7 months. The indications for treatment were endoleak (n = 111), migration (n = 136), or both (n = 94). Technical success was 98.0% with two cases of intraoperative conversion and one case of persistent type IA endoleak. The median follow-up for the cohort was 45.0 months (range, 0-56 months; interquartile range, 25.0 months). Overall, 32 cases had treatment failures that included at least one of the following: death (n = 5), type I/III endoleak (n = 18), graft infection (n = 1), thrombosis (n = 1), aneurysm enlargement >5 mm (n = 9), rupture (n = 4), conversion (n = 9, with 7 after 30 days), and migration (n = 1). Overall, the clinical success for the entire cohort during the follow-up period was 78.8% (119/151). The postmarket registry data confirm that the Zenith Renu AAA Ancillary Graft can be used to treat endovascular repairs that failed due to proximal attachment failures. The salvage treatment with the Renu device had high technical success rate and resulted in clinical success in a majority of patients (78.8%). While failed endovascular repairs can

Relationships between ten-year trends of tropospheric ozone and temperature over Taiwan.

PubMed

Hsu, Kuang-Jung

2007-03-01

The analyses of ten-year ozonesonde observations from 1993 till 2002, over Taipei, Taiwan show influences of climate change. Despite huge increases in its precursor emissions in this region, there were little variations in tropospheric ozone. Results indicate a warmer troposphere, a statistically insignificant rising tropopause, 79+/-206 m per decade, and decreasing tropopause temperature at -1.0+/-0.89 K per decade. The derived mean tropospheric ozone is 40.58+/-10.99 DU, and has a statistically insignificant small trend of -0.78+/-1.7 DU per decade. The derived ten-year vertical trends of temperature and ozone are inversely correlated with each other from the middle troposphere up to the lower stratosphere. The averaged monthly vertical temperature trends show a generally warmer middle troposphere. The tropospheric ozone monthly trend has small increases only in the lower troposphere during winter and spring. Strong decreases occur in summer, from the surface up into the stratosphere. For ozone variation, results suggest that influences of climate forcing are stronger than those from precursor increases. More frequent and/or intense convection in summer and other climate-induced effects may contribute to the less than expected ozone observed in the troposphere.

Observations of vertical velocities in the tropical upper troposphere and lower stratosphere using the Arecibo 430-MHz radar

NASA Technical Reports Server (NTRS)

Cornish, C. R.

1988-01-01

The first clear-air observations of vertical velocities in the tropical upper troposphere and lower stratosphere (8-22 km) using the Arecibo 430-MHz radar are presented. Oscillations in the vertical velocity near the Brunt-Vaisala period are observed in the lower stratosphere during the 12-hour observation period. Frequency power spectra from the vertical velocity time series show a slope between -0.5 and -1.0. Vertical wave number spectra computed from the height profiles of vertical velocities have slopes between -1.0 and -1.5. These observed slopes do not agree well with the slopes of +1/3 and -2.5 for frequency and vertical wave number spectra, respectively, predicted by a universal gravity-wave spectrum model. The spectral power of wave number spectra of a radial beam directed 15 deg off-zenith is enhanced by an order of magnitude over the spectral power levels of the vertical beam. This enhancement suggests that other geophysical processes besides gravity waves are present in the horizontal flow. The steepening of the wave number spectrum of the off-vertical beam in the lower stratosphere to near -2.0 is attributed to a quasi-inertial period wave, which was present in the horizontal flow during the observation period.

Analysis of the summertime buildup of tropospheric ozone abundances over the Middle East and North Africa as observed by the Tropospheric Emission Spectrometer instrument

NASA Astrophysics Data System (ADS)

Liu, Jane J.; Jones, Dylan B. A.; Worden, John R.; Noone, David; Parrington, Mark; Kar, Jay

2009-03-01

We use the GEOS-Chem chemical transport model to interpret observations of tropospheric ozone from the Tropospheric Emission Spectrometer (TES) satellite instrument in summer 2005. Observations from TES reveal elevated ozone in the middle troposphere (500-400 hPa) across North Africa and the Middle East. Observed ozone abundances in the middle troposphere are at a maximum in summer and a minimum in winter, consistent with the previously predicted summertime "Middle East ozone maximum." This summertime enhancement in ozone is associated with the Arabian and Sahara anticyclones, centered over the Zagros and Atlas Mountains, respectively. These anticyclones isolate the middle troposphere over northeast Africa and the Middle East, with westerlies to the north and easterlies to the south, facilitating the buildup of ozone. Over the Middle East, we find that in situ production and transport from Asia provides comparable contributions of 30-35% to the ozone buildup. Over North Africa, in situ production is dominant (at about 20%), with transport from Asia, North America, and equatorial Africa each contributing about 10-15% to the total ozone. We find that although the eastern Mediterranean is characterized by strong descent in the middle and upper troposphere in summer, transport from the boundary layer accounts for about 25% of the local Middle Eastern contribution to the ozone enhancement in the middle troposphere. This upward transport of boundary layer air is associated with orographic lifting along the Zagros Mountains in Iran and the Asir and Hijaz Mountain ranges in Saudi Arabia, and is consistent with TES observations of deuterated water.

Present-day distribution and trends of global tropospheric ozone from satellite observations: Results from the Tropospheric Ozone Assessment Report (TOAR)

NASA Astrophysics Data System (ADS)

Gaudel, A.; Cooper, O. R.; Barret, B.; Boynard, A.; Clerbaux, C.; Pierre-Francois, C.; Huang, G.; Hurtmans, D.; Kerridge, B. J.; Latter, B.; Le Flochmoen, E.; Liu, X.; Neu, J. L.; Siddans, R.; Wespes, C.; Worden, H. M.; Ziemke, J. R.

2017-12-01

Tropospheric ozone is a greenhouse gas and pollutant detrimental to human health and crop and ecosystem productivity. Since 1990 a large portion of the anthropogenic emissions that react in the atmosphere to produce ozone have shifted from North America and Europe to Asia. This rapid shift, coupled with limited ozone monitoring in developing nations, has left scientists unable to answer the most basic questions: Is ozone continuing to decline in nations with strong emission controls? To what extent is ozone increasing in the developing world? IGAC's Tropospheric Ozone Assessment Report (TOAR) has been designed to answer these questions and this presentation will show the results from the TOAR-Climate initiative, focusing on the present-day distribution and trends of global tropospheric ozone from satellite observations. Five satellite products based on OMI (2 products using two different retrieval methods) and IASI (also 2 products using two different retrieval methods) and the OMI/MLS combined product were intercompared. An important result is the close agreement among the five products regarding the quantification of the total mass of all tropospheric ozone, the so called tropospheric ozone burden (TOB). The mean estimate for TOB between 60° N and 60° S is 296 Tg, with all products agreeing within ± 4%. However, on a regional basis the five satellite products have notable differences and there is no agreement in terms of ozone trends over the past decade. Continuing work is exploring the causes of these differences.

Linkages Between Ozone-depleting Substances, Tropospheric Oxidation and Aerosols

NASA Technical Reports Server (NTRS)

Voulgarakis, A.; Shindell, D. T.; Faluvegi, G.

2013-01-01

Coupling between the stratosphere and the troposphere allows changes in stratospheric ozone abundances to affect tropospheric chemistry. Large-scale effects from such changes on chemically produced tropospheric aerosols have not been systematically examined in past studies. We use a composition-climate model to investigate potential past and future impacts of changes in stratospheric ozone depleting substances (ODS) on tropospheric oxidants and sulfate aerosols. In most experiments, we find significant responses in tropospheric photolysis and oxidants, with small but significant effects on methane radiative forcing. The response of sulfate aerosols is sizeable when examining the effect of increasing future nitrous oxide (N2O) emissions. We also find that without the regulation of chlorofluorocarbons (CFCs) through the Montreal Protocol, sulfate aerosols could have increased by 2050 by a comparable amount to the decreases predicted due to relatively stringent sulfur emissions controls. The individual historical radiative forcings of CFCs and N2O through their indirect effects on methane (-22.6mW/sq. m for CFCs and -6.7mW/sq. m for N2O) and sulfate aerosols (-3.0mW/sq. m for CFCs and +6.5mW/sq. m for N2O when considering the direct aerosol effect) discussed here are non-negligible when compared to known historical ODS forcing. Our results stress the importance of accounting for stratosphere-troposphere, gas-aerosol and composition-climate interactions when investigating the effects of changing emissions on atmospheric composition and climate.

Discoveries about Tropospheric Ozone Pollution from Satellite and Sounding

NASA Technical Reports Server (NTRS)

Thompson, Anne M.

2004-01-01

We have been producing near-real time tropospheric ozone satellite maps from the TOMS (Total Ozone Mapping Spectrometer) sensor since 1997. This is most readily done for the tropics, where the stratospheric and tropospheric ozone column amounts can be discriminated readily. Maps for 1996-2000 for the operational Earth-Probe instrument reside at: chttp://www.atmos.umd.edu/-trope>. Pollution in the tropics is influenced by biomass burning and by transport patterns that favor recirculation and in other cases reflect climate variability like the El-Nino-Southern Oscillation [Thompson et al., 2001]. Time permitting, examples of mid-latitude, intercontinental transport of ozone pollution sensed by TOMS will be shown. The satellite view of chemical-dynamical interactions in tropospheric ozone is not adequate to capture vertical variability. Thus, in 1998, NASA's Goddard Space Flight Center and a team of international sponsors established the SHADOZ (Southern Hemisphere ADditional OZonesondes) project to address the gap in tropical ozone soundings. SHADOZ augments launches and provides a public archive of ozonesonde data from twelve tropical stations at http://croc.gsfc.nasa.gov/shadoz. Further insights into the role of chemical and dynamical influences have emerged from the first 4-5 years of SHADOZ data (less than 2000 ozone profiles): (a) highly variable tropospheric ozone; (b) a zonal wave-one pattern in tropospheric column ozone; (c) convective variability affects tropospheric ozone over the Indian and Pacific Ocean; (d) a "tropical Atlantic Paradox" appears in December-January-February.

Retrieval of tropospheric carbon monoxide for the MOPITT experiment

NASA Astrophysics Data System (ADS)

Pan, Liwen; Gille, John C.; Edwards, David P.; Bailey, Paul L.; Rodgers, Clive D.

1998-12-01

A retrieval method for deriving the tropospheric carbon monoxide (CO) profile and column amount under clear sky conditions has been developed for the Measurements of Pollution In The Troposphere (MOPITT) instrument, scheduled for launch in 1998 onboard the EOS-AM1 satellite. This paper presents a description of the method along with analyses of retrieval information content. These analyses characterize the forward measurement sensitivity, the contribution of a priori information, and the retrieval vertical resolution. Ensembles of tropospheric CO profiles were compiled both from aircraft in situ measurements and from chemical model results and were used in retrieval experiments to characterize the method and to study the sensitivity to different parameters. Linear error analyses were carried out in parallel with the ensemble experiments. Results of these experiments and analyses indicate that MOPITT CO column measurements will have better than 10% precision, and CO profile measurement will have approximately three pieces of independent information that will resolve 3-5 tropospheric layers to approximately 10% precision. These analyses are important for understanding MOPITT data, both for application of data in tropospheric chemistry studies and for comparison with in situ measurements.

Future changes in tropospheric ozone under Representative Concentration Pathways (RCPs)

NASA Astrophysics Data System (ADS)

Kawase, Hiroaki; Nagashima, Tatsuya; Sudo, Kengo; Nozawa, Toru

2011-03-01

We consider future changes in tropospheric ozone based on the Representative Concentration Pathways (RCPs), which are new emission and concentration scenarios for the 5th coupled model intercomparison project. In contrast to the SRES scenarios, all the RCP scenarios assume an emission reduction of NOx by the late 21st Century that has the potential to achieve tropospheric ozone reduction. However, increasing radiative forcing (RF) due to greenhouse gases and changes in CH4 concentration also contribute to differences in the tropospheric ozone distribution among RCP scenarios. In the RCP4.5 and RCP6.0, assuming the stabilization of RF, the increase in tropospheric ozone due to enhanced residual circulation is cancelled out by the ozone reduction due to ozone precursor reductions. In contrast, in the RCP8.5, assuming increasing RF even after 2100, further enhanced residual circulation and significant increase in CH4 cause a dramatic increase in tropospheric ozone.

Augmentation of Quasi-Zenith Satellite Positioning System Using High Altitude Platforms Systems (HAPS)

NASA Astrophysics Data System (ADS)

Tsujii, Toshiaki; Harigae, Masatoshi

Recently, some feasibility studies on a regional positioning system using the quasi-zenith satellites and the geostationary satellites have been conducted in Japan. However, the geometry of this system seems to be unsatisfactory in terms of the positioning accuracy in north-south direction. In this paper, an augmented satellite positioning system by the High Altitude Platform Systems (HAPS) is proposed since the flexibility of the HAPS location is effective to improve the geometry of satellite positioning system. The improved positioning performance of the augmented system is also demonstrated.

Tropospheric Emissions: Monitoring of Pollution (TEMPO)

NASA Technical Reports Server (NTRS)

Zoogman, P.; Liu, X.; Suleiman, R. M.; Pennington, W. F.; Flittner, D. E.; Al-Saadi, J. A.; Hilton, B. B.; Nicks, D. K.; Newchurch, M. J.; Carr, J. L.;

A Madden-Julian Oscillation in Tropospheric Ozone

NASA Technical Reports Server (NTRS)

Ziemke, J. R.; Chandra, S.

2003-01-01

This is the first study to indicate a Madden-Julian Oscillation (MJO) in tropospheric ozone. Tropospheric ozone is derived using differential measurements of total column ozone and stratospheric column ozone measured from total ozone mapping spectrometer (TOMS) and microwave limb sounder (MLS) instruments. Two broad regions of significant MJO signal are identified in the tropics, one in the western Pacific and the other in the eastern Pacific. Over both regions, MJO variations in tropospheric ozone represent 5-10 Dobson Unit (DU) peak-to-peak anomalies. These variations are significant compared to mean background amounts of 20 DU or less over most of the tropical Pacific. MJO signals of this magnitude would need to be considered when investigating and interpreting particular pollution events since ozone is a precursor of the hydroxyl (OH) radical, the main oxidizing agent of pollutants in the lower atmosphere.

Using GPS RO L1 data for calibration of the atmospheric path delay model for data reduction of the satellite altimetery observations.

NASA Astrophysics Data System (ADS)

Petrov, L.

2017-12-01

Processing satellite altimetry data requires the computation of path delayin the neutral atmosphere that is used for correcting ranges. The path delayis computed using numerical weather models and the accuracy of its computationdepends on the accuracy of numerical weather models. Accuracy of numerical modelsof numerical weather models over Antarctica and Greenland where there is a very sparse network of ground stations, is not well known. I used the dataset of GPS RO L1 data, computed predicted path delay for ROobservations using the numerical whether model GEOS-FPIT, formed the differences with observed path delay and used these differences for computationof the corrections to the a priori refractivity profile. These profiles wereused for computing corrections to the a priori zenith path delay. The systematic patter of these corrections are used for de-biasing of the the satellite altimetry results and for characterization of the systematic errorscaused by mismodeling atmosphere.

Tropospheric Emission Spectrometer for the Earth Observing System

NASA Technical Reports Server (NTRS)

Glavich, Thomas A.; Beer, Reinhard

1991-01-01

A Tropospheric Emission Spectrometer (TES) for the Earth Observing System (EOS) series of polar-orbiting platforms is described. TES is aimed at studying tropospheric chemistry, in particular, the exchange of gases between the surface and the atmosphere, urban and regional pollution, acid rain precursors, sources and sinks of greenhouse gases, and the interchange of gases between the troposphere and the stratosphere. TES is a high-resolution (0.025/cm) infrared Fourier transform spectrometer operating in the passive thermal-emission mode in a very wide spectral range (600 to 4350/cm; 2.3 to 16.7 microns). TES has 32 spatial pixels in each of four optically conjugated linear detector arrays, each optimized for a different spectral region.

New Results and Insight into Tropospheric Composition - (TES) Tropospheric Emission Spectrometer

NASA Technical Reports Server (NTRS)

Gunson, Michael R.; Eldering, Annmarie

2006-01-01

This viewgraph presentation describes the scientific challenges along with the chemical and dynamic processes that govern tropospheric ozone. The contents include: 1) The challenge and why; 2) The how to do 'it'; 3) Did 'it' work; 4) What we are trying to do with 'it'; 5) What else is happening; and 6) What next.

Estimating the Tropospheric Ozone Distribution by the Assimilation of Satellite Data

NASA Technical Reports Server (NTRS)

Hayashi, Hiroo; Stajner, Ivanka; Winslow, Nathan; Jones, Dylan B. A.; Pawson, Steven; Thompson, Anne M.

2003-01-01

Tropospheric ozone is important to the environment, because it acts as a strong oxidant to control the concentrations of many reduced gases (methane, carbon monoxide, ... ), its radiative forcing plays a significant role in the greenhouse effect, and direct contact with ozone is harmful to human health. Tropospheric ozone, whose main sources are intrusion from the stratosphere and chemical production from source gases associated with urban pollution or biomass burning, varies on a wide range of spatial and temporal scales. Its transport and chemistry can be influenced by weather, seasonal, or multiannual variability. Despite the importance of tropospheric ozone, it contributes only about 10% of the total ozone loading in the atmosphere. Consequently, satellite instruments lose sensitivity below the stratospheric ozone peak, and provide little information about middle and lower tropospheric ozone. This talk will discuss recent modifications made to the satellite ozone data assimilation system at NASA's Data Assimilation Office (DAO) in order to provide better tropospheric ozone columns and profiles. We use a version of the system that assimilates only the data from the Solar Backscatter UltraViolet/2 (SBUV/2) instrument. The quality of the assimilated ozone in the tropical troposphere is evaluated by comparison with independent observations obtained from the Southern Hemispheric Additional Ozonesondes (SHADOZ) network. It is shown that the quality of ozone fields is sensitive to the winds used in the transport model. Increasing the vertical resolution of the model also has a beneficial impact. The assimilated ozone in the lower troposphere was substantially improved by inclusion of tropospheric ozone production, loss, and dry deposition rates from the Harvard GEOS-CHEM model. The mechanisms behind these results will be examined and the implications for our understanding of tropospheric ozone will be discussed.

Tropospheric and ionospheric media calibrations based on global navigation satellite system observation data

NASA Astrophysics Data System (ADS)

Feltens, Joachim; Bellei, Gabriele; Springer, Tim; Kints, Mark V.; Zandbergen, René; Budnik, Frank; Schönemann, Erik

2018-06-01

Context: Calibration of radiometric tracking data for effects in the Earth atmosphere is a crucial element in the field of deep-space orbit determination (OD). The troposphere can induce propagation delays in the order of several meters, the ionosphere up to the meter level for X-band signals and up to tens of meters, in extreme cases, for L-band ones. The use of media calibrations based on Global Navigation Satellite Systems (GNSS) measurement data can improve the accuracy of the radiometric observations modelling and, as a consequence, the quality of orbit determination solutions. Aims: ESOC Flight Dynamics employs ranging, Doppler and delta-DOR (Delta-Differential One-Way Ranging) data for the orbit determination of interplanetary spacecraft. Currently, the media calibrations for troposphere and ionosphere are either computed based on empirical models or, under mission specific agreements, provided by external parties such as the Jet Propulsion Laboratory (JPL) in Pasadena, California. In order to become independent from external models and sources, decision fell to establish a new in-house internal service to create these media calibrations based on GNSS measurements recorded at the ESA tracking sites and processed in-house by the ESOC Navigation Support Office with comparable accuracy and quality. Methods: For its concept, the new service was designed to be as much as possible depending on own data and resources and as less as possible depending on external models and data. Dedicated robust and simple algorithms, well suited for operational use, were worked out for that task. This paper describes the approach built up to realize this new in-house internal media calibration service. Results: Test results collected during three months of running the new media calibrations in quasi-operational mode indicate that GNSS-based tropospheric corrections can remove systematic signatures from the Doppler observations and biases from the range ones. For the ionosphere, a

Overview of new GNSS tropospheric products for GNSS-meteorology and their assessment at Geodetic Observatory Pecny (CZ)

NASA Astrophysics Data System (ADS)

Dousa, J.; Vaclavovic, P.; Gyori, G.

2012-12-01

Geodetic Observatory Pecný (GOP) has a long-term experience in the estimation of precise tropospheric parameters from GNSS permanent stations, in particular under the limited timelines of near real time. More than a decade, the GOP zenith total delays (ZTD) contributed to various projects in Europe (COST-716, TOUGH, E-GVAP, E-GVAP II) and the operational ZTD hourly updated product flows via the meteorological observation exchange network - GTS - to the end users worldwide. Currently, the GOP regional ZTD product is operationally assimilated in Météo France and UK MetOffice at least and further exploited in various ways at many other meteorological institutions. New developments at GOP over last three years consist of a) implementation and assessment of the global hourly ZTD product of about 170 stations, b) implementation of routine multi-GNSS (GPS+GLONASS) ZTD European product, and c) implementation of ultra-fast/real-time ZTD product. The GOP global ZTD product has been implemented on request of the meteorological institutions running global numerical weather forecasting models. The global ZTD product was seriously evaluated over ten months (Oct 2009 - Aug 2011) when compared to reprocessed EUREF and IGS ZTDs, radiosondes and ZTDs derived from UK MetOffice's global numerical weather model. After the evaluation (and on special request of UK MetOffice) the product has been switched from testing to operational status within the framework of the EUMETNET EIG GPS Water Vapour Programme (E-GVAP) and officially disseminated via the GTS network. The GOP multi-GNSS ZTD solution has been tested since 2009 shortly after developing GOP ultra-rapid GPS+GLONASS orbits for the International GNSS Service (IGS). A specific bias of mean value 1.5 mm was identified between GPS- and GLONASS-only ZTD at that time, and relation to the IGS05 antenna phase centre offset and variation models (PCO+PCV) identified. Consequently, the implementation of a routine operation has been done

The profile algorithm for microwave delay estimation from water vapor radiometer data

NASA Technical Reports Server (NTRS)

Robinson, Steven E.

1988-01-01

A new algorithm has been developed for the estimation of tropospheric microwave path delays from water vapor radiometer (WVR) data, which does not require site and weather dependent empirical parameters to produce accuracy better than 0.3 cm of delay. Instead of taking the conventional linear approach, the new algorithm first uses the observables with an emission model to determine an approximate form of the vertical water vapor distribution, which is then explicitly integrated to estimate wet path delays in a second step. The intrinsic accuracy of this algorithm, excluding uncertainties caused by the radiometers and the emission model, has been examined for two channel WVR data using path delays and corresponding simulated observables computed from archived radiosonde data. It is found that annual rms errors for a wide range of sites average 0.18 cm in the absence of clouds, 0.22 cm in cloudy weather, and 0.19 cm overall. In clear weather, the new algorithm's accuracy is comparable to the best that can be obtained from conventional linear algorithms, while in cloudy weather it offers a 35 percent improvement.

Report of the NASA working group on tropospheric program planning

NASA Technical Reports Server (NTRS)

Seinfeld, J. H.; Allario, F.; Bandeen, W. R.; Chameides, W. L.; Davis, D. D.; Hinkley, E. D.; Stewart, R. W.

1981-01-01

Increased understanding of the chemical phenomena occurring in the troposphere was the research goal. Emphasis was placed on tropospheric impact on environmental quality, including public health, agriculture, climate, and weather.

Ozone Profiles and Tropospheric Ozone from Global Ozone Monitoring Experiment

NASA Technical Reports Server (NTRS)

Liu, X.; Chance, K.; Sioris, C. E.; Sparr, R. J. D.; Kuregm, T. P.; Martin, R. V.; Newchurch, M. J.; Bhartia, P. K.

2003-01-01

Ozone profiles are derived from backscattered radiances in the ultraviolet spectra (290-340 nm) measured by the nadir-viewing Global Ozone Monitoring Experiment using optimal estimation. Tropospheric O3 is directly retrieved with the tropopause as one of the retrieval levels. To optimize the retrieval and improve the fitting precision needed for tropospheric O3, we perform extensive wavelength and radiometric calibrations and improve forward model inputs. Retrieved O3 profiles and tropospheric O3 agree well with coincident ozonesonde measurements, and the integrated total O3 agrees very well with Earth Probe TOMS and Dobson/Brewer total O3. The global distribution of tropospheric O3 clearly shows the influences of biomass burning, convection, and air pollution, and is generally consistent with our current understanding.

Optimization of GPS water vapor tomography technique with radiosonde and COSMIC historical data

NASA Astrophysics Data System (ADS)

Ye, Shirong; Xia, Pengfei; Cai, Changsheng

2016-09-01

The near-real-time high spatial resolution of atmospheric water vapor distribution is vital in numerical weather prediction. GPS tomography technique has been proved effectively for three-dimensional water vapor reconstruction. In this study, the tomography processing is optimized in a few aspects by the aid of radiosonde and COSMIC historical data. Firstly, regional tropospheric zenith hydrostatic delay (ZHD) models are improved and thus the zenith wet delay (ZWD) can be obtained at a higher accuracy. Secondly, the regional conversion factor of converting the ZWD to the precipitable water vapor (PWV) is refined. Next, we develop a new method for dividing the tomography grid with an uneven voxel height and a varied water vapor layer top. Finally, we propose a Gaussian exponential vertical interpolation method which can better reflect the vertical variation characteristic of water vapor. GPS datasets collected in Hong Kong in February 2014 are employed to evaluate the optimized tomographic method by contrast with the conventional method. The radiosonde-derived and COSMIC-derived water vapor densities are utilized as references to evaluate the tomographic results. Using radiosonde products as references, the test results obtained from our optimized method indicate that the water vapor density accuracy is improved by 15 and 12 % compared to those derived from the conventional method below the height of 3.75 km and above the height of 3.75 km, respectively. Using the COSMIC products as references, the results indicate that the water vapor density accuracy is improved by 15 and 19 % below 3.75 km and above 3.75 km, respectively.

Tropospheric ozone as a fungal elicitor.

PubMed

Zuccarini, Paolo

2009-03-01

Tropospheric ozone has been proven to trigger biochemical plant responses that are similar to the ones induced by an attack of fungal pathogens,i.e. it resembles fungal elicitors.This suggests that ozone can represent a valid tool for the study of stress responses and induction of resistance to pathogens. This review provides an overview of the implications of such a phenomenon for basic and applied research. After an introduction about the environmental implications of tropospheric ozone and plant responses to biotic stresses, the biochemistry of ozone stress is analysed, pointing out its similarities with plant responses to pathogens and its possible applications.

Impact of Tropospheric Ozone on Summer Climate in China

NASA Astrophysics Data System (ADS)

Li, Shu; Wang, Tijian; Zanis, Prodromos; Melas, Dimitris; Zhuang, Bingliang

2018-04-01

The spatial distribution, radiative forcing, and climatic effects of tropospheric ozone in China during summer were investigated by using the regional climate model RegCM4. The results revealed that the tropospheric ozone column concentration was high in East China, Central China, North China, and the Sichuan basin during summer. The increase in tropospheric ozone levels since the industrialization era produced clear-sky shortwave and clear-sky longwave radiative forcing of 0.18 and 0.71 W m-2, respectively, which increased the average surface air temperature by 0.06 K and the average precipitation by 0.22 mm day-1 over eastern China during summer. In addition, tropospheric ozone increased the land-sea thermal contrast, leading to an enhancement of East Asian summer monsoon circulation over southern China and a weakening over northern China. The notable increase in surface air temperature in northwestern China, East China, and North China could be attributed to the absorption of longwave radiation by ozone, negative cloud amount anomaly, and corresponding positive shortwave radiation anomaly. There was a substantial increase in precipitation in the middle and lower reaches of the Yangtze River. It was related to the enhanced upward motion and the increased water vapor brought by strengthened southerly winds in the lower troposphere.

Impact of Stratospheric Ozone Zonal Asymmetries on the Tropospheric Circulation

NASA Technical Reports Server (NTRS)

Tweedy, Olga; Waugh, Darryn; Li, Feng; Oman, Luke

2015-01-01

The depletion and recovery of Antarctic ozone plays a major role in changes of Southern Hemisphere (SH) tropospheric climate. Recent studies indicate that the lack of polar ozone asymmetries in chemistry climate models (CCM) leads to a weaker and warmer Antarctic vortex, and smaller trends in the tropospheric mid-latitude jet and the surface pressure. However, the tropospheric response to ozone asymmetries is not well understood. In this study we report on a series of integrations of the Goddard Earth Observing System Chemistry Climate Model (GEOS CCM) to further examine the effect of zonal asymmetries on the state of the stratosphere and troposphere. Integrations with the full, interactive stratospheric chemistry are compared against identical simulations using the same CCM except that (1) the monthly mean zonal mean stratospheric ozone from first simulation is prescribed and (2) ozone is relaxed to the monthly mean zonal mean ozone on a three day time scale. To analyze the tropospheric response to ozone asymmetries, we examine trends and quantify the differences in temperatures, zonal wind and surface pressure among the integrations.

Ozone density measurements in the troposphere and stratosphere of Natal

NASA Technical Reports Server (NTRS)

Kirchhoff, V. W. J. H.; Motta, A. G.

1983-01-01

Ozone densitities were measured in the troposphere and stratosphere of Natal using ECC sondes launches on balloons. The data analyzed so far show tropospheric densities and total ozone contents larger than expected.

World-wide increase in tropospheric methane, 1978-1983

NASA Technical Reports Server (NTRS)

Blake, D. R.; Rowland, F. S.

1986-01-01

Techniques used to assess methane concentration in the troposphere are described, and data obtained during the period from 1978 to 1983 are presented in detail. Tropospheric methane concentrations in remote locations averaged a yearly world-wide increase of 0.018 + or - 0.002 parts per million by volume (ppmv). Average world-wide tropospheric concentration of methane in dry air was 1.625 ppmv at the end of 1983 measured against an NBS standard certified as 0.97 ppmv. Contributing to this steady increase in methane concentration are increases in the source strengths from cattle and rice fields, which in turn result from CO, CH4 and HO coupling. Among the physical and chemical effects is an increase in greenhouse warming of about 0.04 C per decade.

New Insights in Tropospheric Ozone and its Variability

NASA Technical Reports Server (NTRS)

Oman, Luke D.; Douglass, Anne R.; Ziemke, Jerry R.; Rodriquez, Jose M.

2011-01-01

We have produced time-slice simulations using the Goddard Earth Observing System Version 5 (GEOS-5) coupled to a comprehensive stratospheric and tropospheric chemical mechanism. These simulations are forced with observed sea surface temperatures over the past 25 years and use constant specified surface emissions, thereby providing a measure of the dynamically controlled ozone response. We examine the model performance in simulating tropospheric ozone and its variability. Here we show targeted comparisons results from our simulations with a multi-decadal tropical tropospheric column ozone dataset obtained from satellite observations of total column ozone. We use SHADOZ ozonesondes to gain insight into the observed vertical response and compare with the simulated vertical structure. This work includes but is not limited to ENSO related variability.

