Boreal Winter MJO Teleconnection in the Community Atmosphere Model Version 5 with the Unified Convection Parameterization

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

Yoo, Changhyun; Park, Sungsu; Kim, Daehyun

2015-10-01

The Madden-Julian Oscillation (MJO), the dominant mode of tropical intraseasonal variability, influences weather and climate in the extratropics through atmospheric teleconnection. In this study, two simulations using the Community Atmosphere Model version 5 (CAM5) - one with the default shallow and deep convection schemes and the other with the Unified Convection scheme (UNICON) - are employed to examine the impacts of cumulus parameterizations on the simulation of the boreal wintertime MJO teleconnection in the Northern Hemisphere. We demonstrate that the UNICON substantially improves the MJO teleconnection. When the UNICON is employed, the simulated circulation anomalies associated with the MJO bettermore » resemble the observed counterpart, compared to the simulation with the default convection schemes. Quantitatively, the pattern correlation for the 300-hPa geopotential height anomalies between the simulations and observation increases from 0.07 for the default schemes to 0.54 for the UNICON. These circulation anomalies associated with the MJO further help to enhance the surface air temperature and precipitation anomalies over North America, although room for improvement is still evident. Initial value calculations suggest that the realistic MJO teleconnection with the UNICON is not attributed to the changes in the background wind, but primarily to the improved tropical convective heating associated with the MJO.« less

The Modulation of Tropical Storm Activity in the Western North Pacific by the Madden-Julian Oscillation in GEOS-5 AGCM Experiments

NASA Technical Reports Server (NTRS)

Kim, Dongmin; Lee, Myong-In; Kim, Hye-Mi; Schubert, Siegfried D.; Yoo, Jin Ho

2014-01-01

This study examines the influence of the Madden-Julian Oscillation (MJO) on tropical storm (TS) activity in the western North Pacific, using observations and GEOS-5 simulations at 50-km horizontal resolution. While GEOS-5 produces an MJO of faster propagation and weaker amplitude, it nevertheless reproduces the observed modulation of TS activity by the MJO with the highest TS genesis and increased track density in the active phases of MJO. The study suggests that the simulation of the sub-seasonal variability of TS activity could be improved by improving the simulations of the MJO in climate models.

Role of Longwave Cloud-Radiation Feedback in the Simulation of the Madden-Julian Oscillation

NASA Technical Reports Server (NTRS)

Kim, Daehyun; Ahn, Min-Seop; Kang, In-Sik; Del Genio, Anthony D.

2015-01-01

The role of the cloud-radiation interaction in the simulation of the Madden-Julian oscillation (MJO) is investigated. A special focus is on the enhancement of column-integrated diabatic heating due to the greenhouse effects of clouds and moisture in the region of anomalous convection. The degree of this enhancement, the greenhouse enhancement factor (GEF), is measured at different precipitation anomaly regimes as the negative ratio of anomalous outgoing longwave radiation to anomalous precipitation. Observations show that the GEF varies significantly with precipitation anomaly and with the MJO cycle. The greenhouse enhancement is greater in weak precipitation anomaly regimes and its effectiveness decreases monotonically with increasing precipitation anomaly. The GEF also amplifies locally when convection is strengthened in association with the MJO, especially in the weak precipitation anomaly regime (less than 5 mm day(exp -1)). A robust statistical relationship is found among CMIP5 climate model simulations between the GEF and the MJO simulation fidelity. Models that simulate a stronger MJO also simulate a greater GEF, especially in the weak precipitation anomaly regime (less than 5 mm day(exp -1)). Models with a greater GEF in the strong precipitation anomaly regime (greater than 30 mm day(-1)) represent a slightly slower MJO propagation speed. Many models that lack the MJO underestimate the GEF in general and in particular in the weak precipitation anomaly regime. The results herein highlight that the cloud-radiation interaction is a crucial process for climate models to correctly represent the MJO.

Madden–Julian Oscillation prediction skill of a new-generation global model demonstrated using a supercomputer

PubMed Central

Miyakawa, Tomoki; Satoh, Masaki; Miura, Hiroaki; Tomita, Hirofumi; Yashiro, Hisashi; Noda, Akira T.; Yamada, Yohei; Kodama, Chihiro; Kimoto, Masahide; Yoneyama, Kunio

2014-01-01

Global cloud/cloud system-resolving models are perceived to perform well in the prediction of the Madden–Julian Oscillation (MJO), a huge eastward -propagating atmospheric pulse that dominates intraseasonal variation of the tropics and affects the entire globe. However, owing to model complexity, detailed analysis is limited by computational power. Here we carry out a simulation series using a recently developed supercomputer, which enables the statistical evaluation of the MJO prediction skill of a costly new-generation model in a manner similar to operational forecast models. We estimate the current MJO predictability of the model as 27 days by conducting simulations including all winter MJO cases identified during 2003–2012. The simulated precipitation patterns associated with different MJO phases compare well with observations. An MJO case captured in a recent intensive observation is also well reproduced. Our results reveal that the global cloud-resolving approach is effective in understanding the MJO and in providing month-long tropical forecasts. PMID:24801254

Madden-Julian Oscillation prediction skill of a new-generation global model demonstrated using a supercomputer.

PubMed

Miyakawa, Tomoki; Satoh, Masaki; Miura, Hiroaki; Tomita, Hirofumi; Yashiro, Hisashi; Noda, Akira T; Yamada, Yohei; Kodama, Chihiro; Kimoto, Masahide; Yoneyama, Kunio

2014-05-06

Global cloud/cloud system-resolving models are perceived to perform well in the prediction of the Madden-Julian Oscillation (MJO), a huge eastward -propagating atmospheric pulse that dominates intraseasonal variation of the tropics and affects the entire globe. However, owing to model complexity, detailed analysis is limited by computational power. Here we carry out a simulation series using a recently developed supercomputer, which enables the statistical evaluation of the MJO prediction skill of a costly new-generation model in a manner similar to operational forecast models. We estimate the current MJO predictability of the model as 27 days by conducting simulations including all winter MJO cases identified during 2003-2012. The simulated precipitation patterns associated with different MJO phases compare well with observations. An MJO case captured in a recent intensive observation is also well reproduced. Our results reveal that the global cloud-resolving approach is effective in understanding the MJO and in providing month-long tropical forecasts.

Comparison of Moist Static Energy and Budget between the GCM-Simulated Madden–Julian Oscillation and Observations over the Indian Ocean and Western Pacific

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

Wu, Xiaoqing; Deng, Liping

The moist static energy (MSE) anomalies and MSE budget associated with the Madden–Julian oscillation (MJO) simulated in the Iowa State University General Circulation Model (ISUGCM) over the Indian and Pacific Oceans are compared with observations. Different phase relationships between MJO 850-hPa zonal wind, precipitation, and surface latent heat flux are simulated over the Indian Ocean and western Pacific, which are greatly influenced by the convection closure, trigger conditions, and convective momentum transport (CMT). The moist static energy builds up from the lower troposphere 15–20 days before the peak of MJO precipitation, and reaches the maximum in the middle troposphere (500–600more » hPa) near the peak of MJO precipitation. The gradual lower-tropospheric heating and moistening and the upward transport of moist static energy are important aspects of MJO events, which are documented in observational studies but poorly simulated in most GCMs. The trigger conditions for deep convection, obtained from the year-long cloud resolving model (CRM) simulations, contribute to the striking difference between ISUGCM simulations with the original and modified convection schemes and play the major role in the improved MJO simulation in ISUGCM. Additionally, the budget analysis with the ISUGCM simulations shows the increase in MJO MSE is in phase with the horizontal advection of MSE over the western Pacific, while out of phase with the horizontal advection of MSE over the Indian Ocean. However, the NCEP analysis shows that the tendency of MJO MSE is in phase with the horizontal advection of MSE over both oceans.« less

Constraints on Cumulus Parameterization from Simulations of Observed MJO Events

NASA Technical Reports Server (NTRS)

Del Genio, Anthony; Wu, Jingbo; Wolf, Audrey B.; Chen, Yonghua; Yao, Mao-Sung; Kim, Daehyun

2015-01-01

Two recent activities offer an opportunity to test general circulation model (GCM) convection and its interaction with large-scale dynamics for observed Madden-Julian oscillation (MJO) events. This study evaluates the sensitivity of the Goddard Institute for Space Studies (GISS) GCM to entrainment, rain evaporation, downdrafts, and cold pools. Single Column Model versions that restrict weakly entraining convection produce the most realistic dependence of convection depth on column water vapor (CWV) during the Atmospheric Radiation Measurement MJO Investigation Experiment at Gan Island. Differences among models are primarily at intermediate CWV where the transition from shallow to deeper convection occurs. GCM 20-day hindcasts during the Year of Tropical Convection that best capture the shallow–deep transition also produce strong MJOs, with significant predictability compared to Tropical Rainfall Measuring Mission data. The dry anomaly east of the disturbance on hindcast day 1 is a good predictor of MJO onset and evolution. Initial CWV there is near the shallow–deep transition point, implicating premature onset of deep convection as a predictor of a poor MJO simulation. Convection weakly moistens the dry region in good MJO simulations in the first week; weakening of large-scale subsidence over this time may also affect MJO onset. Longwave radiation anomalies are weakest in the worst model version, consistent with previous analyses of cloud/moisture greenhouse enhancement as the primary MJO energy source. The authors’ results suggest that both cloud-/moisture-radiative interactions and convection–moisture sensitivity are required to produce a successful MJO simulation.

Impact of the Indian part of the summer MJO on West Africa using nudged climate simulations

NASA Astrophysics Data System (ADS)

Mohino, Elsa; Janicot, Serge; Douville, Hervé; Li, Laurent Z. X.

2012-06-01

Observational evidence suggests a link between the summer Madden Julian Oscillation (MJO) and anomalous convection over West Africa. This link is further studied with the help of the LMDZ atmospheric general circulation model. The approach is based on nudging the model towards the reanalysis in the Asian monsoon region. The simulation successfully captures the convection associated with the summer MJO in the nudging region. Outside this region the model is free to evolve. Over West Africa it simulates convection anomalies that are similar in magnitude, structure, and timing to the observed ones. In accordance with the observations, the simulation shows that 15-20 days after the maximum increase (decrease) of convection in the Indian Ocean there is a significant reduction (increase) in West African convection. The simulation strongly suggests that in addition to the eastward-moving MJO signal, the westward propagation of a convectively coupled equatorial Rossby wave is needed to explain the overall impact of the MJO on convection over West Africa. These results highlight the use of MJO events to potentially predict regional-scale anomalous convection and rainfall spells over West Africa with a time lag of approximately 15-20 days.

Simulations of Madden-Julian Oscillation in High Resolution Atmospheric General Circulation Model

NASA Astrophysics Data System (ADS)

Deng, Liping; Stenchikov, Georgiy; McCabe, Matthew; Bangalath, HamzaKunhu; Raj, Jerry; Osipov, Sergey

2014-05-01

The simulation of tropical signals, especially the Madden-Julian Oscillation (MJO), is one of the major deficiencies in current numerical models. The unrealistic features in the MJO simulations include the weak amplitude, more power at higher frequencies, displacement of the temporal and spatial distributions, eastward propagation speed being too fast, and a lack of coherent structure for the eastward propagation from the Indian Ocean to the Pacific (e.g., Slingo et al. 1996). While some improvement in simulating MJO variance and coherent eastward propagation has been attributed to model physics, model mean background state and air-sea interaction, studies have shown that the model resolution, especially for higher horizontal resolution, may play an important role in producing a more realistic simulation of MJO (e.g., Sperber et al. 2005). In this study, we employ unique high-resolution (25-km) simulations conducted using the Geophysical Fluid Dynamics Laboratory global High Resolution Atmospheric Model (HIRAM) to evaluate the MJO simulation against the European Center for Medium-range Weather Forecasts (ECMWF) Interim re-analysis (ERAI) dataset. We specifically focus on the ability of the model to represent the MJO related amplitude, spatial distribution, eastward propagation, and horizontal and vertical structures. Additionally, as the HIRAM output covers not only an historic period (1979-2012) but also future period (2012-2050), the impact of future climate change related to the MJO is illustrated. The possible changes in intensity and frequency of extreme weather and climate events (e.g., strong wind and heavy rainfall) in the western Pacific, the Indian Ocean and the Middle East North Africa (MENA) region are highlighted.

Interaction of deep and shallow convection is key to Madden-Julian Oscillation simulation

NASA Astrophysics Data System (ADS)

Zhang, Guang J.; Song, Xiaoliang

2009-05-01

This study investigates the role of the interaction between deep and shallow convection in MJO simulation using the NCAR CAM3. Two simulations were performed, one using a revised Zhang-McFarlane convection scheme for deep convection and the Hack scheme for shallow convection, and the other disallowing shallow convection below 700 mb in the tropical belt. The two simulations produce dramatically different MJO characteristics. While the control simulation produces realistic MJOs, the simulation without shallow convection has very weak MJO signals in the Indian Ocean and western Pacific. Composite analysis finds that shallow convection serves to precondition the lower troposphere by moistening it ahead of deep convection. It also produces enhanced low-level mass convergence below 850 mb ahead of deep convection. This work, together with previous studies, suggests that a correct simulation of the interaction between deep and shallow convection is key to MJO simulation in global climate models.

The impact of the diurnal cycle on the propagation of Madden-Julian Oscillation convection across the Maritime Continent

DOE PAGES

Hagos, Samson M.; Zhang, Chidong; Feng, Zhe; ...

2016-09-19

Influences of the diurnal cycle of convection on the propagation of the Madden-Julian Oscillation (MJO) across the Maritime Continent (MC) are examined using cloud-permitting regional model simulations and observations. A pair of ensembles of control (CONTROL) and no-diurnal cycle (NODC) simulations of the November 2011 MJO episode are performed. In the CONTROL simulations, the MJO signal is weakened as it propagates across the MC, with much of the convection stalling over the large islands of Sumatra and Borneo. In the NODC simulations, where the incoming shortwave radiation at the top of the atmosphere is maintained at its daily mean value,more » the MJO signal propagating across the MC is enhanced. Examination of the surface energy fluxes in the simulations indicates that in the presence of the diurnal cycle, surface downwelling shortwave radiation in CONTROL simulations is larger because clouds preferentially form in the afternoon. Furthermore, the diurnal co-variability of surface wind speed and skin temperature results in a larger sensible heat flux and a cooler land surface in CONTROL compared to NODC simulations. Here, an analysis of observations indicates that the modulation of the downwelling shortwave radiation at the surface by the diurnal cycle of cloudiness negatively projects on the MJO intraseasonal cycle and therefore disrupts the propagation of the MJO across the MC.« less

MJO-Related Tropical Convection Anomalies Lead to More Accurate Stratospheric Vortex Variability in Subseasonal Forecast Models.

PubMed

Garfinkel, C I; Schwartz, C

2017-10-16

The effect of the Madden-Julian Oscillation (MJO) on the Northern Hemisphere wintertime stratospheric polar vortex in the period preceding stratospheric sudden warmings is evaluated in operational subseasonal forecasting models. Reforecasts which simulate stronger MJO-related convection in the Tropical West Pacific also simulate enhanced heat flux in the lowermost stratosphere and a more realistic vortex evolution. The time scale on which vortex predictability is enhanced lies between 2 and 4 weeks for nearly all cases. Those stratospheric sudden warmings that were preceded by a strong MJO event are more predictable at ∼20 day leads than stratospheric sudden warmings not preceded by a MJO event. Hence, knowledge of the MJO can contribute to enhanced predictability, at least in a probabilistic sense, of the Northern Hemisphere polar stratosphere.

Potential role of salinity in ENSO and MJO predictions

NASA Astrophysics Data System (ADS)

Zhu, J.; Kumar, A.; Murtugudde, R. G.; Xie, P.

2017-12-01

Studies have suggested that ocean salinity can vary in response to ENSO and MJO. For example, during an El Niño event, sea surface salinity decreases in the western and central equatorial Pacific, as a result of zonal advection of low salinity water by anomalous eastward surface currents, and to a lesser extent as a result of a rainfall excess associated with atmospheric convection and warm water displacements. However, the effect of salinity on ENSO and MJO evolutions and their forecasts has been less explored. In this analysis, we explored the potential role of salinity in ENSO and MJO predictions by conducting sensitivity experiments with NCEP CFSv2. Firstly, two forecasts experiments are conducted to explore its effect on ENSO predictions, in which the interannual variability of salinity in the ocean initial states is either included or excluded. Comparisons suggested that the salinity variability is essential to correctly forecast the 2007/08 La Niña starting from April 2007. With realistic salinity initial states, the tendency to decay of the subsurface cold condition during the spring and early summer 2007 was interrupted by positive salinity anomalies in the upper central Pacific, which working together with the Bjerknes positive feedback, contributed to the development of the La Niña event. Our study suggests that ENSO forecasts will benefit from more accurate sustained salinity observations having large-scale spatial coverage. We also assessed the potential role of salinity in MJO by evaluating a long coupled free run that has a relatively realistic MJO simulation and a set of predictability experiment, both based on CFSv2. Diagnostics of the free run suggest that, while the intraseasonal SST variations lead convections by a quarter cycle, they are almost in phase only with changes in barrier layer thickness, thereby suggesting an active role of salinity on SST. Its effect on MJO predictions is further explored by controlling the surface salinity feedback during the predictability experiments.

Characterization of Moist Processes Associated With Changes in the Propagation of the MJO With Increasing CO2

PubMed Central

Kim, Daehyun; Sobel, Adam H.; Del Genio, Anthony; Wu, Jingbo

2017-01-01

Abstract The processes that lead to changes in the propagation and maintenance of the Madden‐Julian Oscillation (MJO) as a response to increasing CO2 are examined by analyzing moist static energy budget of the MJO in a series of NASA GISS model simulations. It is found changes in MJO propagation is dominated by several key processes. Horizontal moisture advection, a key process for MJO propagation, is found to enhance predominantly due to an increase in the mean horizontal moisture gradients. The terms that determine the strength of the advecting wind anomalies, the MJO horizontal scale and the dry static stability, are found to exhibit opposing trends that largely cancel out. Furthermore, reduced sensitivity of precipitation to changes in column moisture, i.e., a lengthening in the convective moisture adjustment time scale, also opposes enhanced propagation. The dispersion relationship of Adames and Kim, which accounts for all these processes, predicts an acceleration of the MJO at a rate of ∼3.5% K−1, which is consistent with the actual phase speed changes in the simulation. For the processes that contribute to MJO maintenance, it is found that damping by vertical MSE advection is reduced due to the increasing vertical moisture gradient. This weaker damping is nearly canceled by weaker maintenance by cloud‐radiative feedbacks, yielding the growth rate from the linear moisture mode theory nearly unchanged with the warming. Furthermore, the estimated growth rates are found to be a small, negative values, suggesting that the MJO in the simulation is a weakly damped mode. PMID:29497477

The Madden-Julian Oscillation in the NCAR Community Earth System Model Coupled Data Assimilation System

NASA Astrophysics Data System (ADS)

Chatterjee, A.; Anderson, J. L.; Moncrieff, M.; Collins, N.; Danabasoglu, G.; Hoar, T.; Karspeck, A. R.; Neale, R. B.; Raeder, K.; Tribbia, J. J.

2014-12-01

We present a quantitative evaluation of the simulated MJO in analyses produced with a coupled data assimilation (CDA) framework developed at the National Center for Atmosphere Research. This system is based on the Community Earth System Model (CESM; previously known as the Community Climate System Model -CCSM) interfaced to a community facility for ensemble data assimilation (Data Assimilation Research Testbed - DART). The system (multi-component CDA) assimilates data into each of the respective ocean/atmosphere/land model components during the assimilation step followed by an exchange of information between the model components during the forecast step. Note that this is an advancement over many existing prototypes of coupled data assimilation systems, which typically assimilate observations only in one of the model components (i.e., single-component CDA). The more realistic treatment of air-sea interactions and improvements to the model mean state in the multi-component CDA recover many aspects of MJO representation, from its space-time structure and propagation (see Figure 1) to the governing relationships between precipitation and sea surface temperature on intra-seasonal scales. Standard qualitative and process-based diagnostics identified by the MJO Task Force (currently under the auspices of the Working Group on Numerical Experimentation) have been used to detect the MJO signals across a suite of coupled model experiments involving both multi-component and single-component DA experiments as well as a free run of the coupled CESM model (i.e., CMIP5 style without data assimilation). Short predictability experiments during the boreal winter are used to demonstrate that the decay rates of the MJO convective anomalies are slower in the multi-component CDA system, which allows it to retain the MJO dynamics for a longer period. We anticipate that the knowledge gained through this study will enhance our understanding of the MJO feedback mechanisms across the air-sea interface, especially regarding ocean impacts on the MJO as well as highlight the capability of coupled data assimilation systems for related tropical intraseasonal variability predictions.

A Madden-Julian oscillation event realistically simulated by a global cloud-resolving model.

PubMed

Miura, Hiroaki; Satoh, Masaki; Nasuno, Tomoe; Noda, Akira T; Oouchi, Kazuyoshi

2007-12-14

A Madden-Julian Oscillation (MJO) is a massive weather event consisting of deep convection coupled with atmospheric circulation, moving slowly eastward over the Indian and Pacific Oceans. Despite its enormous influence on many weather and climate systems worldwide, it has proven very difficult to simulate an MJO because of assumptions about cumulus clouds in global meteorological models. Using a model that allows direct coupling of the atmospheric circulation and clouds, we successfully simulated the slow eastward migration of an MJO event. Topography, the zonal sea surface temperature gradient, and interplay between eastward- and westward-propagating signals controlled the timing of the eastward transition of the convective center. Our results demonstrate the potential making of month-long MJO predictions when global cloud-resolving models with realistic initial conditions are used.

Meridional Propagation of the MJO/ISO and Asian Monsoon Variability

NASA Technical Reports Server (NTRS)

Wu, Man Li C.; Schubert, Siegfried; Suarez, Max; Pegion, Phil; Waliser, D.

2003-01-01

In this study we examine the links between tropical heating, the Madden Julian Oscillation (MJO)/Intraseasonal Oscillation (ISO), and the Asian monsoon. We are particularly interested in isolating the nature of the poleward propagation of the ISO/MJO in the monsoon region. We examine both observations and idealized "MJO heating" experiments employing the NASA Seasonal-Interannual Prediction Project (NSIPP) atmospheric general circulation model (AGCM). In the idealized 10-member ensemble simulations, the model is forced by climatological SST and an idealized eastward propagating heating profile that is meant to mimic the canonical heating associated with the MJO in the Indian Ocean and western Pacific. In order to understand the impact of SST on the off equatorial convection (or Rossby-wave response), a second set of 10-member ensemble simulations is carried out with the climatological SSTs shifted in time by 6-months. The observational analysis highlights the strong link between the Indian summer monsoon and the tropical ISO/MJO activity and heating. This includes the well-known meridional propagation that affects the summer monsoons of both hemispheres. The AGCM experiments with the idealized eastward propagating MJO-like heating reproduce the observed meridional propagation including the observed seasonal differences. The impact of the SSTs are to enhance the magnitude of the propagation into the summer hemispheres. The results suggest that the winter/summer differences associated with the MJO/ISO are auxiliary features that depend on the MJO's environment (basic state and boundary conditions) and are not the result of fundamental differences in the MJO itself.

Influences of the MJO on the space-time organization of tropical convection

NASA Astrophysics Data System (ADS)

Dias, Juliana; Sakaeda, Naoko; Kiladis, George N.; Kikuchi, Kazuyoshi

2017-08-01

The fact that the Madden-Julian Oscillation (MJO) is characterized by large-scale patterns of enhanced tropical rainfall has been widely recognized for decades. However, the precise nature of any two-way feedback between the MJO and the properties of smaller-scale organization that makes up its convective envelope is not well understood. Satellite estimates of brightness temperature are used here as a proxy for tropical rainfall, and a variety of diagnostics are applied to determine the degree to which tropical convection is affected either locally or globally by the MJO. To address the multiscale nature of tropical convective organization, the approach ranges from space-time spectral analysis to an object-tracking algorithm. In addition to the intensity and distribution of global tropical rainfall, the relationship between the MJO and other tropical processes such as convectively coupled equatorial waves, mesoscale convective systems, and the diurnal cycle of tropical convection is also analyzed. The main findings of this paper are that, aside from the well-known increase in rainfall activity across scales within the MJO convective envelope, the MJO does not favor any particular scale or type of organization, and there is no clear signature of the MJO in terms of the globally integrated distribution of brightness temperature or rainfall.

Predictability of the 1997 and 1998 South Asian Summer Monsoons on the Intraseasonal Time Scale Based on 10 AMIP2 Model Runs

NASA Technical Reports Server (NTRS)

Wu, Man Li C.; Schubert, Siegfried; Einaudi, Franco (Technical Monitor)

2000-01-01

Predictability of the 1997 and 1998 South Asian summer monsoons is examined using National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalyses, and 100 two-year simulations with ten different Atmospheric General Circulation Models (AGCMs) with prescribed sea surface temperature (SST). We focus on the intraseasonal variations of the south Asian summer monsoon associated with the Madden-Julian Oscillation (MJO). The NCEP/NCAR reanalysis shows a clear coupling between SST anomalies and upper level velocity potential anomalies associated with the MJO. We analyze several MJO events that developed during the 1997 and 1998 focusing of the coupling with the SST. The same analysis is carried out for the model simulations. Remarkably, the ensemble mean of the two-year AGCM simulations show a signature of the observed MJO events. The ensemble mean simulated MJO events are approximately in phase with the observed events, although they are weaker, the period of oscillation is somewhat longer, and their onset is delayed by about ten days compared with the observations. Details of the analysis and comparisons among the ten AMIP2 (Atmospheric Model Intercomparison Project) models will be presented in the conference.

Modulation of Heavy Rainfall in the Middle East and North Africa by Madden-Julian Oscillation Using High Resolution Atmospheric General Circulation Model

NASA Astrophysics Data System (ADS)

Deng, L.; Stenchikov, G. L.; McCabe, M. F.; Bangalath, H. K.

2014-12-01

Recently, the modulation of subtropical rainfall by the dominant tropical intraseasonal signal of the Madden-Julian Oscillation (MJO), has been explored through the discussion of the MJO-convection-induced Kelvin and Rossby wave related teleconnection patterns. Our study focuses on characterizing the modulation of heavy rainfall in the Middle East and North Africa (MENA) region by the MJO, using the Geophysical Fluid Dynamics Laboratory (GFDL) global High Resolution Atmospheric Model (HIRAM) simulations (25-km; 1979-2012) and a combination of available atmospheric products from satellite, in-situ and reanalysis data. The observed Hadley Centre Global Sea Ice and Sea Surface Temperature (HadISST) and the simulated SST from GFDL's global coupled carbon-climate Earth System Models (ESM2M) are employed in HIRAM to investigate the sensitivity of the simulated heavy rainfall and MJO to SST. The future trend of the extreme rainfalls and their links to the MJO response to climate change are examined using HIRAM simulations of 2012-2050 with the RCP4.5 and RCP 8.5 scenarios to advance the possibility of characterization and forecasting of future extreme rainfall events in the MENA region.

Physical Mechanisms for the Maintenance of GCM-Simulated Madden-Julian Oscillation over the Indian Ocean and Pacific

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

Deng, Liping; Wu, Xiaoqing

2011-05-05

The kinetic energy budget is conducted to analyze the physical processes responsible for the improved Madden-Julian Oscillation (MJO) simulated by the Iowa State University general circulation models (ISUGCM). The modified deep convection scheme that includes the revised convection closure, convection trigger condition and convective momentum transport (CMT) enhances the equatorial (10oS-10oN) MJO-related perturbation kinetic energy (PKE) in the upper troposphere and leads to more robust and coherent eastward propagating MJO signal. In the MJO source region-the Indian Ocean (45oE-120oE), the upper-tropospheric MJO PKE is maintained by the vertical convergence of wave energy flux and the barotropic conversion through the horizontalmore » shear of mean flow. In the convectively active region-the western Pacific (120oE-180o), the upper-tropospheric MJO PKE is supported by the convergence of horizontal and vertical wave energy fluxes. Over the central-eastern Pacific (180o-120oW), where convection is suppressed, the upper-tropospheric MJO PKE is mainly due to the horizontal convergence of wave energy flux. The deep convection trigger condition produces stronger convective heating which enhances the perturbation available potential energy (PAPE) production and the upward wave energy fluxes, and leads to the increased MJO PKE over the Indian Ocean and western Pacific. The trigger condition also enhances the MJO PKE over the central-eastern Pacific through the increased convergence of meridional wave energy flux from the subtropical latitudes of both hemispheres. The revised convection closure affects the response of mean zonal wind shear to the convective heating over the Indian Ocean and leads to the enhanced upper-tropospheric MJO PKE through the barotropic conversion. The stronger eastward wave energy flux due to the increase of convective heating over the Indian Ocean and western Pacific by the revised closure is favorable to the eastward propagation of MJO and the convergence of horizontal wave energy flux over the central-eastern Pacific. The convection-induced momentum tendency tends to decelerate the upper-tropospheric wind which results in a negative work to the PKE budget in the upper troposphere. However, the convection momentum tendency accelerates the westerly wind below 800 hPa over the western Pacific, which is partially responsible for the improved MJO simulation.« less

The MJO-SSW Teleconnection: Interaction Between MJO-Forced Waves and the Midlatitude Jet

NASA Astrophysics Data System (ADS)

Kang, Wanying; Tziperman, Eli

2018-05-01

The Madden-Julian Oscillation (MJO) was shown to affect both present-day sudden stratospheric warming (SSW) events in the Arctic and their future frequency under global warming scenarios, with implications to the Arctic Oscillation and midlatitude extreme weather. This work uses a dry dynamic core model to understand the dependence of SSW frequency on the amplitude and longitudinal range of the MJO, motivated by the prediction that the MJO will strengthen and broaden its longitudinal range in a warmer climate. We focus on the response of the midlatitude jets and the corresponding generated stationary waves, which are shown to dominate the response of SSW events to MJO forcing. Momentum budget analysis of a large ensemble of spinup simulations suggests that the climatological jet response is driven by the MJO-forced meridional eddy momentum transport. The results suggest that the trends in both MJO amplitude and longitudinal range are important for the prediction of the midlatitude jet response and for the prediction of SSWs in a future climate.

The importance of wind-flux feedbacks during the November CINDY-DYNAMO MJO event

NASA Astrophysics Data System (ADS)

Riley Dellaripa, Emily; Maloney, Eric; van den Heever, Susan

2015-04-01

High-resolution, large-domain cloud resolving model (CRM) simulations probing the importance of wind-flux feedbacks to Madden-Julian Oscillation (MJO) convection are performed for the November 2011 CINDY-DYNAMO MJO event. The work is motivated by observational analysis from RAMA buoys in the Indian Ocean and TRMM precipitation retrievals that show a positive correlation between MJO precipitation and wind-induced surface fluxes, especially latent heat fluxes, during and beyond the CINDY-DYNAMO time period. Simulations are done using Colorado State University's Regional Atmospheric Modeling System (RAMS). The domain setup is oceanic and spans 1000 km x 1000 km with 1.5 km horizontal resolution and 65 stretched vertical levels centered on the location of Gan Island - one of the major CINDY-DYNAMO observation points. The model is initialized with ECMWF reanalysis and Aqua MODIS sea surface temperatures. Nudging from ECMWF reanalysis is applied at the domain periphery to encourage realistic evolution of MJO convection. The control experiment is run for the entire month of November so both suppressed and active, as well as, transitional phases of the MJO are modeled. In the control experiment, wind-induced surface fluxes are activated through the surface bulk aerodynamic formula and allowed to evolve organically. Sensitivity experiments are done by restarting the control run one week into the simulation and controlling the wind-induced flux feedbacks. In one sensitivity experiment, wind-induced surface flux feedbacks are completely denied, while in another experiment the winds are kept constant at the control simulations mean surface wind speed. The evolution of convection, especially on the mesoscale, is compared between the control and sensitivity simulations.

Tropical intraseasonal oscillation simulated in an AMIP-type experiment by NICAM

NASA Astrophysics Data System (ADS)

Kikuchi, Kazuyoshi; Kodama, Chihiro; Nasuno, Tomoe; Nakano, Masuo; Miura, Hiroaki; Satoh, Masaki; Noda, Akira T.; Yamada, Yohei

2017-04-01

It is the first time for the non-hydrostatic icosahedral atmospheric model (NICAM), at a horizontal mesh size of approximately 14-km, to conduct a continuous long-term Atmospheric Model Intercomparison Project-type simulation. This study examines the performance of NICAM in simulating the tropical intraseasonal oscillation (ISO) from a statistical point of view using 30-year data (1979-2008) in the context of the bimodal ISO representation concept proposed by Kikuchi et al., which allows us to examine the seasonally varying behavior of the ISO in great detail, in addition to the MJO working group level 2 diagnostics. It is found that many of the fundamental features of the ISO are well captured by NICAM. The evolution of the ISO convection as well as large-scale circulation over the course of its life cycle is reasonably well reproduced throughout the year. As in the observation, the Madden-Julian oscillation (MJO) mode, characterized by prominent eastward propagation of convection, is predominant during boreal winter, whereas the boreal summer ISO (BSISO) mode, by a combination of pronounced eastward and northward propagation, during summer. The overall shape of the seasonal cycle as measured by the numbers of significant MJO and BSISO days in a month is relatively well captured. Two major biases, however, are also identified. The amplitude of the simulated ISO is weaker by a factor of 2. Significant BSISO events sometimes appear even during winter (December-April), amounting to 30 % of the total significant ISO days as opposed to 2 % in the observation. The results here warrant further studies using the simulation dataset to understand not only many aspects of the dynamics and physics of the ISO but also its role in weather and climate. It is also demonstrated that the concept of the bimodal ISO representation provides a useful framework for assessing model's capability to simulate, and illuminating model's deficiencies in reproducing, the ISO. The nature and causes of the two major biases are also discussed.

Meridional Propagation of the MJO/ISO and Prediction of Off-equatorial Monsoon Variability

NASA Technical Reports Server (NTRS)

Wu, Man Li C.; Schubert, S.; Suarez, M.; Pegion, P.; Waliser, D.