Origins of Tropospheric Ozone Interannual Variation (IAV) over Reunion: A Model Investigation

NASA Technical Reports Server (NTRS)

Liu, Junhua; Rodriguez, Jose M.; Thompson, Anne M.; Logan, Jennifer A.; Douglass, Anne R.; Olsen, Mark A.; Steenrod, Stephen D.; Posny, Francoise

2016-01-01

Observations from long-term ozonesonde measurements show robust variations and trends in the evolution of ozone in the middle and upper troposphere over Reunion Island (21.1 degrees South Latitude, 55.5 degrees East Longitude) in June-August. Here we examine possible causes of the observed ozone variation at Reunion Island using hindcast simulations by the stratosphere-troposphere Global Modeling Initiative chemical transport model for 1992-2014, driven by assimilated Modern-Era Retrospective Analysis for Research and Applications (MERRA) meteorological fields. Reunion Island is at the edge of the subtropical jet, a region of strong stratospheric-tropospheric exchange. Our analysis implies that the large interannual variation (IAV) of upper tropospheric ozone over Reunion is driven by the large IAV of the stratospheric influence. The IAV of the large-scale, quasi-horizontal wind patterns also contributes to the IAV of ozone in the upper troposphere. Comparison to a simulation with constant emissions indicates that increasing emissions do not lead to the maximum trend in the middle and upper troposphere over Reunion during austral winter implied by the sonde data. The effects of increasing emission over southern Africa are limited tothe lower troposphere near the surface in August-September.

The Tropospheric Ozone Assessment Report (TOAR): A community-wide effort to quantify tropospheric ozone in a rapidly changing world

NASA Astrophysics Data System (ADS)

Cooper, O. R.; Schultz, M.; Paoletti, E.; Galbally, I. E.; Naja, M. K.; Tarasick, D. W.; Evans, M. J.; Thompson, A. M.

2017-12-01

Tropospheric ozone is a greenhouse gas and pollutant detrimental to human health and crop and ecosystem productivity. Since 1990 a large portion of the anthropogenic emissions that react in the atmosphere to produce ozone has shifted from North America and Europe to Asia. This rapid shift, coupled with limited ozone monitoring in developing nations, left scientists unable to answer the most basic questions: Which regions of the world have the greatest human and plant exposure to ozone pollution? Is ozone continuing to decline in nations with strong emissions controls? To what extent is ozone increasing in the developing world? How can the atmospheric sciences community facilitate access to the ozone metrics necessary for quantifying ozone's impact on human health and crop/ecosystem productivity? To answer these questions the International Global Atmospheric Chemistry Project (IGAC) initiated the Tropospheric Ozone Assessment Report (TOAR). With over 220 member scientists and air quality specialists from 36 nations, TOAR's mission is to provide the research community with an up-to-date scientific assessment of tropospheric ozone's global distribution and trends from the surface to the tropopause. TOAR has also built the world's largest database of surface ozone observations and generated ozone exposure and dose metrics at thousands of measurement sites around the world, freely accessible for research on the global-scale impact of ozone on climate, human health and crop/ecosystem productivity. Plots of these metrics show the regions of the world with the greatest ozone exposure for humans and crops/ecosystems, at least in areas where observations are available. The results also highlight regions where air quality is improving and where it has degraded. TOAR has also conducted the first intercomparison of tropospheric column ozone from ozonesondes and multiple satellite instruments, which provide similar estimates of the present-day tropospheric ozone burden.

Effects of the 2004 El Nino on Tropospheric Ozone and Water Vapor

NASA Technical Reports Server (NTRS)

Chandra, S.; Ziemke, J. R.; Schoeberl, M. R.; Froidevaux, L.; Read, W. G.; Levelt, P. F.; Bhartia, P. K.

2007-01-01

The global effects of the 2004 El Nino on tropospheric ozone and H2O based on Aura OM1 and MLS measurements are analyzed. Although it was a weak El Nino from a historical perspective, it produced significant changes in these parameters in tropical latitudes. Tropospheric ozone increased by 10-20% over most of the western Pacific region and decreased by about the same amount over the eastern Pacific region. H2O in the upper troposphere showed similar changes but with opposite sign. These zonal changes in tropospheric ozone and H2O are caused by the eastward shift in the Walker circulation in the tropical pacific region during El Nino. For the 2004 El Nino, biomass burning did not have a significant effect on the ozone budget in the troposphere unlike the 1997 El Nino. Zonally averaged tropospheric column ozone did not change significantly either globally or over the tropical and subtropical latitudes.

The tropospheric emission spectrometer (TES) for the Earth Observing System (EOS)

NASA Technical Reports Server (NTRS)

Beer, R.

1992-01-01

In recent years, increasing concern has been expressed about Global Change - the natural and anthropogenic alteration of the Earth's environment involving global greenhouse warming and the associated climate change, urban and regional atmospheric pollution, acid deposition, regional increases in tropospheric zone, and the decrease in stratospheric ozone. A common theme among these problems is that they all involve those tropospheric trace gases which are fundamental to the biosphere-troposphere interaction, the chemistry of the free troposphere itself, and troposphere-stratosphere exchange. The chemical species involved all have spectral signatures within the near and mid infrared that can now be measured by advanced techniques of remote-sensing infrared spectroradiometry. Such a system is the Tropospheric Emission Spectrometer (TES), now in Phase B definition for the Earth Observing System (EOS) polar platforms. TES addresses these objectives by obtaining radiometrically calibrated, linewidth-limited spectral resolution, infrared spectra of the lower atmosphere using both natural thermal emission and reflected sunlight (where appropriate) in three different, but fully programmable, modes: a gobal mode, a pointed mode, and a limb-viewing mode. The goals of TES, its instrumentation, operational modes, sensitivity and data handling are discussed.

Feasibility of Sensing Tropospheric Ozone with MODIS 9.6 Micron Observations

NASA Technical Reports Server (NTRS)

Prabhakara, C.; Iacovazzi, R., Jr.; Moon-Yoo, Jung

2004-01-01

With the infrared observations made by the Moderate Resolution Imaging Spectrometer (MODIS) on board the EOS-Aqua satellite, which include the 9.73 micron channel, a method is developed to deduce horizontal patterns of tropospheric ozone in cloud free conditions on a scale of about 100 km. It is assumed that on such small scale, at a given instant, horizontal changes in stratospheric ozone are small compared to that in the troposphere. From theoretical simulations it is found that uncertainties in the land surface emissivity and the vertical thermal stratification in the troposphere can lead to significant errors in the inferred tropospheric ozone. Because of this reason in order to derive horizontal patterns of tropospheric ozone in a given geographic area a tuning of this method is necessary with the help of a few dependent cases. After tuning, this method is applied to independent cases of MODIS data taken over Los Angeles basin in cloud free conditions to derive horizontal distribution of ozone in the troposphere. Preliminary results indicate that the derived patterns of ozone resemble crudely the patterns of surface ozone reported by EPA.

Science Accomplishments from a Decade of Aura OMI/MLS Tropospheric Ozone Measurements

NASA Technical Reports Server (NTRS)

Ziemke, Jerald R.; Douglass, Anne R.; Joiner, Joanna; Duncan, Bryan N.; Olsen, Mark A.; Oman, Luke D.; Witte, Jacquelyn C.; Liu, X.; Wargan, K.; Schoeberl, Mark R.;

Tropospheric and stratospheric ozone from assimilation of Aura data

NASA Technical Reports Server (NTRS)

Stajner, I.; Wargan, K.; Chang, L.-P.; Hayashi, H.; Pawwson, S.; Froidevaux, L.; Livesey, N.; Bhartia, P. K.

2006-01-01

Ozone is an atmospheric trace gas with multiple impacts on the environment. Global ozone fields are needed for air quality predictions, estimation of the ultraviolet radiation reaching the surface, climate-radiation studies, and may also have an impact on longer-term weather predictions. We estimate global ozone fields in the stratosphere and troposphere by combining the data from EOS Aura satellite with an ozone model using data assimilation. Ozone exhibits a large temporal variability in the lower stratosphere. Our previous work showed that assimilation of satellite data from limb-sounding geometry helps constrain ozone profiles in that region. We assimilated ozone data from the Aura Microwave Limb Sounder (MLS) and the Ozone Monitoring Instrument (OMI) into the ozone system at NASA's Global Modeling and Assimilation Office (GMAO). Ozone is transported within a general circulation model (GCM) which includes parameterizations for stratospheric photochemistry, tropospheric chemistry, and a simple scheme for heterogeneous ozone loss. The focus of this study is on the representation of ozone in the lower stratosphere and tropospheric ozone columns. We plan to extend studies of tropospheric ozone distribution through assimilation of ozone data from the Tropospheric Emission Spectrometer (TES). Comparisons with ozone sondes and occultation data show that assimilation of Aura data reproduces ozone gradients and variability in the lower stratosphere well. We proceed by separating the contributions to temporal changes in the ozone field into those that are due to the model and those that are due to the assimilation of Aura data. The impacts of Aura data are illustrated and their role in the representation of ozone variability in the lower stratosphere and troposphere is shown.

Troposphere-to-stratosphere transport in the tropics

NASA Astrophysics Data System (ADS)

Pommereau, Jean-Pierre

2010-04-01

The analysis of the data collected over Brazil, Northern Australia and Africa from balloons, high altitude aircraft and satellites during the recent HIBISCUS, TROCCINOX, SCOUT-O3 and AMMA European campaigns, has led to significant revision in the understanding of troposphere-to-stratosphere transport. Repeated observations of strong updrafts of adiabatically cooled and washed-out tropospheric air rich in chemical and greenhouse gases by convective overshooting over the three continents, demonstrate the high frequency of occurrence of such events in contrast to their generally assumed scarcity. Moreover, global scale information provided by ODIN and CALIPSO satellite observations suggests that the mechanism could play a major, if not dominant, role in troposphere-to-stratosphere transport in contrast to the generally evoked slow ascent by radiative heating. Ignored by global scale models because of their limited extension and duration, convective overshootings might have a significant impact on the chemistry and climate of the stratosphere.

Advanced corrections for InSAR using GPS and numerical weather models

NASA Astrophysics Data System (ADS)

Foster, J. H.; Cossu, F.; Amelung, F.; Businger, S.; Cherubini, T.

2016-12-01

The complex spatial and temporal changes in the atmospheric propagation delay of the radar signal remain the single biggest factor limiting Interferometric Synthetic Aperture Radar's (InSAR) potential for hazard monitoring and mitigation. A new generation of InSAR systems is being built and launched, and optimizing the science and hazard applications of these systems requires advanced methodologies to mitigate tropospheric noise. We present preliminary results from an investigation into the application of GPS and numerical weather models for generating tropospheric correction fields. We use the Weather Research and Forecasting (WRF) model to generate a 900 m spatial resolution atmospheric model covering the Big Island of Hawaii and an even higher, 300 m resolution grid over Mauna Loa and Kilauea volcanoes. By comparing a range of approaches, from the simplest, using reanalyses based on typically available meteorological observations, through to the "kitchen-sink" approach of assimilating all relevant data sets into our custom analyses, we examine the impact of the additional data sets on the atmospheric models and their effectiveness in correcting InSAR data. We focus particularly on the assimilation of information from the more than 60 GPS sites in the island. We ingest zenith tropospheric delay estimates from these sites directly into the WRF analyses, and also perform double-difference tomography using the phase residuals from the GPS processing to robustly incorporate information on atmospheric heterogeneity from the GPS data into the models. We assess our performance through comparisons of our atmospheric models with external observations not ingested into the model, and through the effectiveness of the derived phase screens in reducing InSAR variance. This work will produce best-practice recommendations for the use of weather models for InSAR correction, and inform efforts to design a global strategy for the NISAR mission, for both low-latency and definitive

Aerosol indirect effect on tropospheric ozone via lightning

NASA Astrophysics Data System (ADS)

Yuan, Tianle; Remer, Lorraine A.; Bian, Huisheng; Ziemke, Jerald R.; Albrecht, Rachel; Pickering, Kenneth E.; Oreopoulos, Lazaros; Goodman, Steven J.; Yu, Hongbin; Allen, Dale J.

2012-09-01

Tropospheric ozone (O3) is a pollutant and major greenhouse gas and its radiative forcing is still uncertain. Inadequate understanding of processes related to O3 production, in particular those natural ones such as lightning, contributes to this uncertainty. Here we demonstrate a new effect of aerosol particles on O3production by affecting lightning activity and lightning-generated NOx (LNOx). We find that lightning flash rate increases at a remarkable rate of 30 times or more per unit of aerosol optical depth. We provide observational evidence that indicates the observed increase in lightning activity is caused by the influx of aerosols from a volcano. Satellite data analyses show O3is increased as a result of aerosol-induced increase in lightning and LNOx, which is supported by modle simulations with prescribed lightning change. O3production increase from this aerosol-lightning-ozone link is concentrated in the upper troposphere, where O3 is most efficient as a greenhouse gas. In the face of anthropogenic aerosol increase our findings suggest that lightning activity, LNOx and O3, especially in the upper troposphere, have all increased substantially since preindustrial time due to the proposed aerosol-lightning-ozone link, which implies a stronger O3 historical radiative forcing. Aerosol forcing therefore has a warming component via its effect on O3 production and this component has mostly been ignored in previous studies of climate forcing related to O3and aerosols. Sensitivity simulations suggest that 4-8% increase of column tropospheric ozone, mainly in the tropics, is expected if aerosol-lighting-ozone link is parameterized, depending on the background emission scenario. We note, however, substantial uncertainties remain on the exact magnitude of aerosol effect on tropospheric O3 via lightning. The challenges for obtaining a quantitative global estimate of this effect are also discussed. Our results have significant implications for understanding past and

Aerosol indirect effect on tropospheric ozone via lightning

NASA Astrophysics Data System (ADS)

Yuan, T.; Remer, L. A.; Bian, H.; Ziemke, J. R.; Albrecht, R. I.; Pickering, K. E.; Oreopoulos, L.; Goodman, S. J.; Yu, H.; Allen, D. J.

2012-12-01

Tropospheric ozone (O3) is a pollutant and major greenhouse gas and its radiative forcing is still uncertain. The unresolved difference between modeled and observed natural background O3 concentrations is a key source of the uncertainty. Here we demonstrate remarkable sensitivity of lightning activity to aerosol loading with lightning activity increasing more than 30 times per unit of aerosol optical depth over our study area. We provide observational evidence that indicates the observed increase in lightning activity is caused by the influx of aerosols from a volcano. Satellite data analyses suggest O3 is increased as a result of aerosol-induced increase in lightning and lightning produced NOx. Model simulations with prescribed lightning change corroborate the satellite data analysis. This aerosol-O3 connection is achieved via aerosol increasing lightning and thus lightning produced nitrogen oxides. This aerosol-lightning-ozone link provides a potential physical mechanism that may account for a part of the model-observation difference in background O3 concentration. More importantly, O3 production increase from this link is concentrated in the upper troposphere, where O3 is most efficient as a greenhouse gas. Both of these implications suggest a stronger O3 historical radiative forcing. This introduces a new pathway, through which increasing in aerosols from pre-industrial time to present day enhances tropospheric O3 production. Aerosol forcing thus has a warming component via its effect on O3 production. Sensitivity simulations suggest that 4-8% increase of tropospheric ozone, mainly in the tropics, is expected if aerosol-lighting-ozone link is parameterized, depending on the background emission scenario. We note, however, substantial uncertainties remain on the exact magnitude of aerosol effect on tropospheric O3 via lightning. The challenges for obtaining a quantitative global estimate of this effect are also discussed. Our results have significant implications

Recent Changes in Tropospheric Ozone in the Tropics

NASA Technical Reports Server (NTRS)

Chandra, S.; Ziemke, J. R.; Einaudi, Franco (Technical Monitor)

2000-01-01

This paper presents a detailed characterization of tropical tropospheric column ozone variability on time scales varying from a few days to a solar cycle. The study is based on more than 20 years (1979 to the present) of tropospheric column ozone time series derived from the convective cloud differential (CCD) method using total ozone mapping spectrometer (TOMS) data. Results indicate three distinct regions in the tropics with distinctly three different zonal characteristics related to seasonal, interannual and solar variabilities. These three regions are the eastern Pacific, Atlantic, and western Pacific. Tropospheric column ozone in the Atlantic region peaks at about the same time (September-October) from 20 N to 20 S. The amplitude of the annual cycle, however, varies from about 3 to 6 Dobson unit (DU) from north to south of the equator. In comparison, the annual cycle in both the eastern and western Pacific is generally week and the phase varies from peak values in March and April in the northern hemisphere to September and October in the southern hemisphere. The interannual pattern in the three regions are also very different. The Atlantic region indicates a quasi biennial oscillation in the tropospheric column ozone which is out of phase with the stratospheric ozone. This is consistent with the photochemical control of this region caused by high pollution and high concentration of ozone producing precursors. The observed pattern, however, does not seem to be related to the interannual variability in ozone precursors related to biomass burning. Instead, it appears to be a manifestation of the UV modulation of upper tropospheric chemistry on a QBO time scale caused by stratospheric ozone. During El Nino events, there is anomalously low ozone in the eastern Pacific and high values in the western Pacific indicating the effects of convectively driven transport. The observed increase of 10-20 DU in tropospheric column ozone in the Indonesian region in the western

Impacts of stratospheric sulfate geoengineering on tropospheric ozone

NASA Astrophysics Data System (ADS)

Xia, Lili; Nowack, Peer J.; Tilmes, Simone; Robock, Alan

2017-10-01

A range of solar radiation management (SRM) techniques has been proposed to counter anthropogenic climate change. Here, we examine the potential effects of stratospheric sulfate aerosols and solar insolation reduction on tropospheric ozone and ozone at Earth's surface. Ozone is a key air pollutant, which can produce respiratory diseases and crop damage. Using a version of the Community Earth System Model from the National Center for Atmospheric Research that includes comprehensive tropospheric and stratospheric chemistry, we model both stratospheric sulfur injection and solar irradiance reduction schemes, with the aim of achieving equal levels of surface cooling relative to the Representative Concentration Pathway 6.0 scenario. This allows us to compare the impacts of sulfate aerosols and solar dimming on atmospheric ozone concentrations. Despite nearly identical global mean surface temperatures for the two SRM approaches, solar insolation reduction increases global average surface ozone concentrations, while sulfate injection decreases it. A fundamental difference between the two geoengineering schemes is the importance of heterogeneous reactions in the photochemical ozone balance with larger stratospheric sulfate abundance, resulting in increased ozone depletion in mid- and high latitudes. This reduces the net transport of stratospheric ozone into the troposphere and thus is a key driver of the overall decrease in surface ozone. At the same time, the change in stratospheric ozone alters the tropospheric photochemical environment due to enhanced ultraviolet radiation. A shared factor among both SRM scenarios is decreased chemical ozone loss due to reduced tropospheric humidity. Under insolation reduction, this is the dominant factor giving rise to the global surface ozone increase. Regionally, both surface ozone increases and decreases are found for both scenarios; that is, SRM would affect regions of the world differently in terms of air pollution. In conclusion

Tropospheric ozone over the North Pacific from ozonesonde observations

NASA Astrophysics Data System (ADS)

Oltmans, S. J.; Johnson, B. J.; Harris, J. M.; Thompson, A. M.; Liu, H. Y.; Chan, C. Y.; VöMel, H.; Fujimoto, T.; Brackett, V. G.; Chang, W. L.; Chen, J.-P.; Kim, J. H.; Chan, L. Y.; Chang, H.-W.

2004-08-01

As part of the Transport and Chemical Evolution over the Pacific (TRACE-P) mission, ozonesondes were used to make ozone vertical profile measurements at nine locations in the North Pacific. At most of the sites there is a multiyear record of observations. From locations in the western Pacific (Hong Kong; Taipei; Jeju Island, Korea; and Naha, Kagoshima, Tsukuba, and Sapporo, Japan), a site in the central Pacific (Hilo, Hawaii), and a site on the west coast of the United States (Trinidad Head, California) both a seasonal and event specific picture of tropospheric ozone over the North Pacific emerges. Ozone profiles over the North Pacific generally show a prominent spring maximum throughout the troposphere. This maximum is tied to the location of the jet stream and its influence on stratosphere-troposphere exchange and the increase in photochemical ozone production through the spring. Prominent layers of enhanced ozone in the middle and upper troposphere north of about 30°N seem to be more closely tied to stratospheric intrusions while biomass burning leads to layers of enhanced ozone in the lower and upper troposphere at Hong Kong (22°N) and Taipei (25°N). The lower free tropospheric layers at Hong Kong are associated with burning in SE Asia, but the upper layer may be associated with either equatorial Northern Hemisphere burning in Africa or SE Asian biomass burning. In the boundary layer at Taipei very high mixing ratios of ozone were observed that result from pollution transport from China in the spring and local urban pollution during the summer. At the ozonesonde site near Tokyo (Tsukuba, 36°N) very large enhancements of ozone are seen in the boundary layer in the summer that are characteristic of urban air pollution. At sites in the mid and eastern Pacific the signature of transport of polluted air from Asia is not readily identifiable from the ozonesonde profile. This is likely due to the more subtle signal and the fact that from the ozone profile and

Tropospheric emissions: monitoring of pollution (TEMPO)

NASA Astrophysics Data System (ADS)

Chance, Kelly; Liu, Xiong; Suleiman, Raid M.; Flittner, David E.; Al-Saadi, Jassim; Janz, Scott J.

2013-09-01

TEMPO was selected in 2012 by NASA as the first Earth Venture Instrument, for launch circa 2018. It will measure atmospheric pollution for greater North America from space using ultraviolet and visible spectroscopy. TEMPO measures from Mexico City to the Canadian tar sands, and from the Atlantic to the Pacific, hourly and at high spatial resolution (~2 km N/S×4.5 km E/W at 36.5°N, 100°W). TEMPO provides a tropospheric measurement suite that includes the key elements of tropospheric air pollution chemistry. Measurements are from geostationary (GEO) orbit, to capture the inherent high variability in the diurnal cycle of emissions and chemistry. The small product spatial footprint resolves pollution sources at sub-urban scale. Together, this temporal and spatial resolution improves emission inventories, monitors population exposure, and enables effective emission-control strategies. TEMPO takes advantage of a commercial GEO host spacecraft to provide a modest cost mission that measures the spectra required to retrieve O3, NO2, SO2, H2CO, C2H2O2, H2O, aerosols, cloud parameters, and UVB radiation. TEMPO thus measures the major elements, directly or by proxy, in the tropospheric O3 chemistry cycle. Multi-spectral observations provide sensitivity to O3 in the lowermost troposphere, substantially reducing uncertainty in air quality predictions. TEMPO quantifies and tracks the evolution of aerosol loading. It provides near-real-time air quality products that will be made widely, publicly available. TEMPO will launch at a prime time to be the North American component of the global geostationary constellation of pollution monitoring together with European Sentinel-4 and Korean GEMS.

Satellite Observations of Tropospheric Ammonia

NASA Astrophysics Data System (ADS)

Shephard, M. W.; Luo, M.; Rinsland, C. P.; Cady-Pereira, K. E.; Beer, R.; Pinder, R. W.; Henze, D.; Payne, V. H.; Clough, S.; Rodgers, C. D.; Osterman, G. B.; Bowman, K. W.; Worden, H. M.

2008-12-01

Global high-spectral resolution (0.06 cm-1) nadir measurements from TES-Aura enable the simultaneous retrieval of a number of tropospheric pollutants and trace gases in addition to the TES standard operationally retrieved products (e.g. carbon monoxide, ozone). Ammonia (NH3) is one of the additional species that can be retrieved in conjunction with the TES standard products, and is important for local, regional, and global tropospheric chemistry studies. Ammonia emissions contribute significantly to several well-known environmental problems, yet the magnitude and seasonal/spatial variability of the emissions are poorly constrained. In the atmosphere, an important fraction of fine particulate matter is composed of ammonium nitrate and ammonium sulfate. These particles are statistically associated with health impacts. When deposited to ecosystems in excess, nitrogen, including ammonia can cause nutrient imbalances, change in ecosystem species composition, eutrophication, algal blooms and hypoxia. Ammonia is also challenging to measure in-situ. Observations of surface concentrations are rare and are particularly sparse in North America. Satellite observations of ammonia are therefore highly desirable. We recently demonstrated that tropospheric ammonia is detectable in the TES spectra and presented some corresponding preliminary retrievals over a very limited range of conditions (Beer et al., 2008). Presented here are results that expand upon these initial TES ammonia retrievals in order to evaluate/validate the retrieval results utilizing in-situ surface observations (e.g. LADCO, CASTNet, EPA /NC State) and chemical models (e.g. GEOS-Chem and CMAQ). We also present retrievals over regions of interest that have the potential to help further understand air quality and the active nitrogen cycle. Beer, R., M. W. Shephard, S. S. Kulawik, S. A. Clough, A. Eldering, K. W. Bowman, S. P. Sander, B. M. Fisher, V. H. Payne, M. Luo, G. B. Osterman, and J. R. Worden, First

Simultaneous presence of O3 and CO bands in the troposphere

NASA Technical Reports Server (NTRS)

Fishman, J.; Seiler, W.; Haagenson, P.

1980-01-01

Vertical profiles of CO and O3 in the troposphere and lower stratosphere have been constructed during a series of flights conducted in July and August 1974 over the American continents between 53 deg S and 67 deg N. The mixing ratios of both gases show large fluctuations with altitude in the Northern Hemisphere. Most of the observed bands of O3 in the free troposphere are coexistent with elevated CO concentrations indicating that this O3 is probably not of stratospheric origin, but most likely produced in the troposphere. From the observations, it is not clear whether these high concentrations of ozone were produced in situ in the remote troposphere or had been transported out of a polluted boundary layer. Isentropic trajectory calculations likewise indicate that the air containing these elevated ozone and carbon monoxide concentrations had been situated in the troposphere for at least 72 h prior to being sampled.

Origins of tropospheric ozone interannual variation over Réunion: A model investigation

NASA Astrophysics Data System (ADS)

Liu, Junhua; Rodriguez, Jose M.; Thompson, Anne M.; Logan, Jennifer A.; Douglass, Anne R.; Olsen, Mark A.; Steenrod, Stephen D.; Posny, Françoise

2016-01-01

Observations from long-term ozonesonde measurements show robust variations and trends in the evolution of ozone in the middle and upper troposphere over Réunion Island (21.1°S, 55.5°E) in June-August. Here we examine possible causes of the observed ozone variation at Réunion Island using hindcast simulations by the stratosphere-troposphere Global Modeling Initiative chemical transport model for 1992-2014, driven by assimilated Modern-Era Retrospective Analysis for Research and Applications meteorological fields. Réunion Island is at the edge of the subtropical jet, a region of strong stratospheric-tropospheric exchange. Our analysis implies that the large interannual variation (IAV) of upper tropospheric ozone over Réunion is driven by the large IAV of the stratospheric influence. The IAV of the large-scale, quasi-horizontal wind patterns also contributes to the IAV of ozone in the upper troposphere. Comparison to a simulation with constant emissions indicates that increasing emissions do not lead to the maximum trend in the middle and upper troposphere over Réunion during austral winter implied by the sonde data. The effects of increasing emission over southern Africa are limited to the lower troposphere near the surface in August-September.

Tropospheric Halogen Chemistry

NASA Astrophysics Data System (ADS)

von Glasow, R.; Crutzen, P. J.

2003-12-01

Halogens are very reactive chemicals that are known to play an important role in anthropogenic stratospheric ozone depletion chemistry, first recognized by Molina and Rowland (1974). However, they also affect the chemistry of the troposphere. They are of special interest because they are involved in many reaction cycles that can affect the oxidation power of the atmosphere indirectly by influencing the main oxidants O3 and its photolysis product OH and directly, e.g., by reactions of the Cl radical with hydrocarbons (e.g., CH4).Already by the middle of the nineteenth century, Marchand (1852) reported the presence of bromine and iodine in rain and other natural waters. He also mentions the benefits of iodine in drinking water through the prevention of goitres and cretinism. In a prophetic monograph "Air and Rain: The Beginnings of a Chemical Climatology," Smith (1872) describes measurements of chloride in rain water, which he states to originate partly from the oceans by a process that he compares with the bursting of "soap bubbles" which produces "small vehicles" that transfer small spray droplets of seawater to the air. From deviations of the sulfate-to-chloride ratio in coastal rain compared to seawater, Smith concluded that chemical processes occur once the particles are airborne.For almost a century thereafter, however, atmospheric halogens received little attention. One exception was the work by Cauer (1939), who reported that iodine pollution has been significant in Western and Central Europe due to the inefficient burning of seaweed, causing mean gas phase atmospheric concentrations as high as or greater than 0.5 μg m-3. In his classical textbook Air Chemistry and Radioactivity, Junge (1963) devoted less than three pages to halogen gas phase chemistry, discussing chlorine and iodine. As reviewed by Eriksson (1959a, b), the main atmospheric source of halogens is sea salt, derived from the bursting of bubbles of air which are produced by ocean waves and other

Stratospheric Ozone Distribution and Tropospheric General Circulation: Interconnections in the UTLS Region

NASA Astrophysics Data System (ADS)

Barodka, S.; Krasovsky, A.; Shalamyansky, A.

2014-12-01

The height of the tropopause, which divided the stratosphere and the troposphere, is a result of two rival categories of processes: the tropospheric vertical convection and the radiative heating of the stratosphere resulting from the ozone cycle. Hence, it is natural that tropospheric and stratospheric phenomena can have effect each other in manifold processes of stratosphere-troposphere interactions. In the present study we focus our attention to the "top-down" side of the interaction: the impact of stratospheric ozone distribution on the features of tropospheric circulation and the associated weather patterns and regional climate conditions. We proceed from analyzes of the observational data performed at the A.I. Voeikov Main Geophysical Observatory, which suggest a distinct correlation between stratospheric ozone distribution, synoptic formations and air-masses boundaries in the upper troposphere and the temperature field of the lower stratosphere [1]. Furthermore, we analyze local features of atmospheric general circulation and stratospheric ozone distribution from the atmospheric reanalyses and general circulation model data, focusing our attention to instantaneous positions of subtropical and polar stationary atmospheric fronts, which define regional characteristics of the general circulation cells in the troposphere and separate global tropospheric air-masses, correspond to distinct meteorological regimes in the TOC field [2, 3]. We assume that by altering the tropopause height, stratospheric ozone-related processes can have an impact on the location of the stationary atmospheric fronts, thereby exerting influence on circulation processes in troposphere and lower stratosphere. For midlatitudes, the tropopause height controls the position of the polar stationary front, which has a direct impact on the trajectory of motion of active vortices on synoptic tropospheric levels, thereby controlling weather patterns in that region and the regional climate. This

DIAL Measurements of Free-Tropospheric Ozone Profiles in Huntsville, AL

NASA Technical Reports Server (NTRS)

Kuang, Shi; Burris, John; Newchurch, Michael J.; Johnson, Steve

2007-01-01

A tropospheric ozone Differential Absorption Lidar (DIAL) system, developed jointly by NASA and the University of Alabama at Huntsville (UAH), measures free-tropospheric ozone profiles between 4-10 km. Located at 192 meters altitude in the Regional Atmospheric Profiling Laboratory for Discovery (RAPCD) on the UAH campus in Huntsville, AL, USA, this tropospheric ozone lidar operates under both daytime and nighttime conditions. Frequent coincident ozonesonde flights and theoretical calculations provide evidence to indicate the retrieval accuracy ranges from better than 8% at 4km to 40%-60% at 10 kin with 750-m vertical resolution and 30-minute integration. With anticipated improvements to allow retrievals at both higher and lower altitudes, this ozone lidar, along with co-located aerosol and Doppler Wind Lidars, will provide a unique 18 dataset for investigations of PBL and free-tropospheric chemical and dynamic processes.