2003-01-01

This study was examine the links between tropical heating, the Madden Julian Oscillation (MJO)/Intraseasonal Oscillation (ISO), and the off-equatorial monsoon development. We examine both observations and idealized "MJO heating" experiments employing the NASA Seasonal-Interannual Prediction Project (NSIPP) atmospheric general circulation model (AGCM). In the simulations, the model is forced by climatological SST and an idealized eastward propagating heating profile that is meant 'to mimic the canonical heating associated with the MJO in the Indian Ocean and western Pacific. The observational analysis highlights the strong link between the Indian summer monsoon and the tropical ISO/MJO activity and heating. Here we focus on the potential for skillful predictions of the monsoon on sub-seasonal time scales associated with the meridional propagation of the ISO/MJO. In particular, we show that the variability of the Indian summer monsoon lags behind the variability of tropical ISO/MJO heating by about 15 days when the tropical heating is around 60E and 90E. This feature of the ISO/MJO is reproduced in the AGCM experiments with the idealized eastward propagating MJO-like heating, suggesting that models with realistic ISO/MJO variability should provide useful skill of monsoon breaks and surges on sub-seasonal time scales.

Identifying a key physical factor sensitive to the performance of Madden-Julian oscillation simulation in climate models

NASA Astrophysics Data System (ADS)

Kim, Go-Un; Seo, Kyong-Hwan

2018-01-01

A key physical factor in regulating the performance of Madden-Julian oscillation (MJO) simulation is examined by using 26 climate model simulations from the World Meteorological Organization's Working Group for Numerical Experimentation/Global Energy and Water Cycle Experiment Atmospheric System Study (WGNE and MJO-Task Force/GASS) global model comparison project. For this, intraseasonal moisture budget equation is analyzed and a simple, efficient physical quantity is developed. The result shows that MJO skill is most sensitive to vertically integrated intraseasonal zonal wind convergence (ZC). In particular, a specific threshold value of the strength of the ZC can be used as distinguishing between good and poor models. An additional finding is that good models exhibit the correct simultaneous convection and large-scale circulation phase relationship. In poor models, however, the peak circulation response appears 3 days after peak rainfall, suggesting unfavorable coupling between convection and circulation. For an improving simulation of the MJO in climate models, we propose that this delay of circulation in response to convection needs to be corrected in the cumulus parameterization scheme.

The MJO Transition from Shallow to Deep Convection in CloudSat/CALIPSO Data and GISS GCM Simulations

NASA Technical Reports Server (NTRS)

DelGenio, Anthony G.; Chen, Yonghua; Kim, Daehyun; Yao, Mao-Sung

2013-01-01

The relationship between convective penetration depth and tropospheric humidity is central to recent theories of the Madden-Julian oscillation (MJO). It has been suggested that general circulation models (GCMs) poorly simulate the MJO because they fail to gradually moisten the troposphere by shallow convection and simulate a slow transition to deep convection. CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) data are analyzed to document the variability of convection depth and its relation to water vapor during the MJO transition from shallow to deep convection and to constrain GCM cumulus parameterizations. Composites of cloud occurrence for 10MJO events show the following anticipatedMJO cloud structure: shallow and congestus clouds in advance of the peak, deep clouds near the peak, and upper-level anvils after the peak. Cirrus clouds are also frequent in advance of the peak. The Advanced Microwave Scanning Radiometer for EarthObserving System (EOS) (AMSR-E) columnwater vapor (CWV) increases by;5 mmduring the shallow- deep transition phase, consistent with the idea of moisture preconditioning. Echo-top height of clouds rooted in the boundary layer increases sharply with CWV, with large variability in depth when CWV is between;46 and 68 mm. International Satellite Cloud Climatology Project cloud classifications reproduce these climatological relationships but correctly identify congestus-dominated scenes only about half the time. A version of the Goddard Institute for Space Studies Model E2 (GISS-E2) GCM with strengthened entrainment and rain evaporation that produces MJO-like variability also reproduces the shallow-deep convection transition, including the large variability of cloud-top height at intermediate CWV values. The variability is due to small grid-scale relative humidity and lapse rate anomalies for similar values of CWV. 1.

Initiation Processes of the Tropical Intraseasonal Variability Simulated in an Aqua-Planet Experiment: What is the Intrinsic Mechanism for MJO Onset?

NASA Astrophysics Data System (ADS)

Takasuka, Daisuke; Satoh, Masaki; Miyakawa, Tomoki; Miura, Hiroaki

2018-04-01

To understand the intrinsic onset mechanism of the Madden-Julian Oscillation (MJO), we simulated a set of initiation processes of MJO-like disturbances in 10 year aqua-planet experiments using a global atmospheric model with a 56 km horizontal mesh and an explicit cloud scheme. Under a condition with a zonally nonuniform sea surface temperature (SST) in the tropics, we reproduced MJO-like disturbances over the western warm pool region. The lagged-composite analysis of detected MJO-like disturbances clarifies the time sequence of three-dimensional dynamic and moisture fields prior to the onset. We found that midtropospheric moistening, a condition that is favorable for deep convection, is particularly obvious in the initiation region 5-9 days before onset. The moistening is caused by two-dimensional horizontal advection due to cross-equatorial shallow circulations associated with mixed Rossby-gravity waves, as well as anomalous poleward flows of a negative Rossby response to suppressed convection. When the midtroposphere is sufficiently moistened, lower tropospheric signals of circumnavigating Kelvin waves trigger active convection. The surface latent heat flux (LHF) feedback contributes to the initial stages of convective organization, while the cloud-radiation feedback contributes to later stages. Sensitivity experiments suggest that circumnavigating Kelvin waves regulate the period of MJO-like disturbances because of efficient convective triggering and that the LHF feedback contributes to rapid convective organization. However, the experiments also reveal that both conditions are not necessary for the existence of MJO-like disturbances. Implications for the relevance of these mechanisms for MJO onset are also discussed.

Modeling the Interaction of the Madden-Julian Oscillation and Quasi-biennial Oscillation

NASA Astrophysics Data System (ADS)

Martin, Z.; Wang, S.; Nie, J.; Sobel, A. H.

2017-12-01

The stratospheric quasi-biennial oscillation (QBO) and the intra-seasonal Madden-Julian oscillation (MJO) are two hallmark features of the tropical atmosphere. Recent observational results have demonstrated a strong correlation between the MJO and the QBO, particularly in boreal winter, with enhanced MJO activity and increased predictability during the easterly phase of the QBO. Despite the robustness of the observational result, the physical processes through which the MJO and QBO interact are unknown and largely unstudied. We demonstrate that the MJO can be simulated in the WRF cloud-resolving model with large-scale forcing taken from the DYNAMO field campaign, during a period when two MJO events were observed and the QBO was in a neutral phase. We look at the effect of forcing the model MJO with idealized temperature anomalies around the tropopause, representative of the easterly and westerly QBO phases. While the model demonstrates some robust relationships between the MJO and QBO - including an increase in the vertical velocity and cloud fraction, and a decrease in OLR during the easterly QBO phase - other variables, such as precipitation, depend on the QBO phase and the particular MJO event in a more complicated manner. We conclude with some preliminary results towards understanding the mechanisms driving the MJO-QBO relationship through examining the effects of cloud-radiative feedback and horizontal moisture advection on the model results.

Extratropical Forcing Triggered the 2015 Madden-Julian Oscillation-El Niño Event.

PubMed

Hong, Chi-Cherng; Hsu, Huang-Hsiung; Tseng, Wan-Ling; Lee, Ming-Ying; Chow, Chun-Hoe; Jiang, Li-Chiang

2017-04-24

In this paper, we report the triggering effect of extratropical perturbation on the onset of an atypical Madden-Julian Oscillation (MJO) and onset of the 2015-16 El Niño in March 2015. The MJO exhibited several unique characteristics: the effect of extratropical forcing, atypical genesis location and timing in the equatorial western Pacific, and the extremity of amplitudes in many aspects. The southward-penetrating northerly associated with the extratropical disturbances in the extratropical western North Pacific contributed to triggering the deep convection and westerly wind burst (WWB) and onset of the MJO over the anomalously warm tropical western Pacific in early March. The persisting strong WWB forced downwelling Kelvin wave-like oceanic perturbation that propagated eastward and led to the onset of the 2015-16 El Niño. The proposed novel extratropical forcing mechanism explaining the unique extratropics-MJO-El Niño association, based on both data diagnostics and numerical experiments, warrants further attention for a more detailed understanding of the onset of the MJO and its potential effect on El Niño.

The impact of the diurnal cycle on the MJO over the Maritime Continent: a modeling study assimilating TRMM rain rate into global analysis

NASA Astrophysics Data System (ADS)

Oh, Ji-Hyun; Kim, Baek-Min; Kim, Kwang-Yul; Song, Hyo-Jong; Lim, Gyu-Ho

2013-02-01

In the present study, we use modeling experiments to investigate the impact of the diurnal cycle on the Madden-Julian Oscillation (MJO) during the Australian summer. Physical initialization and a nudging technique enable us to assimilate the observed Tropical Rainfall Measuring Mission (TRMM) rain rate and atmospheric variables from the National Centers for Environmental Prediction—National Center for Atmospheric Research Reanalysis 2 (R2) into the Florida State University Global Spectral Model (FSUGSM), resulting in a realistic simulation of the MJO. Model precipitation is also significantly improved by TRMM rain rate observation via the physical initialization. We assess the influence of the diurnal cycle on the MJO by modifying the diurnal component during the model integration. Model variables are nudged toward the daily averaged values from R2. Globally suppressing the diurnal cycle (NO_DIURNAL) exerts a strong impact on the Maritime Continent. The mean state of precipitation increases and intraseasonal variability becomes stronger over the region. It is well known that MJO weakens as it passes over the Maritime Continent. However, the MJO maintains its strength in the NO_DIURNAL experiment, and the diminution of diurnal signals during the integration does not change the propagating speed of the MJO. We suggest that diminishing the diurnal cycle in NO_DIURNAL consumes less moist static energy (MSE), which is required to trigger both diurnal and intraseasonal convection. Thus, the remaining MSE may play a major role along with larger convective instability and stronger lower level moisture convergence in intensifying the MJO over the Maritime Continent in the model simulation.

The Effect of the Madden-Julian Oscillation on the Mesospheric Migrating Diurnal Tide: A Study Using SD-WACCM

NASA Astrophysics Data System (ADS)

Yang, Chengyun; Smith, Anne K.; Li, Tao; Dou, Xiankang

2018-05-01

The response of the mesospheric migrating diurnal (DW1) tide to the Madden-Julian oscillation (MJO) is investigated for the first time using a simulation from the Specified-Dynamic Whole Atmosphere Community Climate Model (SD-WACCM), which is driven by reanalysis data. Analysis shows that a significant connection exists between the MJO and the mesospheric DW1 tidal amplitude. During MJO phases 2 and 3, the convection anomalies are associated with enhancement in both the solar insolation absorption and latent heat release in the equatorial troposphere; these in turn lead to stronger DW1 forcing. Conversely, the forcing of DW1 by solar and latent heating in the troposphere is weaker during MJO phase 8. The difference of the tidal amplitude during the opposite MJO phases from the boreal winter mean state is 15-20%. The parameterized gravity wave variations are found to have a significant impact on the DW1 tidal response in some phases of the MJO.

Changes in the Structure and Propagation of the MJO with Increasing CO2

NASA Technical Reports Server (NTRS)

Adames, Angel F.; Kim, Daehyun; Sobel, Adam H.; Del Genio, Anthony; Wu, Jingbo

2017-01-01

Changes in the Madden-Julian Oscillation (MJO) with increasing CO2 concentrations are examined using the Goddard Institute for Space Studies Global Climate Model (GCM). Four simulations performed with fixed CO2 concentrations of 0.5, 1, 2 and 4 times pre-industrial levels using the GCM coupled with a mixed layer ocean model are analyzed in terms of the basic state, rainfall and moisture variability, and the structure and propagation of the MJO.The GCM simulates basic state changes associated with increasing CO2 that are consistent with results from earlier studies: column water vapor increases at approximately 7.1% K(exp -1), precipitation also increases but at a lower rate (approximately 3% K(exp -1)), and column relative humidity shows little change. Moisture and rainfall variability intensify with warming. Total moisture and rainfall variability increases at a rate that is similar to that of the mean state change. The intensification is faster in the MJO-related anomalies than in the total anomalies, though the ratio of the MJO band variability to its westward counterpart increases at a much slower rate. On the basis of linear regression analysis and space-time spectral analysis, it is found that the MJO exhibits faster eastward propagation, faster westward energy dispersion, a larger zonal scale and deeper vertical structure in warmer climates.

The role of SST variability in the simulation of the MJO

NASA Astrophysics Data System (ADS)

Stan, Cristiana

2017-12-01

The sensitivity of the Madden-Julian Oscillation to high-frequency variability (period 1-5 days) of sea surface temperature (SST) is investigated using numerical experiments with the super-parameterized Community Climate System Model. The findings of this study emphasize the importance of air-sea interactions in the simulation of the MJO, and stress the necessity of an accurate representation of ocean variability on short time scales. Eliminating 1-5-day variability of surface boundary forcing reduces the intraseasonal variability (ISV) of the tropics during the boreal winter. The ISV spectrum becomes close to the red noise background spectrum. The variability of atmospheric circulation shifts to longer time scales. In the absence of high-frequency variability of SST the MJO power gets confined to wavenumbers 1-2 and the magnitude of westward power associated with Rossby waves increases. The MJO convective activity propagating eastward from the Indian Ocean does not cross the Maritime Continent, and convection in the western Pacific Ocean is locally generated. In the Indian Ocean convection tends to follow the meridional propagation of SST anomalies. The response of the MJO to 1-5-day variability in the SST is through the charging and discharging mechanisms contributing to the atmospheric column moist static energy before and after peak MJO convection. Horizontal advection and surface fluxes show the largest sensitivity to SST perturbations.

Improved Intraseasonal Variability in the NASA GEOS AGCM with 2-moment Microphysics and a Shallow Cumulus Parameterization

NASA Technical Reports Server (NTRS)

Arnold, Nathan; Barahona, Donifan; Achuthavarier, Deepthi

2017-01-01

Weather and climate models have long struggled to realistically simulate the Madden-Julian Oscillation (MJO). Here we present a significant improvement in MJO simulation in NASA's GEOS atmospheric model with the implementation of 2-moment microphysics and the UW shallow cumulus parameterization. Comparing ten-year runs (2007-2016) with the old (1mom) and updated (2mom+shlw) model physics, the updated model has increased intra-seasonal variance with increased coherence. Surface fluxes and OLR are found to vary more realistically with precipitation, and a moisture budget suggests that changes in rain reevaporation and the cloud longwave feedback help support heavy precipitation. Preliminary results also show improved MJO hindcast skill.

The Madden-Julian oscillation in ECHAM4 coupled and uncoupled general circulation models

DOE PAGES

Sperber, Kenneth R.; Gualdi, Silvio; Legutke, Stephanie; ...

2005-06-29

The Madden-Julian oscillation (MJO) dominates tropical variability on timescales of 30–70 days. During the boreal winter/spring, it is manifested as an eastward propagating disturbance, with a strong convective signature over the eastern hemisphere. The space–time structure of the MJO is analyzed using simulations with the ECHAM4 atmospheric general circulation model run with observed monthly mean sea-surface temperatures (SSTs), and coupled to three different ocean models. The coherence of the eastward propagation of MJO convection is sensitive to the ocean model to which ECHAM4 is coupled. For ECHAM4/OPYC and ECHO-G, models for which ~100 years of daily data is available, Montemore » Carlo sampling indicates that their metrics of eastward propagation are different at the 1% significance level. The flux-adjusted coupled simulations, ECHAM4/OPYC and ECHO-G, maintain a more realistic mean-state, and have a more realistic MJO simulation than the nonadjusted scale interaction experiment (SINTEX) coupled runs. The SINTEX model exhibits a cold bias in Indian Ocean and tropical West Pacific Ocean sea-surface temperature of ~0.5°C. This cold bias affects the distribution of time-mean convection over the tropical eastern hemisphere. Furthermore, the eastward propagation of MJO convection in this model is not as coherent as in the two models that used flux adjustment or when compared to an integration of ECHAM4 with prescribed observed SST. This result suggests that simulating a realistic basic state is at least as important as air–sea interaction for organizing the MJO. While all of the coupled models simulate the warm (cold) SST anomalies that precede (succeed) the MJO convection, the interaction of the components of the net surface heat flux that lead to these anomalies are different over the Indian Ocean. The ECHAM4/OPYC model in which the atmospheric model is run at a horizontal resolution of T42, has eastward propagating zonal wind anomalies and latent heat flux anomalies. However, the integrations with ECHO-G and SINTEX, which used T30 atmospheres, produce westward propagation of the latent heat flux anomalies, contrary to reanalysis. Furthermore, it is suggested that the differing ability of the models to represent the near-surface westerlies over the Indian Ocean is related to the different horizontal resolutions of the atmospheric model employed.« less

Impacts of dynamical ocean coupling in MJO experiments using NICAM/NICOCO

NASA Astrophysics Data System (ADS)

Miyakawa, T.

2016-12-01

The cloud-system resolving atmosphereic model NICAM has been successfull in producing Madden-Julian Oscillations(MJOs), having it's prediction skill estimated to be about 4 weeks in a series of hindcast experiments for winter MJO events during 2003-2012 (Miyakawa et al. 2014). A simple mixed-layer ocean model has been applied with nudging towards a prescribed "persistent anomaly SST", which maintains the initial anomaly with a time-varying climatological seasonal cycle. This setup enables the model to interact with an ocean with reasonably realistic SST, and also run in a "forecast mode", without using any observational information after the initial date. A limitation is that under this setup, the model skill drops if the oceanic anomaly rapidly changes after the initial date in the real world. Here we run a recently developed, full 3D-ocean coupled version NICAM-COCO (NICOCO) and explore its impact on MJO simulations. Dynamical ocean models can produce oceanic waves/currents, but will also have a bias and drift away from reality. In a sub-seasonal simulation (an initial problem), it is essential to compare the merit of having better represented oceanic signals and the demerit of bias/drift. A test case simulation series featuring an MJO that triggered the abrupt termination of a major El Nino in 1998 shows that the abrupt termination occurs in all 9 simulation members, highlighting the merit of ocean coupling. However, this is a case where oceanic signals are at its extremes. We carried out an estimation of MJO prediction skill for a preliminary 1-degree mesh ocean version of NICOCO in a similar manner to Miyakawa et al. (2014). The MJO skill was degraded for simulations that was initialized at RMM phases 1 and 2 (corresponding to the Indian Ocean), while those initialized at phase 8 (Africa) was not strongly affected. The tendency of the model ocean to overestimate the Maritime Continent warm pool SST possibly delays the eastward propagation of MJO convective envelope, accounting for the degrade of prediction skills (phases 1 and 2). Reference:Madden-Julian Oscillation prediction skill of a new-generation global model demonstrated using a supercomputer. Miyakawa, T., M. Satoh, H. Miura, H. Tomita, H. Yashiro, A. T. Noda, Y. Yamada, C. Kodama, M. Kimoto & K. Yoneyama. Nature Comm. 5, 3769, doi:10.1038/ncomms4769.

Tradeoffs in Acceleration and Initialization of Superparameterized Global Atmospheric Models for MJO and Climate Science

NASA Astrophysics Data System (ADS)

Pritchard, M. S.; Bretherton, C. S.; DeMott, C. A.

2014-12-01

New trade-offs are discussed in the cloud superparameterization approach to explicitly representing deep convection in global climate models. Intrinsic predictability tests show that the memory of cloud-resolving-scale organization is not critical for producing desired modes of organized convection such as the Madden-Julian Oscillation (MJO). This has implications for the feasibility of data assimilation and real-world initialization for superparameterized weather forecasting. Climate simulation sensitivity tests demonstrate that 400% acceleration of cloud superparameterization is possible by restricting the 32-128 km scale regime without deteriorating the realism of the simulated MJO but the number of cloud resolving model grid columns is discovered to constrain the efficiency of vertical mixing, with consequences for the simulated liquid cloud climatology. Tuning opportunities for next generation accelerated superparameterized climate models are discussed.

Modeling the MJO rain rates using parameterized large scale dynamics: vertical structure, radiation, and horizontal advection of dry air

NASA Astrophysics Data System (ADS)

Wang, S.; Sobel, A. H.; Nie, J.

2015-12-01

Two Madden Julian Oscillation (MJO) events were observed during October and November 2011 in the equatorial Indian Ocean during the DYNAMO field campaign. Precipitation rates and large-scale vertical motion profiles derived from the DYNAMO northern sounding array are simulated in a small-domain cloud-resolving model using parameterized large-scale dynamics. Three parameterizations of large-scale dynamics --- the conventional weak temperature gradient (WTG) approximation, vertical mode based spectral WTG (SWTG), and damped gravity wave coupling (DGW) --- are employed. The target temperature profiles and radiative heating rates are taken from a control simulation in which the large-scale vertical motion is imposed (rather than directly from observations), and the model itself is significantly modified from that used in previous work. These methodological changes lead to significant improvement in the results.Simulations using all three methods, with imposed time -dependent radiation and horizontal moisture advection, capture the time variations in precipitation associated with the two MJO events well. The three methods produce significant differences in the large-scale vertical motion profile, however. WTG produces the most top-heavy and noisy profiles, while DGW's is smoother with a peak in midlevels. SWTG produces a smooth profile, somewhere between WTG and DGW, and in better agreement with observations than either of the others. Numerical experiments without horizontal advection of moisture suggest that that process significantly reduces the precipitation and suppresses the top-heaviness of large-scale vertical motion during the MJO active phases, while experiments in which the effect of cloud on radiation are disabled indicate that cloud-radiative interaction significantly amplifies the MJO. Experiments in which interactive radiation is used produce poorer agreement with observation than those with imposed time-varying radiative heating. Our results highlight the importance of both horizontal advection of moisture and cloud-radiative feedback to the dynamics of the MJO, as well as to accurate simulation and prediction of it in models.

MJO Signals in Latent Heating: Results from TRMM Retrievals

NASA Technical Reports Server (NTRS)

Zhang, Chidong; Ling, Jian; Hagos, Samson; Tao, Wei-Kuo; Lang, Steve; Takayabu, Yukari N.; Shige, Shoichi; Katsumata, Masaki; Olson, William S.; L'Ecuyer, Tristan

2010-01-01

The Madden-Julian Oscillation (MJO) is the dominant intraseasonal signal in the global tropical atmosphere. Almost all numerical climate models have difficulty to simulate realistic MJO. Four TRMM datasets of latent heating were diagnosed for signals in the MJO. In all four datasets, vertical structures of latent heating are dominated by two components, one deep with its peak above the melting level and one shallow with its peak below. Profiles of the two components are nearly ubiquitous in longitude, allowing a separation of the vertical and zonal/temporal variations when the latitudinal dependence is not considered. All four datasets exhibit robust MJO spectral signals in the deep component as eastward propagating spectral peaks centered at period of 50 days and zonal wavenumber 1, well distinguished from lower- and higher-frequency power and much stronger than the corresponding westward power. The shallow component shows similar but slightly less robust MJO spectral peaks. MJO signals were further extracted from a combination of band-pass (30 - 90 day) filtered deep and shallow components. Largest amplitudes of both deep and shallow components of the MJO are confined to the Indian and western Pacific Oceans. There is a local minimum in the deep components over the Maritime Continent. The shallow components of the MJO differ substantially among the four TRMM datasets in their detailed zonal distributions in the eastern hemisphere. In composites of the heating evolution through the life cycle of the MJO, the shallow components lead the deep ones in some datasets and at certain longitudes. In many respects, the four TRMM datasets agree well in their deep components, but not in their shallow components and the phase relations between the deep and shallow components. These results indicate that caution must be exercised in applications of these latent heating data.

Sensitivity to Madden-Julian Oscillation variations on heavy precipitation over the contiguous United States

NASA Astrophysics Data System (ADS)

Jones, Charles; Carvalho, Leila M. V.

2014-10-01

The Madden-Julian Oscillation (MJO) is the most prominent mode of tropical intraseasonal variability in the climate system and has worldwide influences on the occurrences and forecasts of heavy precipitation. This paper investigates the sensitivity of precipitation over the contiguous United States (CONUS) in a case study (boreal 2004-05 winter). Several major storms affected the western and eastern CONUS producing substantial economic and social impacts including loss of lives. The Weather Research and Forecasting (WRF) model is used to perform experiments to test the significance of the MJO amplitude. The control simulation uses the MJO amplitude observed by reanalysis, whereas the amplitude is modified in perturbation experiments. WRF realistically simulates the precipitation variability over the CONUS, although large biases occur over the Western and Midwest United States. Daily precipitation is aggregated in western, central and eastern sectors and the frequency distribution is analyzed. Increases in MJO amplitude produce moderate increases in the median and interquartile range and large and robust increases in extreme (90th and 95th percentiles) precipitation. The MJO amplitude clearly affects the transport of moisture from the tropical Pacific and Gulf of Mexico into North America providing moist rich air masses and the dynamical forcing that contributes to heavy precipitation.

Revisiting Gill's Circulation. Dynamic Response to Diabatic Heating of Different Horizontal Extents

NASA Astrophysics Data System (ADS)

Reboredo, B.; Bellon, G.

2017-12-01

The horizontal extent of diabatic heating associated with the MJO is thought to be crucial to its development, and the inability of GCMs to simulate the spatial, horizontal organization of clouds is considered a leading hypothesis to explain their limited capacity to simulate MJO events. This prevents the MJO large-circulation response from developing and feeding back on the development of clouds. We apply mid-tropospheric heating of different size in simple linear and non-linear models of the tropical atmosphere following Gill's seminal work on heat-induced tropical circulations. Results show that there is a scale for which the characteristic circulation {Γ c} for the vertical advection of moisture to produce the latent heat mean {Q} gives a rough estimate of the real world MJO scale. Overturning circulation flow rates above {Γ c} account for a circulation that transports more moisture than necessary to be maintained, and below {Γ c}, circulation would not transport enough moisture to maintain circulation. This dynamic scale might constrain the size of the spatially-organised convection necessary to the development of an MJO event. However, other effects are expected to modulate this scale, such as vertical advection of moisture anomalies, horizontal advection, evaporation, radiative heating, and sensible heat fluxes.

The Influence of Atmosphere-Ocean Interaction on MJO Development and Propagation

DTIC Science & Technology

2013-09-30

MJO initiation. Figure 3. Time-height cross section of COAMPS grid 3 domain-averaged (a) diabatic heating, (b) perturbation mixing ratio...moist phase. The diurnal variability of 7 precipitation and diabatic heating that can be seen in Figs. 2 and 3 is not observed in the simulation with

Extratropical response to Fast and Slow episodes of Madden-Julian Oscillation in observation and using intervention experiments with CFSv2

NASA Astrophysics Data System (ADS)

Yadav, P.; Straus, D. M.

2017-12-01

The Madden-Julian Oscillation (MJO) is a potential source of predictability in the extratropics in extended range weather forecasting. The nature of MJO is sporadic and therefore, the mid-latitude response may depend on the nature of the MJO event, in particular the phase speed. We discuss the results of our observational and modeling study of mid-latitude circulation response to Fast and Slow MJO episodes using wintertime ERA-Interim reanalysis data and the CFSv2 coupled model of NOAA. The observational study shows that the mid-latitude response to different propagating speeds is not the same. The propagation speed is defined by the time the OLR takes to propagate from phase 3 to phase 6. The mid-latitude response is assessed in terms of composite maps and frequency of occurrence of robust circulation regimes. Fast episode composite anomalies of 500hPa height show a developing Rossby wave in the mid-Pacific with downstream propagation through MJO phases 2- 4. Development of NAO+ teleconnection pattern is stronger in Slow that in Fast MJO episodes, and occurs with a greater time lag after MJO heating is in the Indian Ocean (phase 3). Previous results find an increase in occurrence of NAO- regime following phase 6. We have found that much of this behavior is due to the slow episodes. Based on these observational results, intervention experiments using CFSv2 are designed to better understand the impact of heating/cooling and to estimate mid-latitude response to Fast and Slow MJO episodes. The added heating experiments consist of 31 year reforecasts for December 1 initial conditions from CFS reanalysis (1980-2011) in which the identical MJO evolution of three-dimensional diabatic heating has been added, thus producing fast and slow MJO episodes with well-defined phase speeds. We will discuss the results of these experiments with a focus on understanding the role of phase speed and interference in setting up the response, and to understand the mechanisms that distinguish fast and slow types of response We will also discuss the diagnostics using Predictable Component Analysis to distinguish the signal forced by common diabatic heating signal from noise, and weather regime response to fast and slow MJO using cluster analysis.

Community-based benchmarking of the CMIP DECK experiments

NASA Astrophysics Data System (ADS)

Gleckler, P. J.

2015-12-01

A diversity of community-based efforts are independently developing "diagnostic packages" with little or no coordination between them. A short list of examples include NCAR's Climate Variability Diagnostics Package (CVDP), ORNL's International Land Model Benchmarking (ILAMB), LBNL's Toolkit for Extreme Climate Analysis (TECA), PCMDI's Metrics Package (PMP), the EU EMBRACE ESMValTool, the WGNE MJO diagnostics package, and CFMIP diagnostics. The full value of these efforts cannot be realized without some coordination. As a first step, a WCRP effort has initiated a catalog to document candidate packages that could potentially be applied in a "repeat-use" fashion to all simulations contributed to the CMIP DECK (Diagnostic, Evaluation and Characterization of Klima) experiments. Some coordination of community-based diagnostics has the additional potential to improve how CMIP modeling groups analyze their simulations during model-development. The fact that most modeling groups now maintain a "CMIP compliant" data stream means that in principal without much effort they could readily adopt a set of well organized diagnostic capabilities specifically designed to operate on CMIP DECK experiments. Ultimately, a detailed listing of and access to analysis codes that are demonstrated to work "out of the box" with CMIP data could enable model developers (and others) to select those codes they wish to implement in-house, potentially enabling more systematic evaluation during the model development process.

Extratropical Forcing Triggered the 2015 Madden–Julian Oscillation–El Niño Event

PubMed Central

Hong, Chi-Cherng; Hsu, Huang-Hsiung; Tseng, Wan-Ling; Lee, Ming-Ying; Chow, Chun-Hoe; Jiang, Li-Chiang

2017-01-01

In this paper, we report the triggering effect of extratropical perturbation on the onset of an atypical Madden–Julian Oscillation (MJO) and onset of the 2015–16 El Niño in March 2015. The MJO exhibited several unique characteristics: the effect of extratropical forcing, atypical genesis location and timing in the equatorial western Pacific, and the extremity of amplitudes in many aspects. The southward-penetrating northerly associated with the extratropical disturbances in the extratropical western North Pacific contributed to triggering the deep convection and westerly wind burst (WWB) and onset of the MJO over the anomalously warm tropical western Pacific in early March. The persisting strong WWB forced downwelling Kelvin wave-like oceanic perturbation that propagated eastward and led to the onset of the 2015–16 El Niño. The proposed novel extratropical forcing mechanism explaining the unique extratropics–MJO–El Niño association, based on both data diagnostics and numerical experiments, warrants further attention for a more detailed understanding of the onset of the MJO and its potential effect on El Niño. PMID:28436491

Meridional Propagation of the MJO/ISO and Prediction of Off-equatorial Monsoon Variability

NASA Technical Reports Server (NTRS)

Wu, Man Li C.; Schubert, S.; Suarez, M.; Pegion, P.; Bacmeister, J.; Waliser, D.

2004-01-01

In this study we examine the links between tropical heating, the Madden Julian Oscillation (MJO)/Intraseasonal Oscillation (ISO), and the off-equatorial monsoon development. We examine both observations and idealized "MJO heating" experiments employing the NASA Seasonal-Interannual Prediction Project (NSIPP) atmospheric general circulation model (AGCM). In the simulations, the model is forced by climatological SST and an idealized eastward propagating heating profile that is meant to mimic the canonical heating associated with the MJO in the Indian Ocean and western Pacific. The observational analysis highlights the strong link between the Indian summer monsoon and the tropical ISO/MJO activity and heating. Here we focus on the potential for skillful predictions of the monsoon on subseasonal time scales associated with the meridional propagation of the ISOMJO. In particular, we show that the variability of the Indian summer monsoon lags behind the variability of tropical ISOMJO heating by about 15 days when the tropical heating is around 60E and 90E. This feature of the ISOMJO is reproduced in the AGCM experiments with the idealized eastward propagating MJO-like heating, suggesting that models with realistic ISOM0 variability should provide useful skill of monsoon breaks and surges on subseasonal time scales.

Diurnal Cycle of Convection and Air-Sea-Land Interaction Associated with MJO over the Maritime Continent

NASA Astrophysics Data System (ADS)

Savarin, A.; Chen, S. S.

2016-12-01

The Madden-Julian Oscillation (MJO) is a dominant mode of intraseasonal variability in the tropics. Large-scale convection fueling the MJO is initiated over the tropical Indian Ocean and propagates eastward across the Maritime Continent (MC) and into the western Pacific as a pattern of alternating phases of active and suppressed convection. As an eastward-propagating MJO convective event encounters the MC, its nature is altered due to the complex interactions with the landmass and topography as well as the warm coastal ocean. In turn, the passage of a large-scale MJO event modulates local conditions over the MC. Previous studies have shown a strong and distinct diurnal cycle of convection over the land and nearby ocean, with an afternoon maximum over land, and a morning maximum over water. These complex interactions are still not well understood. This study aims to improve our understanding on how the resolution of distinct topographic features affects the diurnal cycle of convection in the active and suppressed MJO regimes. We use the Unified Wave Interface - a Coupled Model (UWIN-CM), a fully coupled atmosphere-ocean model to examine the effects that varying model resolution has on the representation of the MJO, the diurnal cycle of convection, and their interaction. Three model simulations of the November-December 2011 MJO event were carried out with resolutions of 12-, 4-, and 1.3-km in the fully coupled setting, and verified against TRMM and DYNAMO field campaign observations. Primary results indicate that increasing model resolution provides a better representation of the MC topography that not only improves the pattern of the diurnal cycle of convection over land. It also increases the amount of precipitation over water to values comparable to TRMM, possibly aiding the MJO's eastward propagation as shown in observational studies.

Why is the Skill of the Models in Reproducing MJO and its Impacts on the South American Monsoon Important for Subseasonal Prediction?

NASA Astrophysics Data System (ADS)

Grimm, A. M.; Silva, T. M.; Hirata, F. E.; Martins, G. P.

2017-12-01

The Madden Julian Oscillation (MJO) influences significantly daily precipitation and the frequency of extreme events during the summer South American monsoon (SAM) in important regions of the continent. One of the main features of the SAM, the South Atlantic Convergence Zone (SACZ), extends from central South America over Southeast Brazil and into the subtropical Atlantic Ocean, affecting very densely populated areas in Southeast Brazil. During the austral summer this region is strongly affected by landslides and floods associated with active SACZ, and the extreme precipitation events receive contribution from synoptic and MJO-related intraseasonal variability. Therefore, it is important to assess the observed impacts of the MJO in its different phases and to evaluate the models' skill in reproducing these phases and their impacts on South America in order to explore extended-range predictability of those events. The MJO cycle is divided into 8 phases according to the temporal evolution of the first two observed modes of multivariate EOF analysis of tropical convection and zonal winds. The teleconnections associated with these impacts are analyzed with simulations and influence functions of a simple model. The results show that two of the MJO phases strongly enhance the extreme events in the SACZ region and indicate the responsible mechanisms, lending these events a higher degree of predictability on subseasonal time-scales. Therefore, in selecting models to build a subseasonal-range forecasting scheme for extreme precipitation events, a necessary step is the assessment of their skill in reproducing MJO and its observed impacts on South America. Well-known models of the S2S Project, among them the ECMWF and CFS-v2 models are analyzed. Their reforecasts for weeks 1, 2, 3, 4 are separately projected onto the first two modes of tropical convection and zonal wind variability in order to identify the predicted MJO phases. Although the skill of one of the models in predicting these phases extends to week 4, generally the useful skill does not extend beyond week 3. The simulation of the impacts over South America, especially on the SACZ, is also assessed for selected models.

Why is the Skill of the Models in Reproducing MJO and its Impacts on the South American Monsoon Important for Subseasonal Prediction?

NASA Astrophysics Data System (ADS)

Gross, S.; Wirth, M.; Schäfler, A.; Ewald, F.; Urbanek, B.; Kiemle, C.; Ehret, G.

2016-12-01

The Madden Julian Oscillation (MJO) influences significantly daily precipitation and the frequency of extreme events during the summer South American monsoon (SAM) in important regions of the continent. One of the main features of the SAM, the South Atlantic Convergence Zone (SACZ), extends from central South America over Southeast Brazil and into the subtropical Atlantic Ocean, affecting very densely populated areas in Southeast Brazil. During the austral summer this region is strongly affected by landslides and floods associated with active SACZ, and the extreme precipitation events receive contribution from synoptic and MJO-related intraseasonal variability. Therefore, it is important to assess the observed impacts of the MJO in its different phases and to evaluate the models' skill in reproducing these phases and their impacts on South America in order to explore extended-range predictability of those events. The MJO cycle is divided into 8 phases according to the temporal evolution of the first two observed modes of multivariate EOF analysis of tropical convection and zonal winds. The teleconnections associated with these impacts are analyzed with simulations and influence functions of a simple model. The results show that two of the MJO phases strongly enhance the extreme events in the SACZ region and indicate the responsible mechanisms, lending these events a higher degree of predictability on subseasonal time-scales. Therefore, in selecting models to build a subseasonal-range forecasting scheme for extreme precipitation events, a necessary step is the assessment of their skill in reproducing MJO and its observed impacts on South America. Well-known models of the S2S Project, among them the ECMWF and CFS-v2 models are analyzed. Their reforecasts for weeks 1, 2, 3, 4 are separately projected onto the first two modes of tropical convection and zonal wind variability in order to identify the predicted MJO phases. Although the skill of one of the models in predicting these phases extends to week 4, generally the useful skill does not extend beyond week 3. The simulation of the impacts over South America, especially on the SACZ, is also assessed for selected models.

Extended-range prediction trials using the global cloud/cloud-system resolving model NICAM and its new ocean-coupled version NICOCO

NASA Astrophysics Data System (ADS)

Miyakawa, Tomoki

2017-04-01

The global cloud/cloud-system resolving model NICAM and its new fully-coupled version NICOCO is run on one of the worlds top-tier supercomputers, the K computer. NICOCO couples the full-3D ocean component COCO of the general circulation model MIROC using a general-purpose coupler Jcup. We carried out multiple MJO simulations using NICAM and the new ocean-coupled version NICOCO to examine their extended-range MJO prediction skills and the impact of ocean coupling. NICAM performs excellently in terms of MJO prediction, maintaining a valid skill up to 27 days after the model is initialized (Miyakawa et al 2014). As is the case in most global models, ocean coupling frees the model from being anchored by the observed SST and allows the model climate to drift away further from reality compared to the atmospheric version of the model. Thus, it is important to evaluate the model bias, and in an initial value problem such as the seasonal extended-range prediction, it is essential to be able to distinguish the actual signal from the early transition of the model from the observed state to its own climatology. Since NICAM is a highly resource-demanding model, evaluation and tuning of the model climatology (order of years) is challenging. Here we focus on the initial 100 days to estimate the early drift of the model, and subsequently evaluate MJO prediction skills of NICOCO. Results show that in the initial 100 days, NICOCO forms a La-Nina like SST bias compared to observation, with a warmer Maritime Continent warm pool and a cooler equatorial central Pacific. The enhanced convection over the Maritime Continent associated with this bias project on to the real-time multi-variate MJO indices (RMM, Wheeler and Hendon 2004), and contaminates the MJO skill score. However, the bias does not appear to demolish the MJO signal severely. The model maintains a valid MJO prediction skill up to nearly 4 weeks when evaluated after linearly removing the early drift component estimated from the 54 simulations. Furthermore, NICOCO outperforms NICAM by far if we focus on events associated with large oceanic signals.

Effects of Tropical Islands on the Diurnal Cycle of Convection and its Influence on the MJO Propagation over the Maritime Continent

NASA Astrophysics Data System (ADS)

Savarin, A.; Chen, S. S.

2017-12-01

The Madden-Julian Oscillation (MJO) is a dominant mode of intraseasonal variability in the tropics. Large-scale convection fueling the MJO is initiated over the tropical Indian Ocean and propagates eastward across the Maritime Continent (MC) and into the western Pacific. Observational studies have shown that near 40-50% of the MJO events cannot pass through the MC, which is known as the MC barrier effect. Previous studies have also shown a strong diurnal cycle of convection over the islands and coastal seas, with an afternoon precipitation maximum over land and high terrain, and an early morning maximum over water and mountain valley areas. As an eastward-propagating MJO convective event passes over the MC, its nature may be altered due to the complex interaction with the large Islands and topography. In turn, the passage of an MJO event modulates local conditions over the MC. The diurnal cycle of convection over the MC and its modulation by the MJO are not well understood and poorly represented in global numerical prediction models. This study aims to improve our understanding of how the diurnal cycle of convection and the presence of islands of the MC affect the eastward propagation of the MJO over the region. To this end, we use the Unified Wave Interface-Coupled Model (UWIN-CM) in its fully-coupled atmosphere-ocean configuration at a convection-permitting (4 km) resolution over the region. The control simulation is from the MJO event that occurred in November-December 2011, and has been verified against the Dynamics of the MJO (DYNAMO) field campaign observations, TRMM precipitation, and reanalysis products. To investigate the effects of the tropical islands on the MJO, we conduct two additional numerical experiments, one with preserved island shape but flattened topography, and one where islands are replaced by water. The difference in the diurnal cycle and convective organization among these experiments will provide some insights on the origin of the MC barrier effect and the physical processes affecting MJO convection over the MC. It is hypothesized that flattening terrain modifies the locations of diurnal precipitation maxima over islands and surrounding seas, while removing islands results in a smoother eastward propagation of the MJO.

CLIVAR Asian-Australian Monsoon Panel Report to Scientific Steering Group-18

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

Sperber, Ken R.; Hendon, Harry H.

2011-05-04

These are a set of slides on CLIVAR Asian-Australian Monsoon Panel Report to Scientific Steering Group-18. These are the major topics covered within: major activities over the past year, AAMP Monsoon Diagnostics/Metrics Task Team, Boreal Summer Asian Monsoon, Workshop on Modelling Monsoon Intraseasonal Variability, Workshop on Interdecadal Variability and Predictability of the Asian-Australian Monsoon, Evidence of Interdecadal Variability of the Asian-Australian Monsoon, Development of MJO metrics/process-oriented diagnostics/model evaluation/prediction with MJOTF and GCSS, YOTC MJOTF, GEWEX GCSS, AAMP MJO Diabatic Heating Experiment, Hindcast Experiment for Intraseasonal Prediction, Support and Coordination for CINDY2011/DYNAMO, Outreach to CORDEX, Interaction with FOCRAII, WWRP/WCRP Multi-Week Predictionmore » Project, Major Future Plans/Activities, Revised AAMP Terms of Reference, Issues and Challenges.« less

Interannual/decadal variability in MJO activity as diagnosed in the 40-year NCEP/NCAR reanalysis and simulated in an ensemble of GISST integrations

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

Slingo, J. M.; Rowell, D. P.; Sperber, K. R.

1999-04-21

The Madden-Julian Oscillation (MJO) is the dominant mode of tropical variability at intraseasonal timescales. It displays substantial interannual variability in intensity which may have important implications for the predictability of the coupled system. The reasons for this interannual variability are not understood. The interannual behaviour of the MJO has been diagnosed initially in the 40-year NCEP/NCAR Reanalysis by calculating the variance of the 20-100 day filtered zonal mean zonal wind (10 o N-10 o S averaged) in a 100- day moving window. The results suggest that prior to the mid-1970s the activity of the MJO was consistently lower than duringmore » the latter part of the record. This may be related to either inadequacies in the data coverage, particularly over the tropical Indian Ocean prior to the introduction of satellite observations, or to the real effects of a decadal timescale warming in the tropical SSTs. This interdecadal trend is captured by the dominant EOF (explaining 28% of the variance) of the monthly mean SSTs (after removal of the mean seasonal cycle), as used in the NCEP/NCAR Reanalysis for the region of the tropics where the MJO is convectively active (i.e., 60 o E-180 o E, 20 o S-20 o N). During the latter part of 1970s there was an abrupt change from a predominantly negative PC1 (i.e. colder Indian Ocean) to a positive PC1 (i.e. warmer Indian Ocean), indicative of a general warming of the tropical Indian Ocean by at least 0.5 o K over the last 40 years. However, on interannual timescales, the teleconnection patterns between MJO activity and SST show only a weak, barely significant, influence of El Niño in which the MJO is more active during the cold phase. As well as the NCEP/NCAR Reanalysis, a 4-member ensemble of 45 year integrations with the Hadley Centre climate model (HADAM2a), forced by observed SSTs for 1949-93, has been used to investigate the relationship between MJO activity and SST. HADAM2a is known to give a reasonable simulation of the MJO, and the extended record provided by this ensemble of integrations allows a more robust investigation of the predictability of MJO activity than was possible with the 40-year NCEP/NCAR Reanalysis. The results have shown that, for the uncoupled system, with the atmosphere being driven by imposed SSTs, there is no reproducibility of the activity of the MJO from year to year. The interannual behaviour of the MJO is not controlled by the phase of El Niño and would appear to be mainly chaotic in character. However, the model results have confirmed the low frequency, interdecadal timescale variability of MJO ac-tivity seen in the NCEP/NCAR Reanalysis. The activity of the MJO is consistently lower in all realisations prior to the mid 1970s, suggesting that the MJO may become more active as tropical SSTs become warmer. This result may have implications for the effects of global warming on the coupled atmosphere-ocean system. The implications of these results for the predictability of the tropical ocean-atmosphere system are im-portant since intraseasonal activity in the atmosphere, associated with MJO's and westerly wind bursts, can have a substantial impact on the Pacific Ocean. As the events in 1997 indicate, MJO activity may have a sig-nificant impact on the magnitude and growth rate of El Niño events. In turn the decadal changes in MJO ac-tivity suggest that if tropical SSTs continue to warm, the activity of the MJO may tend to increase which then might have implications for the future behaviour of El Niño. This work is presented in full by Slingo et al. (1999, Quart. J. Roy. Meteorol. Soc., in press).« less

On the predictability of the interannual behaviour of the Madden-Julian oscillation and its relationship with El Nino

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

Sperber, K.R., LLNL

The Madden-Julian Oscillation (MJO) is the dominant mode of tropical variability at intraseasonal timescales. It displays substantial interannual variability in intensity which may have important implications for the predictability of the coupled system. The reasons for this interannual variability are not understood. The aim of this paper is to investigate whether the interannual behavior of the MJO is related to tropical sea surface temperature (SST) anomalies, particularly El Nino, and hence whether it is predictable. The interannual behavior of the MJO has been diagnosed initially in the 40-year NCEP/ NCAR Reanalysis. The results suggest that prior to the mid-1970s themore » activity of the MJO was consistently lower than during the latter part of the record. This may be related to either inadequacies in the data coverage, particularly over the tropical Indian Ocean prior to the introduction of satellite observations, or to the real effects of a decadal timescale warming in the tropical SSTs. The teleconnection patterns between interannual variations in MJO activity and SST show only a weak, barely significant, influence of El Nino in which the MJO is more active during the cold phase. As well as the NCEP/NCAR Reanalysis, a 4-member ensemble of 45 year integrations with the Hadley Centre climate model (HadAM2a), forced by observed SSTs for 1949-93, has been used to investigate the relationship between MJO activity and SST. HadAM2a is known to give a reasonable simulation of the MJO and the extended record provided by this ensemble of integrations allows a more robust investigation of the predictability of MJO activity than was possible with the 40-year NCEP/NCAR Reanalysis. The results have shown that, for the uncoupled system, with the atmosphere being driven by imposed SSTS, there is no reproducibility for the activity of the MJO from year to year. The interannual behavior of the MJO is not controlled by the phase of El Nino and would appear to be chaotic in character. However, the model results have confirmed the low frequency, decadal timescale variability of MJO activity seen in the NCEP/NCAR Reanalysis. The activity of the MJO is consistently lower in all realizations prior to the mid 1970s, suggesting that the MJO may become more active as tropical SSTs become warmer. This result may have implications for the effects of global warming on the coupled tropical atmosphere-ocean system.« less

Effects of Tropical Islands on the Diurnal Cycle of Convection and its Influence on the MJO Propagation over the Maritime Continent

NASA Astrophysics Data System (ADS)

Savarin, A.; Chen, S. S.

2017-12-01

The Madden-Julian Oscillation (MJO) is a dominant mode of intraseasonal variability in the tropics. Large-scale convection fueling the MJO is initiated over the tropical Indian Ocean and propagates eastward across the Maritime Continent (MC) and into the western Pacific. Studies have shown a strong diurnal cycle of convection over the islands and coastal seas, with an afternoon precipitation maximum over land and high terrain, and an early morning maximum over water and mountain valley areas. Observational studies have also shown that near 40-50% of MJO events cannot pass through the MC, which is known as the MC barrier effect. As an eastward-propagating MJO convective event passes over the MC, its nature may be altered due to the complex interaction with the large Islands and topography. In turn, the passage of an MJO event modulates local conditions over the MC. The diurnal cycle of convection over the MC and its modulation by the MJO are not well understood and poorly represented in global numerical prediction models. This study aims to improve our understanding of how the diurnal cycle of convection and the presence of islands of the MC affect the eastward propagation of the MJO over the region. We use an atmosphere-ocean coupled model at high resolution (4 km) over the region to to model an MJO event that occurred inNovember-December 2011. We perform three simulations, one with the 'real' islands and topography, one where islands retain their shape but the topography is flattened, and one where all the islands are replaced by water. The differences in precipitation organization and structure can help us understand how topography and presence of islands affect the diurnal cycle of convection and the eastward propagation of the MJO. We hypothesize that removing islands will result in a smoother MJO propagation due to a less strongly forced diurnal cycle of convection and lack of land, while flattening terrain will alter the diurnal cycle of convection and the location of precipitation maxima.

Improving and Understanding Climate Models: Scale-Aware Parameterization of Cloud Water Inhomogeneity and Sensitivity of MJO Simulation to Physical Parameters in a Convection Scheme

NASA Astrophysics Data System (ADS)

Xie, Xin

Microphysics and convection parameterizations are two key components in a climate model to simulate realistic climatology and variability of cloud distribution and the cycles of energy and water. When a model has varying grid size or simulations have to be run with different resolutions, scale-aware parameterization is desirable so that we do not have to tune model parameters tailored to a particular grid size. The subgrid variability of cloud hydrometers is known to impact microphysics processes in climate models and is found to highly depend on spatial scale. A scale- aware liquid cloud subgrid variability parameterization is derived and implemented in the Community Earth System Model (CESM) in this study using long-term radar-based ground measurements from the Atmospheric Radiation Measurement (ARM) program. When used in the default CESM1 with the finite-volume dynamic core where a constant liquid inhomogeneity parameter was assumed, the newly developed parameterization reduces the cloud inhomogeneity in high latitudes and increases it in low latitudes. This is due to both the smaller grid size in high latitudes, and larger grid size in low latitudes in the longitude-latitude grid setting of CESM as well as the variation of the stability of the atmosphere. The single column model and general circulation model (GCM) sensitivity experiments show that the new parameterization increases the cloud liquid water path in polar regions and decreases it in low latitudes. Current CESM1 simulation suffers from the bias of both the pacific double ITCZ precipitation and weak Madden-Julian oscillation (MJO). Previous studies show that convective parameterization with multiple plumes may have the capability to alleviate such biases in a more uniform and physical way. A multiple-plume mass flux convective parameterization is used in Community Atmospheric Model (CAM) to investigate the sensitivity of MJO simulations. We show that MJO simulation is sensitive to entrainment rate specification. We found that shallow plumes can generate and sustain the MJO propagation in the model.

Intraseasonal interaction between the Madden-Julian Oscillation and the North Atlantic Oscillation.

PubMed

Cassou, Christophe

2008-09-25

Bridging the traditional gap between the spatio-temporal scales of weather and climate is a significant challenge facing the atmospheric community. In particular, progress in both medium-range and seasonal-to-interannual climate prediction relies on our understanding of recurrent weather patterns and the identification of specific causes responsible for their favoured occurrence, persistence or transition. Within this framework, I here present evidence that the main climate intra-seasonal oscillation in the tropics-the Madden-Julian Oscillation (MJO)-controls part of the distribution and sequences of the four daily weather regimes defined over the North Atlantic-European region in winter. North Atlantic Oscillation (NAO) regimes are the most affected, allowing for medium-range predictability of their phase far exceeding the limit of around one week that is usually quoted. The tropical-extratropical lagged relationship is asymmetrical. Positive NAO events mostly respond to a mid-latitude low-frequency wave train initiated by the MJO in the western-central tropical Pacific and propagating eastwards. Precursors for negative NAO events are found in the eastern tropical Pacific-western Atlantic, leading to changes along the North Atlantic storm track. Wave-breaking diagnostics tend to support the MJO preconditioning and the role of transient eddies in setting the phase of the NAO. I present a simple statistical model to quantitatively assess the potential predictability of the daily NAO index or the sign of the NAO regimes when they occur. Forecasts are successful in approximately 70 per cent of the cases based on the knowledge of the previous approximately 12-day MJO phase used as a predictor. This promising skill could be of importance considering the tight link between weather regimes and both mean conditions and the chances of extreme events occurring over Europe. These findings are useful for further stressing the need to better simulate and forecast the tropical coupled ocean-atmosphere dynamics, which is a source of medium-to-long range predictability and is the Achilles' heel of the current seamless prediction suites.

Solar Modulation of the MJO on Intraseasonal Time Scales

NASA Astrophysics Data System (ADS)

Hood, L. L.

2017-12-01

During the last two years, several groups have reported evidence for an influence of the stratospheric quasi-biennial oscillation (QBO) on the boreal winter Madden-Julian Oscillation (MJO). Specifically, DJF mean MJO amplitudes are somewhat larger on average during the easterly QBO phase at 50 hPa (QBOE) than during the westerly phase (QBOW). A possible mechanism is decreased static stability in the tropical lowermost stratosphere caused by increased upwelling associated with the QBO mean meridional circulation during periods of easterly vertical wind shear. It has also been recently proposed that interannual variability of the boreal winter MJO is influenced by tropical upwelling changes associated with the 11-year solar cycle. The modulation is such that MJO amplitudes are especially large under QBOE/SMIN conditions and especially small under QBOW/SMAX conditions (Hood, GRL, 2017). Here, evidence is presented of a modulation of MJO amplitudes under solar maximum conditions by solar variability on the time scale of the solar rotation period (about 27 days). Specifically, normalized occurrence rates of MJO events with amplitudes greater than a chosen threshold are calculated as a function of phase lag relative to peaks in solar UV flux occurring on the solar rotational time scale. All MJO phases and four solar maximum periods are considered (1979-83; 1989-93; 1999-03; 2011-15). The data are further edited to eliminate periods with relatively weak UV variations. About 130 strong "cycles" remain after editing. When MJO events with amplitudes greater than 1.5 are considered, significant reductions of MJO occurrence rates and associated increases in static stability in the tropical lower stratosphere over the warm pool region are obtained several days following solar UV peaks. The reductions in occurrence rate occur during the December to May period when the MJO is most active and are largest when the QBO is in its easterly phase. For example, under the latter conditions, the mean occurrence rate for MJO amplitudes greater than 2 is reduced from the long-term mean of about 21 per cent to about 7 per cent 2 to 4 days following the UV peak, significant at 95 per cent confidence as estimated from Monte Carlo simulations. Conversely, mean occurrence rates are significantly increased five to ten days following solar UV minima.

Hindcasting the Madden‐Julian Oscillation With a New Parameterization of Surface Heat Fluxes

PubMed Central

Wang, Jingfeng; Lin, Wenshi

2017-01-01

Abstract The recently developed maximum entropy production (MEP) model, an alternative parameterization of surface heat fluxes, is incorporated into the Weather Research and Forecasting (WRF) model. A pair of WRF cloud‐resolving experiments (5 km grids) using the bulk transfer model (WRF default) and the MEP model of surface heat fluxes are performed to hindcast the October Madden‐Julian oscillation (MJO) event observed during the 2011 Dynamics of the MJO (DYNAMO) field campaign. The simulated surface latent and sensible heat fluxes in the MEP and bulk transfer model runs are in general consistent with in situ observations from two research vessels. Compared to the bulk transfer model, the convection envelope is strengthened in the MEP run and shows a more coherent propagation over the Maritime Continent. The simulated precipitable water in the MEP run is in closer agreement with the observations. Precipitation in the MEP run is enhanced during the active phase of the MJO with significantly reduced regional dry and wet biases. Large‐scale ocean evaporation is stronger in the MEP run leading to stronger boundary layer moistening to the east of the convection center, which facilitates the eastward propagation of the MJO. PMID:29399269

Improvements of the Eastward Propagation of the MJO in MIROC6

NASA Astrophysics Data System (ADS)

Hirota, N.; Ogura, T.; Shiogama, H.; Kimoto, M.; Watanabe, M.; Tatebe, H.

2016-12-01

A new version of the atmosphere-ocean general circulation model cooperatively produced by the Japanese research community, known as the Model for Interdisciplinary Research on Climate (MIROC6), has recently been developed. Many aspects of the Madden Julian Oscillation (MJO) simulations are improved compared with its previous version MIROC5. For example, MJO amplitudes underestimated in MIROC5 are enhanced; the MJO convective envelopes over the Indian Ocean, which often decays too early around the Maritime Continent in MIROC5, propagate farther to the Central Pacific; the vertical structure of the MJO related humidity shows more realistic stepwise moistening associated with the transition from shallow convection to deep convection. Our preliminary analyses indicate that these improvements are associated with a newly implemented shallow convection scheme. The shallow convection in MIROC6 transports the boundary layer moisture to the lower free troposphere, mitigating dry biases around 800hPa over the Western Pacific. MIROC6 also shows improvements in climatological mean precipitation. The coupling strength between convection and the free tropospheric humidity, that are consider to have large impacts on the reproducibility of the MJO and the mean states, will also be discussed. Acknowledgment: This work was supported by the Program for Risk Information on Climate Change (SOUSEI program) of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

CORRIGENDUM of the MJO Transition from Shallow to Deep Convection in Cloudsat-Calipso Data and GISS GCM Simulations

NASA Technical Reports Server (NTRS)

Del Genio, Anthony; Chen, Yonghua; Kim, Daehyun; Yao, Mao-Sung

2015-01-01

We have identified several errors in the calculations that were performed to create Fig. 3 of Del Genio et al. (2012). These errors affect the composite evolution of precipitation and column water vapor versus lag relative to the Madden-Julian oscillation (MJO) peak presented in that figure. The precipitation and column water vapor data for the April and November 2009 MJO events were composited incorrectly because the date of the MJO peak at a given longitude was assigned to the incorrect longitude band. In addition, the precipitation data for all MJO events were first accumulated daily and the daily accumulations averaged at each lag to create the composite, rather than the averaging of instantaneous values that was used for other composite figures in the paper. One poorly sampled day in the west Pacific therefore biases the composite precipitation in that region at several lags after the MJO peak. Finally, a 4-day running mean was mistakenly applied to the precipitation and column water vapor data rather than the intended 5-day running mean. The results of the corrections are that an anomalous west Pacific precipitation maximum510 days after the MJO peak is removed and the maximum in west Pacific precipitation one pentad before the MJO peak is now more evident; there is now a clear maximum in precipitation for the entire warm pool one pentad before the MJO peak; west Pacific column water vapor now varies more strongly as a function of lag relative to the peak; and precipitation, and to a lesser extent column water vapor, in general vary more smoothly with time. The corrections do not affect any other parts of the paper nor do they change the scientific conclusions we reached. The 4-day running mean error also affects Figs. 1 and 2 therein, with almost imperceptible impacts that do not affect any results or necessitate major changes to the text.

Forced and Free Intra-Seasonal Variability Over the South Asian Monsoon Region Simulated by 10 AGCMs

NASA Technical Reports Server (NTRS)

Wu, Man Li C.; Kang, In-Sik; Waliser, Duane; Atlas, Robert (Technical Monitor)

2001-01-01

This study examines intra-seasonal (20-70 day) variability in the South Asian monsoon region during 1997/98 in ensembles of 10 simulations with 10 different atmospheric general circulation models. The 10 ensemble members for each model are forced with the same observed weekly sea surface temperature (SST) but differ from each other in that they are started from different initial atmospheric conditions. The results show considerable differences between the models in the simulated 20-70 day variability, ranging from much weaker to much stronger than the observed. A key result is that the models do produce, to varying degrees, a response to the imposed weekly SST. The forced variability tends to be largest in the Indian and western Pacific Oceans where, for some models, it accounts for more than 1/4 of the 20-70 day intra-seasonal variability in the upper level velocity potential during these two years. A case study of a strong observed MJO (intraseasonal oscillation) event shows that the models produce an ensemble mean eastward propagating signal in the tropical precipitation field over the Indian Ocean and western Pacific, similar to that found in the observations. The associated forced 200 mb velocity potential anomalies are strongly phase locked with the precipitation anomalies, propagating slowly to the east (about 5 m/s) with a local zonal wave number two pattern that is generally consistent with the developing observed MJO. The simulated and observed events are, however, approximately in quadrature, with the simulated response 2 leading by 5-10 days. The phase lag occurs because, in the observations, the positive SST anomalies develop upstream of the main convective center in the subsidence region of the MJO, while in the simulations, the forced component is in phase with the SST. For all the models examined here, the intraseasonal variability is dominated by the free (intra-ensemble) component. The results of our case study show that the free variability has a predominately zonal wave number one pattern, and has propagation speeds (10 - 15 m/s) that are more typical of observed MJO behavior away from the convectively active regions. The free variability appears to be synchronized with the forced response, at least, during the strong event examined here. The results of this study support the idea that coupling with SSTs plays an important, though probably not dominant, role in the MJO. The magnitude of the atmospheric response to the SST appears to be in the range of 15% - 30% of the 20-70 day variability over much of the tropical eastern Indian and western Pacific Oceans. The results also highlight the need to use caution when interpreting atmospheric model simulations in which the prescribed SST resolve MJO time scales.

Evolution of Precipitation Structure During the November DYNAMO MJO Event: Cloud-Resolving Model Intercomparison and Cross Validation Using Radar Observations

NASA Astrophysics Data System (ADS)

Li, Xiaowen; Janiga, Matthew A.; Wang, Shuguang; Tao, Wei-Kuo; Rowe, Angela; Xu, Weixin; Liu, Chuntao; Matsui, Toshihisa; Zhang, Chidong

2018-04-01

Evolution of precipitation structures are simulated and compared with radar observations for the November Madden-Julian Oscillation (MJO) event during the DYNAmics of the MJO (DYNAMO) field campaign. Three ground-based, ship-borne, and spaceborne precipitation radars and three cloud-resolving models (CRMs) driven by observed large-scale forcing are used to study precipitation structures at different locations over the central equatorial Indian Ocean. Convective strength is represented by 0-dBZ echo-top heights, and convective organization by contiguous 17-dBZ areas. The multi-radar and multi-model framework allows for more stringent model validations. The emphasis is on testing models' ability to simulate subtle differences observed at different radar sites when the MJO event passed through. The results show that CRMs forced by site-specific large-scale forcing can reproduce not only common features in cloud populations but also subtle variations observed by different radars. The comparisons also revealed common deficiencies in CRM simulations where they underestimate radar echo-top heights for the strongest convection within large, organized precipitation features. Cross validations with multiple radars and models also enable quantitative comparisons in CRM sensitivity studies using different large-scale forcing, microphysical schemes and parameters, resolutions, and domain sizes. In terms of radar echo-top height temporal variations, many model sensitivity tests have better correlations than radar/model comparisons, indicating robustness in model performance on this aspect. It is further shown that well-validated model simulations could be used to constrain uncertainties in observed echo-top heights when the low-resolution surveillance scanning strategy is used.

Moist entropy and water isotopologues in a Walker-type circulation framework of the MJO

NASA Astrophysics Data System (ADS)

Hurley, J. V.; Noone, D.

2017-12-01

The MJO is the principal source of tropical intraseasonal variability, yet we struggle to accurately simulate its observed convective behavior and eastward propagation. There is continued need for evaluating the role of water within the MJO, including evaporation, vertical transport, precipitation, and latent heating of the coupled atmosphere-ocean system. Isotopes are particularly useful for investigating these aspects of the water cycle. Recent contribution to resolve this includes analyses of the joint distribution of water vapor and isotopologue concentrations (dDv), to identify shortcomings in modeling MJO humidity, clouds or convection. Here, we complement the mixing ratio versus isotope approach with analyses of moist entropy, to distinguish the roles of convective and large-scale dynamic processes through the phases of the MJO. We do this in the classic MJO framework of the tropical Walker-type circulations. In this framework, the MJO can be characterized by strengthening and eastward expansion, and subsequent weakening and contraction, of the tropical stream function over the Indian Ocean. Low troposphere westerlies converge with easterlies, giving rise to uplift, convection, and precipitation, at a longitude that propagates east from 88°E to 136°E . In composite structure of the MJO, wet equivalent potential temperature (θq) anomalies have maximum expression at 500 hPa, and westward tilts with altitude. A positive θq anomaly occurs over the uplift and precipitation, and negative θq anomalies both trail and lead the convective center, along subsiding branches of the stream function anomalies. Out of phase with θq, dDv anomalies are positive east of and negative trailing or west of the convective center, suggesting moistening of the atmosphere with limited precipitation efficiency. MJO phase tendencies show θq is coherent with precipitation, and dDv are coherent with the tropical stream function, thus tying moist entropy to convective processes and isotope ratios to the large-scale dynamics. Joint distributions of MJO mixing ratio versus dDv are near or below Rayleigh curves, but θq is higher than would be expected for simple Rayleigh fractionation. To resolve this, we assess MJO θq versus mixing ratio and find vertical mixing likely occurs between the stratosphere and lower troposphere.

Tropical cyclone prediction skills - MJO and ENSO dependence in S2S data sets

NASA Astrophysics Data System (ADS)

Lee, C. Y.; Camargo, S.; Vitart, F.; Sobel, A. H.; Tippett, M.

2017-12-01

The El Niño-Southern Oscillation (ENSO) and the Madden-Julian Oscillation (MJO) are two important climate controls on tropical cyclone (TC) activity. The seasonal prediction skill of dynamical models is determined in large part by their accurate representations of the ENSO-TC relationship. Regarding intraseasonal TC variability, observations suggest MJO to be the primary control. Given the ongoing effort to develop dynamical seasonal-to-subseasonal (S2S) TC predictions, it is important to examine whether the global models, running on S2S timescales, are able to reproduce these known ENSO-TC and MJO-TC relationships, and how this ability affects forecasting skill. Results from the S2S project (from F. Vitart) suggest that global models have skill in predicting MJO phase with up to two weeks of lead time (four weeks for ECMWF). Meanwhile, our results show that, qualitatively speaking, the MJO-TC relationship in storm genesis is reasonably captured, with some models (e.g., ECMWF, BoM, NCEP, MetFr) performing better than the others. However, we also find that model skill in predicting basin-wide genesis and accumulated cyclone energy (ACE) are mainly due to the models' ability to capture the climatological seasonality. Removing the seasonality significantly reduces the models' skill; even the best model (ECMWF) in the most reliable basin (western north Pacific and Atlantic) has very little skill (close to 0.1 in Brier skill score for genesis and close to 0 in rank probability skill score for ACE). This brings up the question: do any factors contribute to intraseasonal TC prediction skill other than seasonality? Is the low skill, after removing the seasonality, due to poor MJO and ENSO simulations, or to poor representation of other ENSO-TC or MJO-TC relationships, such as ENSO's impact on the storm tracks? We will quantitatively discuss the dependence of the TC prediction skill on ENSO and MJO, focusing on Western North Pacific and Atlantic, where we have sufficient sample sizes, and the S2S TC predictions are relatively more skillful. Various skill scores will be applied to genesis and ACE, with subsets of data binned based on ENSO and MJO status. We will also look at MJO and ENSO's impact on TC tracks through cluster analysis, and analyze model skill in each cluster.

The Response of the Southern Hemisphere Middle Atmosphere to the Madden-Julian oscillation during Austral Winter Using the Specified-Dynamics Whole Atmosphere Community Climate Model

NASA Astrophysics Data System (ADS)

Yang, C.; Li, T.; Smith, A. K.; Dou, X.