Tropical Tropospheric Ozone: New Insights from Remote Sensing and Field Studies

NASA Technical Reports Server (NTRS)

Thompson, Anne

1999-01-01

This talk will summarize our recent research in tropical tropospheric ozone studies in the field and from space. New tropospheric ozone and aerosol products from the TOMS (Total Ozone Mapping Spectrometer) satellite instrument will be highlighted (Hudson and Thompson, 1998; Thompson and Hudson, 1999). These are suitable for studying processes like ozone pollution resulting from biomass fires, seasonal and interannual variations and trends. Archived maps of tropospheric ozone over the tropics, from the Nimbus 7 observing period (1979-1992) are available in digital form at our website. Real-time processing of TOMS data has produced images of tropical tropospheric ozone (TTO) since early 1997, using Earth-Probe TOMS; these maps are also available on the homepage.

Upper tropospheric ice sensitivity to sulfate geoengineering

NASA Astrophysics Data System (ADS)

Visioni, Daniele; Pitari, Giovanni; Mancini, Eva

2017-04-01

In light of the Paris Agreement which aims to keep global warming under 2 °C in the next century and considering the emission scenarios produced by the IPCC for the same time span, it is likely that to remain below that threshold some kind of geoengineering technique will have to be deployed. Amongst the different methods, the injection of sulfur into the stratosphere has received much attention considering its effectiveness and affordability. Aside from the rather well established surface cooling sulfate geoengineering (SG) would produce, the investigation on possible side-effects of this method is still ongoing. For instance, some recent studies have investigated the effect SG would have on upper tropospheric cirrus clouds, expecially on the homogenous freezing mechanisms that produces the ice particles (Kuebbeler et al., 2012). The goal of the present study is to better understand the effect of thermal and dynamical anomalies caused by SG on the formation of ice crystals via homogeneous freezing by comparing a complete SG simulation with a RCP4.5 reference case and with a number of sensitivity studies where atmospheric temperature changes in the upper tropospheric region are specified in a schematic way as a function of the aerosol driven stratospheric warming and mid-lower tropospheric cooling. These changes in the temperature profile tend to increase atmospheric stabilization, thus decreasing updraft and with it the amount of water vapor available for homogeneous freezing in the upper troposphere. However, what still needs to be assessed is the interaction between this dynamical effect and the thermal effects of tropospheric cooling (which would increase ice nucleation rates) and stratospheric warming (which would probably extend to the uppermost troposphere via SG aerosol gravitational settling, thus reducing ice nucleation rates), in order to understand how they combine together. Changes in ice clouds coverage could be important for SG, because cirrus ice

Tropospheric Ozone Lidar Network (TOLNet) - Long-term Tropospheric Ozone and Aerosol Profiling for Satellite Continuity and Process Studies

NASA Astrophysics Data System (ADS)

Newchurch, M.; Al-Saadi, J. A.; Alvarez, R. J.; Burris, J.; Cantrell, W.; Chen, G.; De Young, R.; Hardesty, R.; Hoff, R. M.; Kaye, J. A.; kuang, S.; Langford, A. O.; LeBlanc, T.; McDermid, I. S.; McGee, T. J.; Pierce, R.; Senff, C. J.; Sullivan, J. T.; Szykman, J.; Tonnesen, G.; Wang, L.

2012-12-01

An interagency research initiative for ground-based ozone and aerosol lidar profiling recently funded by NASA has important applications to air-quality studies in addition to the goal of serving the GEO-CAPE and other air-quality missions. Ozone is a key trace-gas species, a greenhouse gas, and an important pollutant in the troposphere. High spatial and temporal variability of ozone affected by various physical and photochemical processes motivates the high spatio-temporal lidar profiling of tropospheric ozone for improving the simulation and forecasting capability of the photochemical/air-quality models, especially in the boundary layer where the resolution and precision of satellite retrievals are fundamentally limited. It is well known that there are large discrepancies between the surface and upper-air ozone due to titration, surface deposition, diurnal processes, free-tropospheric transport, and other processes. Near-ground ozone profiling has been technically challenging for lidars due to some engineering difficulties, such as near-range saturation, field-of-view overlap, and signal processing issues. This initiative provides an opportunity for us to solve those engineering issues and redesign the lidars aimed at long-term, routine ozone/aerosol observations from the near surface to the top of the troposphere at multiple stations (i.e., NASA/GSFC, NASA/LaRC, NASA/JPL, NOAA/ESRL, UAHuntsville) for addressing the needs of NASA, NOAA, EPA and State/local AQ agencies. We will present the details of the science investigations, current status of the instrumentation development, data access/protocol, and the future goals of this lidar network. Ozone lidar/RAQMS comparison of laminar structures.

A relation between landsat digital numbers, surface reflectance, and the cosine of the solar zenith angle

USGS Publications Warehouse

Kowalik, William S.; Marsh, Stuart E.; Lyon, Ronald J. P.

1982-01-01

A method for estimating the reflectance of ground sites from satellite radiance data is proposed and tested. The method uses the known ground reflectance from several sites and satellite data gathered over a wide range of solar zenith angles. The method was tested on each of 10 different Landsat images using 10 small sites in the Walker Lake, Nevada area. Plots of raw Landsat digital numbers (DNs) versus the cosine of the solar zenith angle (cos Z) for the the test areas are linear, and the average correlation coefficients of the data for Landsat bands 4, 5, 6, and 7 are 0.94, 0.93, 0.94, and 0.94, respectively. Ground reflectance values for the 10 sites are proportional to the slope of the DN versus cos Z relation at each site. The slope of the DN versus cos Z relation for seven additional sites in Nevada and California were used to estimate the ground reflectances of those sites. The estimates for nearby sites are in error by an average of 1.2% and more distant sites are in error by 5.1%. The method can successfully estimate the reflectance of sites outside the original scene, but extrapolation of the reflectance estimation equations to other areas may violate assumptions of atmospheric homogeneity.

AO/NAO Response to Climate Change. 1; Respective Influences of Stratospheric and Tropospheric Climate Changes

NASA Technical Reports Server (NTRS)

Rind, D.; Perlwitz, J.; Lonergan, P.

2005-01-01

We utilize the GISS Global Climate Middle Atmosphere Model and 8 different climate change experiments, many of them focused on stratospheric climate forcings, to assess the relative influence of tropospheric and stratospheric climate change on the extratropical circulation indices (Arctic Oscillation, AO; North Atlantic Oscillation, NAO). The experiments are run in two different ways: with variable sea surface temperatures (SSTs) to allow for a full tropospheric climate response, and with specified SSTs to minimize the tropospheric change. The results show that tropospheric warming (cooling) experiments and stratospheric cooling (warming) experiments produce more positive (negative) AO/NAO indices. For the typical magnitudes of tropospheric and stratospheric climate changes, the tropospheric response dominates; results are strongest when the tropospheric and stratospheric influences are producing similar phase changes. Both regions produce their effect primarily by altering wave propagation and angular momentum transports, but planetary wave energy changes accompanying tropospheric climate change are also important. Stratospheric forcing has a larger impact on the NAO than on the AO, and the angular momentum transport changes associated with it peak in the upper troposphere, affecting all wavenumbers. Tropospheric climate changes influence both the A0 and NAO with effects that extend throughout the troposphere. For both forcings there is often vertical consistency in the sign of the momentum transport changes, obscuring the difference between direct and indirect mechanisms for influencing the surface circulation.

Clouds and Hazes in Saturn's Troposphere and Stratosphere

NASA Astrophysics Data System (ADS)

Merlet, Cecile; Irwin, P.; Fletcher, L.

2012-10-01

We present new results from the analysis of Saturn's near-infrared spectra measured with the Visual and Infrared Mapping Spectrometer (VIMS) instrument on the Cassini orbiter. VIMS near-infrared data are particularly relevant for the study of clouds and hazes in the troposphere and stratosphere of Saturn. Thermal emission in the 4.5-5.1 wavelength range is absorbed and scattered mainly by tropospheric clouds and radiatively active gases. The vertical structure as well as the optical and physical properties of tropospheric aerosols are obtained from Saturn's thermal emission spectra by using the retrieval algorithm Nemesis. The distribution of tropospheric phosphine and ammonia in gas phase will also be presented here. We managed to break the degeneracies inherent to the retrieval problem by analysing Saturn's thermal emission simultaneously at various viewing geometries. By using this method, we found that VIMS spectra at 4.5-5.1 microns are also sensitive to the hazes formed above the cloud layers. Saturn's reflected sunlight spectra at 0.8-3.5 microns measured with VIMS were also analysed in order to constrain the haze properties in the upper troposphere and lower stratosphere of the planet. Results from both the 0.8-3.5 and 4.5-5.1 wavelength ranges were combined to determine the cloud and haze model most consistent with VIMS spectroscopy over a wide range of viewing geometries and lighting conditions. An increase of temperature below the tropopause, often referred to as the temperature knee, was retrieved from Cassini/CIRS spectra. Seasonal variations of the knee and haze structure are compared, and as a result the assumption of local heating by the hazes to explain this feature will be discussed.

NASA Tropospheric Emission Spectrometer TES Instrument Onboard Aura

NASA Image and Video Library

2004-04-01

Technicians install NASA's Tropospheric Emission Spectrometer (TES) instrument on NASA's Aura spacecraft prior to launch. Launched in July 2004 and designed to fly for two years, the TES mission is currently in an extended operations phase. Mission managers at NASA's Jet Propulsion Laboratory, Pasadena, California, are evaluating an alternate way to collect and process science data from the Tropospheric Emission Spectrometer (TES) instrument on NASA's Aura spacecraft following the age-related failure of a critical instrument component. TES is an infrared sensor designed to study Earth's troposphere, the lowermost layer of Earth's atmosphere, which is where we live. The remainder of the TES instrument, and the Aura spacecraft itself, are operating as expected, and TES continues to collect science data. TES is one of four instruments on Aura, three of which are still operating. http://photojournal.jpl.nasa.gov/catalog/PIA15608

The Variability of the Horizontal Circulation in the Troposphere and Stratosphere: A Comparison

NASA Technical Reports Server (NTRS)

Perlwitz, Judith; Graf, Hans-F.; Hansem, James E. (Technical Monitor)

2001-01-01

The variability of the horizontal circulation in the stratosphere and troposphere of the Northern Hemisphere (NH) is compared by using various approaches. Spatial degrees of freedom (dof) on different time scales were derived. Modes of variability were computed in geopotential height fields at the tropospheric and stratospheric pressure levels by applying multivariate statistical approaches. Features of the spatial and temporal variability of the winterly zonal wind were studied with the help of recurrence and persistence analyses. The geopotential height and zonally-averaged zonal wind at the 50-, 500- and 1000-hPa level are used to investigate the behavior of the horizontal circulation in the lower stratosphere, mid-troposphere and at the near surface level, respectively. It is illustrated that the features of the variability of the horizontal circulation are very similar in the mid-troposphere and at the near surface level. Due to the filtering of tropospheric disturbances by the stratospheric and upper tropospheric zonal mean flow, the variability of the stratospheric circulation exhibits less spatial complexity than the circulation at tropospheric pressure levels. There exist enormous differences in the number of degrees of freedom (or free variability modes) between both atmospheric layers. Results of the analyses clearly show that the concept of a zonally symmetric AO with a simple structure in the troposphere similar to the one in the stratosphere is not valid. It is concluded that the spatially filtered climate change signal can be detected earlier in the stratosphere than in the mid-troposphere or at the near surface level.

On the relationship between tropospheric conditions and widespread hot days in Iran

NASA Astrophysics Data System (ADS)

Asakereh, Hossein; Shadman, Hassan

2018-01-01

The present study investigated how the tropospheric conditions relate to the occurrence of widespread hot days (WHD) in Iran using the data of maximum daily temperature and other tropospheric variables. To better understand the tropospheric conditions during WHD, different patterns of tropospheric circulation were examined systematically. Four tropospheric types were identified based on sea level pressure (SLP). SLP, 500 hPa height, anomaly patterns, and warm advection maps were constructed for typical days of each group. The tropospheric conditions associated with hot days occurred simultaneously with a low-pressure system at sea level, a ridge at middle troposphere over Iran, and a pronounced trough over the Mediterranean Sea at 500 hPa. These conditions caused air mass from subtropical regions toward Iran. That is, northward, northeastward, and even eastward winds injected heat with warm origins toward the country. Hot days compounded by drought conditions have affected many parts of the country in different ways such as decrease in the agricultural products in numerous areas and significant discharge reduction in many rivers. The society is also very likely to face considerable challenges to cope with hot days. The findings of the study can be utilized in climate modeling and climate prediction of hot days in the country. Accordingly, water and electricity consumption can be planned with further precision and water consumption can be managed in crises.

The role of isoprene oxidation in the tropospheric ozone budget in the tropics

NASA Technical Reports Server (NTRS)

Brewer, D. A.; Levine, J. S.

1985-01-01

A comprehensive chemical mechanism for the oxidation of isoprene (a hydrocarbon, C5H8 emitted primarily by vegetation) by OH and O3 in the troposphere was developed and incorporated into a one-dimensional steady-state photochemical model of the troposphere. Flux boundary conditions for NOx (NO + NO2), HNO3, O3, and CO were used to investigate the changes produced in the tropospheric concentrations and integrated column of ozone from including isoprene chemistry in the model. Two calculations were performed at 15 deg N latitude for annual conditions using identical flux boundary conditions for NOx, HNO3, O3, and CO; in one calculation, the chemistry describing isoprene oxidation was included while in the other it was not. Both sets of calculations included reactions describing the chemistry of anthropogenic nonmethane hydrocarbons. The calculations showed decreases in concentrations of ozone throughout the troposphere when isoprene chemistry was included. Concentrations of NOx and HNO3 increased in the lower troposphere and decreased in the upper troposphere while concentrations of CO and PAN increased throughout the troposphere when isoprene chemistry was included. Implications of this study to the budgets of these species in the tropics is discussed.

Long-term tropospheric and lower stratospheric ozone variations from ozonesonde observations

NASA Technical Reports Server (NTRS)

London, J.; Liu, S. C.

1992-01-01

An analysis is presented of the long-term mean pressure-latitude seasonal distribution of tropospheric and lower stratospheric ozone for the four seasons covering, in part, over 20 years of ozonesonde data. The observed patterns show minimum ozone mixing ratios in the equatorial and tropical troposphere except in regions where net photochemical production is dominant. In the middle and upper troposphere, and low stratosphere to 50 mb, ozone increases from the tropics to subpolar latitudes of both hemispheres. In mid stratosphere, the ozone mixing ratio is a maximum over the tropics. The observed vertical ozone gradient is small in the troposphere but increases rapidly above the tropopause. The amplitude of the annual variation increases from a minimum in the tropics to a maximum in polar regions. Also, the amplitude increases with height at all latitudes up to about 30 mb where the phase of the annual variation changes abruptly. The phase of the annual variation is during spring in the boundary layer, summer in mid troposphere, and spring in the upper troposhere and lower stratosphere.

A Madden-Julian Oscillation in Tropospheric Ozone

NASA Technical Reports Server (NTRS)

Ziemke, J. R.; Chandra, S.

2004-01-01

This is the first study to indicate a Madden-Julian Oscillation (MJO) in tropospheric ozone. Tropospheric ozone is derived using differential measurements of total column ozone and stratospheric column ozone measured from total ozone mapping spectrometer (TOMS) and microwave limb sounder (MLS) instruments. Two broad regions of significant MJO signal are identified in the tropics, one in the western Pacific and the other in the eastern Pacific. Over both regions, MJO variations in tropospheric ozone represent 5- 10 DU peak-to-peak anomalies. These variations are significant compared to mean background amounts of 20 DU or less over most of the tropical Pacific. The implications of these results are: (1) model values of TCO in the tropical Pacific region, when accounted for the MJO may be highly variable depending upon the phase of the MJO, and (2) MJO signals of this magnitude would need to be considered when investigating and interpreting particular pollution events since ozone is a precursor of the hydroxyl (OH) radical, the main oxidizing agent of pollutants in the lower atmosphere.

The Impact of Upper Tropospheric Humidity from Microwave Limb Sounder on the Midlatitude Greenhouse Effect

NASA Technical Reports Server (NTRS)

Hu, Hua; Liu, W. Timothy

1998-01-01

This paper presents an analysis of upper tropospheric humidity, as measured by the Microwave Limb Sounder, and the impact of the humidity on the greenhouse effect in the midlatitudes. Enhanced upper tropospheric humidity and an enhanced greenhouse effect occur over the storm tracks in the North Pacific and North Atlantic. In these areas, strong baroclinic activity and the large number of deep convective clouds transport more water vapor to the upper troposphere, and hence increase greenhouse trapping. The greenhouse effect increases with upper tropospheric humidity in areas with a moist upper troposphere (such as areas over storm tracks), but it is not sensitive to changes in upper tropospheric humidity in regions with a dry upper troposphere, clearly demonstrating that there are different mechanisms controlling the geographical distribution of the greenhouse effect in the midlatitudes.

Tropospheric Emissions: Monitoring of Pollution (TEMPO)

NASA Astrophysics Data System (ADS)

Chance, K.; Liu, X.; Suleiman, R. M.; Flittner, D. E.; Al-Saadi, J. A.; Janz, S. J.; Tempo Science Team

2013-05-01

TEMPO has been selected by NASA as the first Earth Venture Instrument. It will measure atmospheric pollution for greater North America from space using ultraviolet/visible spectroscopy. TEMPO measures from Mexico City to the Canadian tar/oil sands, and from the Atlantic to the Pacific, hourly and at high spatial resolution (Mexico City is measured at 1.6 km N/S by 4.5 km E/W). TEMPO provides a tropospheric measurement suite that includes the key elements of tropospheric air pollution chemistry. Measurements are from geostationary (GEO) orbit, to capture the inherent high variability in the diurnal cycle of emissions and chemistry. The small product spatial footprint resolves pollution sources at sub-urban scale. Together, this temporal and spatial resolution improves emission inventories, monitors population exposure, and enables effective emission-control strategies. TEMPO takes advantage of a GEO host spacecraft to provide a modest cost mission that measures the spectra required to retrieve O3, NO2, SO2, H2CO, C2H2O2, H2O, aerosols, cloud parameters, and UVB radiation. TEMPO thus measures the major elements, directly or by proxy, in the tropospheric O3 chemistry cycle. Multi-spectral observations provide sensitivity to O3 in the lowermost troposphere, reducing uncertainty in air quality predictions by 50%. TEMPO quantifies and tracks the evolution of aerosol loading. It provides near-real-time air quality products that will be made widely, publicly available. TEMPO makes the first tropospheric trace gas measurements from GEO, by building on the heritage of five spectrometers flown in low-earth-orbit (LEO). These LEO instruments measure the needed spectra, although at coarse spatial and temporal resolutions, to the precisions required for TEMPO and use retrieval algorithms developed for them by TEMPO Science Team members and currently running in operational environments. This makes TEMPO an innovative use of a well proven technique, able to produce a revolutionary

Tropospheric Emissions: Monitoring of Pollution (TEMPO)

NASA Astrophysics Data System (ADS)

Chance, Kelly; Liu, Xiong; Suleiman, Raid M.; Flittner, David E.; Al-Saadi, Jassim; Janz, Scott J.

2014-06-01

TEMPO, selected by NASA as the first Earth Venture Instrument, will measure atmospheric pollution for greater North America from space using ultraviolet and visible spectroscopy. TEMPO measures from Mexico City to the Canadian oil sands, and from the Atlantic to the Pacific, hourly and at high spatial resolution. TEMPO provides a tropospheric measurement suite that includes the key elements of tropospheric air pollution chemistry. Measurements are from geostationary (GEO) orbit, to capture the inherent high variability in the diurnal cycle of emissions and chemistry. The small product spatial footprint resolves pollution sources at sub-urban scale. Together, this temporal and spatial resolution improves emission inventories, monitors population exposure, and enables effective emission-control strategies. TEMPO takes advantage of a GEO host spacecraft to provide a modest-cost mission that measures the spectra required to retrieve O3, NO2, SO2, H2CO, C2H2O2, H2O, aerosols, cloud parameters, and UVB radiation. TEMPO thus measures the major elements, directly or by proxy, in the tropospheric O3 chemistry cycle. Multi-spectral observations provide sensitivity to O3 in the lowermost troposphere, reducing uncertainty in air quality predictions by 50 %. TEMPO quantifies and tracks the evolution of aerosol loading. It provides near-real-time air quality products that will be made widely, publicly available. TEMPO makes the first tropospheric trace gas measurements from GEO, by building on the heritage of five spectrometers flown in low-earth-orbit (LEO). These LEO instruments measure the needed spectra, although at coarse spatial and temporal resolutions, to the precisions required for TEMPO and use retrieval algorithms developed for them by TEMPO Science Team members and currently running in operational environments. This makes TEMPO an innovative use of a well-proven technique, able to produce a revolutionary data set. TEMPO provides much of the atmospheric measurement

Tropospheric Emissions: Monitoring of Pollution (TEMPO)

NASA Astrophysics Data System (ADS)

Chance, K.; Liu, X.; Suleiman, R. M.; Flittner, D. E.; Janz, S. J.

2012-12-01

TEMPO is a proposed concept to measure pollution for greater North America using ultraviolet/visible spectroscopy. TEMPO measures from Mexico City to the Canadian tar/oil sands, and from the Atlantic to the Pacific, hourly and at high spatial resolution (9 km2). TEMPO provides a tropospheric measurement suite that includes the key elements of tropospheric air pollution chemistry. Measurements are from geostationary (GEO) orbit, to capture the inherent high variability in the diurnal cycle of emissions and chemistry. The small product spatial footprint resolves pollution sources at sub-urban scale. Together, this temporal and spatial resolution improves emission inventories, monitors population exposure, and enables effective emission-control strategies. TEMPO takes advantage of a GEO host spacecraft to provide a modest cost mission that measures the spectra required to retrieve O3, NO2, SO2, H2CO, C2H2O2, H2O, aerosols, cloud parameters, and UVB radiation. TEMPO thus measures the major elements, directly or by proxy, in the tropospheric O3 chemistry cycle. Multi-spectral observations provide sensitivity to O3 in the lowermost troposphere, reducing uncertainty in air quality predictions by 50%. TEMPO quantifies and tracks the evolution of aerosol loading. It provides near-real-time air quality products that will be made widely, publicly available. TEMPO makes the first tropospheric trace gas measurements from GEO, by building on the heritage of five spectrometers flown in low-earth-orbit (LEO). These LEO instruments measure the needed spectra, although at coarse spatial and temporal resolutions, to the precisions required for TEMPO and use retrieval algorithms developed for them by TEMPO Science Team members and currently running in operational environments. This makes TEMPO an innovative use of a well proven technique, able to produce a revolutionary data set. TEMPO provides much of the atmospheric measurement capability recommended for GEO-CAPE in the 2007

The Response of Tropical Tropospheric Ozone to ENSO

NASA Technical Reports Server (NTRS)

Oman, L. D.; Ziemke, J. R.; Douglass, A. R.; Waugh, D. W.; Lang, C.; Rodriguez, J. M.; Nielsen, J. E.

2011-01-01

We have successfully reproduced the Ozone ENSO Index (OEI) in the Goddard Earth Observing System (GEOS) chemistry-climate model (CCM) forced by observed sea surface temperatures over a 25-year period. The vertical ozone response to ENSO is consistent with changes in the Walker circulation. We derive the sensitivity of simulated ozone to ENSO variations using linear regression analysis. The western Pacific and Indian Ocean region shows similar positive ozone sensitivities from the surface to the upper troposphere, in response to positive anomalies in the Nino 3.4 Index. The eastern and central Pacific region shows negative sensitivities with the largest sensitivity in the upper troposphere. This vertical response compares well with that derived from SHADOZ ozonesondes in each region. The OEI reveals a response of tropospheric ozone to circulation change that is nearly independent of changes in emissions and thus it is potentially useful in chemistry-climate model evaluation.

Effect of Ram and Zenith Exposure on the Optical Properties of Polymers in Space

NASA Technical Reports Server (NTRS)

Li, Yuachun; de Groh, Kim K.; Banks, Bruce A.; Leneghan, Halle; Asmar, Olivia

2017-01-01

The temperature of spacecraft is influenced by the solar absorptance and thermal emittance of the external spacecraft materials. Optical and thermal properties can degrade over time in the harsh low Earth orbital (LEO) space environment where spacecraft external materials are exposed to various forms of radiation, thermal cycling, and atomic oxygen. Therefore, it is important to test the durability of spacecraft materials in the space environment. One objective of the Polymers and Zenith Polymers Experiments was to determine the effect of LEO space exposure on the optical properties of various spacecraft polymers. These experiments were flown as part of the Materials International Space Station Experiment 7 (MISSE 7) mission on the exterior of the International Space Station (ISS) for 1.5 years. Samples were flown in ram, wake or zenith directions, receiving varying amounts of atomic oxygen and solar radiation exposure. Total and diffuse reflectance and transmittance of flight and corresponding control samples were obtained post-flight using a Cary 5000 UV-Vis-NIR Spectrophotometer. Integrated air mass zero solar absorptance (s) of the flight and control samples were computed from the total transmittance and reflectance, and compared. The optical data are compared with similar polymers exposed to space for four years as part of MISSE 2, and with atomic oxygen erosion data, to help understand the degradation of these polymers in the space environment. Results show that prolonged space exposure increases the solar absorptance of some materials. Knowing which polymers remain stable will benefit future spacecraft design.

Free tropospheric ozone production following entrainment of urban plumes into deep convection

NASA Technical Reports Server (NTRS)

Pickering, Kenneth E.; Thompson, Anne M.; Scala, John R.; Tao, Wei-Kuo; Dickerson, Russell R.; Simpson, Joanne

1992-01-01

It is shown that rapid vertical transport of air from urban plumes through deep convective clouds can cause substantial enhancement of the rate of O3 production in the free troposphere. Simulation of convective redistribution and subsequent photochemistry of an urban plume from Oklahoma City during the 1985 PRESTORM campaign shows enhancement of O3 production in the free tropospheric cloud outflow layer by a factor of almost 4. In contrast, simulation of convective transport of an urban plume from Manaus, Brazil, into a prestine free troposphere during GTE/ABLE 2B (1987), followed by a photochemical simulation, showed enhancement of O3 production by a factor of 35. The reasons for the different enhancements are (1) intensity of cloud vertical motion; (2) initial boundary layer O3 precursor concentrations; and (3) initial amount of background free tropospheric NO(x). Convective transport of ozone precursors to the middle and upper troposphere allows the resulting O3 to spread over large geographic regions, rather than being confined to the lower troposphere where loss processes are much more rapid. Conversely, as air with lower NO descends and replaces more polluted air, there is greater O3 production efficiency per molecule of NO in the boundary layer following convective transport. As a result, over 30 percent more ozone could be produced in the entire tropospheric column in the first 24 hours following convective transport of urban plumes.

Discoveries about Tropospheric Ozone Pollution from Satellite and Soundings

NASA Technical Reports Server (NTRS)

Thompson, Anne M.

2004-01-01

We have been producing near-red time tropospheric ozone satellite maps from the TOMS (Total Ozone Mapping Spectrometer) sensor since 1997. Maps for 1996-2000 for the operational Earth-Probe instrument are at:. Pollution in the tropics is influenced by biomass burning and by transport patterns that favor recirculation and in other cases reflect climate variability like the El-Nino-Southern Oscillation [Thompson et al., 2001]. The satellite view of chemical-dynamical interactions in tropospheric ozone is not adequate to capture vertical gradients in pollution. Thus, in 1998, NASA's Goddard Space Flight Center and a team of international sponsors established the SHADOZ (Southern Hemisphere ADditional OZonesondes) project to address the gap in tropical ozone soundings. SHADOZ augments launches and provides a public archive of ozonesonde data from twelve tropical stations at http://croc.gsfc.nasa.gov/shadoz. Further insights into the role of chemical and dynamical influences have emerged from the first 4-5 years of SHADOZ data (more than 2000 ozone profiles). Highly variable tropospheric ozone and a zonal wave-one pattern in tropospheric ozone suggest that dynamics is as important as pollution in determining tropical ozone distributions.

Tropical Tropospheric Ozone Climatology: Approaches Based on SHADOZ Observations

NASA Technical Reports Server (NTRS)

Thompson, Anne M.; Witte, Jacquelyn C.; Chatfield, Robert B.; Hudson, Robert D.; Andrade, Marcos; Coetzee, Geert J. R.; Posny, Francoise

2004-01-01

The SHADOZ (Southern Hemisphere Additional Ozonesondes) ozone sounding network was initiated in 1998 to improve the coverage of tropical in-situ ozone measurements for satellite validation, algorithm development and related process studies. Over 2000 soundings have been archived at the central website, , for 12 stations that span the entire equatorial zone [Thompson et al., JGR, 108,8238, 2003]. The most striking features of tropospheric ozone profiles in SHADOZ are: (1) persistent longitudinal variability in tropospheric ozone profiles, with a 10-15 DU column-integrated difference between Atlantic and Pacific sites; (2) intense short-term variability triggered by changing meteorological conditions and advection of pollution. The implications of these results for profile climatologies and trends are described along with several approaches to classifying ozone profiles: 1) Seasonal means during MAM (March-April-May) and SON (September-October-November); 2) Maxima and minima, identified through correlation of TOMS-derived TTO (tropical tropospheric ozone) column depth with the sonde integrated tropospheric ozone column; and 3) Meteorological regimes, a technique that is effective in the subtropics where tropical and mid-latitude conditions alternate.

Origins of tropospheric ozone interannual variation (IAV) over Réunion: A model investigation.

PubMed

Liu, Junhua; Rodriguez, Jose M; Thompson, Anne M; Logan, Jennifer A; Douglass, Anne R; Olsen, Mark A; Steenrod, Stephen D; Posny, Francoise

2016-01-16

Observations from long-term ozonesonde measurements show robust variations and trends in the evolution of ozone in the middle and upper troposphere over Réunion Island (21.1°S, 55.5°E) in June-August. Here we examine possible causes of the observed ozone variation at Réunion Island using hindcast simulations by the stratosphere-troposphere Global Modeling Initiative chemical transport model (GMI-CTM) for 1992-2014, driven by assimilated Modern-Era Retrospective Analysis for Research and Applications (MERRA) meteorological fields. Réunion Island is at the edge of the subtropical jet, a region of strong stratospheric-tropospheric exchange (STE). Our analysis implies that the large interannual variation (IAV) of upper tropospheric ozone over Réunion is driven by the large IAV of the stratospheric influence. The IAV of the large-scale, quasi-horizontal wind patterns also contributes to the IAV of ozone in the upper troposphere. Comparison to a simulation with constant emissions indicates that increasing emissions do not lead to the maximum trend in the middle and upper troposphere over Réunion during austral winter implied by the sonde data. The effects of increasing emission over southern Africa are limited to the lower troposphere near the surface in August - September.

Origins of tropospheric ozone interannual variation (IAV) over Réunion: A model investigation

PubMed Central

Liu, Junhua; Rodriguez, Jose M.; Thompson, Anne M.; Logan, Jennifer A.; Douglass, Anne R.; Olsen, Mark A.; Steenrod, Stephen D.; Posny, Francoise

2018-01-01

Observations from long-term ozonesonde measurements show robust variations and trends in the evolution of ozone in the middle and upper troposphere over Réunion Island (21.1°S, 55.5°E) in June-August. Here we examine possible causes of the observed ozone variation at Réunion Island using hindcast simulations by the stratosphere-troposphere Global Modeling Initiative chemical transport model (GMI-CTM) for 1992–2014, driven by assimilated Modern-Era Retrospective Analysis for Research and Applications (MERRA) meteorological fields. Réunion Island is at the edge of the subtropical jet, a region of strong stratospheric-tropospheric exchange (STE). Our analysis implies that the large interannual variation (IAV) of upper tropospheric ozone over Réunion is driven by the large IAV of the stratospheric influence. The IAV of the large-scale, quasi-horizontal wind patterns also contributes to the IAV of ozone in the upper troposphere. Comparison to a simulation with constant emissions indicates that increasing emissions do not lead to the maximum trend in the middle and upper troposphere over Réunion during austral winter implied by the sonde data. The effects of increasing emission over southern Africa are limited to the lower troposphere near the surface in August – September. PMID:29657911

Non Urban Troposphere Composition Symposium, Hollywood, Fla., November 10-12, 1976, Proceedings

NASA Technical Reports Server (NTRS)

1977-01-01

Papers are presented which originate from a conference on 'The Non-Urban Troposphere Composition', held in 1976. Attention is given to distributions of nitrous oxide in the atmosphere, and to tropospheric and stratospheric compositions which are perturbed by NO(x) emissions from high-altitude aircraft. Ozone is studied in terms of in situ measurements; various meteorological analyses of tropopause folding, ozone measurements in the Boston area, and ozone measurements in rural areas are presented. A one-dimensional model used to study tropospheric photochemistry numerically is presented as are vertical profiles of tropospheric and stratospheric molecular hydrogen. The oxidation of ammonia, methane, and hydrogen sulfide is assessed in nonurban tropospheres along with nonurban measurements of ethane and methane for various atmospheric conditions. With reference to the particle size distribution of chloride in the marine aerosol, organic and inorganic chlorine concentrations are evaluated, and measurements of sea-air CO2 flux by eddy correlation are investigated.

Tropospheric Ozone as a Short-lived Chemical Climate Forcer

NASA Technical Reports Server (NTRS)

Pickering, Kenneth E.

2012-01-01

Tropospheric ozone is the third most important greenhouse gas according to the most recent IPCC assessment. However, tropospheric ozone is highly variable in both space and time. Ozone that is located in the vicinity of the tropopause has the greatest effect on climate forcing. Nitrogen oxides (NOx) are the most important precursors for ozone In most of the troposphere. Therefore, pollution that is lofted upward in thunderstorm updrafts or NOx produced by lightning leads to efficient ozone production in the upper troposphere, where ozone is most important climatically. Global and regional model estimates of the impact of North American pollution and lightning on ozone radiative forcing will be presented. It will be shown that in the Northern Hemisphere summer, the lightning effect on ozone radiative forcing can dominate over that of pollution, and that the radiative forcing signal from North America extends well into Europe and North Africa. An algorithm for predicting lightning flash rates and estimating lightning NOx emissions is being incorporated into the NASA GEOS-5 Chemistry and Climate Model. Changes in flash rates and emissions over an ENSO cycle and in future climates will be assessed, along with the resulting changes in upper tropospheric ozone. Other research on the production of NOx per lightning flash and its distribution in the vertical based on cloud-resolving modeling and satellite observations will be presented. Distributions of NO2 and O3 over the Middle East from the OMI instrument on NASA's Aura satellite will also be shown.

Tropospheric Ozone Over the North Pacific from Ozonesdonde Observations

NASA Technical Reports Server (NTRS)

Oltmans, S. J.; Johnson, B. J.; Harris, J. M.; Thompson, A. M.; Liu, H. Y.; Voemel, H.; Chan, C. Y.; Fujimoto, T.; Brackett, V. G.; Chang, W. L.

2003-01-01

As part of the TRACE-P mission, ozone vertical profile measurements were made at a number of locations in the North Pacific. At most of the sites there is also a multi-year record of ozonesonde observations. From seven locations in the western Pacific (Hong Kong; Taipei; Jeju Island, Korea; and Naha, Kagoshima, Tsukuba, and Sapporo, Japan), a site in the central Pacific (Hilo, HI), and a site on the west coast of the U.S. (Trinidad Head, CA) both a seasonal and event specific picture of tropospheric ozone over the North Pacific emerges. At all of the sites there is a pronounced spring maximum through the troposphere. There are, however, differences in the timing and strength of this feature. Over Japan the northward movement of the jet during the spring and summer influences the timing of the seasonal maximum. The ozone profiles suggest that transport of ozone rich air from the stratosphere plays a strong role in the development of this maximum. During March and April at Hong Kong ozone is enhanced in a layer that extends from the lower free troposphere into the upper troposphere that likely has its origin in biomass burning in northern Southeast Asia and equatorial Africa. During the winter the Pacific subtropical sites (latitude -25N) are dominated by air with a low-latitude, marine source that gives low ozone amounts particularly in the upper troposphere. In the summer in the boundary layer at all of the sites marine air dominates and ozone amounts are generally quite low (less than 25 ppb). The exception is near large population centers (Tokyo and Taipei but not Hong Kong) where pollution events can give amounts in excess of 80 ppb. During the TRACE-P intensive campaign period (February-April 2001) tropospheric ozone amounts were rather typical of those seen in the long-term records of the stations with multi-year soundings.

Deep-space navigation with differenced data types. Part 3: An expanded information content and sensitivity analysis

NASA Technical Reports Server (NTRS)

Estefan, J. A.; Thurman, S. W.

1992-01-01

An approximate six-parameter analytic model for Earth-based differential range measurements is presented and is used to derive a representative analytic approximation for differenced Doppler measurements. The analytical models are tasked to investigate the ability of these data types to estimate spacecraft geocentric angular motion, Deep Space Network station oscillator (clock/frequency) offsets, and signal-path calibration errors over a period of a few days, in the presence of systematic station location and transmission media calibration errors. Quantitative results indicate that a few differenced Doppler plus ranging passes yield angular position estimates with a precision on the order of 0.1 to 0.4 micro-rad, and angular rate precision on the order of 10 to 25 x 10(exp -12) rad/sec, assuming no a priori information on the coordinate parameters. Sensitivity analyses suggest that troposphere zenith delay calibration error is the dominant systematic error source in most of the tracking scenarios investigated; as expected, the differenced Doppler data were found to be much more sensitive to troposphere calibration errors than differenced range. By comparison, results computed using wideband and narrowband (delta) VLBI under similar circumstances yielded angular precisions of 0.07 to 0.4 micro-rad, and angular rate precisions of 0.5 to 1.0 x 10(exp -12) rad/sec.

Deep-space navigation with differenced data types. Part 3: An expanded information content and sensitivity analysis

NASA Technical Reports Server (NTRS)

Estefan, J. A.; Thurman, S. W.

1992-01-01

An approximate six-parameter analytic model for Earth-based differenced range measurements is presented and is used to derive a representative analytic approximation for differenced Doppler measurements. The analytical models are tasked to investigate the ability of these data types to estimate spacecraft geocentric angular motion, Deep Space Network station oscillator (clock/frequency) offsets, and signal-path calibration errors over a period of a few days, in the presence of systematic station location and transmission media calibration errors. Quantitative results indicate that a few differenced Doppler plus ranging passes yield angular position estimates with a precision on the order of 0.1 to 0.4 microrad, and angular rate precision on the order of 10 to 25(10)(exp -12) rad/sec, assuming no a priori information on the coordinate parameters. Sensitivity analyses suggest that troposphere zenith delay calibration error is the dominant systematic error source in most of the tracking scenarios investigated; as expected, the differenced Doppler data were found to be much more sensitive to troposphere calibration errors than differenced range. By comparison, results computed using wide band and narrow band (delta)VLBI under similar circumstances yielded angular precisions of 0.07 to 0.4 /microrad, and angular rate precisions of 0.5 to 1.0(10)(exp -12) rad/sec.

Chemical Modeling of the Reactivity of Short-Lived Greenhouse Gases: A Model Inter-Comparison Prescribing a Well-Measured, Remote Troposphere

NASA Technical Reports Server (NTRS)

Prather, Michael J.; Flynn, Clare M.; Zhu, Xin; Steenrod, Stephen D.; Strode, Sarah A.; Fiore, Arlene M.; Correa, Gustavo; Murray, Lee T.; Lamarque, Jean-Francois

2018-01-01

We develop a new protocol for merging in situ measurements with 3-D model simulations of atmospheric chemistry with the goal of integrating over the data to identify the most reactive air parcels in terms of tropospheric production and loss of the greenhouse gases ozone and methane. Presupposing that we can accurately measure atmospheric composition, we examine whether models constrained by such measurements agree on the chemical budgets for ozone and methane. In applying our technique to a synthetic data stream of 14,880 parcels along 180W, we are able to isolate the performance of the photochemical modules operating within their global chemistry-climate and chemistry-transport models, removing the effects of modules controlling tracer transport, emissions, and scavenging. Differences in reactivity across models are driven only by the chemical mechanism and the diurnal cycle of photolysis rates, which are driven in turn by temperature, water vapor, solar zenith angle, clouds, and possibly aerosols and overhead ozone, which are calculated in each model. We evaluate six global models and identify their differences and similarities in simulating the chemistry through a range of innovative diagnostics. All models agree that the more highly reactive parcels dominate the chemistry (e.g., the hottest 10% of parcels control 25-30% of the total reactivities), but do not fully agree on which parcels comprise the top 10%. Distinct differences in specific features occur, including the regions of maximum ozone production and methane loss, as well as in the relationship between photolysis and these reactivities. Unique, possibly aberrant, features are identified for each model, providing a benchmark for photochemical module development. Among the 6 models tested here, 3 are almost indistinguishable based on the inherent variability caused by clouds, and thus we identify 4, effectively distinct, chemical models. Based on this work, we suggest that water vapor differences in

A new algorithm for microwave delay estimation from water vapor radiometer data

NASA Technical Reports Server (NTRS)

Robinson, S. E.

1986-01-01

A new algorithm has been developed for the estimation of tropospheric microwave path delays from water vapor radiometer (WVR) data, which does not require site and weather dependent empirical parameters to produce high accuracy. Instead of taking the conventional linear approach, the new algorithm first uses the observables with an emission model to determine an approximate form of the vertical water vapor distribution which is then explicitly integrated to estimate wet path delays, in a second step. The intrinsic accuracy of this algorithm has been examined for two channel WVR data using path delays and stimulated observables computed from archived radiosonde data. It is found that annual RMS errors for a wide range of sites are in the range from 1.3 mm to 2.3 mm, in the absence of clouds. This is comparable to the best overall accuracy obtainable from conventional linear algorithms, which must be tailored to site and weather conditions using large radiosonde data bases. The new algorithm's accuracy and flexibility are indications that it may be a good candidate for almost all WVR data interpretation.

"Cloud Slicing" : A New Technique to Derive Tropospheric Ozone Profile Information from Satellite Measurements

NASA Technical Reports Server (NTRS)

Ziemke, J. R.; Chandra, S.; Bhartia, P. K.; Einaudi, Franco (Technical Monitor)

2000-01-01

A new technique denoted cloud slicing has been developed for estimating tropospheric ozone profile information. All previous methods using satellite data were only capable of estimating the total column of ozone in the troposphere. Cloud slicing takes advantage of the opaque property of water vapor clouds to ultraviolet wavelength radiation. Measurements of above-cloud column ozone from the Nimbus 7 total ozone mapping spectrometer (TOMS) instrument are combined together with Nimbus 7 temperature humidity and infrared radiometer (THIR) cloud-top pressure data to derive ozone column amounts in the upper troposphere. In this study tropical TOMS and THIR data for the period 1979-1984 are analyzed. By combining total tropospheric column ozone (denoted TCO) measurements from the convective cloud differential (CCD) method with 100-400 hPa upper tropospheric column ozone amounts from cloud slicing, it is possible to estimate 400-1000 hPa lower tropospheric column ozone and evaluate its spatial and temporal variability. Results for both the upper and lower tropical troposphere show a year-round zonal wavenumber 1 pattern in column ozone with largest amounts in the Atlantic region (up to approx. 15 DU in the 100-400 hPa pressure band and approx. 25-30 DU in the 400-1000 hPa pressure band). Upper tropospheric ozone derived from cloud slicing shows maximum column amounts in the Atlantic region in the June-August and September-November seasons which is similar to the seasonal variability of CCD derived TCO in the region. For the lower troposphere, largest column amounts occur in the September-November season over Brazil in South America and also southern Africa. Localized increases in the tropics in lower tropospheric ozone are found over the northern region of South America around August and off the west coast of equatorial Africa in the March-May season. Time series analysis for several regions in South America and Africa show an anomalous increase in ozone in the lower

Changes in tropospheric composition and air quality due to stratospheric ozone depletion.

PubMed

Solomon, Keith R; Tang, Xiaoyan; Wilson, Stephen R; Zanis, Prodromos; Bais, Alkiviadis F

2003-01-01

Increased UV-B through stratospheric ozone depletion leads to an increased chemical activity in the lower atmosphere (the troposphere). The effect of stratospheric ozone depletion on tropospheric ozone is small (though significant) compared to the ozone generated anthropogenically in areas already experiencing air pollution. Modeling and experimental studies suggest that the impacts of stratospheric ozone depletion on tropospheric ozone are different at different altitudes and for different chemical regimes. As a result the increase in ozone due to stratospheric ozone depletion may be greater in polluted regions. Attributable effects on concentrations are expected only in regions where local emissions make minor contributions. The vertical distribution of NOx (NO + NO2), the emission of volatile organic compounds and the abundance of water vapor, are important influencing factors. The long-term nature of stratospheric ozone depletion means that even a small increase in tropospheric ozone concentration can have a significant impact on human health and the environment. Trifluoroacetic acid (TFA) and chlorodifluoroacetic acid (CDFA) are produced by the atmospheric degradation of hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). TFA has been measured in rain, rivers, lakes, and oceans, the ultimate sink for these and related compounds. Significant anthropogenic sources of TFA other than degradation HCFCs and HFCs have been identified. Toxicity tests under field conditions indicate that the concentrations of TFA and CDFA currently produced by the atmospheric degradation of HFCs and HCFCs do not present a risk to human health and the environment. The impact of the interaction between ozone depletion and future climate change is complex and a significant area of current research. For air quality and tropospheric composition, a range of physical parameters such as temperature, cloudiness and atmospheric transport will modify the impact of UV-B. Changes in the

Tropospheric ozone observations - How well can we assess tropospheric ozone changes?

NASA Astrophysics Data System (ADS)

Tarasick, D. W.; Galbally, I. E.; Ancellet, G.; Leblanc, T.; Wallington, T. J.; Ziemke, J. R.; Steinbacher, M.; Stähelin, J.; Vigouroux, C.; Hannigan, J. W.; García, O. E.; Foret, G.; Zanis, P.; Liu, X.; Weatherhead, E. C.; Petropavlovskikh, I. V.; Worden, H. M.; Osman, M.; Liu, J.; Lin, M.; Cooper, O. R.; Schultz, M. G.; Granados-Muñoz, M. J.; Thompson, A. M.; Cuesta, J.; Dufour, G.; Thouret, V.; Hassler, B.; Trickl, T.

2017-12-01

Since the early 20th century, measurements of ozone in the free troposphere have evolved and changed. Data records have different uncertainties and biases, and differ with respect to coverage, information content, and representativeness. Almost all validation studies employ ECC ozonesondes. These have been compared to UV-absorption measurements in a number of intercomparison studies, and show a modest ( 1-5%) high bias in the troposphere, with an uncertainty of 5%, but no evidence of a change over time. Umkehr, lidar, FTIR, and commercial aircraft all show modest low biases relative to the ECCs, and so -- if the ECC biases are transferable -- all agree within 1σ with the modern UV standard. Relative to the UV standard, Brewer-Mast sondes show a 20% increase in sensitivity from 1970-1995, while Japanese KC sondes show an increase of 5-10%. Combined with the shift of the global ozonesonde network to ECCs, this can induce a false positive trend, in analyses based on sonde data. Passive sounding methods -- Umkehr, FTIR and satellites -- have much lower vertical resolution than active methods, and this can limit the attribution of trends. Satellite biases are larger than those of other measurement systems, ranging between -10% and +20%, and standard deviations are large: about 10-30%, versus 5-10% for sondes, aircraft, lidar and ground-based FTIR. There is currently little information on measurement drift for satellite measurements of tropospheric ozone. This is an evident area of concern if satellite retrievals are used for trend studies. The importance of ECC sondes as a transfer standard for satellite validation means that efforts to homogenize existing records, by correcting for known changes and by adopting strict standard operating procedures, should continue, and additional research effort should be put into understanding and reducing sonde uncertainties. Representativeness is also a potential source of large errors, which are difficult to quantify. The global

Remote Sensing of Tropospheric Pollution from Space

NASA Technical Reports Server (NTRS)

Fishman, Jack; Bowman, Kevin W.; Burrows, John P.; Chance, Kelly V.; Edwards, David P.; Martin, Randall V.; Morris, Gary A.; Pierce, R. Bradley; Ziemke, Jerald R.; Al-Saadi, Jassim A.;

On Springtime Ozone Enhancements in the Lower Troposphere Over Beijing

NASA Astrophysics Data System (ADS)

Huang, J.; Liu, H.; Chan, C.; Crawford, J. H.; Considine, D. B.; Zhang, Y.; Zheng, X.; Oltmans, S. J.; Liu, S. C.; Thouret, V.

2012-12-01

Tropospheric ozone is an important greenhouse gas, the primary source of hydroxyl radical (OH) that controls the tropospheric oxidizing capacity, and a major air pollutant near the surface. Previous studies showed that ozone concentrations in the lower troposphere (LT) over Beijing have increased over the past two decades as a result of rapid industrialization in China. As part of an ozonesonde sounding campaign, called Transport of Air Pollutants and Tropospheric Ozone over China (TAPTO-China), intensive measurements of ozone vertical profiles (16 in total) were conducted in Beijing during April 11 - May 15, 2005. Thirteen vertical profiles were also sampled by the Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) program during April 3 - May 29, 2005. High ozone concentrations (up to 94.7 ppbv) were frequently observed in the LT (~1.5-2km) during this period. We evaluate here the capability of a 3-D chemical transport model (GEOS-Chem at 2°x2.5° resolution) to reproduce these ozone enhancements, and use the model to examine transport pathways for ozone pollution and quantify their sources. The model captures the occurrences but significantly underestimates the magnitude of ozone enhancements. By tagging ozone produced in different source regions and conducting sensitivity simulations with the model, we show that Asian troposphere and Asian anthropogenic pollution made the major contributions to those ozone enhancements. Contributions from European and North American troposphere and anthropogenic pollution reduced during these events, compared to those days without ozone enhancements. We find that most of the ozone enhancements observed in the LT occurred under southerly wind and warmer conditions. Their occurrence frequency appears to be related to the onset of Asian summer monsoon. The influence of regional transport from different source regions in East Asia will also be discussed.

A demonstration of high precision GPS orbit determination for geodetic applications

NASA Technical Reports Server (NTRS)

Lichten, S. M.; Border, J. S.

1987-01-01

High precision orbit determination of Global Positioning System (GPS) satellites is a key requirement for GPS-based precise geodetic measurements and precise low-earth orbiter tracking, currently under study at JPL. Different strategies for orbit determination have been explored at JPL with data from a 1985 GPS field experiment. The most successful strategy uses multi-day arcs for orbit determination and includes fine tuning of spacecraft solar pressure coefficients and station zenith tropospheric delays using the GPS data. Average rms orbit repeatability values for 5 of the GPS satellites are 1.0, 1.2, and 1.7 m in altitude, cross-track, and down-track componenets when two independent 5-day fits are compared. Orbit predictions up to 24 hours outside the multi-day arcs agree within 4 m of independent solutions obtained with well tracked satellites in the prediction interval. Baseline repeatability improves with multi-day as compared to single-day arc orbit solutions. When tropospheric delay fluctuations are modeled with process noise, significant additional improvement in baseline repeatability is achieved. For a 246-km baseline, with 6-day arc solutions for GPS orbits, baseline repeatability is 2 parts in 100 million (0.4-0.6 cm) for east, north, and length components and 8 parts in 100 million for the vertical component. For 1314 and 1509 km baselines with the same orbits, baseline repeatability is 2 parts in 100 million for the north components (2-3 cm) and 4 parts in 100 million or better for east, length, and vertical components.

Plant responses to tropospheric ozone

USDA-ARS?s Scientific Manuscript database

Tropospheric ozone is the second most abundant air pollutant and an important component of the global climate change. Over five decades of research on the phytotoxicity of ozone in model plants systems, crop plants and forest trees have provided some insight into the physiological, biochemical and m...

Applications of Satellite Observations of Tropospheric Composition

NASA Astrophysics Data System (ADS)

Monks, Paul S.; Beirle, Steffen

A striking feature of the field of tropospheric composition is the sheer number of chemical species that have been detected and measured with satellite instruments. The measurements have found application both in atmospheric chemistry itself, providing evidence, for example, of unexpected cryochemistry in the Arctic regions, and also in environmental monitoring with, for example, the observed growth in NO2 emissions over eastern Asia. Chapter 8 gives an overview of the utility of satellite observations for measuring tropospheric composition, dealing with each of the many compounds seen in detail. A comprehensive compound by compound table of the many studies performed is a most useful feature.

Tropospheric emissions: Monitoring of pollution (TEMPO)

NASA Astrophysics Data System (ADS)

Zoogman, P.; Liu, X.; Suleiman, R. M.; Pennington, W. F.; Flittner, D. E.; Al-Saadi, J. A.; Hilton, B. B.; Nicks, D. K.; Newchurch, M. J.; Carr, J. L.; Janz, S. J.; Andraschko, M. R.; Arola, A.; Baker, B. D.; Canova, B. P.; Chan Miller, C.; Cohen, R. C.; Davis, J. E.; Dussault, M. E.; Edwards, D. P.; Fishman, J.; Ghulam, A.; González Abad, G.; Grutter, M.; Herman, J. R.; Houck, J.; Jacob, D. J.; Joiner, J.; Kerridge, B. J.; Kim, J.; Krotkov, N. A.; Lamsal, L.; Li, C.; Lindfors, A.; Martin, R. V.; McElroy, C. T.; McLinden, C.; Natraj, V.; Neil, D. O.; Nowlan, C. R.; O`Sullivan, E. J.; Palmer, P. I.; Pierce, R. B.; Pippin, M. R.; Saiz-Lopez, A.; Spurr, R. J. D.; Szykman, J. J.; Torres, O.; Veefkind, J. P.; Veihelmann, B.; Wang, H.; Wang, J.; Chance, K.

2017-01-01

TEMPO was selected in 2012 by NASA as the first Earth Venture Instrument, for launch between 2018 and 2021. It will measure atmospheric pollution for greater North America from space using ultraviolet and visible spectroscopy. TEMPO observes from Mexico City, Cuba, and the Bahamas to the Canadian oil sands, and from the Atlantic to the Pacific, hourly and at high spatial resolution ( 2.1 km N/S×4.4 km E/W at 36.5°N, 100°W). TEMPO provides a tropospheric measurement suite that includes the key elements of tropospheric air pollution chemistry, as well as contributing to carbon cycle knowledge. Measurements are made hourly from geostationary (GEO) orbit, to capture the high variability present in the diurnal cycle of emissions and chemistry that are unobservable from current low-Earth orbit (LEO) satellites that measure once per day. The small product spatial footprint resolves pollution sources at sub-urban scale. Together, this temporal and spatial resolution improves emission inventories, monitors population exposure, and enables effective emission-control strategies. TEMPO takes advantage of a commercial GEO host spacecraft to provide a modest cost mission that measures the spectra required to retrieve ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), formaldehyde (H2CO), glyoxal (C2H2O2), bromine monoxide (BrO), IO (iodine monoxide), water vapor, aerosols, cloud parameters, ultraviolet radiation, and foliage properties. TEMPO thus measures the major elements, directly or by proxy, in the tropospheric O3 chemistry cycle. Multi-spectral observations provide sensitivity to O3 in the lowermost troposphere, substantially reducing uncertainty in air quality predictions. TEMPO quantifies and tracks the evolution of aerosol loading. It provides these near-real-time air quality products that will be made publicly available. TEMPO will launch at a prime time to be the North American component of the global geostationary constellation of pollution monitoring

Future changes in large-scale transport and stratosphere-troposphere exchange

NASA Astrophysics Data System (ADS)

Abalos, M.; Randel, W. J.; Kinnison, D. E.; Garcia, R. R.

2017-12-01

Future changes in large-scale transport are investigated in long-term (1955-2099) simulations of the Community Earth System Model - Whole Atmosphere Community Climate Model (CESM-WACCM) under an RCP6.0 climate change scenario. We examine artificial passive tracers in order to isolate transport changes from future changes in emissions and chemical processes. The model suggests enhanced stratosphere-troposphere exchange in both directions (STE), with decreasing tropospheric and increasing stratospheric tracer concentrations in the troposphere. Changes in the different transport processes are evaluated using the Transformed Eulerian Mean continuity equation, including parameterized convective transport. Dynamical changes associated with the rise of the tropopause height are shown to play a crucial role on future transport trends.

Thermodynamic constraint on the depth of the global tropospheric circulation.

PubMed

Thompson, David W J; Bony, Sandrine; Li, Ying

2017-08-01

The troposphere is the region of the atmosphere characterized by low static stability, vigorous diabatic mixing, and widespread condensational heating in clouds. Previous research has argued that in the tropics, the upper bound on tropospheric mixing and clouds is constrained by the rapid decrease with height of the saturation water vapor pressure and hence radiative cooling by water vapor in clear-sky regions. Here the authors contend that the same basic physics play a key role in constraining the vertical structure of tropospheric mixing, tropopause temperature, and cloud-top temperature throughout the globe. It is argued that radiative cooling by water vapor plays an important role in governing the depth and amplitude of large-scale dynamics at extratropical latitudes.

Oxidation of mercury by bromine in the subtropical Pacific free troposphere

NASA Astrophysics Data System (ADS)

Gratz, L. E.; Ambrose, J. L.; Jaffe, D. A.; Shah, V.; Jaeglé, L.; Stutz, J.; Festa, J.; Spolaor, M.; Tsai, C.; Selin, N. E.; Song, S.; Zhou, X.; Weinheimer, A. J.; Knapp, D. J.; Montzka, D. D.; Flocke, F. M.; Campos, T. L.; Apel, E.; Hornbrook, R.; Blake, N. J.; Hall, S.; Tyndall, G. S.; Reeves, M.; Stechman, D.; Stell, M.

2015-12-01

Mercury is a global toxin that can be introduced to ecosystems through atmospheric deposition. Mercury oxidation is thought to occur in the free troposphere by bromine radicals, but direct observational evidence for this process is currently unavailable. During the 2013 Nitrogen, Oxidants, Mercury and Aerosol Distributions, Sources and Sinks campaign, we measured enhanced oxidized mercury and bromine monoxide in a free tropospheric air mass over Texas. We use trace gas measurements, air mass back trajectories, and a chemical box model to confirm the origin and chemical history of the sampled air mass. We find the presence of elevated oxidized mercury to be consistent with oxidation of elemental mercury by bromine atoms in this subsiding upper tropospheric air mass within the subtropical Pacific High, where dry atmospheric conditions are conducive to oxidized mercury accumulation. Our results support the role of bromine as the dominant oxidant of mercury in the upper troposphere.

Extratropical Influence of Upper Tropospheric Water Vapor on Greenhouse Warming

NASA Technical Reports Server (NTRS)

Hu, H.; Liu, W.

1998-01-01

The purpose of this paper is to re-examine the impact of upper tropospheric water vapor on greenhouse warming in midlatitudes by analyzing the recent observations of the upper tropospheric water vapor from the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite (UARS), in conjuction with other space-based measurement and model simulation products.

The global consequences of increasing tropospheric ozone concentrations

NASA Technical Reports Server (NTRS)

Fishman, Jack

1989-01-01

Recent analyses of long term records of tropospheric ozone measurements in the Northern Hemisphere suggest that it is increasing at a rate of 1 to 2 percent per year. Because of this, it is argued that the amount of atmospheric warming due to increasing tropospheric ozone is comparable to, or possibly even greater than, the amount of warming due to the increase of carbon dioxide. Unlike all other climatically important trace gases, ozone is toxic, and increases in its concentration will result in serious environmental damage, as well as impairment of human health.

Gas-phase tropospheric chemistry of 2,3,7,8-tetrafuorinated dibenzo-p-dioxin.

PubMed

Zhang, Chenxi; Sun, Xiaomin

2014-01-15

Growing attention has been devoted to understanding the formation and destruction of polyfluorinated dibenzo-p-dioxins (PFDDs). High-accuracy molecular orbital calculations have been performed to investigate the tropospheric oxidation reaction of 2,3,7,8-tetrafuorinated dibenzo-p-dioxin (TFDD) initiated by OH radical, NO3 radical and O3. The rate constant of TFDD reaction triggered by the OH radical, NO3 radical and O3 is about 2.30 × 10(-11)cm(3) molecule(-l) s(-l), 3.18 × 10(-13)cm(3) molecule(-l) s(-l), and 3.30 × 10(-19)cm(3) molecule(-l) s(-l), respectively. OH radical is the major gas phase tropospheric sink for TFDD. Once TFDD-OH intermediates are produced in the initial reactions, they can react with tropospheric O2 subsequently to generate peroxy radical isomers. The TFDD-OH-O2 can further react with tropospheric NO via isomerization or combination, resulting that the dioxin ring will be ruptured completely. This study can serve as a template for tropospheric degradation of the gaseous PFDDs, which is beneficial for assessing their tropospheric behaviors. © 2013 Elsevier B.V. All rights reserved.

Sources of Springtime Tropospheric Ozone Over North China: A Modeling Analysis of Ozonesonde and Satellite Observations

NASA Astrophysics Data System (ADS)

Liu, H.; Chan, C.; Huang, J.; Zhang, Y.; Choi, H.; Crawford, J. H.; Considine, D. B.; Zheng, X.; Oltmans, S. J.; Liu, S. C.; Zhang, L.; Liu, X.; Thouret, V.