2017-12-01

Using the Specified-Dynamic (SD) Whole Atmosphere Community Climate Model (WACCM), we investigated the effects of the Madden-Julian oscillation (MJO) on the mid-winter stratosphere and mesosphere in the southern hemisphere (SH). The most significant responses of the SH polar cap temperature to the MJO are found 30 days after MJO Phase 1 (P1) and 10 days after the MJO Phase 5 (P5) in both the ERA-interim reanalysis and the SD-WACCM simulation. The 200 and 500 hPa geopotential height anomalies in the SH reveal that wave trains emanate from the Indian and Pacific Oceans when the MJO convection is enhanced in the eastern Indian Ocean and the western Pacific. As a result, the upward propagation and dissipation of planetary waves (PWs) in the mid- and high- latitude of the SH stratosphere is significantly enhanced, the Brewer-Dobson (BD) circulation in the SH stratosphere strengthens, and temperatures in the SH polar stratosphere increase. Wavenumber 1 in the stratosphere is the dominant component of the PW perturbation induced by the MJO convection. Filtering by the modified SH stratospheric winds alters the gravity waves (GWs) that propagate to the mesosphere. The dissipation and breaking of these waves causes anomalous downwelling in the mid- and high- latitudes of the mesosphere. The circulation changes, in turn, result in significant anomalous cooling in the mesosphere in response to MJO P1 and P5 at lags of 10 days and 30 days, respectively.

Consequences of systematic model drift in DYNAMO MJO hindcasts with SP-CAM and CAM5

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

Hannah, Walter M.; Maloney, Eric D.; Pritchard, Michael S.

Hindcast simulations of MJO events during the dynamics of the MJO (DYNAMO) field campaign are conducted with two models, one with conventional parameterization (CAM5) and a comparable model that utilizes superparameterization (SP–CAM). SP–CAM is shown to produce a qualitatively better reproduction of the fluctuations of precipitation and low–level zonal wind associated with the first two DYNAMO MJO events compared to CAM5. Interestingly, skill metrics using the real–time multivariate MJO index (RMM) suggest the opposite conclusion that CAM5 has more skill than SP–CAM. This inconsistency can be explained by a systematic increase of RMM amplitude with lead time, which results frommore » a drift of the large–scale wind field in SP–CAM that projects strongly onto the RMM index. CAM5 hindcasts exhibit a contraction of the moisture distribution, in which extreme wet and dry conditions become less frequent with lead time. SP–CAM hindcasts better reproduce the observed moisture distribution, but also have stronger drift patterns of moisture budget terms, such as an increase in drying by meridional advection in SP–CAM. This advection tendency in SP–CAM appears to be associated with enhanced off–equatorial synoptic eddy activity with lead time. In conclusion, systematic drift moisture tendencies in SP–CAM are of similar magnitude to intraseasonal moisture tendencies, and therefore are important for understanding MJO prediction skill.« less

The Madden-Julian Oscillation and its Impact on Northern Hemisphere Weather Predictability during Wintertime

NASA Technical Reports Server (NTRS)

Jones, Charles; Waliser, Duane E.; Lau, K. M.; Stern, W.

2003-01-01

The Madden-Julian Oscillation (MJO) is known as the dominant mode of tropical intraseasonal variability and has an important role in the coupled-atmosphere system. This study used twin numerical model experiments to investigate the influence of the MJO activity on weather predictability in the midlatitudes of the Northern Hemisphere during boreal winter. The National Aeronautics and Space Administration (NASA) Goddard laboratory for the Atmospheres (GLA) general circulation model was first used in a 10-yr simulation with fixed climatological SSTs to generate a validation data set as well as to select initial conditions for active MJO periods and Null cases. Two perturbation numerical experiments were performed for the 75 cases selected [(4 MJO phases + Null phase) _ 15 initial conditions in each]. For each alternative initial condition, the model was integrated for 90 days. Mean anomaly correlations in the midlatitudes of the Northern Hemisphere (2O deg N_60 deg.N) and standardized root-mean-square errors were computed to validate forecasts and control run. The analyses of 500-hPa geopotential height, 200-hPa Streamfunction and 850-hPa zonal wind component systematically show larger predictability during periods of active MJO as opposed to quiescent episodes of the oscillation.

Evaluation of Regional Extended-Range Prediction for Tropical Waves Using COAMPS®

NASA Astrophysics Data System (ADS)

Hong, X.; Reynolds, C. A.; Doyle, J. D.; May, P. W.; Chen, S.; Flatau, M. K.; O'Neill, L. W.

2014-12-01

The Navy's Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS1) in a two-way coupled mode is used for two-month regional extended-range prediction for the Madden-Julian Oscillation (MJO) and Tropical Cyclone 05 (TC05) that occurred during the DYNAMO period from November to December 2011. Verification and statistics from two experiments with 45-km and 27-km horizontal resolutions indicate that 27-km run provides a better representation of the three MJO events that occurred during this 2-month period, including the two convectively-coupled Kelvin waves associated with the second MJO event as observed. The 27-km run also significantly reduces forecast error after 15-days, reaching a maximum bias reduction of 89% in the third 15-day period due to the well represented MJO propagation over the Maritime Continent. Correlations between the model forecasts and observations or ECMWF analyses show that the MJO suppressed period is more difficult to predict than the active period. In addition, correlation coefficients for cloud liquid water path (CLWP) and precipitation are relatively low for both cases compared to other variables. The study suggests that a good simulation of TC05 and a good simulation of the Kelvin waves and westerly wind bursts are linked. Further research is needed to investigate the capability in regional extended-range forecasts when the lateral boundary conditions are provided from a long-term global forecast to allow for an assessment of potential operational forecast skill. _____________________________________________________ 1COAMPS is a registered trademark of U.S. Naval Research Laboratory

Structure of the Madden-Julian oscillation in coupled and uncoupled versions of the superparameterized community atmosphere model

NASA Astrophysics Data System (ADS)

Benedict, James J.

The Madden-Julian Oscillation (MJO), an eastward-propagating atmospheric disturbance resembling a transient Walker cell, dominates intraseasonal (20--100 days) variability in the tropical Indian and West Pacific Ocean regions. The phenomenon is most active during the Northern Hemisphere winter and is characterized by cyclic periods of suppressed (dry phase) and active (wet phase) cloudiness and precipitation. Numerous complexities---multi-scale interactions of moist convection and large-scale wave dynamics, air-sea fluxes and feedbacks, topographical impacts, and tropical-extratropical interactions---challenge our ability to fully understand the MJO and result in its poor representation in most current general circulation models (GCMs). This study examines the representation of the MJO in a modified version of the NCAR Community Atmosphere Model (CAM). The modifications involve substituting conventional boundary layer, turbulence, and cloud parameterizations with a configuration of cloud-resolving models (CRMs) embedded into each GCM grid cell in a technique termed "superparameterization" (SP). Unlike many GCMs including the standard CAM, the SP-CAM displays robust intraseasonal convective variability. Two SP-CAM simulations are utilized in this study: one forced by observed sea-surface temperatures (SSTs; "uncoupled") and a second identical to the first except for a new treatment of tropical SSTs in which a simplified mixed-layer ocean model is used to predict SST anomalies that are coupled to the atmosphere ("coupled"). Key physical features of the MJO are captured in the uncoupled SP-CAM. Ahead (east) of the disturbance there is meridional boundary layer moisture convergence and a vertical progression of warmth, moisture, and convective heating from the lower to upper troposphere. The space-time dynamical response to convective heating is also reproduced, especially the vertical structure of anomalous westerly wind and its migration into the region of heavy rainfall as the disturbance propagates eastward. Advective drying processes in the MJO wake are also represented well. The coupled SP-CAM shows more realistic MJO eastward propagation, signal coherence and spatial structure relative to the uncoupled SP-CAM. The improvement varies with longitude but generally stems from better space-time relationships among MJO convective heating, its dynamical response, SSTs, surface fluxes, boundary layer properties, and vertical moisture structure. Coupled MJO events in the Indian Ocean display more realistic intensity; in the West Pacific, the coupled SP-CAM overestimates convective strength but shows an improved vertical structure relative to the uncoupled SP-CAM. Biases related to MJO convection are also examined. Overestimated convective intensity in the West Pacific appears to be linked to basic state biases, Maritime Continent topographical impacts, unrealistic convection-wind-evaporation feedbacks, and the neglect of convective momentum transport in the model. Phase errors between observed and simulated boundary layer moisture appear to stem from an unrealistic representation of shallow cumuli.

Vertical structure and physical processes of the Madden-Julian oscillation: Linking hindcast fidelity to simulated diabatic heating and moistening

DOE PAGES

Klingaman, Nicholas P.; Woolnough, Steven J.; Jiang, Xianan; ...

2015-04-10

Here, many theories for the Madden-Julian oscillation (MJO) focus on diabatic processes, particularly the evolution of vertical heating and moistening. Poor MJO performance in weather and climate models is often blamed on biases in these processes and their interactions with the large-scale circulation. We introduce one of the three components of a model evaluation project, which aims to connect MJO fidelity in models to their representations of several physical processes, focusing on diabatic heating and moistening. This component consists of 20 day hindcasts, initialized daily during two MJO events in winter 2009–2010. The 13 models exhibit a range of skill:more » several have accurate forecasts to 20 days lead, while others perform similarly to statistical models (8–11 days). Models that maintain the observed MJO amplitude accurately predict propagation, but not vice versa. We find no link between hindcast fidelity and the precipitation-moisture relationship, in contrast to other recent studies. There is also no relationship between models' performance and the evolution of their diabatic heating profiles with rain rate. A more robust association emerges between models' fidelity and net moistening: the highest-skill models show a clear transition from low-level moistening for light rainfall to midlevel moistening at moderate rainfall and upper level moistening for heavy rainfall. The midlevel moistening, arising from both dynamics and physics, may be most important. Accurately representing many processes may be necessary but not sufficient for capturing the MJO, which suggests that models fail to predict the MJO for a broad range of reasons and limits the possibility of finding a panacea.« less

Diurnal warming impacts on atmospheric and oceanic evolution during the suppressed phase of the Madden Julian Oscillation

NASA Astrophysics Data System (ADS)

Clayson, C. A.; Roberts, J.

2016-02-01

The Madden-Julian Oscillation (MJO) represents a prominent mode of intraseasonal tropical variability as manifest by coherent large-scale changes in atmospheric circulation, convection, and thermodynamic processes. Its impacts are far-reaching with influences on monsoons, flooding, droughts, and tropical storms. The characteristic timescale of the MJO is positioned in a gap between synoptic forecasting and longer range seasonal to interannual predictions, but has been shown to be dependent on diurnally-varying sea surface temperature (SST). In this work, we leverage a wide suite of satellite products with in situ oceanographic data over the 2002-2012 period to investigate the rectification effects of strong ocean diurnal warming onto the development of intraseasonal SST variability, and whether there a detectable influence on the diurnal cycle of cloud-radiative effects in the suppressed phase of the MJO. Diurnally-varying SST is used as a conditional sampling parameter, along with AIRS/AMSU-A temperature and moisture profiles, surface winds, radiative and turbulent surface fluxes, and precipitation. We use composite daily average atmospheric BL depths, changes in lower-tropospheric stability, and moist static energy to evaluate changes in convective inhibition based on the diurnal variability of surface parcel characteristics due to turbulent heat fluxes, and compare with diurnal changes in cloud-radiative effects and precipitation. Argo floats and ocean modeling experiments are used to examine the upper ocean response. An ensemble of MJO simulations are generated using Argo profiles and satellite-derived surface forcing from which the systematic impacts of diurnal variability on the generation of the intraseasonal SST warming are evaluated. These simulations inform the importance of diurnal variations in surface boundary forcing to upper ocean mixing and the integrated contribution to SST warming over the typical duration of a suppressed phase of the MJO.

Investigating the Sensitivity of Model Intraseasonal Variability to Minimum Entrainment

NASA Astrophysics Data System (ADS)

Hannah, W. M.; Maloney, E. D.

2008-12-01

Previous studies have shown that using a Relaxed Arakawa-Schubert (RAS) convective parameterization with appropriate convective triggers and assumptions about rain re-evaporation produces realistic intraseasonal variability. RAS represents convection with an ensemble of clouds detraining at different heights, each with different entrainment rate, the highest clouds having the lowest entrainment rates. If tropospheric temperature gradients are weak and boundary layer moist static energy is relatively constant, then by limiting the minimum entrainment rate deep convection is suppressed in the presence of dry tropospheric air. This allows moist static energy to accumulate and be discharged during strong intraseasonal convective events, which is consistent with the discharge/recharge paradigm. This study will examine the sensitivity of intra-seasonal variability to changes in minimum entrainment rate in the NCAR-CAM3 with the RAS scheme. Simulations using several minimum entrainment rate thresholds will be investigated. A frequency-wavenumber analysis will show the improvement of the MJO signal as minimum entrainment rate is increased. The spatial and vertical structure of MJO-like disturbances will be examined, including an analysis of the time evolution of vertical humidity distribution for each simulation. Simulated results will be compared to observed MJO events in NCEP-1 reanalysis and CMAP precipitation.

Influence of Madden-Julian Oscillation (MJO) on Rainfall Variability over West Africa at Intraseasonal Timescale

NASA Astrophysics Data System (ADS)

Niang, C.

2015-12-01

Intraseasonal variability of rainfall over West Africa plays a significant role in the economy of the region and is highly linked to agriculture and water resources. This research study aims to investigate the relationship between Madden Julian Oscillation (MJO) and rainfall over West Africa during the boreal summer in the the state-of-the-art Atmospheric Model Intercomparison Project (AMIP) type simulations performed by Atmosphere General Circulation Models (GCMs) forced with prescribed Sea Surface Temperature (SST). It aims to determine the impact of MJO on rainfall and convection over West Africa and identify the dynamical processes which are involved in the state-of-the-art climate simulations. The simulations show in general good skills in capturing its main characteristics as well as its influence on rainfall over West Africa. On the global scale, most models simulated an eastward spatio-temporal propagation of enhanced and suppressed convection similar to the observed. However, over West Africa the MJO signal is weak in few of the models although there is a good coherence in the eastward propagation. The influence on rainfall is well captured in both Sahel and Guinea regions thereby adequately producing the transition between positive and negative rainfall anomalies through the different phases as seen in the observation. Furthermore, the results show that strong active convective phase is clearly associated with the African Easterly Jet (AEJ) but the weak convective phase is associated with a much weaker AEJ particularly over coastal Ghana. In assessing the mechanisms which are involved in the above impacts the convectively equatorial coupled waves (CCEW) are analysed separately. The analysis of the longitudinal propagation of zonal wind at 850hPa and outgoing longwave radiation (OLR) shows that the CCEW are very weak and their extention are very limited beyong West African region. It was found that the westward coupled equatorial Rossby waves are needed to bring out the MJO-convection link over the region and this relationship is well reproduced by all the models. Results also confirmed that it may be possible to predict the anomalous convection over West Africa with a time lead of 15-20 day with regard to Indian Ocean and AMIP simulations performed well in this regard.

QBO-MJO Connection

NASA Astrophysics Data System (ADS)

Zhang, Chidong; Zhang, Bosong

2018-03-01

Activities of the Madden-Julian Oscillation (MJO) in boreal winter has recently been found to be stronger in easterly phases of the stratospheric quasi-biennial oscillation (QBO) than its westerly phases. This QBO-MJO connection was investigated in this study using a method that identifies individual MJO events by tracking their eastward propagating signals in precipitation. Stronger MJO activities in QBO easterly phases are a consequence of more MJO days, not larger amplitudes of individual MJO events as previously thought. More MJO days come from more MJO events initiated over the Indian Ocean and their longer duration because of a weaker barrier effect of the Maritime Continent on MJO propagation. Zonal heterogeneity exists in the connection between QBO, MJO, and tropical total precipitation in general. This poses a challenge to our current understanding of the MJO dynamics, which has yet to fully include upper-tropospheric and stratospheric processes.

On the Role of Surface Friction in Tropical Intraseasonal Oscillation

NASA Technical Reports Server (NTRS)

Chao, Winston C.; Chen, Baode

1999-01-01

The Madden-Julian oscillation (MJO), or the tropical intraseasonal oscillation, has attracted much attention, ever since its discovery in the early seventies for reasons of both scientific understanding and practical forecasts. Among the theoretical interpretations of the MJO, the wave-CISK (conditional instability of the second kind) mechanism is the most popular. The basic idea of the wave-CISK interpretation is that the cooperation between the low-level convergence associated with the eastward moving Kelvin wave and the cumulus convection generates an eastward moving Kelvin-wave-like mode. Later it was recognized that the MJO has an important Rossby-wave-like component. However linear analysis and numerical simulations based on it (even when conditional heating is used) have revealed two problems with the wave-CISK interpretation; i.e., excessive speed and the most preferred scale being zero or grid scale. Chao (1995) presented a discussion of these problems and attributed these problems to the particular type of expression for the cumulus heating used in the linear analyses and numerical studies (i.e., the convective heating is proportional to low-level convergence and a fixed vertical heating profile). It should be pointed out that in the relatively successful simulation of MJO with general circulation models the problem of grid scale being the most preferred scale does not appear and die problem of excessive speed is not as severe as in the linear analysis.

Predictability of the North Atlantic Oscillation on Intraseasonal Time Scales

DTIC Science & Technology

2013-09-30

skill when realistic MJO-related tropical diabatic heating is added to the models. (4) To diagnose the dynamical mechanisms by which the tropical...was added to each of the 50 simulations, has also been completed. Figure 1 shows the 50-member ensemble mean of the 500 hPa diabatic heating (averaged...contour interval of 2 oC/day. Separately, the added MJO diabatic heating is shown in black contours in the left panel with a contour interval of 0.5 oC

Effective control parameters in a deep convection scheme for improved simulation of the Madden-Julian oscillation

NASA Astrophysics Data System (ADS)

Choi, Jin-Ho; Seo, Kyong-Hwan

2017-06-01

This work seeks to find the most effective parameters in a deep convection scheme (relaxed Arakawa-Schubert scheme) of the National Centers of Environmental Prediction Climate Forecast System model for improved simulation of the Madden-Julian Oscillation (MJO). A suite of sensitivity experiments are performed by changing physical components such as the relaxation parameter of mass flux for adjustment of the environment, the evaporation rate from large-scale precipitation, the moisture trigger threshold using relative humidity of the boundary layer, and the fraction of re-evaporation of convective (subgrid-scale) rainfall. Among them, the last two parameters are found to produce a significant improvement. Increasing the strength of these two parameters reduces light rainfall that inhibits complete formation of the tropical convective system or supplies more moisture that help increase a potential energy to large-scale environment in the lower troposphere (especially at 700 hPa), leading to moisture preconditioning favorable for further development and eastward propagation of the MJO. In a more humid environment, more organized MJO structure (i.e., space-time spectral signal, eastward propagation, and tilted vertical structure) is produced.

Barrier Effect of the Indo-Pacific Maritime Continent on the MJO: Perspectives from Tracking MJO Precipitation

NASA Astrophysics Data System (ADS)

Zhang, C.; Ling, J.

2016-12-01

To advance the study of the barrier effect of the Indo-Pacific Maritime Continent (MC) on the MJO, we propose two criteria to judge explanations for this phenomenon. The first one is that such explanations should include specific features of the MC, namely, its intricate land-sea distributions and elevated terrains. The second is that they should include mechanisms for some MJO events to overcome the barrier effect as well as the barrier effect itself. Guided by these criteria, we have used a precipitation-tracking method to identify MJO events, distinguish those that propagate across the MC (MJO-C) from those that are blocked by the MC (MJO-B), and compare these two types of MJO events and their large-scale environments. The barrier effect cannot be explained in terms of the strength and horizontal scale or distributions of MJO convection as it approaches the MC from the Indian Ocean. A distinction between MJO-B and MJO-C is their ratios of precipitation over the sea vs. land in the MC. MJO events may propagate through the MC when their convection over the sea of the MC is sufficiently developed and dominates that over land. This may happen for two reasons. One is stronger precipitation over land that occurs before the arrival of MJO convection centers, which is assisted by greater low-level moisture flux convergence over the MC. This stronger "vanguard of precipitation" for MJO-C would make the ground wetter and thus reduce land-locked diurnal convection that has been proposed to be detrimental to MJO propagation through the MC. Another possible reason for the more vigorous development of MJO-C convection over the sea is higher SST in the MC before MJO convection centers enter the region.

Intra-seasonal Mixed Layer Process Variability from the ECCO Ocean Data Assimilation Product: Preliminary Analysis Relevant to DYNAMO

NASA Astrophysics Data System (ADS)

Halkides, D. J.; Waliser, D. E.; Lee, T.; Lucas, L. E.; Murtugudde, R. G.

2010-12-01

The Madden Julian Oscillation (MJO), the dominant feature of 30-90 day variability in the tropical Indian (IO) and Pacific (PO) Oceans, plays an important role in air-sea interactions and affects multi-scale phenomena ranging from hurricanes to ENSO. Understanding the MJO requires knowledge of ocean mixed layer (ML) heat budgets. As part of a model-data intercomparison planned for 2011-13 to support the Dynamics of the MJO (DYNAMO) project (a US branch of the CINDY2011 international field program), we perform ML heat budget calculations using a heat-conserving assimilation product from the Estimating the Circulation and Climate of the Ocean (ECCO) project to study the onset and evolution of MJO scale anomalies in the tropics. For the IO, we focus on the western equatorial basin and the southwest IO thermocline ridge. Here, upwelling processes are very important, indicating a slab or 1-D ocean model is insufficient for accurate MJO simulation. We also examine several locations across the equatorial PO. For example, in the eastern PO, we compare results from ECCO to prior studies with different findings: one based on incomplete mooring data indicating vertical processes dominate, another based on model output that indicates meridional advection dominates in the same area. In ECCO, subsurface process and horizontal advection terms are both important, but their relationships to the net tendency vary spatially. This work has implications for understanding MJO onset and development, associated air-sea interactions, ramifications for multi-scale cross-equatorial heat transport (especially in the IO), and, it is likely to be important in constructing a predictive index for MJO onset. We present budgets in terms of variability of the atmospheric and oceanic circulations, as well as mixed layer and barrier layer depths, and we address DYNAMO’s third hypothesis: “The barrier-layer, wind and shear driven mixing, shallow thermocline, and mixing-layer entrainment all play essential roles in MJO initiation in the Indian Ocean by controlling the upper-ocean heat content and SST, and thereby surface flux feedback.”

Precipitable water vapor budget associated with MJO represented in newly-released JRA-55 reanalysis data

NASA Astrophysics Data System (ADS)

Yokoi, S.

2013-12-01

The Japan Meteorological Agency (JMA) recently released a new reanalysis dataset JRA-55 with the use of a JMA operational prediction model and 4D-VAR data assimilation. To evaluate merit in utilizing the JRA-55 dataset to investigate dynamics of the tropical intraseasonal variability (ISV) including the Madden-Julian Oscillation (MJO), this study examines ISV-scale precipitable water vapor (PWV) budget over the period 1989-2012. The ISV-scale PWV anomaly related to the boreal-winter MJO propagates eastward along with precipitation, consistent with the SSM/I PWV product. Decomposition of the PWV tendency into that simulated by the model and the analysis increment estimated by the data assimilation reveals that the model makes the PWV anomaly move eastward. On the other hand, the analysis increment exhibits positive values over the area where the PWV anomaly is positive, indicating that the model tends to damp the MJO signal. Note that the analysis increment over the Maritime Continent has comparable magnitude to the model tendency. The positive analysis increment may mainly be caused by an excess of precipitation anomaly with respect to the magnitude of PWV anomaly. In addition to the boreal-winter MJO, this study also examines the PWV budget associated with northward-propagating ISV during the boreal summer and find similar relationship between the PWV anomaly and analysis increment.

Assessing the Importance of the Evaporation-Wind Feedback Mechanism in the Modulation of Simulated Madden-Julian Oscillations

NASA Technical Reports Server (NTRS)

Colon, Edward; Lindesay, James; Suarez, Max J.

1998-01-01

An examination of simulated Madden-Julian Oscillation (MJO) response to active and suppressed air-sea interactions is made using an aquaplanet model employing a realistic representation of the hydrologic cyle. In general, the evaporation-wind feedback (EWF) results from a coupling between tropical zonal surface wind stresses and evaporation anomalies. Recent observational and theoretical studies have questioned the significance of EWF in sustaining the predominantly wavenumber 1 eastward propagating mode commonly attributed to the interaction between large scale convergence and cumulus-scale convection (conditional instability of the second kind, CISK). To ascertain the nature of the EWF dependence on lower boundary conditions and thus quantify its effect on MJO development, a series of numerical experiments were conducted employing various zonally symmetric sea surface temperature (SST) distributions with active and suppressed EWF mechanisms. Results suggest that a correlation exists between tropical SSTs and the efficacy of the EWF in vertically redistributing heat acquired through surface wind stresses. It has been determined that the removal of the EWF is not a crucial factor in the dampening of the simulated MJO at high equatorial SSTs. The additional energy fed into the developing convective mode by the EWF selectively amplifies higher order wave modes in all numerical experiments thus boosting overall variances in oscillatory responses.

Role of Madden-Julian Oscillation in Modulating Monsoon Retreat

NASA Astrophysics Data System (ADS)

Singh, Madhu; Bhatla, R.

2018-01-01

The Madden-Julian oscillation (MJO) is the major fluctuation in tropical weather on a seasonal scale. The impact of MJO on different epochs, viz., onset, advance and active break is well known. There can be several MJO events in a season and it may enhance/suppress the retreat process. The present study aims to find the MJO-modulated retreat of monsoon. The results suggest that the fastest retreat of monsoon occurred in the years 2007 and 2008, while slowest retreat of monsoon occurred in the year 1979. The retreat features of the Indian summer monsoon (ISM) are investigated with the MJO phase and amplitude variations. The daily MJO indices for the retreat period 1979-2016 are used. The results reveal that the MJO strength decreases during the transition phase (i.e., summer monsoon to winter monsoon transition). The monsoon retreat is most favored by strong MJO phase 4 and phase 5. The fastest retreat of monsoon occurred in the years 2007 and 2008, while the slowest retreat of monsoon occurred in the year 1979. There exists a weak positive correlation between the MJO amplitude and the retreat period of monsoon. The monsoon retreat is most favored by strong MJO phase 4 and phase 5. The MJO amplitude variations during MJO phases 1-8 suggest that the MJO amplitude decreases with increase in retreat period. The MJO-modulated retreat results in slow retreat of monsoon, whereas fast and normal retreat of monsoon is seen on rare occasions. Weak MJO events lead to normal retreat of monsoon.

Simulations of Cloud-Radiation Interaction Using Large-Scale Forcing Derived from the CINDY/DYNAMO Northern Sounding Array

NASA Technical Reports Server (NTRS)

Wang, Shuguang; Sobel, Adam H.; Fridlind, Ann; Feng, Zhe; Comstock, Jennifer M.; Minnis, Patrick; Nordeen, Michele L.

2015-01-01

The recently completed CINDY/DYNAMO field campaign observed two Madden-Julian oscillation (MJO) events in the equatorial Indian Ocean from October to December 2011. Prior work has indicated that the moist static energy anomalies in these events grew and were sustained to a significant extent by radiative feedbacks. We present here a study of radiative fluxes and clouds in a set of cloud-resolving simulations of these MJO events. The simulations are driven by the large-scale forcing data set derived from the DYNAMO northern sounding array observations, and carried out in a doubly periodic domain using the Weather Research and Forecasting (WRF) model. Simulated cloud properties and radiative fluxes are compared to those derived from the S-PolKa radar and satellite observations. To accommodate the uncertainty in simulated cloud microphysics, a number of single-moment (1M) and double-moment (2M) microphysical schemes in the WRF model are tested. The 1M schemes tend to underestimate radiative flux anomalies in the active phases of the MJO events, while the 2M schemes perform better, but can overestimate radiative flux anomalies. All the tested microphysics schemes exhibit biases in the shapes of the histograms of radiative fluxes and radar reflectivity. Histograms of radiative fluxes and brightness temperature indicate that radiative biases are not evenly distributed; the most significant bias occurs in rainy areas with OLR less than 150 W/ cu sq in the 2M schemes. Analysis of simulated radar reflectivities indicates that this radiative flux uncertainty is closely related to the simulated stratiform cloud coverage. Single-moment schemes underestimate stratiform cloudiness by a factor of 2, whereas 2M schemes simulate much more stratiform cloud.

Barrier Effect of the Indo-Pacific Maritime Continent on the MJO

NASA Astrophysics Data System (ADS)

Ling, Jian; Zhang, Chidong

2017-04-01

Explanations for the barrier effect of the Indo-Pacific Maritime Continent (MC) on the MJO should satisfy two criteria. First, they should include specific features of the MC, namely, its intricate land-sea distributions and elevated terrains. Second, they should include mechanisms for both the barrier effect and its overcoming by some MJO events. Guided by these two criteria, we applied a precipitation-tracking method to identify MJO events that propagate across the MC (MJO-C) and those that are blocked by the MC (MJO-B). About a half of MJO events that form over the Indian Ocean propagate through the MC. Most of them (> 75%) become weakened over the MC. The barrier effect cannot be explained in terms of the strength, horizontal scale, or spatial distribution of MJO convection when it approaches the MC from the west. A distinction between MJO-B and MJO-C is their precipitation over the sea vs. land in the MC region. MJO-C events rain more over the sea than over land, whereas land rainfall dominates for MJO-B. This suggests that inhibiting convective development over the sea could be a possible mechanism for the barrier effect of the MC. Preceding conditions for MJO-C include stronger low-level zonal moisture flux convergence and higher SST higher in the MC region. Possible connections between these large-scale conditions and the land vs. sea distributions of MJO rainfall through the diurnal cycle are discussed.

Intraseasonal variability of sea level and circulation in the Gulf of Thailand: the role of the Madden-Julian Oscillation

NASA Astrophysics Data System (ADS)

Oliver, Eric C. J.

2014-01-01

Intraseasonal variability of the tropical Indo-Pacific ocean is strongly related to the Madden-Julian Oscillation (MJO). Shallow seas in this region, such as the Gulf of Thailand, act as amplifiers of the direct ocean response to surface wind forcing by efficient setup of sea level. Intraseasonal ocean variability in the Gulf of Thailand region is examined using statistical analysis of local tide gauge observations and surface winds. The tide gauges detect variability on intraseasonal time scales that is related to the MJO through its effect on local wind. The relationship between the MJO and the surface wind is strongly seasonal, being most vigorous during the monsoon, and direction-dependent. The observations are then supplemented with simulations of sea level and circulation from a fully nonlinear barotropic numerical ocean model (Princeton Ocean Model). The numerical model reproduces well the intraseasonal sea level variability in the Gulf of Thailand and its seasonal modulations. The model is then used to map the wind-driven response of sea level and circulation in the entire Gulf of Thailand. Finally, the predictability of the setup and setdown signal is discussed by relating it to the, potentially predictable, MJO index.

Nonlinear Advection of Tropospheric Humidity and Cloud and Evaporation Feedbacks in the Madden-Julian Oscillation

NASA Astrophysics Data System (ADS)

Sugiyama, M.; Emanuel, K.; Stone, P.

2006-05-01

Despite active research on the Madden-Julian Oscillation (MJO), general circulation models (GCMs) continue to suffer from poor simulations of this tropical intraseasonal variability, and the theory on the MJO remains elusive. To assist model development and deepen our understanding, we develop a simple new model of the MJO, using the Quasiequilibrium Tropical Circulation Model of Neelin and Zeng. The MJO-like disturbance develops as a single-column instability because of cloud-radiative and surface flux feedbacks, a mechanism identified by Sobel and Gildor in their study on a tropical hot spot. Two processes contribute to the eastward movement: Nonlinear advection of the tropospheric humidity to the west, and convergence-induced moistening to the east. The key to the model disturbance is the interplay between tropospheric humidity and precipitation, moisture-convection feedback. As the humidity field propagates eastward by advection and convergence-induced moistening, the precipitation field follows. This study points to possible research areas on GCM parameterizations: 1) the effect of tropospheric humidity on moist convection; 2) the impact of downdraft-enhanced gustiness on surface heat flux; and 3) relationship between precipitation and cloud-radiative forcing.

Examining Changes to the Madden-Julian Oscillation in a Warmer Climate Using CMIP5 Models

NASA Astrophysics Data System (ADS)

Rushley, Stephanie

Five models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) that reasonably represent the Madden-Julian Oscillation (MJO) are used to examine the response of the MJO to greenhouse gas induced warming. Changes in the MJO's amplitude, zonal scale, and phase speed are examined using daily-mean precipitation during boreal winter (November to April) when the MJO is strongest. The MJO precipitation variance increases with tropics mean surface temperature. However, the westward moving waves of the same temporal and spatial scales increase at about the same rate, suggesting that the maintenance mechanism for the MJO does not change with warming. On the other hand, a robust increase in phase speed of the MJO is found with a rate of 5-12% per degree of surface warming. The robust increase in the MJO phase speed are examined using the linear moisture wave theory of Adames and Kim (2016). In this theory, the MJO phase speed is determined by the horizontal moisture gradient in the lower troposphere, the gross dry stability, the convective moisture adjustment timescale, and zonal wavenumber of the MJO. All CMIP5 models examined show an increase in the horizontal humidity gradient, the gross dry stability and the convective moisture adjustment timescale, while exhibiting a decrease in the zonal wavenumber of the MJO. The increase in the horizontal humidity gradient and zonal scale of the MJO act to increase the speed of the MJO by enhancing horizontal moisture advection associated with the MJO, while the gross dry stability and convective moisture adjustment timescale act to slow down the MJO by dampening the horizontal moisture advection process. In all the models, the combined effects of the four key parameters act to speed up the MJO, matching the calculated phase speed changes with warming in the models.

Planetary circulations in the presence of transient and self-induced heating

NASA Technical Reports Server (NTRS)

Salby, Murry L.; Garcia, Rolando R.

1993-01-01

The research program focuses on large-scale circulations and their interaction with the global convective pattern. An 11-year record of global cloud imagery and contemporaneous fields of motion and temperature have been used to investigate organized convection and coherent variability of the tropical circulation operating on intraseasonal time scales. This study provides a detailed portrait of tropical variability associated with the so-called Madden-Julian Oscillation (MJO). It reveals the nature, geographical distribution, and seasonality of discrete convective signal, which is a measure of feedback between the circulation and the convective pattern. That discrete spectral behavior has been evaluated in light of natural variability of the ITCZ associated with climatological convection. A composite signature of the MJO, based on cross-covariance statistics of cloud cover, motion, and temperature, has been constructed to characterize the lifecycle of the disturbance in terms of these properties. The composite behavior has also been used to investigate the influence the MJO exerts on the zonal-mean circulation and the involvement of the MJO in transfers of momentum between the atmosphere and the solid Earth. The aforementioned observational studies have led to the production of two animations. One reveals the convective signal in band-pass filtered OLR and compares it to climatological convection. The other is a 3-dimensional visualization of the composite lifecycle of the MJO. With a clear picture of the MJO in hand, feedback between the circulation and the convective pattern can be diagnosed meaningfully in numerical simulations. This process is being explored in calculations with the linearized primitive equations on the sphere in the presence of realistic stability and shear. The numerical framework represents climatological convection as a space-time stochastic process and wave-induced convection in terms of the vertically-integrated moisture flux convergence. In these calculations, frictional convergence near the equator emerges as a key to feedback between the circulation and the convective pattern. At low latitudes, nearly geostrophic balance in the boundary layer gives way to frictional balance. This shifts the wave-induced convection into phase with the temperature anomaly and allows the attending heating to feed back positively onto the circulation. The calculations successfully reproduce the salient features of the MJO. They are being used to understand the growth and decay phases of the composite lifecycle and the conditions that favor amplification of the MJO.

MJO prediction skill of the subseasonal-to-seasonal (S2S) prediction models

NASA Astrophysics Data System (ADS)

Son, S. W.; Lim, Y.; Kim, D.

2017-12-01

The Madden-Julian Oscillation (MJO), the dominant mode of tropical intraseasonal variability, provides the primary source of tropical and extratropical predictability on subseasonal to seasonal timescales. To better understand its predictability, this study conducts quantitative evaluation of MJO prediction skill in the state-of-the-art operational models participating in the subseasonal-to-seasonal (S2S) prediction project. Based on bivariate correlation coefficient of 0.5, the S2S models exhibit MJO prediction skill ranging from 12 to 36 days. These prediction skills are affected by both the MJO amplitude and phase errors, the latter becoming more important with forecast lead times. Consistent with previous studies, the MJO events with stronger initial amplitude are typically better predicted. However, essentially no sensitivity to the initial MJO phase is observed. Overall MJO prediction skill and its inter-model spread are further related with the model mean biases in moisture fields and longwave cloud-radiation feedbacks. In most models, a dry bias quickly builds up in the deep tropics, especially across the Maritime Continent, weakening horizontal moisture gradient. This likely dampens the organization and propagation of MJO. Most S2S models also underestimate the longwave cloud-radiation feedbacks in the tropics, which may affect the maintenance of the MJO convective envelop. In general, the models with a smaller bias in horizontal moisture gradient and longwave cloud-radiation feedbacks show a higher MJO prediction skill, suggesting that improving those processes would enhance MJO prediction skill.

Modeling, Simulation, and Forecasting of Subseasonal Variability

NASA Technical Reports Server (NTRS)

Waliser, Duane; Schubert, Siegfried; Kumar, Arun; Weickmann, Klaus; Dole, Randall

2003-01-01

A planning workshop on "Modeling, Simulation and Forecasting of Subseasonal Variability" was held in June 2003. This workshop was the first of a number of meetings planned to follow the NASA-sponsored workshop entitled "Prospects For Improved Forecasts Of Weather And Short-Term Climate Variability On Sub-Seasonal Time Scales" that was held April 2002. The 2002 workshop highlighted a number of key sources of unrealized predictability on subseasonal time scales including tropical heating, soil wetness, the Madden Julian Oscillation (MJO) [a.k.a Intraseasonal Oscillation (ISO)], the Arctic Oscillation (AO) and the Pacific/North American (PNA) pattern. The overarching objective of the 2003 follow-up workshop was to proceed with a number of recommendations made from the 2002 workshop, as well as to set an agenda and collate efforts in the areas of modeling, simulation and forecasting intraseasonal and short-term climate variability. More specifically, the aims of the 2003 workshop were to: 1) develop a baseline of the "state of the art" in subseasonal prediction capabilities, 2) implement a program to carry out experimental subseasonal forecasts, and 3) develop strategies for tapping the above sources of predictability by focusing research, model development, and the development/acquisition of new observations on the subseasonal problem. The workshop was held over two days and was attended by over 80 scientists, modelers, forecasters and agency personnel. The agenda of the workshop focused on issues related to the MJO and tropicalextratropical interactions as they relate to the subseasonal simulation and prediction problem. This included the development of plans for a coordinated set of GCM hindcast experiments to assess current model subseasonal prediction capabilities and shortcomings, an emphasis on developing a strategy to rectify shortcomings associated with tropical intraseasonal variability, namely diabatic processes, and continuing the implementation of an experimental forecast and model development program that focuses on one of the key sources of untapped predictability, namely the MJO. The tangible outcomes of the meeting included: 1) the development of a recommended framework for a set of multi-year ensembles of 45-day hindcasts to be carried out by a number of GCMs so that they can be analyzed in regards to their representations of subseasonal variability, predictability and forecast skill, 2) an assessment of the present status of GCM representations of the MJO and recommendations for future steps to take in order to remedy the remaining shortcomings in these representations, and 3) a final implementation plan for a multi-institute/multi-nation Experimental MJO Prediction Program.

Simulations of cloud-radiation interaction using large-scale forcing derived from the CINDY/DYNAMO northern sounding array

DOE PAGES

Wang, Shuguang; Sobel, Adam H.; Fridlind, Ann; ...

2015-09-25

The recently completed CINDY/DYNAMO field campaign observed two Madden-Julian oscillation (MJO) events in the equatorial Indian Ocean from October to December 2011. Prior work has indicated that the moist static energy anomalies in these events grew and were sustained to a significant extent by radiative feedbacks. We present here a study of radiative fluxes and clouds in a set of cloud-resolving simulations of these MJO events. The simulations are driven by the large scale forcing dataset derived from the DYNAMO northern sounding array observations, and carried out in a doubly-periodic domain using the Weather Research and Forecasting (WRF) model. simulatedmore » cloud properties and radiative fluxes are compared to those derived from the S-Polka radar and satellite observations. Furthermore, to accommodate the uncertainty in simulated cloud microphysics, a number of single moment (1M) and double moment (2M) microphysical schemes in the WRF model are tested.« less

Connecting Observations and Reanalysis of the MJO with Theory

NASA Astrophysics Data System (ADS)

Powell, S. W.

2017-12-01

Over the past few years, refined theories have been advanced the explain the onset and/or propagation of the Madden-Julian Oscillation over the tropical warm pool. For example, Adames and Kim (2016) built on Sobel and Maloney (2012, 2013) to describe the MJO as a dispersive moisture wave whose instability mechanism is a radiative-convective instability supported by anvils of large mesoscale systems. Wang and Chen (2016) describe a similar frictionally coupled moisture mode that captures many basic features of the canonically observed MJO. Arnold and Randall (2015) hypothesize that the MJO might be described as self-aggregation of convection over the Indian Ocean. Fuchs and Raymond (2017) describe the MJO as a first baroclinic dispersive mode in a simplified model with a linear WISHE instability that shows decreased propagation speeds for lower wavelengths. Not all of these theories can be correct, and quite possibly none of them are fully. Intelligent use of observations and reanalysis of past MJO events can help guide development of MJO theory. For example, Powell (2017) shows that in MERRA-2 reanalysis, the MJO propagates as a convectively coupled Kelvin wave over the Western Hemisphere then transitions abruptly into a slower moving mode over the Indian Ocean. A complete MJO theory must account for both forms as, and when, the MJO circumnavigates. Observations (like TRMM and GPM data) and reanalysis can reveal the relative roles of cloud-scale processes and large-scale free tropospheric horizontal advection in "pre-moistening" the troposphere in the location of MJO initiation where subsequent propagation of an existing MJO occurs. This can, for example, help validate or refute aspects of moisture mode theory that require large-scale dynamics to moisten an area ahead of an active envelope of MJO-related convection before the MJO can propagate eastward. Radar and satellite observations might yield some insight into whether convective self-aggregation is a real phenomenon or if upscale growth of cloud elements into mesoscale systems is actually more responsible for the apparent large-scale organization of convection in the tropics, let alone within the MJO. I will present a few such examples of how careful exploration of observations and reanalysis might help guide MJO theory during the next several years.

Multi-Reanalysis Comparison of Variability in Analysis Increment of Column-Integrated Water Vapor Associated with Madden-Julian Oscillation

NASA Astrophysics Data System (ADS)

Yokoi, S.

2014-12-01

This study conducts a comparison of three reanalysis products (JRA-55, JRA-25, and ERA-Interim) in representation of Madden-Julian Oscillation (MJO), focusing on column-integrated water vapor (CWV) that is considered as an essential variable for discussing MJO dynamics. Besides the analysis fields of CWV, which exhibit spatio-temporal distributions that are quite similar to satellite observations, CWV tendency simulated by forecast models and analysis increment calculated by data assimilation are examined. For JRA-55, it is revealed that, while its forecast model is able to simulate eastward propagation of the CWV anomaly, it tends to weaken the amplitude, and data assimilation process sustains the amplitude. The multi-reanalysis comparison of the analysis increment further reveals that this weakening bias is probably caused by excessively weak cloud-radiative feedback represented by the model. This bias in the feedback strength makes anomalous moisture supply by the vertical advection term in the CWV budget equation too insensitive to precipitation anomaly, resulting in reduction of the amplitude of CWV anomaly. ERA-Interim has a nearly opposite feature; the forecast model represents excessively strong feedback and unrealistically strengthens the amplitude, while the data assimilation weakens it. These results imply the necessity of accurate representation of the cloud-radiative feedback strength for a short-term MJO forecast, and may be evidence to support the argument that this feedback is essential for the existence of MJO. Furthermore, this study demonstrates that the multi-reanalysis comparison of the analysis increment will provide useful information for identifying model biases and, potentially, for estimating parameters that are difficult to estimate solely from observation data, such as gross moist stability.

Evaluating MJO Event Initiation and Decay in the Skeleton Model using an RMM-like Index

DTIC Science & Technology

2015-11-25

climatology and document 35 the occurrence of primary, continuing, and terminating MJO events in the skeleton model. The 36 overall amount of MJO...solutions in a framework consistent with observations including MJO event 104 climatology and the precursor conditions associated with the initiation and...the 112 7 model along with several applications that include a comparison to the observed MJO event 113 climatology and identification of

Optimal error analysis of the intraseasonal convection due to uncertainties of the sea surface temperature in a coupled model

NASA Astrophysics Data System (ADS)

Li, Xiaojing; Tang, Youmin; Yao, Zhixiong

2017-04-01

The predictability of the convection related to the Madden-Julian Oscillation (MJO) is studied using a coupled model CESM (Community Earth System Model) and the climatically relevant singular vector (CSV) approach. The CSV approach is an ensemble-based strategy to calculate the optimal initial error on climate scale. In this study, we focus on the optimal initial error of the sea surface temperature in Indian Ocean, where is the location of the MJO onset. Six MJO events are chosen from the 10 years model simulation output. The results show that the large values of the SVs are mainly located in the bay of Bengal and the south central IO (around (25°S, 90°E)), which is a meridional dipole-like pattern. The fast error growth of the CSVs have important impacts on the prediction of the convection related to the MJO. The initial perturbations with the SV pattern result in the deep convection damping more quickly in the east Pacific Ocean. Moreover, the sensitivity studies of the CSVs show that different initial fields do not affect the CSVs obviously, while the perturbation domain is a more responsive factor to the CSVs. The rapid growth of the CSVs is found to be related to the west bay of Bengal, where the wind stress starts to be perturbed due to the CSV initial error. These results contribute to the establishment of an ensemble prediction system, as well as the optimal observation network. In addition, the analysis of the error growth can provide us some enlightment about the relationship between SST and the intraseasonal convection related to the MJO.

Disruptions of El Niño–Southern Oscillation teleconnections by the Madden–Julian Oscillation

USGS Publications Warehouse

Hoell, Andrew; Barlow, Mathew; Wheeler, Mathew; Funk, Christopher C.

2014-01-01

The El Niño–Southern Oscillation (ENSO) is the leading mode of interannual variability, with global impacts on weather and climate that have seasonal predictability. Research on the link between interannual ENSO variability and the leading mode of intraseasonal variability, the Madden–Julian oscillation (MJO), has focused mainly on the role of MJO initiating or terminating ENSO. We use observational analysis and modeling to show that the MJO has an important simultaneous link to ENSO: strong MJO activity significantly weakens the atmospheric branch of ENSO. For weak MJO conditions relative to strong MJO conditions, the average magnitude of ENSO-associated tropical precipitation anomalies increases by 63%, and the strength of hemispheric teleconnections increases by 58%. Since the MJO has predictability beyond three weeks, the relationships shown here suggest that there may be subseasonal predictability of the ENSO teleconnections to continental circulation and precipitation.

Variability of upper ocean thermohaline structure during a MJO event from DYNAMO aircraft observations

NASA Astrophysics Data System (ADS)

Alappattu, Denny P.; Wang, Qing; Kalogiros, John; Guy, Nick; Jorgensen, David P.

2017-02-01

This paper reports upper ocean thermohaline structure and variability observed during the life cycle of an intense Madden Julian Oscillation (MJO) event occurred in the southern tropical Indian Ocean (14°S-Eq, 70°E-81°E). Water column measurements for this study were collected using airborne expendable probes deployed from NOAA's WP-3D Orion aircraft operated as a part of Dynamics of MJO field experiment conducted during November-December 2011. Purpose of the study is twofold; (1) to provide a statistical analysis of the upper ocean properties observed during different phases of MJO and, (2) to investigate how the upper ocean thermohaline structure evolved in the study region in response to the MJO induced perturbation. During the active phase of MJO, mixed layer depth (MLD) had a characteristic bimodal distribution. Primary and secondary modes were at ˜34 m and ˜65 m, respectively. Spatial heterogeneity of the upper ocean response to the MJO forcing was the plausible reason for bimodal distribution. Thermocline and isothermal layer depth deepened, respectively, by 13 and 19 m from the suppressed through the restoring phase of MJO. Thicker (>30 m) barrier layers were found to occur more frequently in the active phase of MJO, associated with convective rainfalls. Additionally, the water mass analysis indicated that, in the active phase of this MJO event the subsurface was dominated by Indonesian throughflow, nonetheless intrusion of Arabian Sea high saline water was also noted near the equator.

Large-scale precipitation tracking and the MJO over the Maritime Continent and Indo-Pacific warm pool

NASA Astrophysics Data System (ADS)

Kerns, Brandon W.; Chen, Shuyi S.

2016-08-01

A large-scale precipitation tracking (LPT) method is developed to track convection and precipitation associated with the Madden-Julian oscillation (MJO) using the Tropical Rainfall Measurement Mission 3B42 rainfall data from October to March 1998-2015. LPT uses spatially smoothed 3 day rainfall accumulation to identify and track precipitation features in time with a minimum size of 300,000 km2 and time continuity at least 10 days. While not all LPT systems (LPTs) are attributable to the MJO, among the 199 LPTs, there were 42 with a mean eastward propagation of at least 2 m s-1, which are considered to be MJO convective initiation events. These LPTs capture the diversity of the MJO convection, which is not well depicted by the Real-time Multivariate MJO (RMM) index or the outgoing longwave radiation MJO index. During the 17 years, there were 17 instances out of 45 with a MJO signature in the RMM without eastward propagating LPTs. Among the 42 eastward propagating LPTs, 24 propagated across the Maritime Continent (MC), which confirms the MC barrier effect. Among the cases that crossed the MC from the Indian Ocean to the western Pacific (MC crossing), 18 (75%) had a significant MJO signature in the RMM index. In contrast, only six (33%) of the non-MC-crossing cases occurred with a RMM MJO signal. There is a significant seasonal and interannual variability with MC-crossing LPTs occurring in December more commonly than other months. More MC-crossing events were observed during La Niña than El Niño, which is consistent with the observations of stronger and more frequent MJO events identified by RMM during La Niña years.

MJO (Madden-Julian Oscillation) Analysis of the Chlorophyll-a Distribution in Western Waters Bengkulu

NASA Astrophysics Data System (ADS)

Haryanto, Y. D.; Fitrianti, N.; Hartoko, A.; Anggoro, S.; Zainuri, M.

2017-02-01

The global phenomenon Madden-Julian Oscillation (MJO) is one of the dominant oscillation in the equatorial region of the Indian Ocean that oscillates between 30-60 days and experience the process of convection movement from west to east. MJO has a correlation of high intensity rainfall of the area in its path. During his journey eastward, the MJO is influenced by the position of the sun. When the sun in the equatorial MJO moves straight east. Meanwhile, when the position of the sun in the south of the equator, MJO shifted slightly to the south of the equator, known as the propagation of the south-east (south-eastern propagation). When the position of the sun is in the north of the equator, MJO shifted slightly to the north of the equator, known as the propagation of the north-east (north-east of propagation). Waters west of Bengkulu has a huge potential in the fisheries sector, which is situated overlooking the Indian Ocean. The phenomenon MJO influence on rainfall, sea surface temperature, and the concentration of chlorophyll-a. This study aims to look at the temporal distribution of sea surface temperature and chlorophyll-a and decide how MJO relationship with SST and precipitation conditions and increasing the amount of chlorophyll during the phase of the MJO in Bengkulu waters. The dataset used is data of chlorophyll-a which download in oceancolor.gfsc.nasa.gov , sea surface temperature data is used is a model of Kaplan Extended V2, RMM1 index data and RMM2 on www.bom.gov.au and rainfall data of Bengkulu region. The method used is descriptive statistical methods, Conditional Probability and logistics regression. From the above explanation can be said that there is a relationship between the incidence of MJO by the number of chlorophyll-a. Odds the addition of chlorophyll-a have a linear relationship with the duration of the incident MJO in Bengkulu, odds increase the amount of chlorophyll-a in Bengkulu region reaches a threshold value of 0.5, it means that the length occurrence MJO able to identify increasing the number of chlorophyll-a in Bengkulu.

MJO influence on ENSO effects in precipitation and temperature over South America

NASA Astrophysics Data System (ADS)

Shimizu, M. H.; Bombardi, R. J.; Ambrizzi, T.

2013-12-01

Researches on the effects of the El Niño Southern Oscillation (ENSO) over precipitation and temperature, such as drought, flood, and anomalous high or cold temperatures, have great importance because of the impact of ENSO on the environment, society, and economy. Several studies have reported the influences of ENSO over South American precipitation and temperature climatological patterns, such as drier than normal conditions over northeast Brazil during the warm phase (El Niño) and wetter than normal conditions over northeast Brazil in the cold phase (La Niña). However, some recent studies focusing on the Northern Hemisphere have indicated that the basic response of ENSO is dependent on the phase of the Madden-Julian Oscillation (MJO). The MJO is characterized by the eastward propagation of the convection from Indian to Central Pacific Ocean and is related to variations in the position and intensity of the South Atlantic Convergence Zone (SACZ). The present work investigates the combined response of the phases of these two distinct phenomena, ENSO and MJO, over South America. Our goal is to explore the relative importance of the MJO to precipitation and temperature anomalies during ENSO events. MJO events were defined using the MJO index created by Jones and Carvalho (2012) based on empirical orthogonal functions analysis. ENSO phases were defined according to the Oceanic Niño Index provided by the National Oceanic and Atmospheric Administration (NOAA). A composite analysis with each combination of the phases of ENSO and MJO was performed to obtain the mean patterns of temperature and precipitation over South America for the months of November to March (austral summer). The results showed that the precipitation and temperature anomalies patterns observed during ENSO events, without the concurrent occurrence of the MJO, can be strengthened or weakened during events where ENSO and MJO occur simultaneously. Moreover, the effect on the anomalies patterns in these events depends on the MJO phase. During El Niño events, MJO phases 1 and 5 seem to intensify the anomaly patterns over northwest and northeast of South America, respectively. In addition, during the MJO phase 3, these patterns are weaker over northern and stronger over southern South America. During Niña events, MJO phases 3 and 5 presented more precipitation in the region of the SACZ. These results suggest that the influence of ENSO over South America depends on the MJO phase and on the position of convection over the Tropical Indian/Pacific Oceans associated with this phase, which triggers eastward propagating wave trains.

Impact of resolving the diurnal cycle in an ocean-atmosphere GCM. Part 2: A diurnally coupled CGCM

NASA Astrophysics Data System (ADS)

Bernie, D. J.; Guilyardi, E.; Madec, G.; Slingo, J. M.; Woolnough, S. J.; Cole, J.

2008-12-01

Coupled ocean atmosphere general circulation models (GCM) are typically coupled once every 24 h, excluding the diurnal cycle from the upper ocean. Previous studies attempting to examine the role of the diurnal cycle of the upper ocean and particularly of diurnal SST variability have used models unable to resolve the processes of interest. In part 1 of this study a high vertical resolution ocean GCM configuration with modified physics was developed that could resolve the diurnal cycle in the upper ocean. In this study it is coupled every 3 h to atmospheric GCM to examine the sensitivity of the mean climate simulation and aspects of its variability to the inclusion of diurnal ocean-atmosphere coupling. The inclusion of the diurnal cycle leads to a tropics wide increase in mean sea surface temperature (SST), with the strongest signal being across the equatorial Pacific where the warming increases from 0.2°C in the central and western Pacific to over 0.3°C in the eastern equatorial Pacific. Much of this warming is shown to be a direct consequence of the rectification of daily mean SST by the diurnal variability of SST. The warming of the equatorial Pacific leads to a redistribution of precipitation from the Inter tropical convergence zone (ITCZ) toward the equator. In the western Pacific there is an increase in precipitation between Papa new guinea and 170°E of up to 1.2 mm/day, improving the simulation compared to climatology. Pacific sub tropical cells are increased in strength by about 10%, in line with results of part 1 of this study, due to the modification of the exchange of momentum between the equatorially divergent Ekman currents and the geostropic convergence at depth, effectively increasing the dynamical response of the tropical Pacific to zonal wind stresses. During the spring relaxation of the Pacific trade winds, a large diurnal cycle of SST increases the seasonal warming of the equatorial Pacific. When the trade winds then re-intensify, the increase in the dynamical response of the ocean leads to a stronger equatorial upwelling. These two processes both lead to stronger seasonal basin scale feedbacks in the coupled system, increasing the strength of the seasonal cycle of the tropical Pacific sector by around 10%. This means that the diurnal cycle in the upper ocean plays a part in the coupled feedbacks between ocean and atmosphere that maintain the basic state and the timing of the seasonal cycle of SST and trade winds in the tropical Pacific. The Madden-Julian Oscillation (MJO) is examined by use of a large scale MJO index, lag correlations and composites of events. The inclusion of the diurnal cycle leads to a reduction in overall MJO activity. Precipitation composites show that the MJO is stronger and more coherent when the diurnal cycle of coupling is resolved, with the propagation and different phases being far more distinct both locally and to larger lead times across the tropical Indo-Pacific. Part one of this study showed that that diurnal variability of SST is modulated by the MJO and therefore increases the intraseasonal SST response to the different phases of the MJO. Precipitation-based composites of SST variability confirm this increase in the coupled simulations. It is argued that including this has increased the thermodynamical coupling of the ocean and atmosphere on the timescale of the MJO (20-100 days), accounting for the improvement in the MJO strength and coherency seen in composites of precipitation and SST. These results show that the diurnal cycle of ocean-atmosphere interaction has profound impact on a range of up-scale variability in the tropical climate and as such, it is an important feature of the modelled climate system which is currently either neglected or poorly resolved in state of the art coupled models.

Convectively coupled equatorial waves within the MJO during CINDY/DYNAMO: slow Kelvin waves as building blocks

NASA Astrophysics Data System (ADS)

Kikuchi, Kazuyoshi; Kiladis, George N.; Dias, Juliana; Nasuno, Tomoe

2018-06-01

This study examines the relationship between the MJO and convectively coupled equatorial waves (CCEWs) during the CINDY2011/DYNAMO field campaign using satellite-borne infrared radiation data, in order to better understand the interaction between convection and the large-scale circulation. The spatio-temporal wavelet transform (STWT) enables us to document the convective signals within the MJO envelope in terms of CCEWs in great detail, through localization of space-time spectra at any given location and time. Three MJO events that occurred in October, November, and December 2011 are examined. It is, in general, difficult to find universal relationships between the MJO and CCEWs, implying that MJOs are diverse in terms of the types of disturbances that make up its convective envelope. However, it is found in all MJO events that the major convective body of the MJO is made up mainly by slow convectively coupled Kelvin waves. These Kelvin waves have relatively fast phase speeds of 10-13 m s-1 outside of, and slow phase speeds of 8-9 m s-1 within the MJO. Sometimes even slower eastward propagating signals with 3-5 m s-1 phase speed show up within the MJO, which, as well as the slow Kelvin waves, appear to comprise major building blocks of the MJO. It is also suggested that these eastward propagating waves often occur coincident with n = 1 WIG waves, which is consistent with the schematic model from Nakazawa in 1988. Some practical aspects that facilitate use of the STWT are also elaborated upon and discussed.

Enhancement of vegetation-rainfall feedbacks on the Australian summer monsoon by the Madden-Julian Oscillation

NASA Astrophysics Data System (ADS)

Notaro, Michael

2018-01-01

A regional climate modeling analysis of the Australian monsoon system reveals a substantial modulation of vegetation-rainfall feedbacks by the Madden Julian Oscillation (MJO), both of which operate at similar sub-seasonal time scales, as evidence that the intensity of land-atmosphere interactions is sensitive to the background atmospheric state. Based on ensemble experiments with imposed modification of northern Australian leaf area index (LAI), the atmospheric responses to LAI anomalies are composited for negative and positive modes of the propagating MJO. In the regional climate model (RCM), northern Australian vegetation feedbacks are characterized by evapotranspiration (ET)-driven rainfall responses, with the moisture feedback mechanism dominating over albedo and roughness feedback mechanisms. During November-April, both Tropical Rainfall Measuring Mission and RCM data reveal MJO's pronounced influence on rainfall patterns across northern Australia, tropical Indian Ocean, Timor Sea, Arafura Sea, and Gulf of Carpentaria, with the MJO dominating over vegetation feedbacks in terms of regulating monsoon rainfall variability. Convectively-active MJO phases support an enhancement of positive vegetation feedbacks on monsoon rainfall. While the MJO imposes minimal regulation of ET responses to LAI anomalies, the vegetation feedback-induced responses in precipitable water, cloud water, and rainfall are greatly enhanced during convectively-active MJO phases over northern Australia, which are characterized by intense low-level convergence and efficient precipitable water conversion. The sub-seasonal response of vegetation-rainfall feedback intensity to the MJO is complex, with significant enhancement of rainfall responses to LAI anomalies in February during convectively-active MJO phases compared to minimal modulation by the MJO during prior and subsequent calendar months.

Moisture Budget of the MJO over the Maritime Continent

NASA Astrophysics Data System (ADS)

Kim, J. E.; Zhang, C.; Kiladis, G. N.; Bechtold, P.

2017-12-01

The Maritime Continent (MC) often acts as a barrier for the eastward propagation of the MJO originating from the Indian Ocean (IO). Convective anomalies associated with the MJO tend to weaken over the MC, and MJO convection sometimes fails to pass through the MC. MJO events observed during the DYNAMO field campaign during late 2011 to early 2012 are not an exception in this regard. Modulation of convection for DYNAMO MJOs over the MC is investigated using moisture budget analysis of a reforecast product by the ECMWF Integrated Forecasting System (IFS). Vertical profiles of diabatic drying and heating by physical processes from convection, microphysics, and radiation schemes in IFS under the weak temperature gradient (WTG) environment enable us to estimate vertically resolved processes that control local moistening and drying associated with the MJO. We will compare three-dimensional moisture budgets over the IO and MC to understand which processes contribute to the changes in the MJO propagation and intensity over the MC.

Mechanisms of convective cloud organization by cold pools over tropical warm ocean during the AMIE/DYNAMO field campaign

DOE PAGES

Feng, Zhe; Hagos, Samson; Rowe, Angela K.; ...

2015-04-03

This paper investigates the mechanisms of convective cloud organization by precipitation-driven cold pools over the warm tropical Indian Ocean during the 2011 Atmospheric Radiation Measurement (ARM) Madden-Julian Oscillation (MJO) Investigation Experiment / Dynamics of the MJO (AMIE/DYNAMO) field campaign. A high-resolution regional model simulation is performed using the Weather Research and Forecasting model during the transition from suppressed to active phases of the November 2011 MJO. The simulated cold pool lifetimes, spatial extent and thermodynamic properties agree well with the radar and ship-borne observations from the field campaign. The thermodynamic and dynamic structures of the outflow boundaries of isolated andmore » intersecting cold pools in the simulation and the associated secondary cloud populations are examined. Intersecting cold pools last more than twice as long, are twice as large, 41% more intense (measured by buoyancy), and 62% deeper than isolated cold pools. Consequently, intersecting cold pools trigger 73% more convective clouds than isolated ones. This is possibly due to stronger outflows that enhance secondary updraft velocities by up to 45%. However, cold pool-triggered convective clouds grow into deep convection not because of the stronger secondary updrafts at cloud base, but rather due to closer spacing (aggregation) between clouds and larger cloud clusters that formed along the cold pool boundaries when they intersect. The close spacing of large clouds moistens the local environment and reduces entrainment drying, allowing the clouds to further develop into deep convection. Implications to the design of future convective parameterization with cold pool-modulated entrainment rates are discussed.« less

Dynamical Structure of Madden-Julian Oscillation over Malay Peninsula

NASA Astrophysics Data System (ADS)

Djamil, Y. S.; Koh, T. Y.; Chandimala, J.; Teo, C. K.

2014-12-01

Madden-Julian Oscillation (MJO) is the dominant weather event in the intraseasonal time scale over Malay Peninsula region. The MJO signals are represented by the first two modes of radiosonde records extracted using Extended Empirical Orthogonal Function (EEOF) analyses which we label as Local Multivariate MJO (LMM). LMM is able to capture the spatio-temporal profile of MJO along the global tropics in all seasons. With the help of LMM, we clarify the dynamical and thermodynamical structure of the MJO over Malay Peninsula, including the unique "boomerang-shaped" feature in the time-height temperature profile identified in previous literature.

The Impact of the Diurnal Cycle of Clouds and Precipitation over the Maritime Continent on the Propagation of the MJO into the Western Pacific

NASA Astrophysics Data System (ADS)

Burleyson, C. D.; Hagos, S. M.; Feng, Z.

2016-12-01

The processes that determine the interaction between the islands of the maritime continent (MC) and the eastward propagation of the Madden-Julian Oscillation (MJO) are poorly understood. We are undertaking a series of observational and modeling analyses aimed at understanding how clouds and precipitation over the islands of the MC lead to changes in the intensity of the MJO (inferred by the amplitude of the Real-time Multivariate MJO index [RMM] and other metrics) as it crosses the MC. One component of our analysis uses the long-term measurements from the DOE Atmospheric Radiation Measurement (ARM) sites in the Tropical Western Pacific (TWP) to examine cloud radiative effects as the MJO crosses the MC. Using the multi-year ARM dataset and a cloud resolving model (CRM), we show that the MJO interacts with the diurnal cycle of surface heating, clouds, and precipitation over the islands of the MC in a way that weakens it. Additionally, using a satellite climatology based on the TRMM 3B42 dataset we found that MJO episodes that weaken as they cross the MC are characterized by more frequent precipitation and warmer sea surface temperatures (SSTs) south of the equator and less frequent precipitation north of the equator compared to cases where the MJO intensifies. The north-south polarity in SSTs suggests a seasonal dependence in the ability of the MJO to cross the MC. This seasonality was confirmed by looking the seasonal distribution of changes in MJO amplitude as it crosses the MC. Consistent with the SST result, we found that MJO episodes that intensify as they cross the MC are more likely to occur during the northern hemisphere summer and less likely to occur during the northern hemisphere winter (Fig. 1). A regional CRM and satellite observations are used jointly to explore the processes responsible for this seasonality and to examine the impact of interannual oscillations such as ENSO and monsoons on the ability of the MJO to cross the MC. Fig. 1. The annual distribution of the day of the year when the MJO approaches the MC for cases where the RMM amplitude decreases (black lines) and increases (orange lines) across the MC.

Identification of MJO Signal on Various Elevation Station Rainfall in Southern Papua, Indonesia

NASA Astrophysics Data System (ADS)

Sakya, A. E.; Permana, D.; Makmur, E. E. S.; Handayani, A. S.; Hanggoro, W.; Setyadi, G.

2016-12-01

The Madden-Julian Oscillation (MJO) is the dominant mode of intraseasonal variability in tropical rainfall on the large scale, but its signal is often obscured in individual station data, where effects are most directly felt at the local level. The characteristic of the MJO during its propagation through the Maritime Continent has always been a challenge to comprehend despite decades of research attempts in that region. Unique topography over the Maritime Continent is believed to act as one of the vanguard of precipitation triggered by the MJO. Such condition leads to a maximize amplitude of the diurnal cycle of precipitation over land on phase 2 and 5, even before the arrival of the MJO. Papua in Indonesia is one of the wettest regions on Earth and is at the heart of the MJO envelope. Aiming to investigate the effect of topography and coastline distance on MJO in southern Papua, 14 years of rainfall data from 12 stations in PTFI AWS network at various elevations (9 meters to 4400 meters above sea level) have been utilized. The results show a strong MJO modulation in rainfall variability with variance of 30 - 100 days in the region. These results suggest a strong impact of MJO on rainfall at various elevations in southern Papua which confirm the previous studies. The peak rainfall rates were observed at phase 3 at lower elevation and coastline stations and phase 4 at middle and high elevation stations. The study also investigated the relationship between MJO phases and diurnal precipitation cycle at all stations. At low elevation and coastline stations, diurnal rainfall variation is more variable with high rainfall observed at afternoon to midnight and after midnight. This is due to the local effect of land-sea breeze system. While in middle and high elevation stations, rainfall peak was observed at afternoon to midnight. The results show the impact of MJO in diurnal rainfall variation at all stations.

Influence of the Madden-Julian oscillation and Caribbean low-level jet on east Pacific easterly waves

NASA Astrophysics Data System (ADS)

Maloney, E. D.; Whitaker, J.