2012-12-01

Tropospheric ozone concentrations and emissions of NOx have both increased significantly over China as a result of rapid industrialization during the past decade. These trends degrade local and regional air quality and have important effects on background tropospheric ozone and surface ozone over downwind North Pacific and North America. In-situ observations of tropospheric ozone over China are therefore essential to testing and improving our understanding of the impact of Asian anthropogenic (versus natural) emissions and various chemical, physical, and dynamical processes on both regional and global tropospheric ozone. Despite their critical importance, in-situ observations of tropospheric ozone profiles over China have been few and far between in most of the country. To investigate the ensemble of processes that control the distribution, variability, and sources of springtime tropospheric ozone over China and its surrounding regions, an intensive ozonesonde sounding campaign, called Transport of Air Pollutants and Tropospheric Ozone over China (TAPTO-China), was conducted at nine locations across China in the springs of 2004 (South China) and 2005 (North China). In this paper, we use a global 3-D model of tropospheric chemistry (GEOS-Chem) to examine the characteristics of distribution and variability and quantify various sources of tropospheric ozone over North China by analysis of intensive ozonesonde data obtained at four stations in North / Northwest China during the second phase of TAPTO-China (April-May 2005). These four stations include Xining (36.43N, 101.45E), Beijing (39.80N, 116.18E), Longfengshan (44.44N, 127.36E), and Aletai (47.73N, 88.08E). We drive GEOS-Chem with two sets of assimilated meteorological observations (GEOS-4 and GEOS-5) from the Goddard Earth Observing System (GEOS) of the NASA Global Modeling and Assimilation Office (GAMO), allowing us to examine the impacts of variability in meteorology. We show that the observed tropospheric

Laser Sounder for Global Measurement of CO2 Concentrations in the Troposphere from Space

NASA Technical Reports Server (NTRS)

Abshire, James B.; Riris, Haris; Kawa, S. Randy; Sun, Xiaoli; Chen, Jeffrey; Stephen, Mark A.; Collatz, G. James; Mao, Jianping; Allan, Graham

2007-01-01

nm band. This band is free from interference from other gases and has temperature insensitive absorption lines. During the measurement the lasers are tuned on- and off- a selected CO2 line near 1572 nm and a selected O2 line near 768 nm in the Oxygen A band at kHz rates. The lasers use tunable diode seed lasers followed by fiber amplifiers, and have spectral widths much narrower than the gas absorption lines. The receiver uses a 1-m diameter telescope and photon counting detectors and measures the background light and energies of the laser echoes from the surface. The extinction and column densities for the CO2 and O2 gases are estimated from the ratio of the on and offline surface echo via the differential optical absorption technique. Our technique rapidly alternates between several on-line wavelengths set to the sides of the selected gas absorption lines. It exploits the atmospheric pressure broadening of the lines to weight the measurement sensitivity to the atmospheric column below 5 km. This maximizes sensitivity to CO2 in the boundary layer, where variations caused by surface sources and sinks are largest. Simultaneous measurements of O2 column will use an identical approach with an O2 line. Thee laser frequencies are tunable and have narrow (MHz) line widths. In combination with sensitive photon counting detectors these enables much higher spectral resolution and precision than is possible with passive spectrometer. 1aser backscatter profiles are also measured, which permits identifying measurements made to cloud tops and through aerosol layers. The measurement approach using lasers in common-nadir-zenith path allows retrieving CO2 column mixing ratios in the lower troposphere irrespective of sun angle. Pulsed laser signals, time gated receiver and a narrow receiver field-of-view are used to isolate the surface laser echo signals and to exclude photons scattered from clouds and aerosols. Nonetheless, the optical absorption change due to a change of a few ppO2

Tropospheric Ozone and Biomass Burning

NASA Astrophysics Data System (ADS)

Chandra, S.; Ziemke, J. R.; Bhartia, P. K.

2001-05-01

This paper studies the significance of pyrogenic (e.g., biomass burning) emissions in the production of tropospheric ozone in the tropics associated with the forest and savanna fires in the African, South American, and Indonesian regions. Using aerosol index (AI) and tropospheric column ozone (TCO) time series from 1979 to 2000 derived from the Nimbus-7 and Earth Probe TOMS measurements, our study shows significant differences in the seasonal and spatial characteristics of pyrogenic emissions north and south of the equator in the African region and Brazil in South America. In general, they are not related to the seasonal and spatial characteristics of tropospheric ozone in these regions. In the Indonesian region, the most significant increase in TCO occurred during September and October 1997, following large-scale forest and savanna fires associated with the El Niño-induced dry condition. However, the increase in TCO extended over most of the western Pacific well outside the burning region and was accompanied by a decrease in the eastern Pacific resembling a west-to-east dipole about the dateline. The net increase in TCO integrated over the tropical region between 15N and 15S was about 6-8 Tg (terragram) over the mean climatological value of about 72 Tg. This increase is within the range of interannual variability of TCO in the tropical region and does not necessarily suggest a photochemical source related to biomass burning. The interannual variability in TCO appears to be out of phase with the interannual variability of stratospheric column ozone (SCO). These variabilities seem to be manifestations of solar cycle and quasi-biennial oscillations.

Tropospheric Ozone and Biomass Burning

NASA Technical Reports Server (NTRS)

Chandra, Sushil; Ziemke, J. R.; Bhartia, P. K.; Einaudi, Franco (Technical Monitor)

2001-01-01

This paper studies the significance of pyrogenic (e.g., biomass burning) emissions in the production of tropospheric ozone in the tropics associated with the forest and savanna fires in the African, South American, and Indonesian regions. Using aerosol index (Al) and tropospheric column ozone (TCO) time series from 1979 to 2000 derived from the Nimbus-7 and Earth Probe TOMS measurements, our study shows significant differences in the seasonal and spatial characteristics of pyrogenic emissions north and south of the equator in the African region and Brazil in South America. In general, they are not related to the seasonal and spatial characteristics of tropospheric ozone in these regions. In the Indonesian region, the most significant increase in TCO occurred during September and October 1997, following large-scale forest and savanna fires associated with the El Nino-induced dry season. However, the increase in TCO extended over most of the western Pacific well outside the burning region and was accompanied by a decrease in the eastern Pacific resembling a west-to-east dipole about the date-line. The net increase in TCO integrated over the tropical region between 15 deg N and 15 deg S was about 6-8 Tg (1 Tg = 10(exp 12) gm) over the mean climatological value of about 72 Tg. This increase is well within the range of interannual variability of TCO in the tropical region and does not necessarily suggest a photochemical source related to biomass burning. The interannual variability in TCO appears to be out of phase with the interannual variability of stratospheric column ozone (SCO). These variabilities seem to be manifestations of solar cycle and quasibiennial oscillations.

Measurements of tropospheric nitric acid over the Western United States and Northeastern Pacific Ocean

NASA Technical Reports Server (NTRS)

Lebel, P. J.; Huebert, B. J.; Schiff, H. I.; Vay, S. A.; Vanbramer, S. E.; Hastie, D. R.

1990-01-01

Over 240 measurements of nitric acid (HNO3) were made in the free troposphere as well as in the boundary layer. Marine HNO3 measurement results were strikingly similar to results from GAMETAG and other past atmospheric field experiments. The marine boundary layer HNO3 average, 62 parts-per-trillion by volume (pptv), was 1/3 lower than the marine free tropospheric average, 108 pptv, suggesting that the boundary layer is a sink for tropospheric nitric acid, probably by dry deposition. Nitric acid measurements on a nighttime continental flight gave a free tropospheric average of 218 pptv, substantially greater than the daytime continental free tropospheric 5-flight average of 61 pptv. However, the nighttime results may be influenced by highly convective conditions that existed from thunderstorms in the vicinity during that night flight. The continental boundary layer HNO3 average of 767 pptv is an order of magnitude greater than the free tropospheric average, indicating that the boundary layer is a source of free tropospheric HNO3. The distribution of continental boundary layer HNO3 data, from averages of 123 over rural Nevada and Utah to 1057 pptv in the polluted San Joaquin Valley of California suggest a close tie between boundary layer HNO3 and anthropogenic activity.

Tropospheric and Airborne Emission Spectrometers

NASA Technical Reports Server (NTRS)

Glavich, Thomas; Beer, Reinhard

1996-01-01

X This paper describes the development of two related instruments, the Tropospheric Emission Spectrometer (TES) and the Airborne Emission Spectrometer (AES). Both instruments are infrared imaging Fourier Transform Spectrometers, used for measuring the state of the lower atmosphere, and in particular the measurement of ozone and ozone sources and sinks.

Zenith Movie showing Phoenix's Lidar Beam (Animation)

NASA Technical Reports Server (NTRS)

2008-01-01

[figure removed for brevity, see original site] Click on image for animation

A laser beam from the Canadian-built lidar instrument on NASA's Phoenix Mars Lander can be seen in this contrast-enhanced sequence of 10 images taken by Phoenix's Surface Stereo Imager on July 26, 2008, during early Martian morning hours of the mission's 61st Martian day after landing.

The view is almost straight up and includes about 1.5 kilometer (about 1 mile) of the length of the beam. The camera, from its position close to the lidar on the lander deck, took the images through a green filter centered on light with wavelength 532 nanometers, the same wavelength of the laser beam. The movie has been artificially colored to to approximately match the color that would be seen looking through this filter on Mars. Contrast is enhanced to make the beam more visible.

The lidar beam can be seen extending from the lower right to the upper right, near the zenith, as it reflects off particles suspended in the atmosphere. Particles that scatter the beam directly into the camera can be seen to produce brief sparkles of light. In the background, dust can be seen drifting across the sky pushed by winds aloft.

The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

Sensitivity of EAS measurements to the energy spectrum of muons

NASA Astrophysics Data System (ADS)

Espadanal, J.; Cazon, L.; Conceição, R.

2017-01-01

We have studied how the energy spectrum of muons at production affects some of the most common measurements related to muons in extensive air shower studies, namely, the number of muons at the ground, the slope of the lateral distribution of muons, the apparent muon production depth, and the arrival time delay of muons at ground. We found that by changing the energy spectrum by an amount consistent with the difference between current models (namely EPOS-LHC and QGSJET-II.04), the muon surface density at ground increases 5% at 20° zenith angle and 17% at 60° zenith angle. This effect introduces a zenith angle dependence on the reconstructed number of muons which might be experimentally observed. The maximum of the muon production depth distribution at 40° increases ∼ 10 g/cm2 and ∼ 0 g/cm2 at 60°, which, from pure geometrical considerations, increases the arrival time delay of muons. There is an extra contribution to the delay due to the subluminal velocities of muons of the order of ∼ 3 ns at all zenith angles. Finally, changes introduced in the logarithmic slope of the lateral density function are less than 2%.

Diurnal variation of tropospheric relative humidity in tropical regions

NASA Astrophysics Data System (ADS)

Moradi, Isaac; Arkin, Philip; Ferraro, Ralph; Eriksson, Patrick; Fetzer, Eric

2016-06-01

Despite the importance of water vapor especially in the tropical region, the diurnal variations of water vapor have not been completely investigated in the past due to the lack of adequate observations. Measurements from Sondeur Atmosphérique du Profil d'Humidité Intertropicale par Radiométrie (SAPHIR) onboard the low inclination Megha-Tropiques satellite with frequent daily revisits provide a valuable dataset for investigating the diurnal and spatial variation of tropospheric relative humidity in the tropical region. In this study, we first transformed SAPHIR observations into layer-averaged relative humidity, then partitioned the data based on local observation time into 24 bins with a grid resolution of one degree. Afterwards, we fitted Fourier series to the binned data. Finally, the mean, amplitude, and diurnal peak time of relative humidity in tropical regions were calculated for each grid point using either the measurements or Fourier series. The results were separately investigated for different SAPHIR channels as well as for relative humidity with respect to both liquid and ice phases. The results showed that the wet and dry regions are, respectively, associated with convective and subsidence regions which is consistent with the previous studies. The mean tropospheric humidity values reported in this study are generally 10 to 15 % higher than those reported using infrared observations which is because of strict cloud screening for infrared measurements. The results showed a large inhomogeneity in diurnal variation of tropospheric relative humidity in tropical region. The diurnal amplitude was larger over land than over ocean and the oceanic amplitude was larger over convective regions than over subsidence regions. The results showed that the diurnal amplitude is less than 10 % in middle and upper troposphere, but it is up to 30 % in lower troposphere over land. Although the peak of RH generally occurs over night or in early morning, there are several

First determination of the tropospheric CO abundance in Saturn

NASA Astrophysics Data System (ADS)

Fouchet, Thierry; Lellouch, Emmanuel; Cavalié, Thibault; Bézard, Bruno

2017-10-01

In Giant Planets, CO has two potential origins: i) an external source in form of cometary impacts, infalling ring/satellite dust or/and interplanetary particles; ii) an internal origin that involves convective transport from the deep, dense, hot atmosphere where the thermodynamic equilibrium CO abundance is relatively large.In Saturn, submilimeter stratospheric CO emissions have been detected (Cavalié et al. A&A, 510, A88, 2010; Cavalié et al. Icarus, 203, 531, 2009), suggesting a cometary impact 200 years ago. In contrast, no observation was in position to confirm or rule out the presence of CO in Saturn's troposphere (Noll et al. Icarus, 89, 168, 1990).Here, we present CRIRES/ELT 5-μm observations of Saturn that definitely confirm the presence of CO in Saturn's troposphere. We will present the derived CO abundance and its implication for Saturn's tropospheric transport rate and water deep abundance.

Space Opportunities for Tropospheric Chemistry Research

NASA Technical Reports Server (NTRS)

Levine, Joel S. (Editor)

1987-01-01

The objective of this workshop was to assess future technological and scientific directions for measurements of tropospheric trace gases and aerosols from space. Various instrument technologies were considered including spectrometry, gas correlation filter radiometry, spectral radiometry, and lidar.

Tropospheric chemistry research in the U.S.: 1991-1994

NASA Astrophysics Data System (ADS)

Penner, Joyce E.; Atherton, Cynthia S.; Dignon, Jane

1995-07-01

The troposphere is chemically complex. Many of the important species in the troposphere are short-lived, with lifetimes less than or of order of a month. Hence, the composition of the troposphere is regionally diverse, leading to regionally diverse chemical processes which control that composition. With the advent of three-dimensional models and regionally-specific estimates of emissions, however, it has become clear that human activity has perturbed the composition of even short-lived species over vast regions of the globe. The list of short-lived species of concern includes the reactive nitrogen oxides, reactive sulfur, ozone, nonmethane hydrocarbons and carbon monoxide. Observations have established that increases in the long-lived species such as carbon dioxide, methane, nitrous oxide, and the chlorofluorocarbons are taking place with important resulting impacts on stratospheric chemistry. Further, there is some indication that carbonyl sulfide (a major precursor to stratospheric aerosols) may have an important anthropogenic source. Growth of pollutants such as these are of concern because they act as greenhouse gases or aerosol precursors (CO2, CH4, O3, N2O, chlorofluorocarbons, carbonyl sufide, reactive sulfur), as agents for depletion of stratospheric ozone (N2O, chlorofluorocarbons), are harmful to vegetation (O3, acids) or act as nutrients (nitrate, sulfate, trace metals). The chemical interactions are important to understand, because the build up of pollutants depends not only on the rates of their release into the troposphere but on their rate of removal in the troposphere. Removal rates depend on processes which determine the rate of oxidation of the component (which for most species proceeds mainly by reaction with the hydroxyl radical) or through precipitation scavenging or dissolution in the ocean (which requires that the pollutant or its oxidation product(s) be soluble in water).

Quantification of HCl from high-resolution, ground-based, infrared solar spectra in the 3000 per cm region

NASA Technical Reports Server (NTRS)

Goldman, A.; Murcray, F. J.; Blatherwick, R. D.; Murcray, D. G.

1986-01-01

Recent ground-based infrared solar spectra at 0.02 per cm resolution in the 3000 per cm region have been analyzed for the atmospheric content of HCl. Nonlinear spectral least-squares fitting applied to spectra obtained at several zenith angles shows little sensitivity of the results to tropospheric HCl but provides an accurate measurement of the total column amount.

21 Layer troposphere-stratosphere climate model

NASA Technical Reports Server (NTRS)

Rind, D.; Suozzo, R.; Lacis, A.; Russell, G.; Hansen, J.

1984-01-01

The global climate model is extended through the stratosphere by increasing the vertical resolution and raising the rigid model top to the 0.01 mb (75 km) level. The inclusion of a realistic stratosphere is necessary for the investigation of the climate effects of stratospheric perturbations, such as changes of ozone, aerosols or solar ultraviolet irradiance, as well as for studying the effect on the stratosphere of tropospheric climate changes. The observed temperature and wind patterns throughout the troposphere and stratosphere are simulated. In addition to the excess planetary wave amplitude in the upper stratosphere, other model deficiences include the Northern Hemisphere lower stratospheric temperatures being 5 to 10 C too cold in winter at high latitudes and the temperature at 50 to 60 km altitude near the equator are too cold. Methods of correcting these deficiencies are discussed.

Upper-Tropospheric Winds Derived from Geostationary Satellite Water Vapor Observations

NASA Technical Reports Server (NTRS)

Velden, Christopher S.; Hayden, Christopher M.; Nieman, Steven J.; Menzel, W. Paul; Wanzong, Steven; Goerss, James S.

1997-01-01

The coverage and quality of remotely sensed upper-tropospheric moisture parameters have improved considerably with the deployment of a new generation of operational geostationary meteorological satellites: GOES-8/9 and GMS-5. The GOES-8/9 water vapor imaging capabilities have increased as a result of improved radiometric sensitivity and higher spatial resolution. The addition of a water vapor sensing channel on the latest GMS permits nearly global viewing of upper-tropospheric water vapor (when joined with GOES and Meteosat) and enhances the commonality of geostationary meteorological satellite observing capabilities. Upper-tropospheric motions derived from sequential water vapor imagery provided by these satellites can be objectively extracted by automated techniques. Wind fields can be deduced in both cloudy and cloud-free environments. In addition to the spatially coherent nature of these vector fields, the GOES-8/9 multispectral water vapor sensing capabilities allow for determination of wind fields over multiple tropospheric layers in cloud-free environments. This article provides an update on the latest efforts to extract water vapor motion displacements over meteorological scales ranging from subsynoptic to global. The potential applications of these data to impact operations, numerical assimilation and prediction, and research studies are discussed.

Modeling and Observations of the Response of Tropical Tropospheric Ozone to ENSO

NASA Technical Reports Server (NTRS)

Oman, L. D.; Douglass, A. R.; Ziemke, J. R.; Waugh, D. W.; Lang, C.; Rodriquez, J. M.; Nielsen, J. E.

2012-01-01

The El Nino-Southern Oscillation (ENSO) is the dominant mode of tropical variability on interannual time scales. ENSO appears to extend its influence into the chemical composition of the tropical troposphere, Recent results have revealed an ENSO induced wave-1 anomaly in observed tropical tropospheric column ozone, This results in a dipole over the western and eastern tropical Pacific, whereby differencing the two regions produces an ozone anomaly with an extremely high correlation to the Nino 3.4 Index. We have successfully reproduced this result using the Goddard Earth Observing System Version 5 (GEOS-5) general circulation model coupled to a comprehensive stratospheric and tropospheric chemical mechanism forced with observed sea surface temperatures over the past 25 years, An examination of the modeled ozone field reveals the vertical contributions of tropospheric ozone to the column over the western and eastern Pacific region, We will show targeted comparisons with SHADOZ ozonesondes over these regions to provide insight into the vertical structure. Also, comparisons with NASA's Aura satellite Microwave Limb Sounder (MLS) and Tropospheric Emissions Spectrometer (TES) instruments and other appropriate data sets will be shown. In addition, the water vapor response to ENSO will be compared to help illuminate its role relative to dynamics in impacting ozone concentrations. These results indicate that the tropospheric ozone response to ENSO is potentially a very useful chemistry-climate diagnostic and should be considered in future modeling assessments.

Radiative forcing perturbation due to observed increases in tropospheric ozone at Hohenpeissenberg

NASA Technical Reports Server (NTRS)

Wang, Wei-Chyung; Bojkov, Rumen D.; Zhuang, Yi-Cheng

1994-01-01

The effect on surface temperature due to changes in atmospheric O3 depends highly on the latitude where the change occurs. Previous sensitivity calculations indicate that ozone changes in the upper troposphere and lower stratosphere are more effective in causing surface temperature change (Wang et al., 1980). Long term ground-based observations show that tropospheric ozone, especially at the tropopause region, has been increasing at middle and high latitudes in the Northern Hemisphere (NATO, 1988; Quadrennial Ozone Symposium, 1992). These increases will enhance the greenhouse effect and increase the radiative forcing to the troposphere-surface system, which is opposite to the negative radiative forcing calculated from the observed stratospheric ozone depletion recently reported in WMO (1992). We used more than two thousands regularly measured ozonesondes providing reliable vertical O3 distribution at Hohenpeissenberg (47N; 11E) for the 1967-1990 to study the instantaneous solar and longwave radiative forcing the two decades 1971-1990 and compare the forcing with those caused by increasing CO2, CH4, N2O, and CFCs. Calculations are also made to compare the O3 radiative forcing between stratospheric depletion and tropospheric increase. Results indicate that the O3 changes will induce a positive radiative forcing dominated by tropospheric O3 increase and the magnitude of the forcing is comparable to that due to CO2 increases during the two decades. The significant implications of the tropospheric O3 increase to the global climate are discussed.

Ground Experiments of Remote Synchronization for Onboard Crystal Oscillator of Quasi-Zenith Satellites - Use of Multiple Positioning Signals for Feedback Control

DTIC Science & Technology

2007-01-01

Iwata, A. Iwasaki, Y. Fukuyama, F. Tappero, K. Hagimoto, T. Ikegami , and H. Murakami, 2004, “Ground Testbed for Quasi-Zenith Satellite Remote...JSASS, Tokyo), ISTS 2004-f-16. [7] T. Iwata, F. Tappero, M. Imae, Y. Fukuyama, K. Hagimoto, H. Murakami, T. Ikegami , A. Iwasaki, K. Nakajima, and Y

Characteristics of intercontinental transport of tropospheric ozone from Africa to Asia

NASA Astrophysics Data System (ADS)

Han, Han; Liu, Jane; Yuan, Huiling; Zhuang, Bingliang; Zhu, Ye; Wu, Yue; Yan, Yuhan; Ding, Aijun

2018-03-01

In this study, we characterize the transport of ozone from Africa to Asia through the analysis of the simulations of a global chemical transport model, GEOS-Chem, from 1987 to 2006. The receptor region Asia is defined within 5-60° N and 60-145° E, while the source region Africa is within 35° S-15° N and 20° W-55° E and within 15-35° N and 20° W-30° E. The ozone generated in the African troposphere from both natural and anthropogenic sources is tracked through tagged ozone simulation. Combining this with analysis of trajectory simulations using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, we find that the upper branch of the Hadley cell connects with the subtropical westerlies in the Northern Hemisphere (NH) to form a primary transport pathway from Africa to Asia in the middle and upper troposphere throughout the year. The Somali jet that runs from eastern Africa near the equator to the Indian subcontinent in the lower troposphere is the second pathway that appears only in NH summer. The influence of African ozone mainly appears over Asia south of 40° N. The influence shows strong seasonality, varying with latitude, longitude, and altitude. In the Asian upper troposphere, imported African ozone is largest from March to May around 30° N (12-16 ppbv) and lowest during July-October around 10° N ( ˜ 2 ppbv). In the Asian middle and lower troposphere, imported African ozone peaks in NH winter between 20 and 25° N. Over 5-40° N, the mean fractional contribution of imported African ozone to the overall ozone concentrations in Asia is largest during NH winter in the middle troposphere ( ˜ 18 %) and lowest in NH summer throughout the tropospheric column ( ˜ 6 %). This seasonality mainly results from the collective effects of the ozone precursor emissions in Africa and meteorology and chemistry in Africa, in Asia and along the transport pathways. The seasonal swing of the Hadley circulation and subtropical westerlies along the

An assessment of potential impact of alternative fluorocarbons on tropospheric ozone

NASA Technical Reports Server (NTRS)

Niki, Hiromi

1990-01-01

While the chlorofuorocarbons (CFCs) such as CFC-11 (CFCl3) and CFC-12 (CF2Cl2) are chemically inert in the troposphere, the hydrogen-containing halocarbons being considered as their replacements can, to a large extent, be removed in the troposphere by the HO radical. These alternative halocarbons include the hydrochlorofluorocarbons (HCFCs) 123 (CF3CHCl2), 141b (CFCl2CH3), 142b (CF2ClCH3), 22 (CHF2Cl), and 124 (CF3CHFCl) and the hydrofluorocarbons (HCFs) 134a (CF3CH2F), 152a (CHF2CH3) and 125 (CF3CHF2). Listed are the rate constants (k) for the HO radical reaction of these compounds and their estimated chemical lifetimes in the troposphere. In this table, values of the lifetimes of these selected HCFCs and HCFs are seen to vary by more than a factor of more than ten ranging from 1.6 years for HFC 152a and HCFC 125 to as long as 28 years for HFC 125. Clearly, from the standpoint of avoiding or minimizing impact on stratospheric O3, those halocarbons with short tropospheric lifetimes are the desirable alternates. However, potential environmental consequences of their degradation in the troposphere should be assessed and taken into account in the selection process.

Impact of Stratospheric Ozone Distribution on Features of Tropospheric Circulation

NASA Astrophysics Data System (ADS)

Barodka, Siarhei; Krasouski, Aliaksandr; Mitskevich, Yaroslav; Shalamyansky, Arkady

2016-04-01

In this work we study connections between stratospheric ozone distribution and general circulation patterns in the troposphere and aim to investigate the causal relationship between them, including the practical side of the influence of stratospheric ozone on tropospheric medium-range weather and regional climate. Analysis of several decades of observational data, which has been performed at the A.I. Voeikov Main Geophysical Observatory, suggests a clear relation between the stratospheric ozone distribution, upper stratospheric temperature field and planetary-scale air-masses boundaries in the troposphere [1]. Furthermore, it has been shown that each global air-mass, which can be attributed to the corresponding circulation cell in a conceptual model of tropospheric general circulation, has a distinct "regime" of ozone vertical distribution in the stratosphere [1-3]. Proceeding from atmospheric reanalyses combined with satellite and ground-based observations, we study time evolution of the upper-level frontal zones (stationary fronts) with the relevant jet streams, which can be treated as boundaries of global air-masses, in connection with the tropopause height and distribution of ozone in the stratosphere. For that, we develop an algorithm for automated identification of jet streams, stationary fronts and tropopause surface from gridded data (reanalyses or modelling results), and apply it for several cases associated with rapid changes in the stratospheric temperature and ozone fields, including SSW events over Eastern Siberia. Aiming to study the causal relationship between the features of tropospheric circulation and changes in the stratospheric ozone field, we estimate the time lag between these categories of processes on different time scales. Finally, we discuss the possibility to use the elementary circulation mechanisms classification (by B.L. Dzerdzeevski) in connection with analysis of the stratospheric ozone field and the relevant stratosphere-troposphere

The impact of higher-order ionospheric effects on estimated tropospheric parameters in Precise Point Positioning

NASA Astrophysics Data System (ADS)

Zus, F.; Deng, Z.; Wickert, J.

2017-08-01

The impact of higher-order ionospheric effects on the estimated station coordinates and clocks in Global Navigation Satellite System (GNSS) Precise Point Positioning (PPP) is well documented in literature. Simulation studies reveal that higher-order ionospheric effects have a significant impact on the estimated tropospheric parameters as well. In particular, the tropospheric north-gradient component is most affected for low-latitude and midlatitude stations around noon. In a practical example we select a few hundred stations randomly distributed over the globe, in March 2012 (medium solar activity), and apply/do not apply ionospheric corrections in PPP. We compare the two sets of tropospheric parameters (ionospheric corrections applied/not applied) and find an overall good agreement with the prediction from the simulation study. The comparison of the tropospheric parameters with the tropospheric parameters derived from the ERA-Interim global atmospheric reanalysis shows that ionospheric corrections must be consistently applied in PPP and the orbit and clock generation. The inconsistent application results in an artificial station displacement which is accompanied by an artificial "tilting" of the troposphere. This finding is relevant in particular for those who consider advanced GNSS tropospheric products for meteorological studies.

Lidar Profiling In the lower Troposphere: experience from PECAN

NASA Astrophysics Data System (ADS)

Demoz, Belay B.; Delgado, Ruben; Caroll, Brian; Vermeesch, Kevin; Whiteman, David N.; Sakai, Ricardo; Tesfay, Sium; Cooper, Lorenza

2018-04-01

Results from the PECAN (Plains Elevated Convection at Night) campaign are discussed. In particular, the utility of simple backscatter lidars/ceilometers in quantifying atmospheric dynamics parameters and variables as well as evolution of the lower tropospheric dynamics are made. Cases of bore wave dynamics and the potential of these events in lofting of low level, moist, airmass and its consequence in thunderstorm initiation are made. A suite of thermodynamic profiling instruments are combined and compared to describe and visualize lower tropospheric dynamic evolution.

Uncertainties in models of tropospheric ozone based on Monte Carlo analysis: Tropospheric ozone burdens, atmospheric lifetimes and surface distributions

NASA Astrophysics Data System (ADS)

Derwent, Richard G.; Parrish, David D.; Galbally, Ian E.; Stevenson, David S.; Doherty, Ruth M.; Naik, Vaishali; Young, Paul J.

2018-05-01

Recognising that global tropospheric ozone models have many uncertain input parameters, an attempt has been made to employ Monte Carlo sampling to quantify the uncertainties in model output that arise from global tropospheric ozone precursor emissions and from ozone production and destruction in a global Lagrangian chemistry-transport model. Ninety eight quasi-randomly Monte Carlo sampled model runs were completed and the uncertainties were quantified in tropospheric burdens and lifetimes of ozone, carbon monoxide and methane, together with the surface distribution and seasonal cycle in ozone. The results have shown a satisfactory degree of convergence and provide a first estimate of the likely uncertainties in tropospheric ozone model outputs. There are likely to be diminishing returns in carrying out many more Monte Carlo runs in order to refine further these outputs. Uncertainties due to model formulation were separately addressed using the results from 14 Atmospheric Chemistry Coupled Climate Model Intercomparison Project (ACCMIP) chemistry-climate models. The 95% confidence ranges surrounding the ACCMIP model burdens and lifetimes for ozone, carbon monoxide and methane were somewhat smaller than for the Monte Carlo estimates. This reflected the situation where the ACCMIP models used harmonised emissions data and differed only in their meteorological data and model formulations whereas a conscious effort was made to describe the uncertainties in the ozone precursor emissions and in the kinetic and photochemical data in the Monte Carlo runs. Attention was focussed on the model predictions of the ozone seasonal cycles at three marine boundary layer stations: Mace Head, Ireland, Trinidad Head, California and Cape Grim, Tasmania. Despite comprehensively addressing the uncertainties due to global emissions and ozone sources and sinks, none of the Monte Carlo runs were able to generate seasonal cycles that matched the observations at all three MBL stations. Although

How well can global chemistry models calculate the reactivity of short-lived greenhouse gases in the remote troposphere, knowing the chemical composition

NASA Astrophysics Data System (ADS)

Prather, Michael J.; Flynn, Clare M.; Zhu, Xin; Steenrod, Stephen D.; Strode, Sarah A.; Fiore, Arlene M.; Correa, Gustavo; Murray, Lee T.; Lamarque, Jean-Francois

2018-05-01

We develop a new protocol for merging in situ measurements with 3-D model simulations of atmospheric chemistry with the goal of integrating these data to identify the most reactive air parcels in terms of tropospheric production and loss of the greenhouse gases ozone and methane. Presupposing that we can accurately measure atmospheric composition, we examine whether models constrained by such measurements agree on the chemical budgets for ozone and methane. In applying our technique to a synthetic data stream of 14 880 parcels along 180° W, we are able to isolate the performance of the photochemical modules operating within their global chemistry-climate and chemistry-transport models, removing the effects of modules controlling tracer transport, emissions, and scavenging. Differences in reactivity across models are driven only by the chemical mechanism and the diurnal cycle of photolysis rates, which are driven in turn by temperature, water vapor, solar zenith angle, clouds, and possibly aerosols and overhead ozone, which are calculated in each model. We evaluate six global models and identify their differences and similarities in simulating the chemistry through a range of innovative diagnostics. All models agree that the more highly reactive parcels dominate the chemistry (e.g., the hottest 10 % of parcels control 25-30 % of the total reactivities), but do not fully agree on which parcels comprise the top 10 %. Distinct differences in specific features occur, including the spatial regions of maximum ozone production and methane loss, as well as in the relationship between photolysis and these reactivities. Unique, possibly aberrant, features are identified for each model, providing a benchmark for photochemical module development. Among the six models tested here, three are almost indistinguishable based on the inherent variability caused by clouds, and thus we identify four, effectively distinct, chemical models. Based on this work, we suggest that water vapor

Spatio-temporal assessment and seasonal variation of tropospheric ozone in Pakistan during the last decade.