2017-12-01

The east Pacific warm pool in which easterly waves (EWs) exist exhibits basic state variability associated with the Madden-Julian oscillation (MJO) and Caribbean low-level jet (CLLJ). This study compares and contrasts composite changes in the background environment, eddy kinetic energy EKE budget, moisture budget, and EW tracks during MJO and CLLJ events. While previous studies have shown that the MJO influences jet activity in the east Pacific, the influence of the MJO and CLLJ on EWs is not synonymous. The MJO has a more extensive influence in the main EW path along the Central American coast, while the CLLJ is a stronger modulator of the ITCZ. Anomalous low-level westerly MJO and CLLJ periods are associated with favorable conditions for EW development along the main EW path, although the impact of the MJO is more extensive. Easterly MJO and CLLJ periods support enhanced EW development along the ITCZ, although the CLLJ is a greater modulator of EW tracks in this region, likely associated with basic state changes that favor convection and its influence on the EKE budget. EW growth in the ITCZ during easterly MJO periods is more reliant on barotropic conversion as an energy source than for strong CLLJ period waves, when EAPE to EKE conversion associated with ITCZ convection is more important. A moisture budget analysis for ITCZ waves shows that strong CLLJ period waves have stronger horizontal advection in front of the wave axis relative to easterly MJO periods waves. These differences in horizontal advection are interpreted in the context of a linearized horizontal advection budget. The results highlight that the influence of these phenomena on east Pacific EWs should be considered distinct.

Short-term Climate Simulations of African Easterly Waves with a Global Mesoscale Model

NASA Astrophysics Data System (ADS)

Shen, B. W.

2015-12-01

Recent high-resolution global model simulations ( Shen et al., 2010a, 2010b, 2012; 2013), which were conducted to examine the role of multiscale processes associated with tropical waves in the predictability of mesoscale tropical cyclones (TCs), suggested that a large-scale system (e.g., tropical waves) can provide determinism on the prediction of TC genesis, making it possible to extend the lead time of genesis predictions. Selected cases include the relationship between (i) TC Nargis (2008) and an Equatorial Rossby wave; (ii) Hurricane Helene (2006) and an intensifying African Easterly Wave (AEW); (iii) Twin TCs (2002) and a mixed Rossby-gravity wave during an active phase of the Madden Julian Oscillation (MJO); (iv) Hurricane Sandy (2012) and tropical waves during an active phase of the MJO. In this talk, thirty-day simulations with different model configurations are presented to examine the model's ability to simulate AEWs and MJOs and their association with tropical cyclogenesis. I will first discuss the simulations of the initiation and propagation of 6 consecutive AEWs in late August 2006 and the mean state of the African easterly jet (AEJ) over both Africa and downstream in the tropical Atlantic. By comparing our simulations with NCEP analysis and satellite data (e.g., TRMM), it is shown that the statistical characteristics of individual AEWs are realistically simulated with larger errors in the 5th and th AEWs. Results from the sensitivity experiments suggest the following: 1) accurate representations of non-linear interactions between the atmosphere and land processes are crucial for improving the simulations of the AEWs and the AEJ; 2) improved simulations of an individual AEW and its interaction with local environments (e.g., the Guinea Highlands) could provide determinism for hurricane formation downstream. Of interest is the potential to extend the lead time for predicting hurricane formation (e.g., a lead time of up to 22 days) as the 4th AEW is realistically simulated; 3) however, the dependence of AEW simulations on accurate dynamic and surface initial conditions and boundary conditions poses a challenge in simulating their modulation on hurricane activity. In addition to the simulations of AEWs, I will also present the 30-day simulations of selected MJO cases.

Exploring the Utility of the Planned CYGNSS Mission for Investigating the Initiation and Development of the Madden-Julian Oscillation

NASA Technical Reports Server (NTRS)

Lang, Timothy; Mecikalski, John; Li, Xuanli; Chronis, Themis; Brewer, Alan; Churnside, James; Rutledge, Steve

2014-01-01

CYGNSS is a planned constellation consisting of multiple micro-satellites that leverage the Global Positioning System (GPS) to provide rapidly updated, high resolution (approx. 15-50 km, approx. 4 h) surface wind speeds (via bi-static scatterometry) over the tropical oceans in any weather condition, including heavy rainfall. The approach of the work to be presented at this conference is to utilize a limited-domain, cloud-system resolving model (Weather Research and Forecasting or WRF) and its attendant data assimilation scheme (Three-Dimensional Variational Assimilation or 3DVAR) to investigate the utility of the CYGNSS mission for helping characterize key convectiveto- mesoscale processes - such as surface evaporation, moisture advection and convergence, and upscale development of precipitation systems - that help drive the initiation and development of the Madden-Julian Oscillation (MJO) in the equatorial Indian Ocean. The proposed work will focus on three scientific objectives. Objective 1 is to produce a high-resolution surface wind dataset resolution (approx. 0.5 h, approx. 1-4 km) for multiple MJO onsets using WRF-assimilated winds and other data from the DYNAmics of the MJO (DYNAMO) field campaign, which took place during October 2011 - March 2012. Objective 2 is to study the variability of surface winds during MJO onsets at temporal and spatial scales of finer resolution than future CYGNSS data. The goal is to understand how sub-CYGNSS-resolution processes will shape the observations made by the satellite constellation. Objective 3 is to ingest simulated CYGNSS data into the WRF model in order to perform observing system simulation experiments (OSSEs). These will be used to test and quantify the potential beneficial effects provided by CYGNSS, particularly for characterizing the physical processes driving convective organization and upscale development during the initiation and development of the MJO. The proposed research is ideal for answering important questions about the CYGNSS mission, such as the representativeness of surface wind retrievals in the context of the complex airflow processes that occur during heavy precipitation, as well as the tradeoffs in retrieval accuracy that result from finer spatial resolution of the CYGNSS winds versus increased errors/noisiness in those data. Research plans and initial progress toward these objectives will be presented.

Predictability and Coupled Dynamics of MJO During DYNAMO

DTIC Science & Technology

2013-09-30

1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Predictability and Coupled Dynamics of MJO During DYNAMO ...Model (LIM) for MJO predictions and apply it in retrospective cross-validated forecast mode to the DYNAMO time period. APPROACH We are working as...a team to study MJO dynamics and predictability using several models as team members of the ONR DRI associated with the DYNAMO experiment. This is a

Atmospheric study of the impact of Borneo vortex and Madden-Julian oscillation over Western Indonesian maritime area

NASA Astrophysics Data System (ADS)

Saragih, R. M.; Fajarianti, R.; Winarso, P. A.

2018-03-01

During the Asian winter Monsoon (November-March), the Indonesia Maritime Continent is an area of deep convection. In that period, there is a synoptic scale disturbance over Northwest of Borneo Island called Borneo vortex. In addition to the impact of Asian Winter Monsoon, Madden-Julian Oscillation (MJO) also have an impact on deep convection during an active period. This study aims to study the impact of interaction Borneo vortex and MJO (during MJO active period in phase 3, 4 and 5) and rainfall condition over the western part of Indonesia Maritime Continent using compositing technique in the period of November-March 2015/2016. The parameters used to identify the incidence of Borneo vortex, MJO, and its interaction is vertical velocity. When MJO is active, Borneo vortex occurs most often in phase 5 and at least in phase 3. However, Borneo vortex occurs most often when the MJO is inactive. The interaction between Borneo vortex and MJO seems may affect not so much rainfall occurrence in the western part of IMC.

Maximum covariance analysis to identify intraseasonal oscillations over tropical Brazil

NASA Astrophysics Data System (ADS)

Barreto, Naurinete J. C.; Mesquita, Michel d. S.; Mendes, David; Spyrides, Maria H. C.; Pedra, George U.; Lucio, Paulo S.

2017-09-01

A reliable prognosis of extreme precipitation events in the tropics is arguably challenging to obtain due to the interaction of meteorological systems at various time scales. A pivotal component of the global climate variability is the so-called intraseasonal oscillations, phenomena that occur between 20 and 100 days. The Madden-Julian Oscillation (MJO), which is directly related to the modulation of convective precipitation in the equatorial belt, is considered the primary oscillation in the tropical region. The aim of this study is to diagnose the connection between the MJO signal and the regional intraseasonal rainfall variability over tropical Brazil. This is achieved through the development of an index called Multivariate Intraseasonal Index for Tropical Brazil (MITB). This index is based on Maximum Covariance Analysis (MCA) applied to the filtered daily anomalies of rainfall data over tropical Brazil against a group of covariates consisting of: outgoing longwave radiation and the zonal component u of the wind at 850 and 200 hPa. The first two MCA modes, which were used to create the { MITB}_1 and { MITB}_2 indices, represent 65 and 16 % of the explained variance, respectively. The combined multivariate index was able to satisfactorily represent the pattern of intraseasonal variability over tropical Brazil, showing that there are periods of activation and inhibition of precipitation connected with the pattern of MJO propagation. The MITB index could potentially be used as a diagnostic tool for intraseasonal forecasting.

An MJO-Mediated Mechanism to Explain ENSO and IOD Impacts on East African Short Rains

NASA Astrophysics Data System (ADS)

Zaitchik, B. F.; Berhane, F.; Gnanadesikan, A.

2015-12-01

Previous studies have found that the El Nino Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) have significant impacts on rainfall over East Africa (EA) during the short rains (Oct-Dec). However, not all ENSO and IOD events are associated with significant precipitation anomalies over EA. Our analysis shows that the IOD and ENSO influence EA rainfall by modifying the MJO. Composite analysis of rainfall and outgoing longwave radiation data show that the MJO over the Indian Ocean (phases 2 and 3 of the Wheeler and Hendon index) is associated with significant increase in precipitation over EA during El Niño. In La Niña and non-ENSO years, the MJO over the Indian Ocean has very weak impacts on EA convection and precipitation. Although previous studies have found that El Niño / La Niña events are associated with anomalous wetness/dryness over EA, the associations are not evident in the absence of the MJO. Similarly, the IOD exhibits strong associations with EA precipitation when there is MJO activity over the Indian Ocean. During the positive phase of the IOD, the MJO over the Indian Ocean has impacts that extend to EA. In the absence of the MJO, however, the IOD shows weak associations with EA precipitation. Furthermore, there are more MJO days in the Indian Ocean during El Niño and positive IOD events, which implies stronger impacts on EA. During La Niña events more MJO days are observed in the Pacific Ocean, favoring subsidence over the western Indian Ocean and dry anomalies over EA. These observations suggest two critical MJO-related questions that must be addressed in order to explain EA short rain variability typically attributed to ENSO or IOD: first, how do ENSO and IOD modify background conditions in a way that causes Indian Ocean MJO activity to be more strongly connected to EA under El Niño and IOD positive conditions, and second, why is it that El Niño and IOD positive states slow MJO propagation over the Indian Ocean and speed it over the Pacific? This presentation will review mechanisms consistent with each phenomenon, including changes in lower troposphere wind patterns, upper level mean flow, vorticity gradients associated with ∂2U/∂2y, and zonal temperature gradients affecting the coupling between convection and the induced convergence of moist static energy.

Sensitivity of MJO propagation to a robust positive Indian Ocean dipole event in the superparameterized CAM

DOE PAGES

Benedict, James J.; Pritchard, Michael S.; Collins, William D.

2015-11-23

The superparameterized Community Atmosphere Model (SPCAM) is used to investigate the impact and geographic sensitivity of positive Indian Ocean Dipole (+IOD) sea-surface temperatures (SSTs) on Madden-Julian oscillation (MJO) propagation. The goal is to clarify potentially appreciable +IOD effects on MJO dynamics detected in prior studies by using a global model with explicit convection representation. Prescribed climatological October SSTs and variants of the SST distribution from October 2006, a +IOD event, force the model. Modest MJO convection weakening over the Maritime Continent occurs when either climatological SSTs, or +IOD SST anomalies restricted to the Indian Ocean, are applied. However, severe MJOmore » weakening occurs when either +IOD SST anomalies are applied globally or restricted to the equatorial Pacific. MJO disruption is associated with time-mean changes in the zonal wind profile and lower moist static energy (MSE) in subsiding air masses imported from the Subtropics by Rossby-like gyres. On intraseasonal scales, MJO disruption arises from significantly smaller MSE accumulation, weaker meridional advective moistening, and overactive submonthly eddies that mix drier subtropical air into the path of MJO convection. These results (1) demonstrate that SPCAM reproduces observed time-mean and intraseasonal changes during +IOD episodes, (2) reaffirm the role that submonthly eddies play in MJO propagation and show that such multiscale interactions are sensitive to interannual SST states, and (3) suggest that boreal fall +IOD SSTs local to the Indian Ocean have a significantly smaller impact on Maritime Continent MJO propagation compared to contemporaneous Pacific SST anomalies which, for October 2006, resemble El Ninõ-like conditions.« less

Sensitivity of MJO propagation to a robust positive Indian Ocean dipole event in the superparameterized CAM

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

Benedict, James J.; Pritchard, Michael S.; Collins, William D.

The superparameterized Community Atmosphere Model (SPCAM) is used to investigate the impact and geographic sensitivity of positive Indian Ocean Dipole (+IOD) sea-surface temperatures (SSTs) on Madden-Julian oscillation (MJO) propagation. The goal is to clarify potentially appreciable +IOD effects on MJO dynamics detected in prior studies by using a global model with explicit convection representation. Prescribed climatological October SSTs and variants of the SST distribution from October 2006, a +IOD event, force the model. Modest MJO convection weakening over the Maritime Continent occurs when either climatological SSTs, or +IOD SST anomalies restricted to the Indian Ocean, are applied. However, severe MJOmore » weakening occurs when either +IOD SST anomalies are applied globally or restricted to the equatorial Pacific. MJO disruption is associated with time-mean changes in the zonal wind profile and lower moist static energy (MSE) in subsiding air masses imported from the Subtropics by Rossby-like gyres. On intraseasonal scales, MJO disruption arises from significantly smaller MSE accumulation, weaker meridional advective moistening, and overactive submonthly eddies that mix drier subtropical air into the path of MJO convection. These results (1) demonstrate that SPCAM reproduces observed time-mean and intraseasonal changes during +IOD episodes, (2) reaffirm the role that submonthly eddies play in MJO propagation and show that such multiscale interactions are sensitive to interannual SST states, and (3) suggest that boreal fall +IOD SSTs local to the Indian Ocean have a significantly smaller impact on Maritime Continent MJO propagation compared to contemporaneous Pacific SST anomalies which, for October 2006, resemble El Ninõ-like conditions.« less

Westerly wind bursts simulated in CAM4 and CCSM4

NASA Astrophysics Data System (ADS)

Lian, Tao; Tang, Youmin; Zhou, Lei; Islam, Siraj Ul; Zhang, Chan; Li, Xiaojing; Ling, Zheng

2018-02-01

The equatorial westerly wind bursts (WWBs) play an important role in modulating and predicting the El Niño-Southern Oscillation (ENSO). In this study, the ability of the Community Atmospheric Model version 4 (CAM4) and the Community Climate System Model version 4 (CCSM4) in simulating WWBs is systematically evaluated. Many characteristics of WWBs, including their longitude distributions, durations, zonal extensions, variabilities at seasonal, intraseasonal, and interannual timescales, as well as their relations with the Madden-Julian Oscillation (MJO) and ENSO, are discussed. Generally speaking, these characteristics of WWBs can be successfully reproduced by CAM4, owning to the improvement of the deep convection in the model. In CCSM4, significant bias such as the lack of the equatorial Pacific WWBs in boreal spring season and the weak modulation by a strong MJO are found. Our findings confirm the fact that the WWBs are greatly modulated by the surface temperature. It's also suggested that improving the air-sea coupling in CCSM4 may improve model performance in simulating WWBs, and may further improve the predictability of ENSO in the coupled model.

Variability of winter and summer surface ozone in Mexico City on the intraseasonal timescale

NASA Astrophysics Data System (ADS)

Barrett, Bradford S.; Raga, Graciela B.

2016-12-01

Surface ozone concentrations in Mexico City frequently exceed the Mexican standard and have proven difficult to forecast due to changes in meteorological conditions at its tropical location. The Madden-Julian Oscillation (MJO) is largely responsible for intraseasonal variability in the tropics. Circulation patterns in the lower and upper troposphere and precipitation are associated with the oscillation as it progresses eastward around the planet. It is typically described by phases (labeled 1 through 8), which correspond to the broad longitudinal location of the active component of the oscillation with enhanced precipitation. In this study we evaluate the intraseasonal variability of winter and summer surface ozone concentrations in Mexico City, which was investigated over the period 1986-2014 to determine if there is a modulation by the MJO that would aid in the forecast of high-pollution episodes. Over 1 000 000 hourly observations of surface ozone from five stations around the metropolitan area were standardized and then binned by active phase of the MJO, with phase determined using the real-time multivariate MJO index. Highest winter ozone concentrations were found in Mexico City on days when the MJO was active and in phase 2 (over the Indian Ocean), and highest summer ozone concentrations were found on days when the MJO was active and in phase 6 (over the western Pacific Ocean). Lowest winter ozone concentrations were found during active MJO phase 8 (over the eastern Pacific Ocean), and lowest summer ozone concentrations were found during active MJO phase 1 (over the Atlantic Ocean). Anomalies of reanalysis-based cloud cover and UV-B radiation supported the observed variability in surface ozone in both summer and winter: MJO phases with highest ozone concentration had largest positive UV-B radiation anomalies and lowest cloud-cover fraction, while phases with lowest ozone concentration had largest negative UV-B radiation anomalies and highest cloud-cover fraction. Furthermore, geopotential height anomalies at 250 hPa favoring reduced cloudiness, and thus elevated surface ozone, were found in both seasons during MJO phases with above-normal ozone concentrations. Similar height anomalies at 250 hPa favoring enhanced cloudiness, and thus reduced surface ozone, were found in both seasons during MJO phases with below-normal ozone concentrations. These anomalies confirm a physical pathway for MJO modulation of surface ozone via modulation of the upper troposphere.

Role of cold surge and MJO on rainfall enhancement over indonesia during east asian winter monsoon

NASA Astrophysics Data System (ADS)

Fauzi, R. R.; Hidayat, R.

2018-05-01

Intensity of precipitation in Indonesia is influenced by convection and propagation of southwest wind. Objective of this study is to analyze the relationship between cold surge and the phenomenon of intra-seasonal climate variability Madden-julian Oscillation (MJO) for affecting precipitation in Indonesia. The data used for identifying the occurrence of cold surge are meridional wind speed data from the ERA-Interim. In addition, this study also used RMM1 and RMM2 index data from Bureau of Meteorology (BOM) for identifying MJO events. The results showed that during East Asian Winter Monsoon (EAWM) in 15 years (2000-2015), there are 362 cold surge events, 186 MJO events, and 113 cold surge events were associated with MJO events. The spread of cold surge can penetrate to equator and brought mass of water vapor that causes dominant precipitation in the Indonesian Sea up to 50-75% from climatological precipitation during EAWM. The MJO convection activity that moves from west to east also increases precipitation, but the distribution of rainfall is wider than cold surge, especially in Eastern Indonesia. MJO and cold surge simultaneously can increase rainfall over 100-150% in any Indonesian region that affected by MJO and cold surge events. The mechanism of heavy rainfall is illustrated by high activity of moisture transport in areas such as Java Sea and coastal areas of Indonesia.

Leveraging the MJO for Predicting Envelopes of Tropical Wave and Synoptic Activity at Multi-Week Lead Times

DTIC Science & Technology

2013-09-30

GEWEX GASS MJO Diabatic Heating Experiment, 2) Intraseasonal Variability Hindcast Experiment (ISVHE) C. Conduct more comprehensive analysis on the...since her Ph.D. study. Key partners include M. Zhao (GFDL) and J. Ridout (NRL). Both Zhao and Ridout are contributors to the MJO multi-model diabatic ...a paper and submitted to the Journal of the Atmospheric Sciences (Guo et al. 2013). We have also begun acquiring model data from the MJO Diabatic

Air-Sea Heat Flux Transfer for MJO Initiation Processes during DYNAMO/CINDY2011 in Extended-Range Forecasts

NASA Astrophysics Data System (ADS)

Hong, X.; Reynolds, C. A.; Doyle, J. D.

2016-12-01

In this study, two-sets of monthly forecasts for the period during the Dynamics of Madden-Julian Oscillation (MJO)/Cooperative Indian Ocean Experiment of Intraseasonal Variability (DAYNAMO/CINDY) in November 2011 are examined. Each set includes three forecasts with the first set from Navy Global Environmental Model (NAVGEM) and the second set from Navy's non-hydrostatic Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS®1). Three NAVGEM monthly forecasts have used sea surface temperature (SST) from persistent at the initial time, from Navy Coupled Ocean Data Assimilation (NCODA) analysis, and from coupled NAVGEM-Hybrid Coordinate Ocean Model (HYCOM) forecasts. Examination found that NAVGEM can predict the MJO at 20-days lead time using SST from analysis and from coupled NAVGEM-HYCOM but cannot predict the MJO using the persistent SST, in which a clear circumnavigating signal is absent. Three NAVGEM monthly forecasts are then applied as lateral boundary conditions for three COAMPS monthly forecasts. The results show that all COAMPS runs, including using lateral boundary conditions from the NAVGEM that is without the MJO signal, can predict the MJO. Vertically integrated moisture anomaly and 850-hPa wind anomaly in all COAMPS runs have indicated strong anomalous equatorial easterlies associated with Rossby wave prior to the MJO initiation. Strong surface heat fluxes and turbulence kinetic energy have promoted the convective instability and triggered anomalous ascending motion, which deepens moist boundary layer and develops deep convection into the upper troposphere to form the MJO phase. The results have suggested that air-sea interaction process is important for the initiation and development of the MJO. 1COAMPS® is a registered trademark of the Naval Research Laboratory

Characteristics of Precipitation, Cloud, and Latent Heating Associated with the Madden-Julian Oscillation

NASA Technical Reports Server (NTRS)

Lau, K-M.; Wu, H-T.

2010-01-01

This study investigates the evolution of cloud and rainfall structures associated with Madden Julian oscillation (MJO) using Tropical Rainfall Measuring Mission (TRMM) data. Two complementary indices are used to define MJO phases. Joint probability distribution functions (PDFs) of cloud-top temperature and radar echo-top height are constructed for each of the eight MJO phases. The genesis stage of MJO convection over the western Pacific (phases 1 and 2) features a bottom-heavy PDF, characterized by abundant warm rain, low clouds, suppressed deep convection, and higher sea surface temperature (SST). As MJO convection develops (phases 3 and 4), a transition from the bottom-heavy to top-heavy PDF occurs. The latter is associated with the development of mixed-phase rain and middle-to-high clouds, coupled with rapid SST cooling. At the MJO convection peak (phase 5), a top-heavy PDF contributed by deep convection with mixed-phase and ice-phase rain and high echo-top heights (greater than 5 km) dominates. The decaying stage (phases 6 and 7) is characterized by suppressed SST, reduced total rain, increased contribution from stratiform rain, and increased nonraining high clouds. Phase 7, in particular, signals the beginning of a return to higher SST and increased warm rain. Phase 8 completes the MJO cycle, returning to a bottom-heavy PDF and SST conditions similar to phase 1. The structural changes in rain and clouds at different phases of MJO are consistent with corresponding changes in derived latent heating profiles, suggesting the importance of a diverse mix of warm, mixed-phase, and ice-phase rain associated with low-level, congestus, and high clouds in constituting the life cycle and the time scales of MJO.

Influence of Madden-Julian Oscillation on water budget transported by the Somali low-level jet and the associated Indian summer monsoon rainfall

NASA Astrophysics Data System (ADS)

Ordonez, Paulina; Ribera, Pedro; Gallego, David; Pena-Ortiz, Cristina

2013-10-01

Recent studies suggest that there is a strong linkage between the moisture uptake over the equatorial area of the Somali low level jet (SLLJ) and the rainfall variability over most of continental India. Additionally, the Madden-Julian Oscillation (MJO) strongly modulates the intraseasonal variability of the Indian summer monsoon rainfall, since the northward propagation of the boreal summer MJO is closely associated with the active and break phases of monsoon rainfall. But a question remains open: is there a relationship between the moisture transported by the SLLJ and the MJO evolution? In this paper, a Lagrangian approach is used to track the evaporation minus precipitation (E - P) evolution along trajectories of particles initially situated over the equatorial region of SLLJ. The impact of the MJO on the water budget transport of the SLLJ is examined by making composites of the obtained (E-P) fields for the different MJO phases. The spatial structures of the boreal summer intraseasonal oscillation are revealed in our results, which strongly suggest that the main responsible for the rainfall variability associated to the MJO in these regions are the changes in the moisture advected by the SLLJ. In order to assess the MJO-SLLJ interaction, an analysis of the total-column mass and the total-column specific humidity transported by the SLLJ during the MJO life cycle is performed. While a systematic difference between air mass advected to India during active and break phases of MJO is not detected, changes in the moisture of particles are found, with wet (dry) anomalies over enhanced (suppressed) convection region. This result implicitly leads to assume air-sea interaction processes.

How the SSW Can Make the Different Response of Stratosphere to MJO during Boreal Winters

NASA Astrophysics Data System (ADS)

Yang, C.

2016-12-01

Using the ERA-Interim data, we investigated the effects of Madden-Julian oscillation (MJO) on the mid-winter stratosphere in the northern hemisphere focusing on the occurrence or non-occurrence of stratospheric sudden warming (SSW). In the years in which SSW occurred (SSW years), the polar cap temperature response to MJO is stronger than that in the years in which SSW does not occur (non-SSW years). In the SSW years, the northern polar upper stratosphere temperature becomes warmer than normal at a lag of 15-20 days after the MJO phase 3 (P3). However, in the non-SSW years, the northern polar temperature is cooler 15-20 days after MJO P3, and becomes warmer after this period. The wavenumber 1 (WN1) and wavenumber 2 (WN2) PWs anomalies in the northern stratosphere caused by MJO P3 are just opposite between SSW and non-SSW winters. In response to MJO P3, WN1 and WN2 are responsible for the enhanced upward propagation of EP Flux in non-SSW and SSW winters, respectively. Whether in SSW or non-SSW winters, the variations of WN1 and WN2 PWs have a similar period to that of MJO (30-90 days). In the southern hemisphere, the upward propagation of WN2 PWs is enhanced after 20 days following MJO P3 in SSW winters while it is significantly depressed since 10 days after P3 in non-SSW years. As suggested by composite of residual circulation, the variation of the Brewer-Dobson circulation is in accordance with that of polar temperature.

Improved intraseasonal variability in the NASA GEOS AGCM with 2-moment microphysics and a shallow cumulus parameterization

NASA Astrophysics Data System (ADS)

Arnold, N.; Barahona, D.

2017-12-01

Atmospheric general circulation models (AGCMs) have long struggled to realistically represent tropical intraseasonal variability. Here we report progress in simulating the Madden Julian Oscillation (MJO) with the NASA Goddard Earth Observing System (GEOS) AGCM, in free-running simulations utilizing a new two-moment microphysics scheme and the University of Washington shallow cumulus parameterization. Lag composites of intraseasonal signals show significantly improved eastward propagation over the Indian Ocean and maritime region, with increased eastward precipitation variance and more coherent large-scale structure. The dynamics of the MJO are analyzed using a vertically resolved moisture budget, assuming weak temperature gradient conditions. We find that positive longwave radiative heating anomalies associated with high clouds contribute to low-level ascent and moistening, coincident with intraseasonal precipitation anomalies. Horizontal advection generally damps intraseasonal moisture anomalies, but at some longitudes contributes to their eastward tendency. Shallow convection is enhanced to the east of the intraseasonal precipitation maximum, and its associated moistening of the lower free troposphere encourages eastward propagation of deep convection.

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.

Differences in Vertical Structure of the Madden-Julian Oscillation Associated With the Quasi-Biennial Oscillation

NASA Astrophysics Data System (ADS)

Hendon, Harry H.; Abhik, S.

2018-05-01

The Madden-Julian Oscillation (MJO) during boreal winter is more active and propagates eastward farther into the western Pacific during the easterly phase of quasi-biennial oscillation (QBO). Using atmospheric reanalyses for 1980-2012, we show that the MJO-induced upper tropospheric positive temperature anomaly and overriding cold cap anomaly are stronger and more in-phase with the equatorial MJO-convective anomaly during the easterly phase of the QBO. These temperature anomalies combine to destabilize the upper troposphere more in-phase with MJO convection, thus acting to promote stronger MJO convection during the easterly phase of the QBO especially eastward of the Maritime Continent. This enhanced destabilization is promoted by the negative temperature anomaly at the tropopause resulting from the QBO during its easterly phase. These findings can account for the enhanced strength and farther eastward propagation of the MJO during the easterly phase of the QBO, but await confirmation by theoretical and modeling studies that can isolate these effects.

Characteristics Associated with the Madden-Julian Oscillation at Manus Island

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

Deng, Liping; McFarlane, Sally A.; Flaherty, Julia E.

2013-05-15

Ground-based high temporal and vertical resolution datasets from 2002 to 2008 of observations at the Atmospheric Radiation Measurement (ARM) Tropical Western Pacific (TWP) site on Manus Island, Papua New Guinea are used to examine the evolution of clouds and rainfall associated with the MJO life cycle. A composite MJO event is developed based on the NOAA MJO Index 4 using 13 events. The analysis shows that the cloud evolution during the composited MJO life cycle depicts a two-phase structure consisting of a development phase and a mature phase. During the development phase, congestus is the most important cloud type; duringmore » the mature phase, deep convection is the dominant cloud type. Consistent with this two-phase structure, the heavy rainfall frequency also shows a two-peak structure during the MJO life cycle. Light rainfall does not show a clear relation to the MJO life cycle, but shows variability on shorter time scales. From the development phase to the mature phase, the MJO structure shifts from the Type I to Type II structure, showing a different phase relationship between convection and dynamic fields (or wave motion) in the development and mature phases. During the shift, mid-level clouds play an important role in moving moisture to the mid-troposphere and preparing the atmosphere for the following deep convection. The discharge-recharge theory explains some of observed features of the MJO evolution at the ARM TWP Manus Island site.« less

The effect of the MJO on the energetics of El Niño

NASA Astrophysics Data System (ADS)

Lybarger, Nicholas D.; Stan, Cristiana

2017-12-01

The energy budget of the Pacific Ocean is evaluated in the Super-Parameterized Community Climate Model version 4 (SP-CCSM4) on intraseasonal time scales. The budget terms are decomposed to isolate the MJO influence and the ocean current associated with Kelvin waves. Using this decomposition, one can distinguish between El Niño events with strong and weak MJO influence. Composites of El Niño events based on the wind power component associated with the MJO induced wind stress and oceanic Kelvin waves ({{W}_{{MJO},{K}}} ) are compared with composites based only on the atmospheric variability and based only on the oceanic variability. It was found that the composite of events when {{W}_{{MJO},{K}}} is near maximum (+ NMJO,K) shows a greater magnitude of mean perturbation wind power, buoyancy power, and available potential energy than any other case, which is consistent with the greater amplitude Kelvin wave perturbations on the thermocline, as well as the greater amplitude of SST anomalies at the peak of the event. For + NMJO,K, latent heat flux anomalies out of the ocean along the coast of New Guinea are seen coincident with deepening of the mixed layer depth there, suggesting that this is an important region for the thermodynamic influence of the MJO on the ocean. Latent heat flux anomalies into the ocean are seen across the ITCZ in the spring, suggesting a basin wide influence by the MJO on the ocean surface radiation budget in + NMJO,K.

Intraseasonal variability of the West African monsoon and African easterly waves during boreal summer

NASA Astrophysics Data System (ADS)

Alaka, Ghassan J., Jr.

Substantial subseasonal variability in African easterly wave (AEW) activity and cyclogenesis frequency occurs in the main hurricane development region of the Atlantic during boreal summer. A complete understanding of intraseasonal variability in the Atlantic and west Africa during boreal summer requires analysis of how the Madden-Julian Oscillation (MJO) modulates the west African monsoon and consequently AEWs. Because the MJO is predictable a few weeks in advance, understanding how and why the MJO impacts the west African monsoon may have a profound influence on Atlantic tropical cyclone prediction. This study documents the MJO influence on the west African monsoon system during boreal summer using a variety of reanalysis and satellite datasets. This study aims to identify and explain the MJO teleconnection to the west African monsoon, and the processes that induce precipitation and AEW variability in this region. Intraseasonal west African and Atlantic convective anomalies on 30-90 day timescales are likely induced by equatorial Kelvin and Rossby waves generated in the Indian Ocean and west Pacific by the MJO. Previous studies have hypothesized that an area including the Darfur mountains and the Ethiopian highlands is an initiation region for AEWs. It is shown here that the initial MJO influence on precipitation and AEW activity in the African monsoon appears to occur in these regions, where eddy kinetic energy (EKE) anomalies first appear in advance of MJO-induced periods of enhanced and suppressed AEW activity. In the initiation region, upper tropospheric temperature anomalies are reduced, the atmosphere moistens by horizontal advection, and an eastward extension of the African easterly jet occurs in advance of the MJO wet phase of the African monsoon, when AEW activity is also enhanced. These factors all support strong precursor disturbances in the initiation region that seed the African easterly jet and contribute to downstream development of AEWs. Opposite behavior occurs in advance of the MJO dry phase. Moisture and eddy kinetic energy (EKE) budgets are examined to provide further insight as to how the MJO modulates and initiates precipitation and AEW variability in this region. In particular, meridional moisture advection anomalies foster moistening in the initiation region by anomalous flow acting across the mean moisture gradient. Additionally, positive (negative) upstream EKE tendency anomalies in advance of the MJO convective maximum (minimum) over tropical north Africa suggest wave growth (decay) near the entrance of the AEJ, while enhanced (suppressed) conversion of eddy available potential energy (EAPE) to EKE and barotropic conversion maintains downstream AEW growth (decay).