PubMed

Noreen, Asma; Khokhar, Muhammad Fahim; Zeb, Naila; Yasmin, Naila; Hakeem, Khalid Rehman

2018-03-01

This study uses the tropospheric ozone data derived from combined observations of Ozone Monitoring Instrument/Microwave Limb Sounder instruments by using the tropospheric ozone residual method. The main objective was to study the spatial distribution and temporal evolution in the troposphere ozone columns over Pakistan during the time period of 2004 to 2014. Results showed an overall increase of 3.2 ± 1.1 DU in tropospheric ozone columns over Pakistan. Spatial distribution showed enhanced ozone columns in the Punjab and southern Sindh consistent to high population, urbanization, and extensive anthropogenic activities, and exhibited statistically significant temporal increase. Seasonal variations in tropospheric ozone columns are driven by various factors such as seasonality in UV-B fluxes, seasonality in ozone precursor gases such as NO x and volatile organic compounds (caused by temperature dependent biogenic emission) and agricultural fire activities in Pakistan. A strong correlation of 96% (r = 0.96) was found between fire events and tropospheric ozone columns in Pakistan.

A search for solar related changes in tropospheric weather

NASA Technical Reports Server (NTRS)

Mohanakumar, K.

1989-01-01

The possibility that solar variations associated with the 11-year solar cycle may be the cause of the changes in tropospheric weather and climate has been the subject to scientific investigation for several decades. Meteorologists are greatly concerned with the changes in tropospheric phenomena. An attempt was made to find solar activity related changes in tropospheric weather, by the modulation of the quasi-biennial oscillation (QBO) of zonal wind at 50 mb. Rainfall and surface temperature data for a period of about three solar cycles, 1953 to 1988, from various stations in the Indian subcontinent were utilized. By extension, a possible teleconnection was looked for between the temperature changes in middle atmospheric levels and surface temperature when the data are stratified according to east or west phase of the QBO. The temperature data were averaged for January and February to represent the winter temperature and for July and August to represent the summer temperature.

Tropospheric Emissions: Monitoring of Pollution Overview

NASA Technical Reports Server (NTRS)

Chance, Kelly; Liu, Xiong; Suleiman, Raid M.; Flittner, David; Al-Saadi, Jay; Janz, Scott

2015-01-01

TEMPO is now well into its implementation phase, having passed both its Key Decision Point C and the Critical Design Review (CDR) for the instrument. The CDR for the ground systems will occur in March 2016 and the CDR for the Mission component at a later date, after the host spacecraft has been selected. TEMPO is on schedule to measure atmospheric pollution for greater North America from space using ultraviolet and visible spectroscopy. TEMPO measures from Mexico City to the Canadian oil sands, and from the Atlantic to the Pacific, hourly and at high spatial resolution. TEMPO provides a tropospheric measurement suite that includes the key elements of tropospheric air pollution chemistry. Measurements are from geostationary (GEO) orbit, to capture the inherent high variability in the diurnal cycle of emissions and chemistry. The small product spatial footprint resolves pollution sources at sub-urban scale. Together, this temporal and spatial resolution improves emission inventories, monitors population exposure, and enables effective emission-control strategies. TEMPO takes advantage of a GEO host spacecraft to provide a modest cost mission that measures the spectra required to retrieve O3, NO2, SO2, H2CO, C2H2O2, H2O, aerosols, cloud parameters, and UVB radiation. TEMPO thus measures the major elements, directly or by proxy, in the tropospheric O3 chemistry cycle. Multi-spectral observations provide sensitivity to O3 in the lowermost troposphere, substantially reducing uncertainty in air quality predictions by 50 percent. TEMPO quantifies and tracks the evolution of aerosol loading. It provides near-real-time air quality products that will be made widely, publicly available. TEMPO provides much of the atmospheric measurement capability recommended for GEO-CAPE in the 2007 National Research Council Decadal Survey, Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond. Instruments from Europe (Sentinel 4) and Asia (GEMS) will

Global Distribution and Trends of Tropospheric Ozone: An Observation-Based Review

NASA Technical Reports Server (NTRS)

Cooper, O. R.; Parrish, D. D.; Ziemke, J.; Cupeiro, M.; Galbally, I. E.; Gilge, S.; Horowitz, L.; Jensen, N. R.; Lamarque, J.-F.; Naik, V.;

Investigations of Stratosphere-Troposphere Exchange of Ozone Derived From MLS Observations

NASA Technical Reports Server (NTRS)

Olsen, Mark A.; Schoeberl, Mark R.; Ziemke, Jerry R.

2006-01-01

Daily high-resolution maps of stratospheric ozone have been constructed using observations by MLS combined with trajectory information. These fields are used to determine the extratropical stratosphere-troposphere exchange (STE) of ozone for the year 2005 using two diagnostic methods. The resulting two annual estimates compare well with past model- and observational-based estimates. Initial analyses of the seasonal characteristics indicate that significant STE of ozone in the polar regions occurs only during spring and early summer. We also examine evidence that the Antarctic ozone hole is responsible for a rapid decrease in the rate of ozone STE during the SH spring. Subtracting the high-resolution stratospheric ozone fiom OMI total column measurements creates a high-resolution tropospheric ozone residual (HTOR) product. The HTOR fields are compared to the spatial distribution of the ozone STE. We show that the mean tropospheric ozone maxima tend to occur near locations of significant ozone STE. This suggests that STE may be responsible for a significant fraction of many mean tropospheric ozone anomalies.

Twenty years of balloon-borne tropospheric aerosol measurements at Laramie, Wyoming

NASA Technical Reports Server (NTRS)

Hofmann, David J.

1993-01-01

The paper examines the tropospheric aerosol record obtained over the period 1971 to 1990, during which high-altitude balloons with optical particle counters were launched at Laramie, Wyoming, in a long-term study of the stratospheric sulfate aerosol layer. All aerosol particle size ranges display pronounced seasonal variations, with the condensation nuclei concentration and the optically active component showing a summer maximum throughout the troposphere. Mass estimates, assuming spherical sulfate particles, indicate an average column mass between altitudes of 2.5 and 10 km of about 4 and 16 mg/sq m in winter and summer, respectively. Calculated optical depths vary between 0.01 and 0.04 from winter to summer; the estimated mass scattering cross section is about 3 sq m/g throughout the troposphere. There is evidence for a decreasing trend of 1.6-1.8 percent/yr in the optically active tropospheric aerosol over the past 20 yr, which may be related to a similar reduction in SO2 emission in the U.S. over this period.

Derivation of Tropospheric Ozone Climatology and Trends from TOMS Data

NASA Technical Reports Server (NTRS)

Newchurch, Michael J.; McPeters, Rich; Logan, Jennifer; Kim, Jae-Hwan

2002-01-01

This research addresses the following three objectives: (1) Derive tropospheric ozone columns from the TOMS instruments by computing the difference between total-ozone columns over cloudy areas and over clear areas in the tropics; (2) Compute secular trends in Nimbus-7 derived tropospheric Ozone column amounts and associated potential trends in the decadal-scale tropical cloud climatology; (3) Explain the occurrence of anomalously high ozone retrievals over high ice clouds.

The Response of Tropospheric Ozone to ENSO in Observations and a Chemistry-Climate Simulation

NASA Technical Reports Server (NTRS)

Oman, L. D.; Douglass, A. R.; Ziemke, J. R.; Waugh, D. W.; Rodriguez, J. M.; Nielsen, J. E.

2012-01-01

The El Nino-Southern Oscillation (ENSO) is the dominant mode of tropical variability on interannual time scales. ENSO appears to extend its influence into the chemical composition of the tropical troposphere. Recent results have revealed an ENSO induced wave-l anomaly in observed tropical tropospheric column ozone. This results in a dipole over the western and eastern tropical Pacific, whereby differencing the two regions produces an ozone anomaly with an extremely high correlation to the Nino 3.4 Index. We have successfully reproduced this result using the Goddard Earth Observing System Version 5 (GEOS-5) general circulation model coupled to a comprehensive stratospheric and tropospheric chemical mechanism forced with observed sea surface temperatures over the past 25 years. An examination of the modeled ozone field reveals the vertical contributions of tropospheric ozone to the column over the western and eastern Pacific region. We will show targeted comparisons with observations from NASA's Aura satellite Microwave Limb Sounder (MLS), and the Tropospheric Emissions Spectrometer (TES) to provide insight into the vertical structure of ozone changes. The tropospheric ozone response to ENSO could be a useful chemistry-climate model evaluation tool and should be considered in future modeling assessments.

Tropospheric Ozone from Assimilation of Aura Data using Different Definitions of the Tropopause

NASA Technical Reports Server (NTRS)

Stajner, Ivanka; Wargan, K.; Chang, L.-P.; Hayashi, H.; Pawson, S.; Pawson, Steven; Livesey, N.; Bhartia, P. K.

2006-01-01

Ozone data from Aura OMI and MLS instruments were assimilated into the general circulation model (GCM) constrained by assimilated meteorological fields from the Global Modeling and Assimilation Office at NASA Goddard. Properties of tropospheric ozone and their sensitivity to the definition of the tropopause are investigated. Three definitions of the tropopause are considered: (1) dynamical (using potential vorticity and potential temperature), (2) using temperature lapse rate, and (3) using a fixed ozone value. Comparisons of the tropospheric ozone columns using these tropopause definitions will be presented and evaluated against coincident profiles from ozone sondes. Assimilated ozone profiles are used to identify possible tropopause folding events, which are important for stratosphere-troposphere exchange. Each profile is searched for multiple levels at which ozone attains the value typical of the troposphere-stratosphere transition in order to identify possible tropopause folds. Constrained by the dynamics from a global model and by assimilation of Aura ozone data every 3-hours, this data set provides an opportunity to study ozone evolution in the upper troposphere and lower stratosphere with high temporal resolution.

Seasonal Variability in Tropospheric Ozone Distribution Over Qatar

NASA Astrophysics Data System (ADS)

Ayoub, Mohammed; Ackermann, Luis

2015-04-01

We report on the vertical distribution and seasonal variability in tropospheric ozone over the Middle East through one year of weekly ozonesondes launched from Doha, Qatar during 2014. A total of 49 2Z-V7 DMT/EN-SCI Electrochemical Concentration Cell (ECC) ozonesondes employing a 1% buffered potassium iodide solution (KI), coupled with iMet-1-RS GPS radiosondes were launched around 1300 local time. The authors used the SkySonde telemetry software (developed by CIRES and NOAA/ESRL) and developed robust in-house data quality assurance and validation methodologies. The average height of the thermal tropopause is between 15-17.5 km (125-85 hPa). Monthly average relative humidity around the tropopause shows an enhancement during the months of June through the beginning of October. Monthly average temperature profiles show the development of the subtropical subsidence inversion around 5-6 km (450-520 hPa) between the months of April through October. The subsidence inversion is strongest during the months of June and July and is accompanied by a sharp drop in relative humidity over a 100-300 m in the vertical. The monthly average ozone background concentration between the Planetary Boundary Layer (PBL) height and the subsidence inversion increases from 50 ppb in the winter to almost 80 ppb in the summer months. An enhancement of up to 50% in the average ozone in the mid-to-upper troposphere (above the subsidence inversion) is strongest during the summer months (June through September) and results in average concentrations between 80-100 ppb. In the upper troposphere (above 13 km/200 hPa) ozone concentrations are highest during the spring and summer months. This is coupled with a drop in the average height of the tropopause. HYSPLIT back-trajectory analysis shows the enhancement in mid-to-upper tropospheric ozone in the summer is due to persistent high pressure over the Middle East between the months of June through September. Evidence of Stratosphere-Troposphere Exchange

Free tropospheric transport of microorganisms from Asia to North America.

PubMed

Smith, David J; Jaffe, Daniel A; Birmele, Michele N; Griffin, Dale W; Schuerger, Andrew C; Hee, Jonathan; Roberts, Michael S

2012-11-01

Microorganisms are abundant in the troposphere and can be transported vast distances on prevailing winds. This study measures the abundance and diversity of airborne bacteria and fungi sampled at the Mt. Bachelor Observatory (located 2.7 km above sea level in North America) where incoming free tropospheric air routinely arrives from distant sources across the Pacific Ocean, including Asia. Overall deoxyribonucleic acid (DNA) concentrations for microorganisms in the free troposphere, derived from quantitative polymerase chain reaction assays, averaged 4.94 × 10(-5) ng DNA m(-3) for bacteria and 4.77 × 10(-3) ng DNA m(-3) for fungi. Aerosols occasionally corresponded with microbial abundance, most often in the springtime. Viable cells were recovered from 27.4 % of bacterial and 47.6 % of fungal samples (N = 124), with 49 different species identified by ribosomal DNA gene sequencing. The number of microbial isolates rose significantly above baseline values on 22-23 April 2011 and 13-15 May 2011. Both events were analyzed in detail, revealing distinct free tropospheric chemistries (e.g., low water vapor, high aerosols, carbon monoxide, and ozone) useful for ruling out boundary layer contamination. Kinematic back trajectory modeling suggested air from these events probably originated near China or Japan. Even after traveling for 10 days across the Pacific Ocean in the free troposphere, diverse and viable microbial populations, including presumptive plant pathogens Alternaria infectoria and Chaetomium globosum, were detected in Asian air samples. Establishing a connection between the intercontinental transport of microorganisms and specific diseases in North America will require follow-up investigations on both sides of the Pacific Ocean.

Free tropospheric transport of microorganisms from Asia to North America

USGS Publications Warehouse

D. Smith,; Dan Jaffe,; Michele Birmele,; Griffin, Dale W.; Andrew Schuerger,; Hee, J.; Michael Roberts,

2012-01-01

Microorganisms are abundant in the troposphere and can be transported vast distances on prevailing winds. This study measures the abundance and diversity of airborne bacteria and fungi sampled at the Mt. Bachelor Observatory (located 2.7 km above sea level in North America) where incoming free tropospheric air routinely arrives from distant sources across the Pacific Ocean, including Asia. Overall deoxyribonucleic acid (DNA) concentrations for microorganisms in the free troposphere, derived from quantitative polymerase chain reaction assays, averaged 4.94 × 10(-5) ng DNA m(-3) for bacteria and 4.77 × 10(-3) ng DNA m(-3) for fungi. Aerosols occasionally corresponded with microbial abundance, most often in the springtime. Viable cells were recovered from 27.4 % of bacterial and 47.6 % of fungal samples (N = 124), with 49 different species identified by ribosomal DNA gene sequencing. The number of microbial isolates rose significantly above baseline values on 22-23 April 2011 and 13-15 May 2011. Both events were analyzed in detail, revealing distinct free tropospheric chemistries (e.g., low water vapor, high aerosols, carbon monoxide, and ozone) useful for ruling out boundary layer contamination. Kinematic back trajectory modeling suggested air from these events probably originated near China or Japan. Even after traveling for 10 days across the Pacific Ocean in the free troposphere, diverse and viable microbial populations, including presumptive plant pathogens Alternaria infectoria and Chaetomium globosum, were detected in Asian air samples. Establishing a connection between the intercontinental transport of microorganisms and specific diseases in North America will require follow-up investigations on both sides of the Pacific Ocean.

Global observations of tropospheric BrO columns using GOME-2 satellite data

NASA Astrophysics Data System (ADS)

Theys, N.; van Roozendael, M.; Hendrick, F.; Yang, X.; de Smedt, I.; Richter, A.; Begoin, M.; Errera, Q.; Johnston, P. V.; Kreher, K.; de Mazière, M.

2010-11-01

Measurements from the GOME-2 satellite instrument have been analyzed for tropospheric BrO using a residual technique that combines measured BrO columns and estimates of the stratospheric BrO content from a climatological approach driven by O3 and NO2 observations. Comparisons between the GOME-2 results and BrO vertical columns derived from correlative ground-based and SCIAMACHY nadir observations, present a good level of consistency. We show that the adopted technique enables separation of stratospheric and tropospheric fractions of the measured total BrO columns and allows quantitative study of the BrO plumes in polar regions. While some satellite observed plumes of enhanced BrO can be explained by stratospheric descending air, we show that most BrO hotspots are of tropospheric origin, although they are often associated to regions with low tropopause heights as well. Elaborating on simulations using the p-TOMCAT tropospheric chemical transport model, this result is found to be consistent with the mechanism of bromine release through sea salt aerosols production during blowing snow events. Outside polar regions, evidence is provided for a global tropospheric BrO background with column of 1-3×1013 molec/cm2, consistent with previous estimates.

Relationship between changes in the upper and lower tropospheric water vapor: A revisit

NASA Astrophysics Data System (ADS)

Yang, M.; Sun, D. Z.; Zhang, G. J.

2017-12-01

Upper tropospheric water vapor response to enhanced greenhouse gas forcing is as important as the lower tropospheric water vapor response in determining climate sensitivity. Early studies using older versions of climate models have suggested that the upper- and lower-troposphere water vapor changes are more strongly coupled in the climate models than in the observations. Here we reexamine this issue using a state-of-the-art climate model—the NCAR community model CAM5. Specifically, we have calculated the correlations between interannual variations of specific humidity in all levels of the troposphere with that at the surface in CAM5 and in the observations (as represented by the updated ERA-Interim and NCEP reanalysis). It is found that the previously noted biases in how strongly upper tropospheric water vapor and lower troposphere water vapor are linked still exist in CAM5—the change in the tropical averaged upper tropospheric water vapor is more strongly correlated with the change in the surface. However, this bias disappears in the averaged correlation obtained by averaging the point-by-point correlations over the tropics. The spatial pattern of the point-by-point correlations reveals that the better agreement between the model and the observations is related to the opposite model biases in different regions: the correlation is weaker in the model in the western Pacific, but stronger in the central and eastern Pacific. Further analysis of precipitation fields suggests that the weaker (stronger) coupling between tropospheric water vapor and surface moisture over western (central-eastern) Pacific in model is related to weaker (stronger) simulated convective activities in these regions. More specifically, during El Nino, the model has excessive deep convection in the central Pacific, but too littler deep convection in western Pacific. Implications of the results are discussed in the context of climate change as well as in the context of how to improve the model

The global warming potential of methane reassessed with combined stratosphere and troposphere chemistry

NASA Astrophysics Data System (ADS)

Holmes, C. D.; Archibald, A. T.; Eastham, S. D.; Søvde, O. A.

2017-12-01

Methane is a direct and indirect greenhouse gas. The direct greenhouse effect comes from the radiation absorbed and emitted by methane itself. The indirect greenhouse effect comes from radiatively active gases that are produced during methane oxidation: principally O3, H2O, and CO2. Methane also suppresses tropospheric OH, which indirectly affects numerous greenhouses gases and aerosols. Traditionally, the methane global warming potential (GWP) has included the indirect effects on tropospheric O3 and OH and stratospheric H2O, with these effects estimated independently from unrelated tropospheric and stratospheric chemistry models and observations. Using this approach the CH4 is about 28 over 100 yr (without carbon cycle feedbacks, IPCC, 2013). Here we present a comprehensive analysis of the CH4 GWP in several 3-D global atmospheric models capable of simulating both tropospheric and stratospheric chemistry (GEOS-Chem, Oslo CTM3, UKCA). This enables us to include, for the first time, the indirect effects of CH4 on stratospheric O3 and stratosphere-troposphere coupling. We diagnose the GWP from paired simulations with and without a 5% perturbation to tropospheric CH4 concentrations. Including stratospheric chemistry nearly doubles the O3 contribution to CH4 GWP because of O3 production in the lower stratosphere and because CH4 inhibits Cl-catalyzed O3 loss in the upper stratosphere. In addition, stratosphere-troposphere coupling strengthens the chemical feedback on its own lifetime. In the stratosphere, this feedback operates by a CH4 perturbation thickening the stratospheric O3 layer, which impedes UV-driven OH production in the troposphere and prolongs the CH4 lifetime. We also quantify the impact of CH4-derived H2O on the stratospheric HOx cycles but these effects are small. Combining all of the above, these models suggest that the 100-yr GWP of CH4 is over 33.5, a 20% increase over the latest IPCC assessment.

How Can TOLNet Help to Better Understand Tropospheric Ozone? A Satellite Perspective

NASA Technical Reports Server (NTRS)

Johnson, Matthew S.

2018-01-01

Potential sources of a priori ozone (O3) profiles for use in Tropospheric Emissions: Monitoring of Pollution (TEMPO) satellite tropospheric O3 retrievals are evaluated with observations from multiple Tropospheric Ozone Lidar Network (TOLNet) systems in North America. An O3 profile climatology (tropopause-based O3 climatology (TB-Clim), currently proposed for use in the TEMPO O3 retrieval algorithm) derived from ozonesonde observations and O3 profiles from three separate models (operational Goddard Earth Observing System (GEOS-5) Forward Processing (FP) product, reanalysis product from Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA2), and the GEOS-Chem chemical transport model (CTM)) were: 1) evaluated with TOLNet measurements on various temporal scales (seasonally, daily, hourly) and 2) implemented as a priori information in theoretical TEMPO tropospheric O3 retrievals in order to determine how each a priori impacts the accuracy of retrieved tropospheric (0-10 km) and lowermost tropospheric (LMT, 0-2 km) O3 columns. We found that all sources of a priori O3 profiles evaluated in this study generally reproduced the vertical structure of summer-averaged observations. However, larger differences between the a priori profiles and lidar observations were observed when evaluating inter-daily and diurnal variability of tropospheric O3. The TB-Clim O3 profile climatology was unable to replicate observed inter-daily and diurnal variability of O3 while model products, in particular GEOS-Chem simulations, displayed more skill in reproducing these features. Due to the ability of models, primarily the CTM used in this study, on average to capture the inter-daily and diurnal variability of tropospheric and LMT O3 columns, using a priori profiles from CTM simulations resulted in TEMPO retrievals with the best statistical comparison with lidar observations. Furthermore, important from an air quality perspective, when high LMT O3 values were

Secondary ozone peaks in the troposphere over the Himalayas

NASA Astrophysics Data System (ADS)

Ojha, Narendra; Pozzer, Andrea; Akritidis, Dimitris; Lelieveld, Jos

2017-06-01

Layers with strongly enhanced ozone concentrations in the middle-upper troposphere, referred to as secondary ozone peaks (SOPs), have been observed in different regions of the world. Here we use the global ECHAM5/MESSy atmospheric chemistry model (EMAC) to (i) investigate the processes causing SOPs, (ii) explore both their frequency of occurrence and seasonality, and (iii) assess their effects on the tropospheric ozone budget over the Himalayas. The vertical profiles of potential vorticity (PV) and a stratospheric ozone tracer (O3s) in EMAC simulations, in conjunction with the structure of SOPs, suggest that SOPs over the Himalayas are formed by stratosphere-to-troposphere transport (STT) of ozone. The spatial distribution of O3s further shows that such effects are in general most pronounced in the northern part of India. Model simulated ozone distributions and backward air trajectories show that ozone rich air masses, associated with STT, originate as far as northern Africa and the North Atlantic Ocean, the Middle East, as well as in nearby regions in Afghanistan and Pakistan, and are rapidly (within 2-3 days) transported to the Himalayas. Analysis of a 15-year (2000-2014) EMAC simulation shows that the frequency of SOPs is highest during the pre-monsoon season (e.g. 11 % of the time in May), while no intense SOP events are found during the July-October period. The SOPs are estimated to enhance the tropospheric column ozone (TCO) over the central Himalayas by up to 21 %.

Global tropospheric hydroxyl distribution, budget and reactivity

NASA Astrophysics Data System (ADS)

Lelieveld, Jos; Gromov, Sergey; Pozzer, Andrea; Taraborrelli, Domenico

2016-10-01

The self-cleaning or oxidation capacity of the atmosphere is principally controlled by hydroxyl (OH) radicals in the troposphere. Hydroxyl has primary (P) and secondary (S) sources, the former mainly through the photodissociation of ozone, the latter through OH recycling in radical reaction chains. We used the recent Mainz Organics Mechanism (MOM) to advance volatile organic carbon (VOC) chemistry in the general circulation model EMAC (ECHAM/MESSy Atmospheric Chemistry) and show that S is larger than previously assumed. By including emissions of a large number of primary VOC, and accounting for their complete breakdown and intermediate products, MOM is mass-conserving and calculates substantially higher OH reactivity from VOC oxidation compared to predecessor models. Whereas previously P and S were found to be of similar magnitude, the present work indicates that S may be twice as large, mostly due to OH recycling in the free troposphere. Further, we find that nighttime OH formation may be significant in the polluted subtropical boundary layer in summer. With a mean OH recycling probability of about 67 %, global OH is buffered and not sensitive to perturbations by natural or anthropogenic emission changes. Complementary primary and secondary OH formation mechanisms in pristine and polluted environments in the continental and marine troposphere, connected through long-range transport of O3, can maintain stable global OH levels.

Note on the Effect of Horizontal Gradients for Nadir-Viewing Microwave and Infrared Sounders

NASA Technical Reports Server (NTRS)

Joiner, J.; Poli, P.

2004-01-01

Passive microwave and infrared nadir sounders such as the Advanced Microwave Sounding Unit A (AMSU-A) and the Atmospheric InfraRed Sounder (AIRS), both flying on NASA s EOS Aqua satellite, provide information about vertical temperature and humidity structure that is used in data assimilation systems for numerical weather prediction and climate applications. These instruments scan cross track so that at the satellite swath edges, the satellite zenith angles can reach approx. 60 deg. The emission path through the atmosphere as observed by the satellite is therefore slanted with respect to the satellite footprint s zenith. Although radiative transfer codes currently in use at operational centers use the appropriate satellite zenith angle to compute brightness temperature, the input atmospheric fields are those from the vertical profile above the center of the satellite footprint. If horizontal gradients are present in the atmospheric fields, the use of a vertical atmospheric profile may produce an error. This note attempts to quantify the effects of horizontal gradients on AIRS and AMSU-A channels by computing brightness temperatures with accurate slanted atmospheric profiles. We use slanted temperature, water vapor, and ozone fields from data assimilation systems. We compare the calculated slanted and vertical brightness temperatures with AIRS and AMSU-A observations. We show that the effects of horizontal gradients on these sounders are generally small and below instrument noise. However, there are cases where the effects are greater than the instrument noise and may produce erroneous increments in an assimilation system. The majority of the affected channels have weighting functions that peak in the upper troposphere (water vapor sensitive channels) and above (temperature sensitive channels) and are unlikely t o significantly impact tropospheric numerical weather prediction. However, the errors could be significant for other applications such as stratospheric

Observations and modeling of bromine induced mercury oxidation in the tropical free troposphere during TORERO

NASA Astrophysics Data System (ADS)

Coburn, Sean; Wang, Siyuan; terSchure, Arnout; Evans, Matt; Volkamer, Rainer

2013-04-01

The Tropical Ocean tRoposphere Exchange experiment TORERO (Jan/Feb 2012) probed air-sea exchange of very short lived halogens and organic carbon species over the full tropospheric air column above the eastern tropical Pacific Ocean. It is well known that halogens influence the oxidative capacity in the marine boundary layer, but their distribution and abundance is less clear in the tropical free troposphere, where most of tropospheric ozone mass resides, and about 80% of the global methane destruction occurs. The oxidation of elemental mercury (GEM) by halogens (i.e., bromine) further forms gaseous oxidized mercury (GOM), and this oxidation is accelerated at the low temperatures in the free troposphere compared to the boundary layer. Free tropospheric halogen radical abundances are thus of particular importance to understand the entry pathways for GOM deposition from the free troposphere to ecosystem, and the subsequent bio-accumulation of this neurotoxin. This presentation summarizes new observational evidence for halogen vertical distributions over the full tropospheric air column, and their abundance in the tropical troposphere, at mid-latitudes in the Northern and Southern hemisphere. BrO and IO were measured simultaneously by the CU Airborne MAX-DOAS instrument, and organic halogen precursors were measured by online GC-MS (TOGA) during 22 research flights aboard the NSF/NCAR GV aircraft. We employ atmospheric box modeling constrained by observations of gas-phase hydrocarbons, aerosols, photolysis frequencies, and meterological parameters measured aboard the plane to test the observed BrO and IO abundances, and evaluate the rate of GEM oxidation in light of recent updates about the stability of the Hg-Br adduct, and it's fate (Goodsite et al., 2012; Dibble et al., 2012). Finally, we compare our measurements with output from the GEOS-Chem model for selected case studies.

Fourteen-year outcomes of abdominal aortic endovascular repair with the Zenith stent graft.

PubMed

Verzini, Fabio; Romano, Lydia; Parlani, Gianbattista; Isernia, Giacomo; Simonte, Gioele; Loschi, Diletta; Lenti, Massimo; Cao, Piergiorgio

2017-02-01

Long-term results of abdominal aortic aneurysm (AAA) endovascular repair are affected by graft design renewals that tend to improve the performance of older generation prostheses but usually reset the follow-up times to zero. The present study investigated the long-term outcomes of endovascular AAA repair (EVAR) using the Zenith graft, still in use without major modification, in a single center experience. Between 2000 and 2011, 610 patients underwent elective EVAR using the Zenith endograft (Cook Inc, Bloomington, Ind) and represent the study group. Primary outcomes were overall survival, freedom from AAA rupture, and freedom from AAA-related death. Secondary outcomes included freedom from late (>30 days) reintervention, freedom from late (>30 days) conversion to open repair, freedom from aneurysm sac enlargement >5.0 mm and freedom from EVAR failure, defined as a composite of AAA-related death, AAA rupture, AAA growth >5 mm, and any reintervention. Mean age was 73.2 years. Mean aneurysm diameter was 55.3 mm. There were five perioperative deaths (0.8%) and three intraoperative conversions. At a mean follow-up of 99.2 (range, 0-175) months, seven AAA ruptures occurred, all fatal except one. Overall survival was 92.8% ± 1.1% at 1 year, 70.1% ± 1.9% at 5 years, 37.8% ± 2.9% at 10 years, and 24 ± 4% at 14 years. Freedom from AAA-rupture was 99.8% ± 0.02 at 1 year (one case), 99.4% ± 0.04 at 5 years (three cases), and 98.1% ± 0.07 at 10 and 14 years. Freedom from late reintervention and conversion was 98% ± 0.6 at 1 year, 87.7% ± 1.5 at 5 years, 75.7% ± 3.2 at 10 years, and 69.9% ± 5.2 at 14 years. Freedom from aneurysm sac growth >5.0 mm was 99.8% at 1 year, 96.6% ± 0.7 at 5 years, 81.0% ± 3.4 at 10 years, and 74.1% ± 5.8% at 14 years. EVAR failure occurred in 132 (21.6%) patients at 14 years. At multivariate analysis, independent predictors of EVAR failure resulted type I and III endoleak (hazard ratio [HR], 6.7; 95

Enhancement of free tropospheric ozone production by deep convection

NASA Technical Reports Server (NTRS)

Pickering, Kenneth E.; Thompson, Anne M.; Scala, John R.; Tao, Wei-Kuo; Simpson, Joanne

1994-01-01

It is found from model simulations of trace gas and meteorological data from aircraft campaigns that deep convection may enhance the potential for photochemical ozone production in the middle and upper troposphere by up to a factor of 60. Examination of half a dozen individual convective episodes show that the degree of enhancement is highly variable. Factors affecting enhancement include boundary layer NO(x) mixing ratios, differences in the strength and structure of convective cells, as well as variation in the amount of background pollution already in the free troposphere.