Impact of Madden-Julian Oscillation (MJO) on global distribution of total water vapor and column ozone

NASA Astrophysics Data System (ADS)

Fathurochman, Irvan; Lubis, Sandro W.; Setiawan, Sonni

2017-01-01

The Madden-Julian Oscillation (MJO) is the leading mode of intra-seasonal variability in the tropical troposphere, characterized by an eastward moving ‘pulse’ of cloud and rainfall near the equator. In this study, total precipitable water (TPW) and total column ozone (TCO) datasets from ECMWF ERA-Interim reanalysis were used to analyse the impact of the MJO on the distribution of water vapor and column ozone in the tropics from 1979 to 2013. The results show that seasonal variations of TPW modulated by the MJO are maximized in the tropics of about 10°S-10°N during boreal winter, while the variation in TCO is maximized in the mid-latitudes of about 30°S - 40°N in the same season. The composite analysis shows that MJO modulates TPW and TCO anomalies eastward across the globe. The underlying mechanism of the MJO’s impact on TPW is mainly associated with variation of tropical convection modulated by the MJO, while the underlying mechanism of the MJO’s impact on TCO is mainly associated with an intra-seasonal variability of tropopause height modulated by the MJO activity. This knowledge helps to improve the prediction skill of the intra-seasonal variation of water vapor and column ozone in the tropics during boreal winter.

MM5 Modeling of the Madden Julian Oscillation in the Indian and West Pacific Oceans: Implications of 30 70-Day Boundary Effects on MJO Development.

NASA Astrophysics Data System (ADS)

Gustafson, William I., Jr.; Weare, Bryan C.

2004-03-01

The results of an experiment designed to isolate the initiation phase of the Madden Julian oscillation (MJO) from 30 70-day boundary effects is presented. The technique used to accomplish this involves employing the fifth-generation Pennsylvania State University National Center for Atmospheric Research (PSU NCAR) Mesoscale Model (MM5), as first presented in the companion paper to this paper. Two runs, each 2 yr long, are integrated forward from 1 June 1990. The first run, called the control, uses the unmodified National Centers for Environmental Prediction (NCEP) NCAR reanalysis (NRA) dataset for boundary conditions. The second run, called the notched, uses the same NRA dataset for the boundary conditions, with the exception that all signals with periodicities in the 30 70-day range have been removed. Any signals in the 30 70-day range subsequently generated by the notched run are then solely due to signals generated from within the model domain or from signals entering through the domain boundaries with frequencies outside of the MJO band. Comparisons between 2-yr means from each run indicate that filtering the boundaries does not significantly modify the model climatology. The mean wind structure, thermodynamic state, and outgoing longwave radiation (OLR) are almost identical in the control and notched runs. A 30 70-day bandpass filter is used to isolate MJO-like signals in the runs. Comparisons of 30 70-day bandpassed zonal wind, moist static energy (MSE), and OLR reveal that the notched run develops many of the expected characteristics of MJO episodes, but with a weaker signal. Large-scale, organized structures develop that possess seasonal shifts in amplitude, mirroring observed MJO activity, have opposite wind directions in the upper and lower troposphere, and propagate eastward during most strong episodes. The results suggest that neither remnants from previous MJO episodes nor extratropical feedbacks within the MJO time band are necessary for MJO initiation. However, the control run is more organized than the notched run, implying that 30 70 signals outside the model domain influence the MJO signal. There is also some evidence that the recharge discharge mechanism plays a role in MJO formation.

Climate SPHINX: High-resolution present-day and future climate simulations with an improved representation of small-scale variability

NASA Astrophysics Data System (ADS)

Davini, Paolo; von Hardenberg, Jost; Corti, Susanna; Subramanian, Aneesh; Weisheimer, Antje; Christensen, Hannah; Juricke, Stephan; Palmer, Tim

2016-04-01

The PRACE Climate SPHINX project investigates the sensitivity of climate simulations to model resolution and stochastic parameterization. The EC-Earth Earth-System Model is used to explore the impact of stochastic physics in 30-years climate integrations as a function of model resolution (from 80km up to 16km for the atmosphere). The experiments include more than 70 simulations in both a historical scenario (1979-2008) and a climate change projection (2039-2068), using RCP8.5 CMIP5 forcing. A total amount of 20 million core hours will be used at end of the project (March 2016) and about 150 TBytes of post-processed data will be available to the climate community. Preliminary results show a clear improvement in the representation of climate variability over the Euro-Atlantic following resolution increase. More specifically, the well-known atmospheric blocking negative bias over Europe is definitely resolved. High resolution runs also show improved fidelity in representation of tropical variability - such as the MJO and its propagation - over the low resolution simulations. It is shown that including stochastic parameterization in the low resolution runs help to improve some of the aspects of the MJO propagation further. These findings show the importance of representing the impact of small scale processes on the large scale climate variability either explicitly (with high resolution simulations) or stochastically (in low resolution simulations).

Modulation of MJO-Associated North Pacific Storm Track Variation by the QBO

NASA Astrophysics Data System (ADS)

Wang, J.; Kim, H. M.; Chang, E. K. M.; Son, S. W.

2017-12-01

The North Pacific storm track (NPST) is a preferred region of extratropical synoptic-scale disturbances which plays a critical role in the mid-latitude weather and climate variability during the cool season (October to March). Extreme precipitation, heat/cold events, and sub-seasonal variation of the North Atlantic Oscillation (NAO) are found to be caused/modulated by the NPST. Thus investigating the variability of the NPST and the possible precursors for its variation is an important field of research. The Madden-Julian Oscillation (MJO) is the dominant intraseasonal mode in the tropics. A teleconnection between the MJO and the NPST has been realized recently. However, the MJO-NPST relationship shows a significant dependence on the background state. As previous studies primarily kept an eye on the modulation of El Niño Southern Oscillation (ENSO) on the MJO-NPST relationship, this study focuses on the role of the Quasi-Biennial Oscillation (QBO) because the QBO is suggested to make a much larger contribution to the interannual variability of the MJO than ENSO does. Results of this study show a regulation of the MJO-NPST relationship by different phases of the QBO. The amplitude of the MJO associated NPST variation is generally larger in the easterly phase of the QBO (EQBO) than in westerly phase of the QBO (WQBO). The pattern of the NPST variation also exhibits significant differences between the two QBO phases. The analysis of the underlying mechanism from the perspective of intraseasonal mean flow indicates an important role of the MJO associated baroclinicity in the enhanced amplitude of the NPST variation in EQBO years. On the other hand, the pattern differences in the NPST variation during different QBO phases result from changes in the intraseasonal baroclinic energy conversion and corresponding energy propagation. The results of this study suggest a consideration of the QBO impact in reproducing the MJO-midlatitudes teleconnection in general circulation models (GCMs). This study also provides a potential route for the improvement of the sub-seasonal prediction of extratropical storm activities.

Modulation of equatorial Pacific westerly/easterly wind events by the Madden-Julian oscillation and convectively-coupled Rossby waves

NASA Astrophysics Data System (ADS)

Puy, Martin; Vialard, J.; Lengaigne, M.; Guilyardi, E.

2016-04-01

Synoptic wind events in the equatorial Pacific strongly influence the El Niño/Southern Oscillation (ENSO) evolution. This paper characterizes the spatio-temporal distribution of Easterly (EWEs) and Westerly Wind Events (WWEs) and quantifies their relationship with intraseasonal and interannual large-scale climate variability. We unambiguously demonstrate that the Madden-Julian Oscillation (MJO) and Convectively-coupled Rossby Waves (CRW) modulate both WWEs and EWEs occurrence probability. 86 % of WWEs occur within convective MJO and/or CRW phases and 83 % of EWEs occur within the suppressed phase of MJO and/or CRW. 41 % of WWEs and 26 % of EWEs are in particular associated with the combined occurrence of a CRW/MJO, far more than what would be expected from a random distribution (3 %). Wind events embedded within MJO phases also have a stronger impact on the ocean, due to a tendency to have a larger amplitude, zonal extent and longer duration. These findings are robust irrespective of the wind events and MJO/CRW detection methods. While WWEs and EWEs behave rather symmetrically with respect to MJO/CRW activity, the impact of ENSO on wind events is asymmetrical. The WWEs occurrence probability indeed increases when the warm pool is displaced eastward during El Niño events, an increase that can partly be related to interannual modulation of the MJO/CRW activity in the western Pacific. On the other hand, the EWEs modulation by ENSO is less robust, and strongly depends on the wind event detection method. The consequences of these results for ENSO predictability are discussed.

Cloud-Radiative Driving of the Madden-Julian Oscillation as Seen by the A-Train

NASA Technical Reports Server (NTRS)

Del Genio, Anthony; Chen, Yonghua

2015-01-01

Cloud and water vapor radiative heating anomalies associated with convection may be an effective source of moist static energy driving the Madden-Julian Oscillation (MJO). In this paper five years of radiative heating profiles derived from CloudSat radar and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation data are analyzed to document radiative heating anomalies during the MJO. Atmospheric shortwave absorption and surface longwave radiation anomalies are of opposite sign and 10-20% as large as top-of-atmosphere outgoing longwave radiation (OLR) anomalies, confirming that OLR provides a useful estimate of the total column radiative heating anomaly. Positive anomalies generally peak about one week before the MJO peak and are smallest over the Indian Ocean. Anomalies over the Maritime Continent are strongest, and coincident with the MJO peak. Shortwave heating profile anomalies are about half as large as longwave anomalies in the active region of the MJO but generally of opposite sign; thus shortwave heating damps the longwave destabilization of the lower troposphere. The exception is the onset phase of the MJO, where shortwave and longwave heating anomalies due to thin cirrus are both positive in the upper troposphere and exert a stabilizing influence. Specific humidity anomalies in the middle troposphere reach 0.5 g kg(exp. -1), but the associated clear sky heating anomaly is very small. Radiative enhancement of column moist static energy becomes significant about 10 days before the MJO peak, when precipitation anomalies are still increasing, and then remains high after the MJO peak after precipitation has begun to decline.

Impact of the quasi-biennial oscillation on predictability of the Madden-Julian oscillation

NASA Astrophysics Data System (ADS)

Marshall, Andrew G.; Hendon, Harry H.; Son, Seok-Woo; Lim, Yuna

2017-08-01

The Madden-Julian oscillation (MJO) during boreal winter is observed to be stronger during the easterly phase of the quasi-biennial oscillation (QBO) than during the westerly phase, with the QBO zonal wind at 50 hPa leading enhanced MJO activity by about 1 month. Using 30 years of retrospective forecasts from the POAMA coupled model forecast system, we show that this strengthened MJO activity during the easterly QBO phase translates to improved prediction of the MJO and its convective anomalies across the tropical Indo-Pacific region by about 8 days lead time relative to that during westerly QBO phases. These improvements in forecast skill result not just from the fact that forecasts initialized with stronger MJO events, such as occurs during QBO easterly phases, have greater skill, but also from the more persistent behaviour of the MJO for a similar initial amplitude during QBO easterly phases as compared to QBO westerly phases. The QBO is thus an untapped source of subseasonal predictability that can provide a window of opportunity for improved prediction of global climate.

Tracking the MJO Convection and its Impact on the Diurnal Cycle over the Maritime Continent Using Satellite Observations

NASA Astrophysics Data System (ADS)

Kerns, B. W.; Chen, S. S.

2017-12-01

The Indo-Pacific Maritime Continent (MC) is the most active convection center in the tropics, and the most important modes of variability are the diurnal cycle and the Madden-Julian Oscillation (MJO). Previous studies have shown that the MC has strong diurnal variability compared with the rest of the tropics, and the diurnal cycle of convection over the MC is amplified during the passage of an MJO. One outstanding science question is how the passage of the active MJO affects the diurnal cycle. The atmospheric, upper ocean, and land surface forcing factors contributing to the diurnal cycle need to be clarified. In order to address this, large scale precipitation tracking (LPT) is used to identify MJO active and suppressed periods for 2000-2015. To document the diurnal cycle of convection during the active and suppressed periods, TRMM/GPM and mesoscale cloud cluster tracking are used. Finally, the LPT tracking is used to composite the satellite-estimated surface wind, humidity, temperature, cloud cover, and soil moisture over the islands for active versus suppressed MJO periods. In active MJO periods, the diurnal convection in the surrounding marginal seas is enhanced and the diurnal convection over land is decreased. The islands of the MC have greater soil moisture, more cloud cover, and do not warm up as much during the day, leading to a weaker afternoon maximum over land. But how is nocturnal convection over the sea increased? The largest, most mature convective cloud systems are found over the marginal seas in the early morning. This is hypothesized to mainly be a consequence of the longer life cycle of convective systems in the favorable large-scale active MJO. The propagation of the MJO across the MC is facilitated by the enhanced nocturnal deep convection over the sea. In contrast, In the suppressed period the convection is mostly daytime forced convection over land which is locked to the terrain.

MJO prediction using the sub-seasonal to seasonal forecast model of Beijing Climate Center

NASA Astrophysics Data System (ADS)

Liu, Xiangwen; Wu, Tongwen; Yang, Song; Li, Tim; Jie, Weihua; Zhang, Li; Wang, Zaizhi; Liang, Xiaoyun; Li, Qiaoping; Cheng, Yanjie; Ren, Hongli; Fang, Yongjie; Nie, Suping

2017-05-01

By conducting several sets of hindcast experiments using the Beijing Climate Center Climate System Model, which participates in the Sub-seasonal to Seasonal (S2S) Prediction Project, we systematically evaluate the model's capability in forecasting MJO and its main deficiencies. In the original S2S hindcast set, MJO forecast skill is about 16 days. Such a skill shows significant seasonal-to-interannual variations. It is found that the model-dependent MJO forecast skill is more correlated with the Indian Ocean Dipole (IOD) than with the El Niño-Southern Oscillation. The highest skill is achieved in autumn when the IOD attains its maturity. Extended skill is found when the IOD is in its positive phase. MJO forecast skill's close association with the IOD is partially due to the quickly strengthening relationship between MJO amplitude and IOD intensity as lead time increases to about 15 days, beyond which a rapid weakening of the relationship is shown. This relationship transition may cause the forecast skill to decrease quickly with lead time, and is related to the unrealistic amplitude and phase evolutions of predicted MJO over or near the equatorial Indian Ocean during anomalous IOD phases, suggesting a possible influence of exaggerated IOD variability in the model. The results imply that the upper limit of intraseasonal predictability is modulated by large-scale external forcing background state in the tropical Indian Ocean. Two additional sets of hindcast experiments with improved atmosphere and ocean initial conditions (referred to as S2S_IEXP1 and S2S_IEXP2, respectively) are carried out, and the results show that the overall MJO forecast skill is increased to 21-22 days. It is found that the optimization of initial sea surface temperature condition largely accounts for the increase of the overall MJO forecast skill, even though the improved initial atmosphere conditions also play a role. For the DYNAMO/CINDY field campaign period, the forecast skill increases to 27 days in S2S_IEXP2. Nevertheless, even with improved initialization, it is still difficult for the model to predict MJO propagation across the western hemisphere-western Indian Ocean area and across the eastern Indian Ocean-Maritime Continent area. Especially, MJO prediction is apparently limited by various interrelated deficiencies (e.g., overestimated IOD, shorter-than-observed MJO life cycle, Maritime Continent prediction barrier), due possibly to the model bias in the background moisture field over the eastern Indian Ocean and Maritime Continent. Thus, more efforts are needed to correct the deficiency in model physics in this region, in order to overcome the well-known Maritime Continent predictability barrier.

Time-lagged response of the Antarctic atmosphere to tropical MJO convection

NASA Astrophysics Data System (ADS)

Henderson, G. R.; Barrett, B.

2017-12-01

Intraseasonal tropical climate variability has important implications on mid- and high- latitude climate, and in recent studies has been shown to modulate a number of weather processes in the Northern Hemisphere, such as snow depth, sea ice concentration, precipitation, atmospheric rivers, and air temperature. In such studies, the leading mode of tropical intraseasonal variability, the Madden-Julian Oscillation (MJO), has tended to lag tropical convection by approximately 7 days. However, no such consensus exists when considering the relationship and lag between the MJO and the Antarctic atmosphere. This study builds on previous work by further examining the time-lagged response of Southern Hemisphere tropospheric circulation to tropical MJO forcing, with specific focus on the latitude belt associated with the Antarctic Oscillation, during the months of June (Austral winter) and December (Austral summer) using NCEP-DOE Reanalysis 2 data for the years 1970-2016. Principal findings indicate that the time lag with strongest height anomalies depends on both the location of the MJO convection (e.g., the MJO phase) and the season, and that the lagged height anomalies in the Antarctic atmosphere are fairly consistent across different vertical levels and latitudinal bands. In addition, certain MJO phases in December displayed lagged height anomalies indicative of blocking-type atmospheric patterns, with an approximate wavenumber of 4, whereas in June most phases were associated with progressive height anomaly centers displaying a wavenumber-3 type pattern.

Contemporary Model Fidelity over the Maritime Continent: Examination of the Diurnal Cycle, Synoptic, Intraseasonal and Seasonal Variability

NASA Astrophysics Data System (ADS)

Baranowski, D.; Waliser, D. E.; Jiang, X.

2016-12-01

One of the key challenges in subseasonal weather forecasting is the fidelity in representing the propagation of the Madden-Julian Oscillation (MJO) across the Maritime Continent (MC). In reality both propagating and non-propagating MJO events are observed, but in numerical forecast the latter group largely dominates. For this study, comprehensive model performances are evaluated using metrics that utilize the mean precipitation pattern and the amplitude and phase of the diurnal cycle, with a particular focus on the linkage between a model's local MC variability and its fidelity in representing propagation of the MJO and equatorial Kelvin waves across the MC. Subseasonal to seasonal variability of mean precipitation and its diurnal cycle in 20 year long climate simulations from over 20 general circulation models (GCMs) is examined to benchmark model performance. Our results show that many models struggle to represent the precipitation pattern over complex Maritime Continent terrain. Many models show negative biases of mean precipitation and amplitude of its diurnal cycle; these biases are often larger over land than over ocean. Furthermore, only a handful of models realistically represent the spatial variability of the phase of the diurnal cycle of precipitation. Models tend to correctly simulate the timing of the diurnal maximum of precipitation over ocean during local solar time morning, but fail to acknowledge influence of the land, with the timing of the maximum of precipitation there occurring, unrealistically, at the same time as over ocean. The day-to-day and seasonal variability of the mean precipitation follows observed patterns, but is often unrealistic for the diurnal cycle amplitude. The intraseasonal variability of the amplitude of the diurnal cycle of precipitation is mainly driven by model's ability (or lack of) to produce eastward propagating MJO-like signal. Our results show that many models tend to decrease apparent air-sea contrast in the mean precipitation and diurnal cycle of precipitation patterns over the Maritime Continent. As a result, the complexity of those patterns is heavily smoothed, to such an extent in some models that the Maritime Continent features and imprint is almost unrecognizable relative to the eastern Indian Ocean or Western Pacific.

Exploring the Propagation of the Madden-Julian Oscillation (MJO) across the Maritime Continent

DTIC Science & Technology

orthogonal function analysis was developed to identify phases of thestratospheric Quasi-Biennial Oscillation (QBO) by direction and altitude of zonal wind...centers. In the troposphere, positive specifichumidity anomalies within the MJO active envelope and a near-surface moisture foot region in the lower troposphere east of the activeenvelope favor MJO propagation.

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

None

Many storms around the world have roots in the Indian Ocean, where they are churned up by the atmospheric process called the Madden-Julian Oscillation (MJO). PNNL is working to unlock the secrets of the MJO, particularly how it initiates in the Indian Ocean every 30-60 days. Better prediction of the MJO will help resource managers, weather forecasters and people worldwide better prepare for its effects.

Modulation of Atlantic Aerosols by the Madden-Julian Oscillation

NASA Technical Reports Server (NTRS)

Tian, B.; Waliser, D. E.; Kahn, Ralph A.; Wong, S.

2010-01-01

Much like the better-known EI Nino-Southern Oscillation, the Madden-Julian Oscillation (MJO) is a global-scale atmospheric phenomenon. The MJO involves periodic, systematic changes in the distribution of clouds and precipitation over the western Pacific and Indian oceans, along with differences in wind intensity over even more extensive areas, including the north and subtropical Atlantic Ocean. The lead authors of this paper developed a sophisticated mathematical technique for mapping the spatial and temporal behavior of changes in the atmosphere produced by the MJO. In a previous paper, we applied this technique to search for modulation of airborne particle amount in the eastern hemisphere associated with the "wet" (cloudy) vs. "dry" phases of the MJO. The study used primarily AVHRR, MODIS, and TOMS satellite-retrieved aerosol amount, but concluded that other factors, such as cloud contamination of the satellite signals, probably dominated the observed variations. The current paper looks at MJO modulation of desert dust transport eastward across the Atlantic from northern Africa, a region much less subject to systematic cloud contamination than the eastern hemisphere areas studied previously. In this case, a distinct aerosol signal appears, showing that dust is transported westward much more effectively during the MJO phase that favors westward-flowing wind, and such transport is suppressed when the MJO reduces these winds. Aside form the significant achievement in identifying such an effect, the result implies that an important component of global dust transport can be predicted based on the phase of the MJO. As a consequence, the impact of airborne dust on storm development in the Atlantic, and on dust deposition downwind of the desert sources, can also be predicted and more accurately modeled.

On the relationship between the Madden-Julian Oscillation and 2 m air temperature over central Asia in boreal winter

NASA Astrophysics Data System (ADS)

Zhou, Yang; Lu, Youyu; Yang, Ben; Jiang, Jing; Huang, Anning; Zhao, Yong; La, Mengke; Yang, Qing

2016-11-01

Linear regression is used to explore the relationship between the Madden-Julian oscillation (MJO) and 2 m air temperature (T2M) over central Asia in boreal winter during 1979-2012. During MJO phases 3 and 4 (7 and 8), T2M anomalies exhibit a significantly strong, negative (positive) response to the MJO from the Arabian Sea to northwestern China. The anomalies of T2M are essentially influenced by surface net downward long (Ldown) and shortwave radiations, which are caused by the changes in total cloud cover (TCC) and low-level tropospheric air temperature. The anomalies of Ldown that are caused by TCC account for 20-65% of total Ldown. The remaining anomalies of total Ldown are explained by low-level air temperature changes. The 850 hPa air temperature (T850) tendency is mainly affected by the vertical motion over central Asia during MJO phases 1, 2, 4-6, and 8, as well as over northern India during phases 3 and 7. Over Saudi Arabia, Afghanistan, Pakistan, Kazakhstan, and northwestern China, the anomalies of T850 tendency are mainly explained by the temperature advection during phases 3 and 7. TCC and vertical motion are affected by the evolution of the MJO event. The cyclonic (anticyclonic) circulation related to the MJO over central Asia during phases 3 and 4 (7 and 8) causes the transport of cold (warm) air over central Asia. The MJO can be a useful intraseasonal signal to predict winter T2M over central Asia, where temperatures would be colder (warmer) than normal during MJO phases 3 and 4 (7 and 8).

A composite study of the MJO influence on the surface air temperature and precipitation over the Continental United States

NASA Astrophysics Data System (ADS)

Zhou, Shuntai; L'Heureux, Michelle; Weaver, Scott; Kumar, Arun

2012-04-01

The influence of the MJO on the continental United States (CONUS) surface air temperature (SAT) and precipitation is examined based on 30 years of daily data from 1979-2008. Composites are constructed for each of the eight phases of the Wheeler-Hendon MJO index over 12 overlapping three-month seasons. To ensure that the MJO signal is distinguished from other patterns of climate variability, several steps are taken: (a) only days classified as "MJO events" are used in the composites, (b) statistical significance of associated composites is assessed using a Monte Carlo procedure, and (c) intraseasonal frequencies are matched to the unfiltered data. Composites of other fields are also shown in order to examine how the SAT and precipitation anomalies are associated with large-scale circulations providing a link between the tropics and extratropics. The strongest and most significant MJO effects on SAT are found during the northern winter seasons. When enhanced convection is located over the equatorial Indian Ocean, below-average SAT tends to occur in New England and the Great Lakes region. As enhanced tropical convection shifts over the Maritime continent, above-average SAT appears in the eastern states of the US from Maine to Florida. The MJO influence on precipitation is also significant during northern winter seasons. When enhanced convection is located over the Maritime continent, more precipitation is observed in the central plains of the US. Enhanced precipitation also occurs over the west coast of the US when convective activity is stronger over the Indian Ocean. During the northern summer and fall, the MJO impact on precipitation is mainly significant at lower latitudes, over Mexico and southeastern US.

The Diurnal Cycle over the Maritime Continent and its Interaction with the MJO

NASA Astrophysics Data System (ADS)

Matthews, A. J.; Peatman, S.; Baranowski, D. B.; Stevens, D. P.; Heywood, K. J.; Flatau, P. J.; Schmidtko, S.

2014-12-01

The complex land-sea distribution and topography of the maritime continent acts to disrupt or even completely block the eastward propagation of the Madden-Julian Oscillation (MJO) from the Indian Ocean to the western Pacific. This leads to changes in tropical latent heat release and subsequent impacts on global circulation. Convection over the maritime continent is dominated by the diurnal cycle. Where the mean diurnal cycle is strong (over the islands and surrounding seas), 80% of the MJO precipitation signal in the maritime continent is accounted for by changes in the amplitude of the diurnal cycle. The canonical view of the MJO as the smooth eastward propagation of a large-scale precipitation envelope also breaks down over the islands of the Maritime Continent. Instead, a vanguard of precipitation jumps ahead of the main body by approximately 6 days or 2000 km. Hence, there can be enhanced precipitation over Sumatra, Borneo or New Guinea when the large-scale MJO envelope over the surrounding ocean is one of suppressed precipitation. This behaviour is discussed in terms of an interaction between the diurnal cycle and the MJO circulation. The diurnal cycle is also strong in the ocean. Seaglider measurements taken during the CINDY/DYNAMO campaign show the existence of a diurnal warm layer in the upper few metres of the ocean. This has a significant effect on the surface fluxes, of an order of Watts per square metre. The diurnal warm layer is favoured during the inactive phase of the MJO and may act to help precondition the atmosphere to convection. The activities of the MJO Task Force and Subseasonal to Seasonal Prediction project will be discussed in this context.

Outcomes and challenges of global high-resolution non-hydrostatic atmospheric simulations using the K computer

NASA Astrophysics Data System (ADS)

Satoh, Masaki; Tomita, Hirofumi; Yashiro, Hisashi; Kajikawa, Yoshiyuki; Miyamoto, Yoshiaki; Yamaura, Tsuyoshi; Miyakawa, Tomoki; Nakano, Masuo; Kodama, Chihiro; Noda, Akira T.; Nasuno, Tomoe; Yamada, Yohei; Fukutomi, Yoshiki

2017-12-01

This article reviews the major outcomes of a 5-year (2011-2016) project using the K computer to perform global numerical atmospheric simulations based on the non-hydrostatic icosahedral atmospheric model (NICAM). The K computer was made available to the public in September 2012 and was used as a primary resource for Japan's Strategic Programs for Innovative Research (SPIRE), an initiative to investigate five strategic research areas; the NICAM project fell under the research area of climate and weather simulation sciences. Combining NICAM with high-performance computing has created new opportunities in three areas of research: (1) higher resolution global simulations that produce more realistic representations of convective systems, (2) multi-member ensemble simulations that are able to perform extended-range forecasts 10-30 days in advance, and (3) multi-decadal simulations for climatology and variability. Before the K computer era, NICAM was used to demonstrate realistic simulations of intra-seasonal oscillations including the Madden-Julian oscillation (MJO), merely as a case study approach. Thanks to the big leap in computational performance of the K computer, we could greatly increase the number of cases of MJO events for numerical simulations, in addition to integrating time and horizontal resolution. We conclude that the high-resolution global non-hydrostatic model, as used in this five-year project, improves the ability to forecast intra-seasonal oscillations and associated tropical cyclogenesis compared with that of the relatively coarser operational models currently in use. The impacts of the sub-kilometer resolution simulation and the multi-decadal simulations using NICAM are also reviewed.

Regulation of H2O and CO in Tropical Tropopause Layer by the Madden-Julian Oscillation

NASA Technical Reports Server (NTRS)

Wong, Sun; Dessler, Andrew E.

2007-01-01

Impacts of the Madden-Julian oscillation (MJO) on the water vapor (H2O) and carbon monoxide (CO) abundances in the tropical tropopause layer (TTL) are investigated using Aura Microwave Limb Sounder (MLS) data for November 2004 to May 2005. The effects of the eastward propagation of MJO on H2O and CO abundances in the TTL are evident. Deep convection transports H20 into the upper troposphere up to about the 355-365 K level. Around the 365-375 K level, a dry anomaly is collocated with a cold anomaly, which is above a warm anomaly located near the region of convection enhancement. Tropical mean H20 at 375 K is regulated by the MJO through convection enhancement and coherent with the local MJO-related temperature variation. The locations of dehydration follow the eastward propagation of convection enhancement and its area extent depends on the phase of the MJO. Enhancement of deep convection associated with the MJO also injects CO from the lower troposphere to the TTL up to 375 K. However, tropical mean CO at 375 K responds instantaneously to the large injection event occurring over the African continent.

Tribological evaluation of hexagonal boron nitride in modified jatropha oil as sustainable metalworking fluid

NASA Astrophysics Data System (ADS)

Talib, Norfazillah; Rahim, Erween Abd.; Nasir, Ramdziah Md.

2017-11-01

The used of metalworking fluids (MWFs) from petroleum-based oil during machining process contributed negative impact to the humans and environment. Therefore, bio-based oil from vegetable oil was recently explored as an alternative solution to petroleum-based oil to implement sustainable manufacturing process. In this study, modified jatropha oil (MJO5) with and without hexagonal boron nitride (hBN) particles were evaluated through friction and wear test and orthogonal cutting performance in comparison with synthetic ester (SE). MJO5 were mixed with hBN particles at various concentrations (i.e. 0.05, 0.1 and 0.5wt.%). Experimental results showed that the addition of 0.05wt.% of hBN particles in MJO5 (MJO5a) provided lowest coefficient of friction (COF) and smallest wear scar diameter (WSD). MJO5a has the best anti-friction ability by reducing the cutting force and cutting temperature which related to the formation of thinner chips and small tool-chip contact length. MJO5a is the best substitute to SE as sustainable MWFs in the machining operation in regards to the environmental and health concern.

Combined effect of MJO, ENSO and IOD on the intraseasonal variability of northeast monsoon rainfall over south peninsular India

NASA Astrophysics Data System (ADS)

Sreekala, P. P.; Rao, S. Vijaya Bhaskara; Rajeevan, K.; Arunachalam, M. S.

2018-02-01

The present study has examined the combined effect of MJO, ENSO and IOD on the intraseasonal and interannual variability of northeast monsoon rainfall over south peninsular India. The study has revealed that the intraseasonal variation of daily rainfall over south peninsular India during NEM season is associated with various phases of eastward propagating MJO life cycle. Positive rainfall anomaly over south peninsular India and surrounding Indian Ocean (IO) is observed during the strong MJO phases 2, 3 and 4; and negative rainfall anomaly during the strong MJO phases 5,6,7,8 and 1. Above normal (below normal) convection over south peninsular India and suppressed convection over east Indian and West Pacific Ocean, high pressure (low pressure) anomaly over West Pacific Ocean, Positive (negative) SST anomalies over equatorial East and Central Pacific Ocean and easterly wind anomaly (westerly anomaly) over equatorial Indian Ocean are the observed features during the first three MJO (5, 6, 7) phases and all these features are observed in the excess (drought) NEMR composite. This suggests that a similar mode of physical mechanism is responsible for the intraseasonal and interannual variability of northeast monsoon rainfall. The number of days during the first three phases (last four phases) of MJO, where the enhanced convection and positive rainfall anomaly is over Indian Ocean (East Indian ocean and West Pacific Ocean), is more (less) during El Nino and IOD years and less during La Nina and NIOD years and vice versa. The observed excess (deficit) rainfall anomaly over west IO and south peninsular India and deficit (excess) rainfall anomaly over east IO including Bay of Bengal and West Pacific Ocean suggest that the more (less) number of first three phases during El Nino and IOD (La Nina and Negative IOD) is due to the interaction between eastward moving MJO and strong easterlies over equatorial IO present during El Nino and IOD years. This interaction would inhibit the development of long duration MJO and would result in short duration high frequency MJO type which confined over Indian Ocean and south peninsular India and hence make all the El Nino and IOD years to be excess rainfall years for NEM season.

Seasonality and mechanisms of tropical intraseasonal oscillations

NASA Astrophysics Data System (ADS)

Hazra, Abheera; Krishnamurthy, V.

2018-01-01

This study has compared the monsoon intraseasonal oscillation (MISO) during the boreal summer and Madden Julian Oscillation (MJO) during the boreal winter. Based on MISO and MJO in high-resolution three-dimensional diabatic heating, the possible mechanisms are discussed through observational analyses of dynamical and thermodynamical variables. The MISO and MJO are extracted as nonlinear oscillations during boreal summer and winter, respectively, by applying multi-channel singular spectrum analysis on daily anomalies of diabatic heating over the Indo-Pacific region. Lead and lag relations among moisture, temperature and surface fields relative to diabatic heating are analyzed to compare the mechanisms of MISO and MJO. While both the oscillations show eastward propagation, MISO has a strong northward propagation and MJO has a weak southward propagation as well. The analysis shows that MJO and MISO are essentially driven by the same mechanisms but with some difference in the meridional propagation. The westerly shear leads the diabatic heating, while the vorticity has weak correlation. Large-scale circulation creates positive moisture preconditioning before convection and negative moisture preconditioning before suppressed conditions. A positive lower level horizontal advection of temperature and upper level temperature tendencies lead the convective state while a negative lower level horizontal advection of temperature and upper level temperature tendencies lead the suppressed state. There is positive feedback from the SST to atmosphere. The difference in the meridional propagation of MISO and MJO is hypothesized to be because of the different differential heating meridionally during the two seasons.

Predictability and Coupled Dynamics of MJO During DYNAMO

DTIC Science & Technology

2015-02-03

with two complementary atmosphere-only simulations with modified SST conditions. One WRF simulation is forced with the persistent initial SST, lacking...we have contributed to the following subset of accomplishments of the muhi-institutional team: a. Run SC0AR2 ( WRF -ROMS) in downscaling mode for the 2...Regional (SCOAR) Model Seo et al. (2007; 2014, J. Climate), http://scoar.wlklspaces.cotn p^ WRF /RSM C^ ROMS {j^TWo-way coupling ^ One

Initiation of the Madden-Julian Oscillation

ScienceCinema

None

2018-01-16

Many storms around the world have roots in the Indian Ocean, where they are churned up by the atmospheric process called the Madden-Julian Oscillation (MJO). PNNL is working to unlock the secrets of the MJO, particularly how it initiates in the Indian Ocean every 30-60 days. Better prediction of the MJO will help resource managers, weather forecasters and people worldwide better prepare for its effects.