Effect of the 1997 El Niño on the distribution of upper tropospheric cirrus

NASA Astrophysics Data System (ADS)

Massie, Steven; Lowe, Paul; Tie, Xuexi; Hervig, Mark; Thomas, Gary; Russell, James

2000-09-01

Geographical distributions of Halogen Occultation Experiment (HALOE) aerosol extinction data for 1993-1998 are analyzed in the troposphere and stratosphere at pressures between 121 and 46 hPa. The El Niño conditions of 1997 increased upper tropospheric cirrus over the mid-Pacific and decreased cirrus over Indonesia. Longitudinal centroids of cirrus in the Pacific and over Indonesia shifted eastward by 25° in the troposphere in 1997. Longitudinal centroids of aerosol in the lower stratosphere do not exhibit longitudinal shifts in 1997, indicating that the effects of El Niño upon equatorial particle distributions are confined to the troposphere. The correlation of the longitudinal centroids of outgoing longwave radiation and HALOE extinction confirms the spatial relationship between deep convective clouds and upper tropospheric cirrus. The number of cirrus events observed each year in 1993-1998 in the upper troposphere are quite similar for the region from the Indian Ocean to the mid-Pacific (30°S to 30°N, 50° to 240°E).

Study Pollution Impacts on Upper-Tropospheric Clouds with Aura, CloudSat, and CALIPSO Data

NASA Technical Reports Server (NTRS)

Wu, Dong

2007-01-01

This viewgraph presentation reviews the impact of pollution on clouds in the Upper Troposphere. Using the data from the Aura Microwave Limb Sounder (MLS), CloudSat, CALIPSO the presentation shows signatures of pollution impacts on clouds in the upper troposphere. The presentation demonstrates the complementary sensitivities of MLS , CloudSat and CALIPSO to upper tropospheric clouds. It also calls for careful analysis required to sort out microphysical changes from dynamical changes.

Effects of stratospheric ozone recovery on photochemistry and ozone air quality in the troposphere

NASA Astrophysics Data System (ADS)

Zhang, H.; Wu, S.; Huang, Y.; Wang, Y.

2014-04-01

There has been significant stratospheric ozone depletion since the late 1970s due to ozone-depleting substances (ODSs). With the implementation of the Montreal Protocol and its amendments and adjustments, stratospheric ozone is expected to recover towards its pre-1980 level in the coming decades. In this study, we examine the implications of stratospheric ozone recovery for the tropospheric chemistry and ozone air quality with a global chemical transport model (GEOS-Chem). With a full recovery of the stratospheric ozone, the projected increases in ozone column range from 1% over the low latitudes to more than 10% over the polar regions. The sensitivity factor of troposphere ozone photolysis rate, defined as the percentage changes in surface ozone photolysis rate for 1% increase in stratospheric ozone column, shows significant seasonal variation but is always negative with absolute value larger than one. The expected stratospheric ozone recovery is found to affect the tropospheric ozone destruction rates much more than the ozone production rates. Significant decreases in surface ozone photolysis rates due to stratospheric ozone recovery are simulated. The global average tropospheric OH decreases by 1.7%, and the global average lifetime of tropospheric ozone increases by 1.5%. The perturbations to tropospheric ozone and surface ozone show large seasonal and spatial variations. General increases in surface ozone are calculated for each season, with increases by up to 0.8 ppbv in the remote areas. Increases in ozone lifetime by up to 13% are found in the troposphere. The increased lifetimes of tropospheric ozone in response to stratospheric ozone recovery enhance the intercontinental transport of ozone and global pollution, in particular for the summertime. The global background ozone attributable to Asian emissions is calculated to increase by up to 15% or 0.3 ppbv in the Northern Hemisphere in response to the projected stratospheric ozone recovery.

Improvement of OMI Ozone Profile Retrievals in the Troposphere and Lower Troposphere by the Use of the Tropopause-Based Ozone Profile Climatology

NASA Technical Reports Server (NTRS)

Bak, Juseon; Liu, X.; Wei, J.; Kim, J. H.; Chance, K.; Barnet, C.

2011-01-01

An advance algorithm based on the optimal estimation technique has beeen developed to derive ozone profile from GOME UV radiances and have adapted it to OMI UV radiances. OMI vertical resolution : 7-11 km in the troposphere and 10-14 km in the stratosphere. Satellite ultraviolet measurements (GOME, OMI) contain little vertical information for the small scale of ozone, especially in the upper troposphere (UT) and lower stratosphere (LS) where the sharp O3 gradient across the tropopause and large ozone variability are observed. Therefore, retrievals depend greatly on the a-priori knowledge in the UTLS

Influence of Mountains on Arctic Tropospheric Ozone

NASA Astrophysics Data System (ADS)

Whiteway, J. A.; Seabrook, J.

2015-12-01

Tropospheric ozone was measured above Ellesmere Island in the Canadian Arctic during spring using a differential absorption lidar (DIAL). Analysis of the observations revealed that mountains had a significant effect on the vertical distribution of ozone. Ozone depletion events were observed when air that had spent significant time near to the frozen surface of the Arctic Ocean reached Eureka. This air arrived at Eureka by flowing over the surrounding mountains. Surface level ozone depletion events were not observed during periods when mountains blocked the flow of air from over the sea ice. In the case of blocking there was an enhancement in the amount of ozone near the surface as air from the mid troposphere descended in the lee of the mountains. Three case studies will be presented.

Observing and Understanding Tropospheric Ozone Changes

NASA Astrophysics Data System (ADS)

Logan, Jennifer; Schultz, Martin; Oltmans, Samuel

2010-03-01

Tropospheric Ozone Changes Workshop; Boulder, Colorado, 14-16 October 2009; Prompted by the lack of consensus on, and the need to assess current understanding of, long-term changes in tropospheric ozone, a workshop was held in Colorado to (1) evaluate the consistency of data records; (2) assess robust long-term changes; (3) determine how to combine observations and model studies; and (4) define research and observation needs for the future. At the workshop, long-term ozone records from regionally representative surface and mountain sites, ozonesondes, and aircraft were reviewed by region. In western Europe there are several time series of ˜15-40 years from all platforms. Overall, they show a rise in ozone into the middle to late 1990s and a leveling off, or in some cases declines, in the 2000s, in general agreement with precursor emission changes. However, significant differences in detail in the time series from nearby locations provide less confidence in changes before the late 1990s.

Active and widespread halogen chemistry in the tropical and subtropical free troposphere

DOE PAGES

Wang, Siyuan; Schmidt, Johan A.; Baidar, Sunil; ...

2015-06-29

Halogens in the troposphere are increasingly recognized as playing an important role for atmospheric chemistry, and possibly climate. Bromine and iodine react catalytically to destroy ozone (O 3), oxidize mercury, and modify oxidative capacity that is relevant for the lifetime of greenhouse gases. Most of the tropospheric O 3 and methane (CH 4) loss occurs at tropical latitudes. Here we report simultaneous measurements of vertical profiles of bromine oxide (BrO) and iodine oxide (IO) in the tropical and subtropical free troposphere (10°N to 40°S), and show that these halogens are responsible for 34% of the column-integrated loss of tropospheric Omore » 3. The observed BrO concentrations increase strongly with altitude (~3.4 pptv at 13.5 km), and are 2–4 times higher than predicted in the tropical free troposphere. BrO resembles model predictions more closely in stratospheric air. The largest model low bias is observed in the lower tropical transition layer (TTL) over the tropical eastern Pacific Ocean, and may reflect a missing inorganic bromine source supplying an additional 2.5–6.4 pptv total inorganic bromine (Br y), or model overestimated Bry wet scavenging. Our results highlight the importance of heterogeneous chemistry on ice clouds, and imply an additional Bry source from the debromination of sea salt residue in the lower TTL. The observed levels of bromine oxidize mercury up to 3.5 times faster than models predict, possibly increasing mercury deposition to the ocean. Lastly, the halogen-catalyzed loss of tropospheric O 3 needs to be considered when estimating past and future ozone radiative effects.« less

Tropospheric Bromine Chemistry: Implications for Present and Pre-industrial Ozone and Mercury

NASA Technical Reports Server (NTRS)

Parella, J. P.; Jacob, D. J.; Liang, Q.; Zhang, Y.; Mickley, L. J.; Miller, B.; Evans, M. J.; Yang, X.; Pyle, J. A.; Theys, N.;

Active and widespread halogen chemistry in the tropical and subtropical free troposphere

PubMed Central

Wang, Siyuan; Schmidt, Johan A.; Baidar, Sunil; Coburn, Sean; Dix, Barbara; Koenig, Theodore K.; Apel, Eric; Bowdalo, Dene; Campos, Teresa L.; Eloranta, Ed; Evans, Mathew J.; DiGangi, Joshua P.; Zondlo, Mark A.; Gao, Ru-Shan; Haggerty, Julie A.; Hall, Samuel R.; Hornbrook, Rebecca S.; Jacob, Daniel; Morley, Bruce; Pierce, Bradley; Reeves, Mike; Romashkin, Pavel; ter Schure, Arnout; Volkamer, Rainer

2015-01-01

Halogens in the troposphere are increasingly recognized as playing an important role for atmospheric chemistry, and possibly climate. Bromine and iodine react catalytically to destroy ozone (O3), oxidize mercury, and modify oxidative capacity that is relevant for the lifetime of greenhouse gases. Most of the tropospheric O3 and methane (CH4) loss occurs at tropical latitudes. Here we report simultaneous measurements of vertical profiles of bromine oxide (BrO) and iodine oxide (IO) in the tropical and subtropical free troposphere (10°N to 40°S), and show that these halogens are responsible for 34% of the column-integrated loss of tropospheric O3. The observed BrO concentrations increase strongly with altitude (∼3.4 pptv at 13.5 km), and are 2–4 times higher than predicted in the tropical free troposphere. BrO resembles model predictions more closely in stratospheric air. The largest model low bias is observed in the lower tropical transition layer (TTL) over the tropical eastern Pacific Ocean, and may reflect a missing inorganic bromine source supplying an additional 2.5–6.4 pptv total inorganic bromine (Bry), or model overestimated Bry wet scavenging. Our results highlight the importance of heterogeneous chemistry on ice clouds, and imply an additional Bry source from the debromination of sea salt residue in the lower TTL. The observed levels of bromine oxidize mercury up to 3.5 times faster than models predict, possibly increasing mercury deposition to the ocean. The halogen-catalyzed loss of tropospheric O3 needs to be considered when estimating past and future ozone radiative effects. PMID:26124148

Active and Widespread Halogen Chemistry in the Tropical and Subtropical Free Troposphere

NASA Technical Reports Server (NTRS)

Wang, Siyuan; Schmidt, Johan A.; Baidar, Sunil; Coburn, Sean; Dix, Barbara; Koenig, Theodore K.; Apel, Eric; Bowdalo, Dene; Campos, Teresa; Eloranta, Ed;

Active and widespread halogen chemistry in the tropical and subtropical free troposphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Siyuan; Schmidt, Johan A.; Baidar, Sunil

Halogens in the troposphere are increasingly recognized as playing an important role for atmospheric chemistry, and possibly climate. Bromine and iodine react catalytically to destroy ozone (O 3), oxidize mercury, and modify oxidative capacity that is relevant for the lifetime of greenhouse gases. Most of the tropospheric O 3 and methane (CH 4) loss occurs at tropical latitudes. Here we report simultaneous measurements of vertical profiles of bromine oxide (BrO) and iodine oxide (IO) in the tropical and subtropical free troposphere (10°N to 40°S), and show that these halogens are responsible for 34% of the column-integrated loss of tropospheric Omore » 3. The observed BrO concentrations increase strongly with altitude (~3.4 pptv at 13.5 km), and are 2–4 times higher than predicted in the tropical free troposphere. BrO resembles model predictions more closely in stratospheric air. The largest model low bias is observed in the lower tropical transition layer (TTL) over the tropical eastern Pacific Ocean, and may reflect a missing inorganic bromine source supplying an additional 2.5–6.4 pptv total inorganic bromine (Br y), or model overestimated Bry wet scavenging. Our results highlight the importance of heterogeneous chemistry on ice clouds, and imply an additional Bry source from the debromination of sea salt residue in the lower TTL. The observed levels of bromine oxidize mercury up to 3.5 times faster than models predict, possibly increasing mercury deposition to the ocean. Lastly, the halogen-catalyzed loss of tropospheric O 3 needs to be considered when estimating past and future ozone radiative effects.« less

Analysis of 1970-1995 Trends in Tropospheric Ozone at Northern Hemisphere Midlatitudes with the GEOS-CHEM Model

NASA Technical Reports Server (NTRS)

Fusco, Andrew C.; Logan, Jennifer A.

2004-01-01

I ] The causes of trends in tropospheric ozone at Northern Hemisphere midlatitudes from 1970 to 1995 are investigated with the GEOS-CHEM model, a global three-dimensional model of the troposphere driven by assimilated meteorological observations from the Goddard Earth Observing System (GEOS). This model is used to investigate the sensitivity of tropospheric ozone with respect to (1) changes in the anthropogenic emission of nitrogen oxides and nonmethane hydrocarbons, (2) increases in methane concentrations, (3) variations in the stratospheric source of ozone, (4) changes in solar radiation resulting from stratospheric ozone depletion, and ( 5 ) increases in tropospheric temperatures. Model results indicate that local increases in NO, emissions have caused most of the increases seen in lower tropospheric ozone over Europe and Japan. Increases in methane are responsible for roughly one fifth of the anthropogenically induced increase in tropospheric ozone at northern midlatitudes. However, changes in ozone precursors do not adequately explain either the spatial differences in observed ozone trends across midlatitudes or the observed decreases in ozone over Canada throughout the troposphere. We argue that ozone depletion in the lowermost stratosphere is likely to have reduced the stratospheric source by as much as 30% from the early 1970s to the mid 1990s. Model simulations that account for such a reduction along with reported changes in anthropogenic emissions show steep declines of ozone in the upper troposphere and variable increases in the lower troposphere that are more consistent with observations. Differential temperature trends in summer between North America and Europe may account for at least some of the remaining spatial variation in tropospheric ozone trends. Increases in ultraviolet (UV) radiation due to stratospheric ozone depletion do not appear to significantly reduce tropospheric ozone, except at midlatitudes in the Southern Hemisphere following the

Evaluation of ACCMIP Outgoing Longwave Radiation from Tropospheric Ozone Using TES Satellite Observations.

NASA Technical Reports Server (NTRS)

Bowman, Kevin W.; Shindell, Drew Todd; Worden, H. M.; Lamarque, J. F.; Young, P. J.; Stevenson, D. S.; Qu, Z.; delaTorre, M.; Bergmann, D.; Cameron-Smith, P. J.;

Upper-Tropospheric Synoptic-Scale Waves. Part II: Maintenance and Excitation of Quasi Modes.

NASA Astrophysics Data System (ADS)

Rivest, Chantal; Farrell, Brian F.

1992-11-01

In a preceding paper a simple dynamical model for the maintenance of upper-tropospheric waves was proposed: the upper-level Eady normal modes. In this paper it is shown that these modes have counterparts in basic states with positive tropospheric gradients of potential vorticity, and that these counterparts can be maintained and excited on time scales consistent with observations.In the presence of infinitesimal positive tropospheric gradients of potential vorticity, the upper-level normal-mode solutions no longer exist. That the normal-mode solution disappears when gradients are infinitesimal represents an apparent singularity and challenges the interpretation of upper-level synoptic-scale waves as related to the upper-level Eady normal modes. What happens to the upper-level modal solution in the presence of tropospheric gradients of potential vorticity is examined in a series of initial-value experiments. Our results show that they become slowly decaying quasi modes. Mathematically the quasi modes consist of a superposition of singular modes sharply peaked in the phase speed domain, and their decay proceeds as the modes interfere with one another. We repeat these experiments in basic states with a smooth tropopause in the presence of tropospheric and stratospheric gradients, and similar results are obtained.Following a previous study by Farrell, a class of near-optimal initial conditions for the excitation of upper-level waves is identified. The initial conditions consist of upper-tropospheric disturbances that lean against the shear. They strongly excite upper-level waves not only in the absence of tropospheric potential vorticity gradients, but also in their presence. This result is important mathematically since it suggests that quasi modes are as likely to emerge from favorably configured initial disturbances as true normal modes, although the excitation is followed by a slow decay.

Aerosols increase upper tropospheric humidity over the North Western Pacific

NASA Astrophysics Data System (ADS)

Riuttanen, Laura; Bister, Marja; John, Viju; Sundström, Anu-Maija; Dal Maso, Miikka; Räisänen, Jouni; de Leeuw, Gerrit; Kulmala, Markku

2014-05-01

Water vapour in the upper troposphere is highly important for the global radiative transfer. The source of upper tropospheric humidity is deep convection, and aerosol effects on them have got attention only recently. E.g., aerosol effects on deep convective clouds have been missing in general circulation models (Quaas et al., 2009). In deep convection, aerosol effect on cloud microphysics may lead to more ice precipitation and less warm rain (Khain et al., 2005), and thus more water vapour in upper troposphere (Bister & Kulmala, 2011). China outflow region over the Pacific Ocean was chosen as a region for a more detailed study, with latitudes 25-45 N and three longitude slots: 120-149 E, 150-179 E and 150-179 W. In this study, we used satellite measurements of aerosol optical depth (AOD) and upper tropospheric humidity (UTH). AOD was obtained from the MODIS instrument onboard Terra satellite, that crosses the equator southward at 10:30 AM local solar time (Remer et al., 2005). UTH was obtained from a microwave humidity sounder (MHS) onboard MetOp-A satellite, with passing time at 9:30 PM local solar time. It measures relative humidity of a layer extending approximately from 500 to 200 hPa. We binned the AOD and UTH data according to daily rainfall product 3B42 from Tropical Rainfall Measuring Mission (TRMM) satellite. Binning the data according to the amount of precipitation gives us a new way to account for the possible aerosol invigoration effect on convection and to alleviate the contamination and causality problems in aerosol indirect effect studies. In this study, we show for the first time, based on satellite data, that there is a connection between upper tropospheric humidity and aerosols. Anthropogenic aerosols from China increase upper tropospheric humidity, which causes a significant positive local radiative forcing in libRadtran radiative transfer model (Mayer & Kylling, 2005). References: Bister, M. & Kulmala, M. (2011). Atmos. Chem. Phys., 11, 4577

OMI Total and Tropospheric Column Nitrogen Dioxide: Version 2 Status

NASA Technical Reports Server (NTRS)

Gleason, James

2007-01-01

The at-launch version of the OM1 NO2 total and tropospheric NO2 algorithm made a number of assumptions about instrument performance. Our knowledge of tropospheric NO2 has increased in the 3 years since the inital version was delivered. The results of the post-launch validation campaigns and improved atmospheric modelling has lead to changes in the NO2 retrieval algorithm. The algorithm changes and the impacts on the data products will be presented.

Continuing worldwide increase in tropospheric methane, 1978 to 1987

NASA Technical Reports Server (NTRS)

Blake, Donald R.; Rowland, F. Sherwood

1988-01-01

The average worldwide tropospheric mixing ratio of methane has increased by 11 percent from 1.52 parts per million by volume (ppmv) in January 1978 to 1.684 ppmv in September 1987, for an increment of 0.016 + or - 0.001 ppmv per year. Within the limits of the present measurements, the global tropospheric mixing ratio for methane over the past decade is consistent either with a linear growth rate of 0.016 + or - 0.001 ppmv per year or with a slight lessening of the rate of growth over the past 5 years. No indications were found of an effect of the El Nino-Southern Oscillation-El Chichon events of 1982-83 on total global methane, although severe reductions were reported in the Pacific Northwest during that time period.The growth in tropospheric methane may have increased the water concentration in the stratosphere by as much as 28 percent since the 1940s and 45 percent over the past two centuries and thus could have increased the mass of precipitable water available for the formation of polar stratospheric clouds.

Thermal Structure of Titan's Troposphere and Middle Atmosphere

NASA Technical Reports Server (NTRS)

Flasar, F. M.; Achterberg, R. K.; Schinder, P. J.

2011-01-01

The thermal structure of Titan's atmosphere is reviewed, with particular emphasis on recent Cassini-Huygens results. Titan's has a similar troposphere-stratosphere-mesosphere pattern like Earth, but with a much more extended atmosphere, because of the weaker gravity, and also much lower temperatures, because of its greater distance from the sun. Titan's atmosphere exhibits an unusually large range in radiative relaxation times. In the troposphere, these are long compared to seasonal time scales, but in the stratosphere they are much shorter than a season. An exception is near the winter pole, where the stratospheric relaxation times at 100-170 km become comparable to the seasonal time scale; at the warm stratopause, they are comparable to a Titan day. Hence, seasonal behavior in the troposphere should be muted, but significant in the stratosphere. This is reflected in the small meridional contrast observed in temperatures in the troposphere and the large stratospheric contrasts noted above. A surprising feature of the vertical profiles of temperature is the abrupt transition between these regimes in at high northern latitudes in winter, where the temperatures in the lower stratosphere exhibit a sudden drop with increasing altitude. This could be a radiative effect, not associated with spatial variations in gaseous opacity, but rather from an optically thick condensate at thermal-infrared wavelengths. A curious aspect of Titan's middle atmosphere is that the axis of symmetry of the temperature field is tilted by several degrees relative to the rotational axis of the moon itself. Whether this is driven by solar heating or gravitational perturbations is not known. Titan's surface exhibits weak contrasts in temperature, approximately 3 K in the winter hemisphere. At low latitudes, there is evidence of a weak nocturnal boundary layer on the morning terminator, which is not radiatively controlled, but can be explained in terms of vertical mixing with a small eddy

Global observations of tropospheric BrO columns using GOME-2 satellite data

NASA Astrophysics Data System (ADS)

Theys, N.; van Roozendael, M.; Hendrick, F.; Yang, X.; de Smedt, I.; Richter, A.; Begoin, M.; Errera, Q.; Johnston, P. V.; Kreher, K.; de Mazière, M.

2011-02-01

Measurements from the GOME-2 satellite instrument have been analyzed for tropospheric BrO using a residual technique that combines measured BrO columns and estimates of the stratospheric BrO content from a climatological approach driven by O3 and NO2 observations. Comparisons between the GOME-2 results and BrO vertical columns derived from correlative ground-based and SCIAMACHY nadir observations, present a good level of consistency. We show that the adopted technique enables separation of stratospheric and tropospheric fractions of the measured total BrO columns and allows quantitative study of the BrO plumes in polar regions. While some satellite observed plumes of enhanced BrO can be explained by stratospheric descending air, we show that most BrO hotspots are of tropospheric origin, although they are often associated to regions with low tropopause heights as well. Elaborating on simulations using the p-TOMCAT tropospheric chemical transport model, this result is found to be consistent with the mechanism of bromine release through sea salt aerosols production during blowing snow events. No definitive conclusion can be drawn however on the importance of blowing snow sources in comparison to other bromine release mechanisms. Outside polar regions, evidence is provided for a global tropospheric BrO background with column of 1-3 × 1013 molec cm-2, consistent with previous estimates.

Proceedings of a Workshop on Research Needs in Heterogeneous Tropospheric Chemistry

NASA Technical Reports Server (NTRS)

1983-01-01

The role of heterogeneous reactions and processes in the troposphere is critically assessed. The results of this assessment, including identification and prioritization of a number of important and scientifically tractable processes, as well as recommendations of ways in which they can be incorporated into the existing NASA tropospheric chemistry program are presented. Also presented is a detailed summary of the considerations that led to the group's recommendations.

Upper-tropospheric inversion and easterly jet in the tropics

NASA Astrophysics Data System (ADS)

Fujiwara, M.; Xie, S.-P.; Shiotani, M.; Hashizume, H.; Hasebe, F.; VöMel, H.; Oltmans, S. J.; Watanabe, T.

2003-12-01

Shipboard radiosonde measurements revealed a persistent temperature inversion layer with a thickness of ˜200 m at 12-13 km in a nonconvective region over the tropical eastern Pacific, along 2°N, in September 1999. Simultaneous relative humidity measurements indicated that the thin inversion layer was located at the top of a very wet layer with a thickness of 3-4 km, which was found to originate from the intertropical convergence zone (ITCZ) to the north. Radiative transfer calculations suggested that this upper tropospheric inversion (UTI) was produced and maintained by strong longwave cooling in this wet layer. A strong easterly jet stream was also observed at 12-13 km, centered around 4°-5°N. This easterly jet was in the thermal wind balance, with meridional temperature gradients produced by the cloud and radiative processes in the ITCZ and the wet outflow. Furthermore, the jet, in turn, acted to spread inversions further downstream through the transport of radiatively active water vapor. This feedback mechanism may explain the omnipresence of temperature inversions and layering structures in trace gases in the tropical troposphere. Examination of high-resolution radiosonde data at other sites in the tropical Pacific indicates that similar UTIs often appear around 12-15 km. The UTI around 12-15 km may thus be characterized as one of the "climatological" inversions in the tropical troposphere, forming the lower boundary of the so-called tropical tropopause layer, where the tropospheric air is processed photochemically and microphysically before entering the stratosphere.

Source Attribution of Tropospheric Ozone using a Global Model

NASA Astrophysics Data System (ADS)

Coates, J.; Lupascu, A.; Butler, T. M.; Zhu, S.

2016-12-01

Tropospheric ozone is both a short-lived climate forcing pollutant and a radiatively active greenhouse gas. Ozone is not directly emitted into the troposphere but photochemically produced from chemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOCs). Emissions of ozone precursors (NOx and VOCs) have both natural and anthropogenic sources and may be transported away from their sources to produce ozone downwind. Also, transport of ozone from the stratosphere into the troposphere also influences tropospheric ozone levels in some regions. Attributing ozone concentrations to the contributions from different sources would indicate the effects of locally emitted or transported precursors on ozone levels in specific regions. This information could be used to inform the emission reduction strategies of ozone precursors by indicating which emission sources could be targeted for effective reductions thus reducing the burden of ozone pollution. We use a "tagging" approach within the CESM global model to attribute ozone levels to their source emissions. We use different tags to quantify the impact from natural (soils, lightning, stratospheric transport) and anthropogenic (aircraft, biomass burning) sources of NOx and VOCs (including methane) on ozone levels. These source sectors of different global regions are assigned based on the global emissions specified by HTAPv2.2. Using these results, we develop a transboundary source-receptor relationship of ozone concentration to its precursor emission regions. Additionally, the transport of ozone precursors from regional anthropogenic sources is analysed to illustrate the extent to which mitigation strategies of regional emissions aid in mitigating global ozone levels.

Detection of iodine monoxide in the tropical free troposphere

PubMed Central

Dix, Barbara; Baidar, Sunil; Bresch, James F.; Hall, Samuel R.; Schmidt, K. Sebastian; Wang, Siyuan; Volkamer, Rainer

2013-01-01

Atmospheric iodine monoxide (IO) is a radical that catalytically destroys heat trapping ozone and reacts further to form aerosols. Here, we report the detection of IO in the tropical free troposphere (FT). We present vertical profiles from airborne measurements over the Pacific Ocean that show significant IO up to 9.5 km altitude and locate, on average, two-thirds of the total column above the marine boundary layer. IO was observed in both recent deep convective outflow and aged free tropospheric air, suggesting a widespread abundance in the FT over tropical oceans. Our vertical profile measurements imply that most of the IO signal detected by satellites over tropical oceans could originate in the FT, which has implications for our understanding of iodine sources. Surprisingly, the IO concentration remains elevated in a transition layer that is decoupled from the ocean surface. This elevated concentration aloft is difficult to reconcile with our current understanding of iodine lifetimes and may indicate heterogeneous recycling of iodine from aerosols back to the gas phase. Chemical model simulations reveal that the iodine-induced ozone loss occurs mostly above the marine boundary layer (34%), in the transition layer (40%) and FT (26%) and accounts for up to 20% of the overall tropospheric ozone loss rate in the upper FT. Our results suggest that the halogen-driven ozone loss in the FT is currently underestimated. More research is needed to quantify the widespread impact that iodine species of marine origin have on free tropospheric composition, chemistry, and climate. PMID:23345444

Troposphere gradients from the ECMWF in VLBI analysis

NASA Astrophysics Data System (ADS)

Boehm, Johannes; Schuh, Harald

2007-06-01

Modeling path delays in the neutral atmosphere for the analysis of Very Long Baseline Interferometry (VLBI) observations has been improved significantly in recent years by the use of elevation-dependent mapping functions based on data from numerical weather models. In this paper, we present a fast way of extracting both, hydrostatic and wet, linear horizontal gradients for the troposphere from data of the European Centre for Medium-range Weather Forecasts (ECMWF) model, as it is realized at the Vienna University of Technology on a routine basis for all stations of the International GNSS (Global Navigation Satellite Systems) Service (IGS) and International VLBI Service for Geodesy and Astrometry (IVS) stations. This approach only uses information about the refractivity gradients at the site vertical, but no information from the line-of-sight. VLBI analysis of the CONT02 and CONT05 campaigns, as well as all IVS-R1 and IVS-R4 sessions in the first half of 2006, shows that fixing these a priori gradients improves the repeatability for 74% (40 out of 54) of the VLBI baseline lengths compared to fixing zero or constant a priori gradients, and improves the repeatability for the majority of baselines compared to estimating 24-h offsets for the gradients. Only if 6-h offsets are estimated, the baseline length repeatabilities significantly improve, no matter which a priori gradients are used.

GPD+ wet tropospheric corrections for eight altimetric missions for the Sea Level ECV generation

NASA Astrophysics Data System (ADS)

Fernandes, Joana; Lázaro, Clara; Benveniste, Jérôme

2016-04-01

Due to its large spatio-temporal variability, the delay induced by the water vapour and liquid water content of the atmosphere in the altimeter signal or wet tropospheric correction (WTC) is still one of the largest sources of uncertainty in satellite altimetry. In the scope of the Sea Level (SL) Climate Change Initiative (cci) project, the University of Porto (UPorto) has been developing methods to improve the WTC (Fernandes et al., 2015). Started as a coastal algorithm to remove land effects in the microwave radiometers (MWR) on board altimeter missions, the GNSS-derived Path Delay (GPD) methodology evolved to cover the open ocean, including high latitudes, correcting for invalid observations due to land, ice and rain contamination, band instrument malfunction. The most recent version of the algorithm, GPD Plus (GPD+) computes wet path delays based on: i) WTC from the on-board MWR measurements, whenever they exist and are valid; ii) new WTC values estimated through space-time objective analysis of all available data sources, whenever the previous are considered invalid. In the estimation of the new WTC values, the following data sets are used: valid measurements from the on-board MWR, water vapour products derived from a set of 17 scanning imaging radiometers (SI-MWR) on board various remote sensing satellites and tropospheric delays derived from Global Navigation Satellite Systems (GNSS) coastal and island stations. In the estimation process, WTC derived from an atmospheric model such as the European Centre for Medium-range Weather Forecasts (ECMWF) ReAnalysis (ERA) Interim or the operational (Op) model are used as first guess, which is the adopted value in the absence of measurements. The corrections are provided for all missions used to generate the SL Essential Climate Variable (ECV): TOPEX/Poseidon- T/P, Jason-1, Jason-2, ERS-1, ERS-2, Envisat, CryoSat-2 and SARAL/ALtiKa. To ensure consistency and long term stability of the WTC datasets, the radiometers used

Tropospheric Enhancement of Ozone over the UAE

NASA Astrophysics Data System (ADS)

Abbasi, Naveed Ali; Majeed, Tariq; Iqbal, Mazhar; Kaminski, Jacek; Struzewska, Joanna; Durka, Pawel; Tarasick, David; Davies, Jonathan

2015-04-01

We use the Global Environmental Multiscale - Air Quality (GEM-AQ) model to interpret the vertical profiles of ozone acquired with ozone sounding experiments at the meteorological site located at the Abu Dhabi airport. The purpose of this study is to gain insight into the chemical and dynamical structures in the atmosphere of this unique subtropical location (latitude 24.45N; longitude 54.22E). Ozone observations for years 2012 - 2013 reveal elevated ozone abundances in the range from 70 ppbv to 120 ppbv near 500-400 hPa during summer. The ozone abundances in other seasons are much lower than these values. The preliminary results indicate that summertime enhancement in ozone is associated with the Arabian anticyclones centered over the Zagros Mountains in Iran and the Asir and Hijaz Mountain ranges in Saudi Arabia, and is consistent with TES observations of deuterated water. The model also shows considerable seasonal variation in the tropospheric ozone which is transported from the stratosphere by dynamical processes. The domestic production of ozone in the middle troposphere is estimated and compared GEM-AQ model. It is estimated that about 40-50% of ozone in the UAE is transported from the neighbouring petrochemical industries in the Gulf region. We will present ozone sounding data and GEM-AQ results including a discussion on the high levels of the tropospheric ozone responsible for contaminating the air quality in the UAE. This work is supported by National Research Foundation, UAE.

Chapman Solar Zenith Angle variations at Titan

NASA Astrophysics Data System (ADS)

Royer, Emilie M.; Ajello, Joseph; Holsclaw, Gregory; West, Robert; Esposito, Larry W.; Bradley, Eric Todd

2016-10-01

Solar XUV photons and magnetospheric particles are the two main sources contributing to the airglow in the Titan's upper atmosphere. We are focusing here on the solar XUV photons and how they influence the airglow intensity. The Cassini-UVIS observations analyzed in this study consist each in a partial scan of Titan, while the center of the detector stays approximately at the same location on Titan's disk. We used observations from 2008 to 2012, which allow for a wide range of Solar Zenith Angle (SZA). Spectra from 800 km to 1200 km of altitude have been corrected from the solar spectrum using TIMED/SEE data. We observe that the airglow intensity varies as a function of the SZA and follows a Chapman curve. Three SZA regions are identified: the sunlit region ranging from 0 to 50 degrees. In this region, the intensity of the airglow increases, while the SZA decreases. Between SZA 50 and 100 degrees, the airglow intensity decreases from it maximum to its minimum. In this transition region the upper atmosphere of Titan changes from being totally sunlit to being in the shadow of the moon. For SZA 100 to 180 degrees, we observe a constant airglow intensity close to zero. The behavior of the airglow is also similar to the behavior of the electron density as a function of the SZA as observed by Ågren at al (2009). Both variables exhibit a decrease intensity with increasing SZA. The goal of this study is to understand such correlation. We demonstrate the importance of the solar XUV photons contribution to the Titan airglow and prove that the strongest contribution to the Titan dayglow occurs by solar fluorescence rather than the particle impact that predominates at night.

Transition of NOAA's GPS-Met Data Acquisition and Processing System to the Commercial Sector: Inital Results

NASA Astrophysics Data System (ADS)

Jackson, Michael; Blatt, Stephan; Holub, Kirk

2015-04-01

In April of 2014, NOAA/OAR/ESRL Global Systems Division (GSD) and Trimble, in collaboration with Earth Networks, Inc. (ENI) signed a Cooperative Research and Development Agreement (CRADA) to transfer the existing NOAA GPS-Met Data Acquisition and Processing System (GPS-Met DAPS) technology to a commercial Trimble/ENI partnership. NOAA's GPS-Met DAPS is currently operated in a pseudo-operational mode but has proven highly reliable and running at over 95% uptime. The DAPS uses the GAMIT software to ingest dual frequency carrier phase GPS/GNSS observations and ancillary information such as real-time satellite orbits to estimate the zenith-scaled tropospheric (ZTD) signal delays and, where surface MET data are available, retrieve integrated precipitable water vapor (PWV). The NOAA data and products are made available to end users in near real-time. The Trimble/ENI partnership will use the Trimble Pivot™ software with the Atmosphere App to calculate zenith tropospheric (ZTD), tropospheric slant delay, and integrated precipitable water vapor (PWV). Evaluation of the Trimble software is underway starting with a comparison of ZTD and PWV values determined from four sub networks of GPS stations located 1. near NOAA Radiosonde Observation (Upper-Air Observation) launch sites; 2. Stations with low terrain/high moisture variability (Gulf Coast); 3. Stations with high terrain/low moisture variability (Southern California); and 4. Stations with high terrain/high moisture variability (high terrain variability elev. > 1000m). For each network GSD and T/ENI run the same stations for 30 days, compare results, and perform an evaluation of the long-term solution accuracy, precision and reliability. Metrics for success include T/ENI PWV estimates within 1.5 mm of ESRL/GSD's estimates 95% of the time (ZTD uncertainty of less than 10 mm 95% of the time). The threshold for allowable variations in ZTD between NOAA GPS-Met and T/ENI processing are 10mm. The CRADA 1&2 Trimble processing

Subtropical subsidence and surface deposition of oxidized mercury produced in the free troposphere

NASA Astrophysics Data System (ADS)

Shah, Viral; Jaeglé, Lyatt

2017-07-01

Oxidized mercury (Hg(II)) is chemically produced in the atmosphere by oxidation of elemental mercury and is directly emitted by anthropogenic activities. We use the GEOS-Chem global chemical transport model with gaseous oxidation driven by Br atoms to quantify how surface deposition of Hg(II) is influenced by Hg(II) production at different atmospheric heights. We tag Hg(II) chemically produced in the lower (surface-750 hPa), middle (750-400 hPa), and upper troposphere (400 hPa-tropopause), in the stratosphere, as well as directly emitted Hg(II). We evaluate our 2-year simulation (2013-2014) against observations of Hg(II) wet deposition as well as surface and free-tropospheric observations of Hg(II), finding reasonable agreement. We find that Hg(II) produced in the upper and middle troposphere constitutes 91 % of the tropospheric mass of Hg(II) and 91 % of the annual Hg(II) wet deposition flux. This large global influence from the upper and middle troposphere is the result of strong chemical production coupled with a long lifetime of Hg(II) in these regions. Annually, 77-84 % of surface-level Hg(II) over the western US, South America, South Africa, and Australia is produced in the upper and middle troposphere, whereas 26-66 % of surface Hg(II) over the eastern US, Europe, and East Asia, and South Asia is directly emitted. The influence of directly emitted Hg(II) near emission sources is likely higher but cannot be quantified by our coarse-resolution global model (2° latitude × 2.5° longitude). Over the oceans, 72 % of surface Hg(II) is produced in the lower troposphere because of higher Br concentrations in the marine boundary layer. The global contribution of the upper and middle troposphere to the Hg(II) dry deposition flux is 52 %. It is lower compared to the contribution to wet deposition because dry deposition of Hg(II) produced aloft requires its entrainment into the boundary layer, while rain can scavenge Hg(II) from higher altitudes more readily. We find

Global observations of BrO in the troposphere using GOME-2 satellite data

NASA Astrophysics Data System (ADS)

Theys, N.; van Roozendael, M.; Hendrick, F.; Xin, Y.; Isabelle, D.; Richter, A.; Mathias, B.; Quentin, E.; Johnston, P. V.; Kreher, K.; Martine, D.

2010-12-01

Measurements from the GOME-2 satellite instrument have been analyzed for tropospheric BrO using a residual technique that combines measured BrO columns and estimates of the stratospheric BrO content from a climatological approach driven by O3 and NO2 observations. Comparisons between the GOME-2 results and correlative data including ground-based BrO vertical columns and total BrO columns derived from SCIAMACHY nadir observations, present a good level of consistency. We show that the adopted technique enables to separate the stratospheric and tropospheric fractions of the measured total BrO columns and allows studying the BrO plumes in polar region in more detail. While several satellite BrO plumes can largely be explained by an influence of stratospheric descending air, we show that numerous tropospheric BrO hotspots are associated to regions with low tropopause heights as well. Elaborating on simulations using the p-TOMCAT tropospheric chemical transport model, this finding is found to be consistent with the mechanism of bromine release through sea salt aerosols production during blowing snow events. Outside the polar region, evidences are provided for a global tropospheric BrO background with columns of 1-3 x 1013 molec/cm2.

Modelling the global tropospheric molecular hydrogen cycle

NASA Astrophysics Data System (ADS)

Pieterse, G.

2013-01-01

Would urban air quality and climate improve if we replaced the fossil fuels by molecular hydrogen (H2) as an energy carrier? A quantitative answer to this question requires a thorough understanding of the current role of H2 in the Earth’s atmosphere. On its own, H2 does not impact climate, as for example carbon dioxide or methane. However, increasing levels of H2 in the stratosphere can lead to increased ozone loss due to the formation of polar stratospheric clouds. Additionally, the atmospheric lifetime of methane could increase because both H2 and methane are removed by photochemical oxidation with the hydroxyl radical. Consequently, the lifetime of the strong greenhouse gas methane could be prolonged. During the last two decades, more and more experimental data have become available to put tighter constraints on the different sources and sinks that contribute to the global H2 cycle. However, the main removal process, dry deposition due to microbial/enzymatic decomposition of H2 in the soils, still has a rather large uncertainty between 40-99 Tg/yr globally. This is a highly uncertain number compared to the estimated overall amount of 136-166 Tg present in the troposphere. The photochemical removal of H2 from the atmosphere is estimated at 14-24 Tg/yr. Together with the estimates for the burden and dry deposition, this implies a tropospheric lifetime of H2 between 1.1-3.1 years. The atmospheric H2 is replenished by emissions from the Earth’s surfaces due to fossil fuel burning (5-25 Tg/yr), biomass burning (7-21 Tg/yr) and nitrogen fixation processes in the oceans (1-11 Tg/yr) and soils (0-11 Tg/yr). H2 is photochemically produced from methane (15-21 Tg/yr) and non-methane hydrocarbons (10-25 Tg/yr) in the atmosphere. These uncertainties suggest that at present, the global hydrogen cycle is poorly understood. However, this statement would do little justice to the scientific quality of most studies so far. The main purpose of the research in this thesis is to

Oxygenated Organic Chemicals in the Pacific Troposphere: Distribution, Sources and Chemistry

NASA Technical Reports Server (NTRS)

Singh, Hanwant B.; Salas, L.; Chatfield, R.; Czech, E.; Fried, A.; Evans, M.; Jacob, D. J.; Blake, D.; Heikes, B.; Talbot, R.

2003-01-01

Airborne measurements of a large number of oxygenated organic chemicals (Oxorgs) were carried out in the Pacific troposphere (0.1-12 km) in the Spring of 2001 (Feb. 24-April 10). Specifically these measuremen ts included acetone, methylethyl ketone (MEK), methanol, ethanol, ace taldehyde, propionaldehyde, PANS, and organic nitrates. Complementary measurements of formaldehyde, organic peroxides, and tracers were al so available. Ox-orgs were abundant in the clean troposphere and were greatly enhanced in the outflow regions from Asia. Their mixing ratios were typically highest in the lower troposphere and declined toward s the upper troposphere and the lowermost stratosphere. Their total a bundance (Ox-orgs) significantly exceeded that of NMHC (C2-C8 NMHC). A comparison of these data with observations collected some seven yea rs earlier (Feb.-March, 1994), did not reveal any significant changes . Throughout the troposphere mixing ratios of Ox-orgs were strongly c orrelated with each other as well as with tracers of fossil and bioma sshiof'uel combustion. Analysis of the relative enhancement of selected Oxorgs with respect to CH3Cl and CO in twelve sampled plumes, origi nating from fires, is used to assess their primary and secondary sour ces from biomass combustion. The composition of these plumes also ind icates a large shift of reactive nitrogen into the PAN reservoir ther eby limiting ozone formation. The Harvard 3-D photochemical model, th at uses state of the art chemistry and source information, is used to compare simulated and observed mixing ratios of selected species. A 1 -D model is used to explore the chemistry of aldehydes. These results will be presented.

The SEASAT altimeter wet tropospheric range correction revisited

NASA Technical Reports Server (NTRS)

Tapley, D. B.; Lundberg, J. B.; Born, G. H.

1984-01-01

An expanded set of radiosonde observations was used to calculate the wet tropospheric range correction for the brightness temperature measurements of the SEASAT scanning multichannel microwave radiometer (SMMR). The accuracy of the conventional algorithm for wet tropospheric range correction was evaluated. On the basis of the expanded observational data set, the algorithm was found to have a bias of about 1.0 cm, and a standard deviation 2.8 cm. In order to improve the algorithm, the exact linear, quadratic and logarithmic relationships between brightness temperatures and range corrections were determined. Various combinations of measurement parameters were used to reduce the standard deviation between SEASAT SMMR and radiosonde observations to about 2.1 cm. The performance of various range correction formulas is compared in a table.

Enhancement in the upper tropospheric humidity associated with aerosol loading over tropical Pacific

NASA Astrophysics Data System (ADS)

Kottayil, Ajil; Satheesan, K.

2015-12-01

Many modeling studies have indicated that aerosol interactions with clouds increase the upper tropospheric humidity (UTH), but observational evidences are sparse. Using satellite datasets of upper tropospheric humidity and aerosols, this study shows that aerosols increase the upper tropospheric humidity over the tropical North West Pacific (NWP) and North East Pacific (NEP). The observations show an increase in the UTH by 2.8%RH over NEP for an increment of 0.12 in aerosol optical depth (AOD) and 2%RH increase in UTH over NWP for an increment of 0.19 in AOD. The study also quantifies the change in longwave cloud radiative forcing (LWCRF) as a consequence of the increase in UTH due to aerosols. The LWCRF increases by 3.38 W m-2 over NEP and by 4.46 W m-2 over NWP. The result that aerosols increase the upper tropospheric humidity is significant since the latter plays a crucial role in regulating the Earth's radiation budget and water vapor feedback.

Dynamic-Chemical Coupling of the Upper Troposphere and Lower Stratosphere Region

NASA Technical Reports Server (NTRS)

Grewe, Volker; Shindell, Drew T.; Reithmeier, Christian

2000-01-01

The importance of the interaction of chemistry and dynamics in the upper troposphere and lower stratosphere for chemical species like ozone is investigated using two chemistry-climate models. Species emitted in the upper troposphere, like NOx (=NO+NO2) by lightning or aircraft, have the chance to be transported into the lowermost stratosphere. Trajectory calculations suggest that the main transport pathway runs via the Inter Tropical Convergence Zone, across the tropical tropopause and then to higher latitudes, i.e. into the lowermost stratosphere. Longer lifetimes of NOx in the lower stratosphere yield an accumulation of NO. there, which feeds back on upper troposphere chemistry. This effect has been estimated for lightning NO. emissions and reveals a contribution of at least 25% to 40% to the total northern hemisphere mid-latitude lightning increase of either NOx and ozone.

Measurements of ice nucleating particle concentrations at 242 K in the free troposphere

NASA Astrophysics Data System (ADS)

Lacher, L.; Lohmann, U.; Boose, Y.; Zipori, A.; Herrmann, E.; Bukowiecki, N.; Steinbacher, M.; Gute, E.; Kanji, Z. A.

2017-12-01

Clouds containing ice play an important role in the Earth's system, but some fundamental knowledge on their formation and further development is still missing. The phase change from vapor or liquid to ice in the atmosphere can occur heterogeneously in the presence of ice nucleating particles (INPs) at temperatures warmer, and supersaturations lower than required for homogeneous freezing. Only a small fraction of particles in an environment relevant for the occurrence of ice- and mixed-phase clouds are INPs, and their identification and quantification remains challenging. We measure INP concentrations with the ETH Horizontal Ice Nucleation Chamber (HINC) at the High Altitude Research Station Jungfraujoch (JFJ) during several field campaigns in different seasons and years. The measurements are performed at 242 K and above water saturation, representing ice- and mixed-phase clouds conditions. Due to its elevation of 3580 m a.s.l. the site encounters mostly free tropospheric conditions, and is influenced by boundary layer injections up to 80% of the time in summer. JFJ regularly encounters Saharan dust events and receives air masses of marine origin, which can both occur within the free troposphere. Our measurements show that INP concentrations in the free troposphere do not follow a seasonal cycle. They are remarkably constant, with concentrations from 0.5 - 8 L-1 (interquartile range), which compares well to measurements performed under the same conditions at another location within the free troposphere, the Izaña Atmospheric Research Station in Tenerife. At JFJ, correlations with parameters of physical properties of ambient particles, meteorology and air mass characteristics do not show a single best estimator to predict INP concentrations, emphasizing the complexity of ice nucleation in the free troposphere. Increases in INP concentrations of a temporary nature were observed in the free troposphere during Saharan dust events and marine air mass influence, which

Lower tropospheric ozone over India and its linkage to the South Asian monsoon

NASA Astrophysics Data System (ADS)

Lu, Xiao; Zhang, Lin; Liu, Xiong; Gao, Meng; Zhao, Yuanhong; Shao, Jingyuan

2018-03-01

Lower tropospheric (surface to 600 hPa) ozone over India poses serious risks to both human health and crops, and potentially affects global ozone distribution through frequent deep convection in tropical regions. Our current understanding of the processes controlling seasonal and long-term variations in lower tropospheric ozone over this region is rather limited due to spatially and temporally sparse observations. Here we present an integrated process analysis of the seasonal cycle, interannual variability, and long-term trends of lower tropospheric ozone over India and its linkage to the South Asian monsoon using the Ozone Monitoring Instrument (OMI) satellite observations for years 2006-2014 interpreted with a global chemical transport model (GEOS-Chem) simulation for 1990-2010. OMI observed lower tropospheric ozone over India averaged for 2006-2010, showing the highest concentrations (54.1 ppbv) in the pre-summer monsoon season (May) and the lowest concentrations (40.5 ppbv) in the summer monsoon season (August). Process analyses in GEOS-Chem show that hot and dry meteorological conditions and active biomass burning together contribute to 5.8 Tg more ozone being produced in the lower troposphere in India in May than January. The onset of the summer monsoon brings ozone-unfavorable meteorological conditions and strong upward transport, which all lead to large decreases in the lower tropospheric ozone burden. Interannually, we find that both OMI and GEOS-Chem indicate strong positive correlations (r = 0.55-0.58) between ozone and surface temperature in pre-summer monsoon seasons, with larger correlations found in high NOx emission regions reflecting NOx-limited production conditions. Summer monsoon seasonal mean ozone levels are strongly controlled by monsoon strengths. Lower ozone concentrations are found in stronger monsoon seasons mainly due to less ozone net chemical production. Furthermore, model simulations over 1990-2010 estimate a mean annual trend of 0

Tropospheric temperature climatology and trends observed over the Middle East

NASA Astrophysics Data System (ADS)

Basha, Ghouse; Marpu, P. R.; Ouarda, T. B. M. J.

2015-10-01

In this study, we report for the first time, the upper air temperature climatology, and trends over the Middle East, which seem to be significantly affected by the changes associated with hot summer and low precipitation. Long term (1985-2012) radiosonde data from 12 stations are used to derive the mean temperature climatology and vertical trends. The study was performed by analyzing the data at different latitudes. The vertical profiles of air temperature show distinct behavior in terms of vertical and seasonal variability at different latitudes. The seasonal cycle of temperature at the 100 hPa, however, shows an opposite pattern compared to the 200 hPa levels. The temperature at 100 hPa shows a maximum during winter and minimum in summer. Spectral analysis shows that the annual cycle is dominant in comparison with the semiannual cycle. The time-series of temperature data was analyzed using the Bayesian change point analysis and cumulative sum method to investigate the changes in temperature trends. Temperature shows a clear change point during the year 1999 at all stations. Further, Modified Mann-Kendall test was applied to study the vertical trend, and analysis shows statistically significant lower tropospheric warming and cooling in upper troposphere after the year 1999. In general, the magnitude of the trend decreases with altitude in the troposphere. In all the latitude bands in lower troposphere, significant warming is observed, whereas at higher altitudes cooling is noticed based on 28 years temperature observations over the Middle East.

Summertime tropospheric ozone distributions over central and eastern Canada

NASA Technical Reports Server (NTRS)

Anderson, B. E.; Gregory, G. L.; Barrick, J. D.; Collins, J. E., Jr.; Sachse, G. W.; Shipham, M. C.; Hudgins, C. H.

1994-01-01

Ozone measurements were obtained between the surface and the 6-km altitude on aircraft flights over central and eastern Canada during the summer 1990 NASA Global Tropospheric Experiment Arctic Boundary Layer Expedition (GTE/ABLE 3B). Tropospheric O3 budgets for these regions were observed to be highly variable and significantly impacted by long-range transport and regional scale air mass modification processes. For example, integrated O3 abundance below 5-km altitude averaged 40% and 30% greater in air masses influenced by anthropogenic sources and biomass burning, respectively, than in background (polar) air. Conversely, aged air transported from subtropical areas of the Pacific at times reduced O3 abundance in this height interval by up to 20%. Though intrusion of anthropogenic air was infrequent during the experiment period, the influence of biomass-burning emissions was particularly notable as two thirds of the flights sampled air influenced by plumes from fires burning in Alaska and western Canada. The impinging pollution, both natural and anthropogenic, not only elevated O3 levels directly but also was a source of reactive nitrogen (and nonmethane hydrocarbons) which generally increases the tropospheric lifetime of O3 via moderation of photochemical destruction rates.

MOPITT - A gas correlation spectrometer for tropospheric Earth observations

NASA Technical Reports Server (NTRS)

Drummond, James R.; Colley, R.; Dorey, J.; Hackett, J.

1993-01-01

MOPITT (Measurement of Pollution in the Troposphere) is an instrument that will fly on the EOS AM-1 Polar Orbiting Platform, to be launched in mid-1998. The instrument accurately measures the concentration of carbon monoxide (CO) and methane (CH4) gas in the troposphere, using novel and conventional gas correlation spectroscopy techniques. These techniques are used to measure both the column amount and the vertical profile of the two gases in the troposphere. The instrument is nadir viewing and has cross-track scanning ability. It measures upwelling IR radiation through the atmosphere in the 4.6-micron and 2.3-micron bands for CO detection, and 2.2-micron for CH4. The instrument performance is enhanced using Stirling cycle mechanical coolers to maintain the IR detectors at less than 100 K. MOPITT has a total of eight detector channels to measure the total column of atmospheric CH4 gas to a precision of 1 percent, and to measure CO profiles to a precision of 10 percent. The instrument is self-calibrating to ensure data validity using internal targets and an external cold space view.

A simulation study on few parameters of Cherenkov photons in extensive air showers of different primaries incident at various zenith angles over a high altitude observation level

NASA Astrophysics Data System (ADS)

Das, G. S.; Hazarika, P.; Goswami, U. D.

2018-07-01

We have studied the distribution patterns of lateral density, arrival time and angular position of Cherenkov photons generated in Extensive Air Showers (EASs) initiated by γ-ray, proton and iron primaries incident with various energies and at various zenith angles. This study is the extension of our earlier work [1] to cover a wide energy range of ground based γ-ray astronomy with a wide range of zenith angles (≤40°) of primary particles, as well as the extension to study the angular distribution patterns of Cherenkov photons in EASs. This type of study is important for distinguishing the γ-ray initiated showers from the hadronic showers in the ground based γ-ray astronomy, where Atmospheric Cherenkov Technique (ACT) is being used. Importantly, such study gives an insight on the nature of γ-ray and hadronic showers in general. In this work, the CORSIKA 6.990 simulation code is used for generation of EASs. Similarly to the case of Ref. [1], this study also revealed that, the lateral density and arrival time distributions of Cherenkov photons vary almost in accordance with the functions: ρch(r) =ρ0e-βr and tch(r) =t0eΓ/rλ respectively by taking different values of the parameters of functions for the type, energy and zenith angle of the primary particle. The distribution of Cherenkov photon's angular positions with respect to shower axis shows distinctive features depending on the primary type, its energy and the zenith angle. As a whole this distribution pattern for the iron primary is noticeably different from those for γ-ray and proton primaries. The value of the angular position at which the maximum number of Cherenkov photons are concentrated, increases with increase in energy of vertically incident primary, but for inclined primary it lies within a small value (≤1°) for almost all energies and primary types. No significant difference in the results obtained by using the high energy hadronic interaction models, viz., QGSJETII and EPOS has been

Lower-free tropospheric ozone dial measurements over Athens, Greece

NASA Astrophysics Data System (ADS)

Mytilinaios, Michail; Papayannis, Alexandros; Tsaknakis, Georgios

2018-04-01

A compact ozone differential absorption lidar (DIAL) was implemented at the Laboratory of Laser Remote Sensing of the National Technical University of Athens (NTUA), in Athens, Greece. The DIAL system is based on a Nd:YAG laser emitting at 266 nm. A high-pressure Raman cell, filled with D2, was used to generate the λON and λOFF laser wavelength pairs (i.e., 266-289 nm and 289-316 nm, respectively) based on the Stimulated Raman Scattering (SRS) effect. The system was run during daytime and nighttime conditions to obtain the vertical profile of tropospheric ozone in the Planetary Boundary Layer (PBL) and the adjacent free troposphere.

Remote sensing of the troposphere by infrared emission spectroscopy

NASA Technical Reports Server (NTRS)

Beer, Reinhard; Glavich, Thomas A.

1989-01-01

This paper describes the concept of a cryogenic IR imaging Fourier transform spectrometer, called the Tropospheric Emission Spectrometer (TES), designed for observations of the troposphere and lower stratosphere from a near-earth orbit, using natural thermal emission and reflected sunlight. The principal molecular species to be measured by TES are O3, CO, CO2, N2O, H2O, H2O2, NO, NO2, HNO3, NH3, CH4, C2H6, C2H2, SO2, COS, CFCl3, and CF2Cl2. The TES is scheduled for a launch on the second polar platform of the Earth Observing System in 1998.

Understanding tropical upper tropospheric warming: The role of SSTs, convective parameterizations, and observational uncertainties

NASA Astrophysics Data System (ADS)

Po-Chedley, S.; Thorsen, T. J.; Fu, Q.

2015-12-01

Recent research has compared CMIP5 general circulation model (GCM) simulations with satellite observations of warming in the tropical upper troposphere relative to the lower-middle troposphere. Although the pattern of SST warming is important, this research demonstrated that models overestimate increases in static stability between the mid- to upper- tropical troposphere, even when they are forced with historical sea surface temperatures. This discrepancy between satellite-borne microwave sounding unit measurements (MSU) and GCMs is important because it has implications for the strength of the lapse rate and water vapor feedback. The apparent model-observational difference for changes in static stability in the tropical upper troposphere represents an important problem, but it is not clear whether the difference is a result of common biases in GCMs, biases in observational datasets, or both. In this work, we will use GCM simulations to examine the importance of the spatial pattern of SST warming and different convective parameterizations in determining the lapse rate changes in tropical troposphere. We will also consider uncertainties in MSU satellite observations, including changes in the diurnal sampling of temperature and instrument calibration biases when comparing GCMs with the observed record.

Maintenance of coupling between stratosphere and troposphere annular modes in middle and late winter

NASA Astrophysics Data System (ADS)

de La Torre, L.; Gimeno, L.; Nieto, R.; Tesouro, M.; Añel, J. A.; Ribera, P.; García, R.; Hernández, E.

2003-04-01

The main objective of this work is to know when the coupling between stratosphere and troposphere Northern Annular Mode (NAM) is maintained during mid- and late winter (January-February-March) . Daily NAM-index time series calculated at 17 pressure levels from 1000 to 10-hPa for the period 1958-2001 were used in this study, as well as NCAR-NCEP reanalysis to characterize spatial patterns. So, a) we identified periods when coupling between stratospheric and tropospheric NAMs are intense/weak in mid-late winter, b) we tried to characterize these periods in terms of spatial patterns of geopotential anomalies and c) we characterized these periods in terms of stratospheric-tropospheric NAMs cross-correlation structures. Results suggest that: a)there is intense interannual variability in the number of uncoupling/coupling days, b) coupling periods are characterized by strong negative geopotential anomalies over Eurasia, c) there is only positive NAO values in the coupling days composite, c) there is two main pattens of cross-correlations, in one of them troposphere and stratosphere NAM are correlated at lag 0 and in the other troposphere NAM leads stratosphere NAM in about two weeks.

Visible and near-ultraviolet spectroscopy at Thule AFB (76.5 N) from January 28 - February 15, 1988

NASA Technical Reports Server (NTRS)

Mount, G. H.; Sanders, R. W.; Jakoubek, R. O.; Schmeltekopf, A. L.; Solomon, S.

1988-01-01

Near-ultraviolet and visible spectrographs identical to those employed at McMurdo Station, Antarctica (77.8 S) during the austral spring seasons of 1986 and 1987 were used to study the stratosphere above Thule, Greenland (76.5 N) during early spring, 1988. Observations were carried out both at night using the direct moon as a light source, and during the day by collecting the scattered light from the zenith sky when solar zenith angles were less than about 94.5 degrees. Excellent meteorological conditions prevailed in the troposphere and stratosphere at Thule. Surface weather was extremely clear over most of the period, facilitating measurements of the direct light from the moon. The lower stratospheric arctic polar vortex was located very near Thule throughout the observing period, and temperature at the 30 mbar level were typically below -80 C above Thule, according to the National Meteorological Center daily analyses. Thus conditions were favorable for polar stratospheric cloud formation above Thule. Total column ozone abundances were about 350 to 400 Dobson units, and did not suggest a clear temporal trend over the observing period. Stratospheric nitrogen dioxide measurements were complicated by the presence of a large component of tropospheric pollution on many occasions. Stratospheric nitrogen dioxide could be identified on most days using the absorption in the scattered light from the zenith sky, which greatly enhances the stratospheric airmass while suppressing the tropospheric contribution. These measurements suggest that the total vertical column abundance of nitrogen dioxide present over Thule in February was extremely low, sometimes as low as 3 x 10 to the 14th per sq cm. The abundance of nitrogen dioxide increased systemically from about 3 x 10 to the 14th in late January to 1.0 x 10 to the 15th per sq cm in mid-February, perhaps because of photolysis of N2O5 in the upper part of the stratosphere, near 25 to 35 km.

Upper Tropospheric Ozone Between Latitudes 60S and 60N Derived from Nimbus 7 TOMS/THIR Cloud Slicing

NASA Technical Reports Server (NTRS)

Ziemke, Jerald R.; Chandra, Sushil; Bhartia, P. K.

2002-01-01

This study evaluates the spatial distributions and seasonal cycles in upper tropospheric ozone (pressure range 200-500 hPa) from low to high latitudes (60S to 60N) derived from the satellite retrieval method called "Cloud Slicing." Cloud Slicing is a unique technique for determining ozone profile information in the troposphere by combining co-located measurements of cloud-top, pressure and above-cloud column ozone. For upper tropospheric ozone, co-located measurements of Nimbus 7 Total Ozone Mapping Spectrometer (TOMS) above-cloud column ozone, and Nimbus 7 Temperature Humidity Infrared Radiometer (THIR) cloud-top pressure during 1979-1984 were incorporated. In the tropics, upper tropospheric ozone shows year-round enhancement in the Atlantic region and evidence of a possible semiannual variability. Upper tropospheric ozone outside the tropics shows greatest abundance in winter and spring seasons in both hemispheres with largest seasonal and largest amounts in the NH. These characteristics are similar to lower stratospheric ozone. Comparisons of upper tropospheric column ozone with both stratospheric ozone and a proxy of lower stratospheric air mass (i.e., tropopause pressure) from National Centers for Environmental Prediction (NCEP) suggest that stratosphere-troposphere exchange (STE) may be a significant source for the seasonal variability of upper tropospheric ozone almost everywhere between 60S and 60N except in low latitudes around 10S to 25N where other sources (e.g., tropospheric transport, biomass burning, aerosol effects, lightning, etc.) may have a greater role.

Observations of tropospheric trace gases from GOSAT thermal infrared spectra