Predictability and Coupled Dynamics of MJO During DYNAMO

DTIC Science & Technology

2013-09-30

1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Predictability and Coupled Dynamics of MJO During DYNAMO ... DYNAMO time period. APPROACH We are working as a team to study MJO dynamics and predictability using several models as team members of the ONR DRI...associated with the DYNAMO experiment. This is a fundamentally collaborative proposal that involves close collaboration with Dr. Hyodae Seo of the

The Influence of the Madden-Julian Oscillation (mjo) on Extreme Rainfall Over the Central and Southern Peruvian Andes

NASA Astrophysics Data System (ADS)

Heidinger, H.; Jones, C.; Carvalho, L. V.

2015-12-01

Extreme rainfall is important for the Andean region because of the large contribution of these events to the seasonal totals and consequent impacts on water resources for agriculture, water consumption, industry and hydropower generation, as well as the occurrence of floods and landslides. Over Central and Southern Peruvian Andes (CSPA), rainfall exceeding the 90th percentile contributed between 44 to 100% to the total Nov-Mar 1979-2010 rainfall. Additionally, precipitation from a large majority of stations in the CSPA exhibits statistically significant spectral peaks on intraseasonal time-scales (20 to 70 days). The Madden-Julian Oscillation (MJO) is the most important intraseasonal mode of atmospheric circulation and moist convection in the tropics and the occurrence of extreme weather events worldwide. Mechanisms explaining the relationships between the MJO and precipitation in the Peruvian Andes have not been properly described yet. The present study examines the relationships between the activity and phases of the MJO and the occurrence of extreme rainfall over the CSPA. We found that the frequency of extreme rainfall events increase in the CSPA when the MJO is active. MJO phases 5, 6 and 7 contribute to the overall occurrence of extreme rainfall events over the CSPA. However, how the MJO phases modulate extreme rainfall depends on the location of the stations. For instance, extreme precipitation (above the 90th percentile) in stations in the Amazon basin are slightly more sensitive to phases 2, 3 and 4; the frequency of extremes in stations in the Pacific basin increases in phases 5, 6 and 7 whereas phase 2, 3 and 7 modulates extreme precipitation in stations in the Titicaca basin. Greater variability among stations is observed when using the 95th and 99th percentiles to identify extremes. Among the main mechanisms that explain the increase in extreme rainfall events in the Peruvian Andes is the intensification of the easterly moisture flux anomalies, which are favored during certain phases of the MJO. Here dynamical mechanisms linking the MJO to the occurrence of extreme rainfall in stations in the Peruvian Andes are investigated using composites of integrated moisture flux and geopotential height anomalies.

The Influence of Atmosphere-Ocean Interaction on MJO Development and Propagation

DTIC Science & Technology

2012-09-30

feedbacks and their influence on MJO development, and for forecasting of air sea interaction in the Indian Ocean basin and its influence on MJO. The...indicating precipitation maximum over the DYNAMO area and the red line indicating the precipitation anomaly west of Sumatra . The corresponding EOF...characterizing the November episode, relatively weaker October episode and convection situated in the eastern part of the Indian Ocean basin in December

Prediction of North Pacific Height Anomalies During Strong Madden-Julian Oscillation Events

NASA Astrophysics Data System (ADS)

Kai-Chih, T.; Barnes, E. A.; Maloney, E. D.

2017-12-01

The Madden Julian Oscillation (MJO) creates strong variations in extratropical atmospheric circulations that have important implications for subseasonal-to-seasonal prediction. In particular, certain MJO phases are characterized by a consistent modulation of geopotential height in the North Pacific and adjacent regions across different MJO events. Until recently, only limited research has examined the relationship between these robust MJO tropical-extratropical teleconnections and model prediction skill. In this study, reanalysis data (MERRA and ERA-Interim) and ECMWF ensemble hindcasts are used to demonstrate that robust teleconnections in specific MJO phases and time lags are also characterized by excellent agreement in the prediction of geopotential height anoma- lies across model ensemble members at forecast leads of up to 3 weeks. These periods of enhanced prediction capabilities extend the possibility for skillful extratropical weather prediction beyond traditional 10-13 day limits. Furthermore, we also examine the phase dependency of teleconnection robustness by using Linear Baroclinic Model (LBM) and the result is consistent with the ensemble hindcasts : the anomalous heating of MJO phase 2 (phase 6) can consistently generate positive (negative) geopotential height anomalies around the extratropical Pacific with a lead of 15-20 days, while other phases are more sensitive to the variaion of the mean state.

Major modes of short-term climate variability in the newly developed NUIST Earth System Model (NESM)

NASA Astrophysics Data System (ADS)

Cao, Jian; Wang, Bin; Xiang, Baoqiang; Li, Juan; Wu, Tianjie; Fu, Xiouhua; Wu, Liguang; Min, Jinzhong

2015-05-01

A coupled earth system model (ESM) has been developed at the Nanjing University of Information Science and Technology (NUIST) by using version 5.3 of the European Centre Hamburg Model (ECHAM), version 3.4 of the Nucleus for European Modelling of the Ocean (NEMO), and version 4.1 of the Los Alamos sea ice model (CICE). The model is referred to as NUIST ESM1 (NESM1). Comprehensive and quantitative metrics are used to assess the model's major modes of climate variability most relevant to subseasonal-to-interannual climate prediction. The model's assessment is placed in a multi-model framework. The model yields a realistic annual mean and annual cycle of equatorial SST, and a reasonably realistic precipitation climatology, but has difficulty in capturing the spring-fall asymmetry and monsoon precipitation domains. The ENSO mode is reproduced well with respect to its spatial structure, power spectrum, phase locking to the annual cycle, and spatial structures of the central Pacific (CP)-ENSO and eastern Pacific (EP)-ENSO; however, the equatorial SST variability, biennial component of ENSO, and the amplitude of CP-ENSO are overestimated. The model captures realistic intraseasonal variability patterns, the vertical-zonal structures of the first two leading predictable modes of Madden-Julian Oscillation (MJO), and its eastward propagation; but the simulated MJO speed is significantly slower than observed. Compared with the T42 version, the high resolution version (T159) demonstrates improved simulation with respect to the climatology, interannual variance, monsoon-ENSO lead-lag correlation, spatial structures of the leading mode of the Asian-Australian monsoon rainfall variability, and the eastward propagation of the MJO.

Relationships between radiation, clouds, and convection during DYNAMO

NASA Astrophysics Data System (ADS)

Ciesielski, Paul E.; Johnson, Richard H.; Jiang, Xianan; Zhang, Yunyan; Xie, Shaocheng

2017-03-01

The relationships between radiation, clouds, and convection on an intraseasonal time scale are examined with data taken during the Dynamics of the Madden-Julian Oscillation (MJO) field campaign. Specifically, column-net, as well as vertical profiles of radiative heating rates, computed over Gan Island in the central Indian Ocean (IO) are used along with an objective analysis of large-scale fields to examine three MJO events that occurred during the 3 month period (October to December 2011) over this region. Longwave (LW) and shortwave radiative heating rates exhibit tilted structures, reflecting radiative effects associated with the prevalence of shallow cumulus during the dry, suppressed MJO phase followed by increasing deep convection leading into the active phase. As the convection builds going into the MJO active phase, there are increasingly top-heavy anomalous radiative heating rates while the column-net radiative cooling rate progressively decreases. Temporal fluctuations in the cloud radiative forcing, being quite sensitive to changes in high cloudiness, are dominated by LW effects with an intraseasonal variation of 0.4-0.6 K/d. While both the water vapor and cloud fields are inextricably linked, it appears that the tilted radiative structures are more related to water vapor effects. The intraseasonal variation of column-net radiative heating enhances the convective signal in the mean by 20% with a minimum in this enhancement 10 days prior to peak MJO rainfall and maximum 7 days after. This suggests that as MJO convective envelope weakens over the central IO, cloud-radiative feedbacks help maintain the mature MJO as it moves eastward.

Relationships between radiation, clouds, and convection during DYNAMO.

PubMed

Ciesielski, Paul E; Johnson, Richard H; Jiang, Xianan; Zhang, Yunyan; Xie, Shaocheng

2017-03-16

The relationships between radiation, clouds, and convection on an intraseasonal time scale are examined with data taken during the Dynamics of the Madden-Julian Oscillation (MJO) field campaign. Specifically, column-net, as well as vertical profiles of radiative heating rates, computed over Gan Island in the central Indian Ocean (IO) are used along with an objective analysis of large-scale fields to examine three MJO events that occurred during the 3 month period (October to December 2011) over this region. Longwave (LW) and shortwave radiative heating rates exhibit tilted structures, reflecting radiative effects associated with the prevalence of shallow cumulus during the dry, suppressed MJO phase followed by increasing deep convection leading into the active phase. As the convection builds going into the MJO active phase, there are increasingly top-heavy anomalous radiative heating rates while the column-net radiative cooling rate < Q r > progressively decreases. Temporal fluctuations in the cloud radiative forcing, being quite sensitive to changes in high cloudiness, are dominated by LW effects with an intraseasonal variation of ~0.4-0.6 K/d. While both the water vapor and cloud fields are inextricably linked, it appears that the tilted radiative structures are more related to water vapor effects. The intraseasonal variation of column-net radiative heating < Q r > enhances the convective signal in the mean by ~20% with a minimum in this enhancement ~10 days prior to peak MJO rainfall and maximum ~7 days after. This suggests that as MJO convective envelope weakens over the central IO, cloud-radiative feedbacks help maintain the mature MJO as it moves eastward.

Relationships between radiation, clouds, and convection during DYNAMO

PubMed Central

Ciesielski, Paul E.; Johnson, Richard H.; Jiang, Xianan; Zhang, Yunyan; Xie, Shaocheng

2017-01-01

The relationships between radiation, clouds, and convection on an intraseasonal time scale are examined with data taken during the Dynamics of the Madden-Julian Oscillation (MJO) field campaign. Specifically, column-net, as well as vertical profiles of radiative heating rates, computed over Gan Island in the central Indian Ocean (IO) are used along with an objective analysis of large-scale fields to examine three MJO events that occurred during the 3 month period (October to December 2011) over this region. Longwave (LW) and shortwave radiative heating rates exhibit tilted structures, reflecting radiative effects associated with the prevalence of shallow cumulus during the dry, suppressed MJO phase followed by increasing deep convection leading into the active phase. As the convection builds going into the MJO active phase, there are increasingly top-heavy anomalous radiative heating rates while the column-net radiative cooling rate progressively decreases. Temporal fluctuations in the cloud radiative forcing, being quite sensitive to changes in high cloudiness, are dominated by LW effects with an intraseasonal variation of ~0.4–0.6 K/d. While both the water vapor and cloud fields are inextricably linked, it appears that the tilted radiative structures are more related to water vapor effects. The intraseasonal variation of column-net radiative heating enhances the convective signal in the mean by ~20% with a minimum in this enhancement ~10 days prior to peak MJO rainfall and maximum ~7 days after. This suggests that as MJO convective envelope weakens over the central IO, cloud-radiative feedbacks help maintain the mature MJO as it moves eastward. PMID:29082119

Coupled Ocean-Atmosphere Dynamics and Predictability of MJO’s

DTIC Science & Technology

2012-09-30

developed. b. Modeling study of the mechanisms of surface chlorophyll modulation by the MJO Previous studies analyzed ocean color satellite data and...to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data ...with Gupta, SIO) e. Run SCOAR2 in downscaling mode for the 2nd MJO event during the DYNAMO period (led by Seo, WHOI, with Miller, SIO) f. Run and

The Influence of Atmosphere-Ocean Interaction on MJO Development and Propagation

DTIC Science & Technology

2014-09-30

evaluate modeling results and process studies. The field phase of this project is associated with DYNAMO , which is the US contribution to the...influence on ocean temperature 4. Extended run for DYNAMO with high vertical resolution NCOM RESULTS Summary of project results The work funded...model experiments of the November 2011 MJO – the strongest MJO episode observed during the DYNAMO . The previous conceptual model that was based on TOGA

Links Between the Madden-Julian Oscillation and Severe Convective Storms in the U.S.

NASA Astrophysics Data System (ADS)

Barrett, B.

2015-12-01

Recent research has shown a tendency for severe convective storms to vary intraseasonally, including by phase of the Madden-Julian Oscillation (MJO). The MJO is the leading mode of atmospheric intraseasonal variability and is characterized by large regions (1000-5000 km) of anomalous convective activity that generally propagate eastward along the equator. Anomalous upper-troposphere heating associated with this convection generates poleward-propagating Rossby waves that interact with the preexisting extratropical circulation. The projection of this interaction onto the synoptic scale - via the favoring of troughs and ridges at certain positions - is the hypothesized mechanism by which the MJO modulates severe convection. However, one unexplored aspect of this modulation is the extent to which severe convection in winter and early-spring months, especially Jan-Mar, may be influenced by different phases of the MJO. While climatologically rarer than events later in spring, severe thunderstorms in winter and early spring still have potential to be high-impact weather events, especially as they often occur in populated areas of the southeast U.S. that have shown more vulnerability than other regions such as the southern or central plains. Results from other studies (not necessarily focused on the question of severe convective storms) have indicated statistically significant modulation of upper- and mid-tropospheric circulation (from 200 hPa to 700 hPa), surface temperature, and sea level pressure. Thus, it is possible that the MJO's influence also extends to severe storms, as these are ingredients known to affect the likelihood of convective activity in the U.S. Using a methodology similar to other recent MJO studies, the impacts of the MJO on tornado, hail, and wind activity from Jan-Mar will be tested as part of this larger project to understand intraseasonal variability of severe storms.

Relationships between radiation, clouds, and convection during DYNAMO

DOE PAGES

Ciesielski, Paul E.; Johnson, Richard H.; Jiang, Xianan; ...

2017-02-16

In this paper, the relationships between radiation, clouds, and convection on an intraseasonal time scale are examined with data taken during the Dynamics of the Madden-Julian Oscillation (MJO) field campaign. Specifically, column-net, as well as vertical profiles of radiative heating rates, computed over Gan Island in the central Indian Ocean (IO) are used along with an objective analysis of large-scale fields to examine three MJO events that occurred during the 3 month period (October to December 2011) over this region. Longwave (LW) and shortwave radiative heating rates exhibit tilted structures, reflecting radiative effects associated with the prevalence of shallow cumulusmore » during the dry, suppressed MJO phase followed by increasing deep convection leading into the active phase. As the convection builds going into the MJO active phase, there are increasingly top-heavy anomalous radiative heating rates while the column-net radiative cooling rate Q r progressively decreases. Temporal fluctuations in the cloud radiative forcing, being quite sensitive to changes in high cloudiness, are dominated by LW effects with an intraseasonal variation of ~0.4–0.6 K/d. While both the water vapor and cloud fields are inextricably linked, it appears that the tilted radiative structures are more related to water vapor effects. The intraseasonal variation of column-net radiative heating Q r enhances the convective signal in the mean by ~20% with a minimum in this enhancement ~10 days prior to peak MJO rainfall and maximum ~7 days after. Finally, this suggests that as MJO convective envelope weakens over the central IO, cloud-radiative feedbacks help maintain the mature MJO as it moves eastward.« less

Intraseasonal variability of upper-ocean currents and photosynthetic primary production along the U.S. west coast associated with the Madden-Julian Oscillation

NASA Astrophysics Data System (ADS)

Barrett, B.; Davies, A. R.; Steppe, C. N.; Hackbarth, C.

2017-12-01

In the first part of this study, time-lagged composites of upper-ocean currents from February to May of 1993-2016 were binned by active phase of the leading atmospheric mode of intraseasonal variability, the Madden-Julian Oscillation (MJO). Seven days after the convectively active phase of the MJO enters the tropical Indian Ocean, anomalously strong south-southeastward upper-ocean currents are observed along the majority of U.S. west coast. Seven days after the convectively active phase enters the tropical western Pacific Ocean, upper-ocean current anomalies reverse along the U.S. west coast, with weaker southward flow. A physical pathway to the ocean was found for both of these: (a) tropical MJO convection modulates upper-tropospheric heights and circulation over the Pacific Ocean; (b) those anomalous atmospheric heights adjust the strength and position of the Aleutian Low and Hawaiian High; (c) surface winds change in response to the adjusted atmospheric pressure patterns; and (d) those surface winds project onto upper-ocean currents. In the second part of this study, we investigated if the MJO modulated intraseasonal variability of surface wind forcing and upper-ocean currents projected onto phytoplankton abundance along the U.S. west coast. Following a similar methodology, time-lagged, level 3 chlorophyll-a satellite products (a proxy for photosynthetic primary production) were binned by active MJO phase and analyzed for statistical significance using the Student's t test. Results suggest that intraseasonal variability of biological production along the U.S. west coast may be linked to the MJO, particularly since the time scale of the life cycle of phytoplankton is similar to the time scale of the MJO.

Spatio-Temporal Variability of Summer Precipitation in Mexico under the Influence of the MJO, with Emphasis on the Bimodal Pattern

NASA Astrophysics Data System (ADS)

Perdigón, J.; Romero-Centeno, R.; Barrett, B.; Ordoñez-Perez, P.

2017-12-01

In many regions of Mexico, precipitation occurs in a very well defined annual cycle with peaks in May-June and September-October and a relative minimum in the middle of the rainy season known as the midsummer drought (MSD). The MJO is the most important mode of intraseasonal variability in the tropics, and, although some studies have shown its evident influence on summer precipitation in Mexico, its role in modulating the bimodal pattern of the summer precipitation cycle is still an open question. The spatio-temporal variability of summer precipitation in Mexico is analyzed through composite analysis according to the phases of the MJO, using the very high resolution CHIRPS precipitation data base and gridded data from the CFSR reanalysis to analyzing the MJO influence on the atmospheric circulation over Mexico and its adjacent basins. In general, during MJO phases 8-2 (4-6) rainfall is above-normal (below-normal), although, in some cases, the summer rainfall patterns during the same phase present considerable differences. The atmospheric circulation shows low (high) troposphere southwesterly (northeasterly) wind anomalies in southern Mexico under wetter conditions compared with climatological patterns, while the inverse pattern is observed under drier conditions. Composite anomalies of several variables also agreed well with those rainfall anomalies. Finally, a MJO complete cycle that reinforces (weakens) the bimodal pattern of summer rainfall in Mexico was found.

Latent heating characteristics of the MJO computed from TRMM Observations

DOE PAGES

Barnes, Hannah C.; Zuluaga, Manuel D.; Houze, Robert A.

2015-01-14

We report the Tropical Rainfall Measurement Mission's (TRMM) Spectral Latent Heating algorithm shows the contributions of different forms of convection to the latent heating profiles of the Madden-Julian Oscillation over the central Indian and West Pacific Oceans. In both oceanic regions, storms containing broad stratiform regions produce increased upper level heating during active Madden-Julian Oscillation (MJO) phases. The largest differences between the central Indian and West Pacific Ocean heating are associated with heating produced by convective elements. Examination of the most extreme forms of convection shows that mesoscale organized convection often produces at least as much latent heat as youngmore » vigorous deep convection. Heating from nonextreme (often midlevel-topped) convection is an important component of the MJO heating in both regions in all stages of the MJO. Over the central Indian Ocean the heating profile changes from having a maximum at 2 km due to nonextreme convection to a profile during the active stage that has two maxima: one at 3 km due to nonextreme convection and 6 km owing to numerous mature mesoscale storms with broad stratiform precipitation components. Lastly, over the West Pacific, the maxima at 3 and 6 km are present in all MJO stages, but the magnitude of the 6 km maximum sharply increases in the active MJO stage due to an increase in the number of storms with broad stratiform precipitation areas.« less

Atmospheric Radiation Measurement Madden-Julian Oscillation Investigation Experiment Field Campaign Report

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

Long, Chuck

2016-07-01

Every 30–90 days during the Northern Hemisphere winter, the equatorial tropical atmosphere experiences pulses of extraordinarily strong deep convection and rainfall. This phenomenon is referred to as the Madden–Julian Oscillation, or MJO, named after the scientists who identified this cycle. The MJO significantly affects weather and rainfall patterns around the world (Zhang 2013). To improve predictions of the MJO—especially about how it forms and evolves throughout its lifecycle—an international group of scientists collected an unprecedented set of observations from the Indian Ocean and western Pacific region from October 2011 through March 2012 through several coordinated efforts. The coordinated field campaignsmore » captured six distinct MJO cycles in the Indian Ocean. The rich set of observations capturing several MJO events from these efforts will be used for many years to study the physics of the MJO. Here we highlight early research results using data from the Atmospheric Radiation Measurement (ARM) Madden-Julian Oscillation Investigation Experiment (AMIE), sponsored by the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility.« less

Past- and present-day Madden-Julian Oscillation in CNRM-CM5

NASA Astrophysics Data System (ADS)

Song, Eun-Ji; Seo, Kyong-Hwan

2016-04-01

Madden-Julian Oscillation (MJO) in the past (nineteenth century) and present day (twentieth century) is examined using preindustrial and historical experiments of Centre National de Recherches Météorologiques-Coupled Models, version 5 (CNRM-CM5) in Coupled Model Intercomparison Project Phase 5 (CMIP5). The present-day MJO is stronger than the past MJO by 33% and it is ~10% more frequent. In particular, the MJO phases 4-7 signifying deep convection situated over the Maritime continent and western Pacific (WP) are considerably enhanced. These changes are due mainly to greenhouse gas forcing with little impact from nature forcing. Dynamical mechanisms for this change are investigated. A peculiar strengthening of MJO over WP comes from increased basic-state sea surface temperature (SST) over the Central Pacific (CP) and EP. The increase in precipitation over WP results from both the response to enhanced SST over CP and the inverted Walker circulation induced by the EP and CP SST increase. The latter causes a pair of anticyclonic Rossby waves straddling the equator, leading to moisture convergence over WP.

Extended-Range Prediction with Low-Dimensional, Stochastic-Dynamic Models: A Data-driven Approach

DTIC Science & Technology

2012-09-30

characterization of extratropical storms and extremes and link these to LFV modes. Mingfang Ting, Yochanan Kushnir, Andrew W. Robertson...simulating and predicting a wide range of climate phenomena including ENSO, tropical Atlantic sea surface temperatures (SSTs), storm track variability...into empirical prediction models. Use observations to improve low-order dynamical MJO models. Adam Sobel, Daehyun Kim. Extratropical variability

The extratropical 40-day oscillation in the UCLA general circulation model. Part 1: Atmospheric angular momentum

NASA Technical Reports Server (NTRS)

Marcus, S. L.; Ghil, M.; Dickey, J. O.

1994-01-01

Variations in atmospheric angular momentum (AAM) are examined in a three-year simulation of the large-scale atmosphere with perpetual January forcing. The simulation is performed with a version of the University of California at Los Angeles (UCLA) general circulation model that contains no tropical Madden-Julian Oscillation (MJO). In addition, the results of three shorter experiments with no topography are analyzed. The three-year standard topography run contains no significant intraseasonal AAM periodicity in the tropics, consistent with the lack of the MJO, but produces a robust, 42-day AAM oscillation in the Northern Hemisphere (NH) extratropics. The model tropics undergoes a barotropic, zonally symmetric oscillation, driven by an exchange of mass with the NH extratropics. No intraseasonal periodicity is found in the average tropical latent heating field, indicating that the model oscillation is dynamically rather than thermodynamically driven. The no-mountain runs fail to produce an intraseasonal AAM oscillation, consistent with a topographic origin for the NH extratropical oscillation in the standard model. The spatial patterns of the oscillation in the 500-mb height field, and the relationship of the extratropical oscillation to intraseasonal variations in the tropics, will be discussed in Part 2 of this study.

MJO: Asymptotically-Nondivergent Nonlinear Wave?: A Review

NASA Astrophysics Data System (ADS)

Yano, J. I.

2014-12-01

MJO is often considered a convectively-coupled wave. The present talk is going to argue that it is best understood primarily as a nonlinear solitary wave dominated by vorticity. Role of convection is secondary,though likely catalytic. According to Charney's (1963) scale analysis, the large-scale tropical circulations are nondivergent to the leading order, i.e., dominated by rotational flows. Yano et al (2009) demonstrate indeed that is the case for a period dominated by three MJO events. The scale analysis of Yano and Bonazzola (2009, JAS) demonstrates such an asymptotically nondivergent regime is a viable alternative to the traditionally-believed equatorial-wave regime. Wedi and Smolarkiewicz (2010, JAS) in turn, show by numerical computations of a dry system that a MJO-like oscillation for a similar period can indeed be generated by free solitary nonlinear equatorial Rossby-wave dynamicswithout any convective forcing to a system. Unfortunately, this perspective is slow to be accepted with people's mind so much fixed on the role of convection. This situation may be compared to a slow historical process of acceptance of Eady and Charney's baroclinicinstability simply because it does not invoke any convection Ironically, once the nonlinear free-wave view for MJO is accepted, interpretations can more easily be developed for a recent series of numerical model experiments under a global channel configuration overthe tropics with a high-resolution of 5-50 km with or without convection parameterization. All those experiments tend to reproduce observed large-scale circulations associated with MJO rather well, though most of time, they fail to reproduce convective coherency associated with MJO.These large-scale circulations appear to be generated by lateral forcing imposed at the latitudinal walls. These lateral boundaries are reasonably far enough (30NS) to induce any direct influence to the tropics. There is no linear dry equatorial wave that supports this period either. In Wedi and Smolarkiewicz's analysis, such a lateral forcing is essential in order to obtain their nonlinear solitary wave solution. Thus is the leading-order solution for MJO in the same sense as the linear baroclinic instability is a leading-order solution to the midlatitude synoptic-scale storm.

The Climate Variability & Predictability (CVP) Program at NOAA - DYNAMO Recent Project Advancements

NASA Astrophysics Data System (ADS)

Lucas, S. E.; Todd, J. F.; Higgins, W.

2013-12-01

The Climate Variability & Predictability (CVP) Program supports research aimed at providing process-level understanding of the climate system through observation, modeling, analysis, and field studies. This vital knowledge is needed to improve climate models and predictions so that scientists can better anticipate the impacts of future climate variability and change. To achieve its mission, the CVP Program supports research carried out at NOAA and other federal laboratories, NOAA Cooperative Institutes, and academic institutions. The Program also coordinates its sponsored projects with major national and international scientific bodies including the World Climate Research Programme (WCRP), the International Geosphere-Biosphere Programme (IGBP), and the U.S. Global Change Research Program (USGCRP). The CVP program sits within the Earth System Science (ESS) Division at NOAA's Climate Program Office. Dynamics of the Madden-Julian Oscillation (DYNAMO): The Indian Ocean is one of Earth's most sensitive regions because the interactions between ocean and atmosphere there have a discernable effect on global climate patterns. The tropical weather that brews in that region can move eastward along the equator and reverberate around the globe, shaping weather and climate in far-off places. The vehicle for this variability is a phenomenon called the Madden-Julian Oscillation, or MJO. The MJO, which originates over the Indian Ocean roughly every 30 to 90 days, is known to influence the Asian and Australian monsoons. It can also enhance hurricane activity in the northeast Pacific and Gulf of Mexico, trigger torrential rainfall along the west coast of North America, and affect the onset of El Niño. CVP-funded scientists participated in the DYNAMO field campaign in 2011-12. Results from this international campaign are expected to improve researcher's insights into this influential phenomenon. A better understanding of the processes governing MJO is an essential step toward improving their representations in numerical models and improving MJO simulation and prediction. Recent results from CVP-funded projects will be summarized in this poster.

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.

The lagged connection of the positive NAO with the MJO phase 3 in a simplified atmospheric model

NASA Astrophysics Data System (ADS)

Shao, Xiaolu; Song, Jie; Li, Shuanglin

2018-03-01

Based on a simplified nonlinear model and reanalysis data, the lagged connection of the North Atlantic Oscillation (NAO) with the Madden-Julian Oscillation (MJO) in boreal winters is investigated. The positive NAO is observed to occur more frequently about 8-20 days after the onset of the MJO phase 3. A series of heating forcing experiments and initial-value experiments are conducted by utilizing the Geophysical Fluid Dynamics Laboratory (GFDL) dynamical core atmospheric model. The extratropical responses to the tropical heating associated with the MJO phase 3 are characterized by a wave train over the Pacific-North American region with an anticyclone anomaly over the northeastern Pacific and then followed by a positive-NAO-like pattern over the North Atlantic sector. These circulation anomalies generally match the observed lagged-connection well. At the earlier stage, the Rossby wave train excited by the MJO convection propagates into the North Atlantic, leading to a planetary wave anomaly with a low-over-high dipole prior to the positive NAO. At the later stage, the anomalous synoptic eddy vorticity forcing (EVF) streamfunction tendency has a negative-over-positive dipole, which plays a key role in the development of the positive NAO. Further analysis of the initial-value experiments indicates that, for the subsequent formation of the positive NAO, the anomalous circulation over the Indian Ocean aroused by the MJO phase 3 is more crucial than that over the northeastern Pacific.

QBO/solar modulation of the boreal winter Madden-Julian oscillation: A prediction for the coming solar minimum

NASA Astrophysics Data System (ADS)

Hood, Lon L.

2017-04-01

The Madden-Julian oscillation (MJO), also known as the 30-60 day oscillation, is the strongest of the intraseasonal climate oscillations in the tropics and has significant derivative effects on extratropical circulation and intraseasonal climate. It has recently been shown that the stratospheric quasi-biennial oscillation (QBO) modulates the amplitude of the boreal winter MJO such that MJO amplitudes are larger on average during the easterly phase (QBOE) than during the westerly phase (QBOW). A major possible mechanism is the decrease in static stability in the lowermost stratosphere under QBOE conditions resulting from relative upwelling associated with the QBO-induced meridional circulation. Here evidence is presented that tropical upwelling changes related to the 11 year solar cycle also modulate the boreal winter MJO. Based on 37.3 years of MJO amplitude data, the largest amplitudes and occurrence rates, and the weakest static stabilities in the tropical lower stratosphere, occur during the QBOE phase under solar minimum (SMIN) conditions while the smallest amplitudes and strongest static stabilities occur during the QBOW phase under solar maximum (SMAX) conditions. Conversely, when the QBO and solar forcings are opposed (QBOW/SMIN and QBOE/SMAX), the difference in occurrence rates becomes statistically insignificant. During the coming solar minimum, at least one additional winter in the QBOE/SMIN category should occur (possibly as early as 2017/2018) during which especially large MJO amplitudes are expected and an initial test of these results will be possible.

Optimal Initial Perturbations for Ensemble Prediction of the Madden-Julian Oscillation during Boreal Winter

NASA Technical Reports Server (NTRS)

Ham, Yoo-Geun; Schubert, Siegfried; Chang, Yehui

2012-01-01

An initialization strategy, tailored to the prediction of the Madden-Julian oscillation (MJO), is evaluated using the Goddard Earth Observing System Model, version 5 (GEOS-5), coupled general circulation model (CGCM). The approach is based on the empirical singular vectors (ESVs) of a reduced-space statistically determined linear approximation of the full nonlinear CGCM. The initial ESV, extracted using 10 years (1990-99) of boreal winter hindcast data, has zonal wind anomalies over the western Indian Ocean, while the final ESV (at a forecast lead time of 10 days) reflects a propagation of the zonal wind anomalies to the east over the Maritime Continent an evolution that is characteristic of the MJO. A new set of ensemble hindcasts are produced for the boreal winter season from 1990 to 1999 in which the leading ESV provides the initial perturbations. The results are compared with those from a set of control hindcasts generated using random perturbations. It is shown that the ESV-based predictions have a systematically higher bivariate correlation skill in predicting the MJO compared to those using the random perturbations. Furthermore, the improvement in the skill depends on the phase of the MJO. The ESV is particularly effective in increasing the forecast skill during those phases of the MJO in which the control has low skill (with correlations increasing by as much as 0.2 at 20 25-day lead times), as well as during those times in which the MJO is weak.

Scales of convective activity in the MJO (Invited)

NASA Astrophysics Data System (ADS)

Houze, R.

2013-12-01

One of the results of the Dynamics of the Madden-Julian Oscillation (MJO) field experiment (DYNAMO) is the realization that an active period of the MJO is not a continuous stretch of time in which convection and rainfall are occurring. Rather, an active MJO period, as determined by standard statistical treatments of the wind and satellite data such as that of Wheeler and Hendon (2004), has periods of highly suppressed conditions interspersed with bursts or episodes of deep convection and rainfall. At a given location, an MJO cycle is of the order of 30-60 days. The active half of a cycle is then about 2-4 weeks. DYNAMO data show that within this multi-week period rain falls in intermittent bursts of deep convection at intervals of 2-6 days, with each burst lasting 1-2 days. The time between bursts is highly suppressed, such that the convective cloud population consists of shallow non-precipitating cumulus. This intermediate burst timescale is neither the MJO timescale nor the timescale of an individual convective cloud. The modulation on the 2-6 day timescale was related to various types of higher frequency equatorial waves (especially, inertio-gravity waves and easterly waves). The largest individual convective cloud element in the MJO environment is the mesoscale convective system (MCS), which lasts about a half day, much shorter than the time period of the wave-modulated bursts. The intermediate scale bursts reflect an evolution of the cloud population. Numerous individual cloud systems undergo their lifecycles within the envelope of the wave-controlled time period of a few days. At a given site, such as the principal island site of Addu Atoll in DYNAMO, radar observations show that in an intermediate timescale episode the convective ensemble goes through a systematic series of stages characterized by differing proportions of elements of different sizes and intensities. The first stage is a population of shallow non-precipitating cumulus, followed by an ensemble of clouds containing some deeper convective elements. At the time of maximum rain during the episode, the population contains growing mesoscale systems. As the rain episode declines the population contains a substantial number of MCSs with broad stratiform regions. Thus, at least three scales are critical in the active periods of an MJO: the MJO scale, the equatorial wave scale of 2-6 days, and the scale of individual clouds, the largest of which are MCSs. This presentation will document the large-scale environment conditions on each of these scales, the population characteristics of the convection during the wave-modulated bursts, and of the individual cloud systems themselves.

Prediction and Predictability of the Madden Julian Oscillation in the NASA GEOS-5 Seasonal-to-Subseasonal System

NASA Technical Reports Server (NTRS)

Achuthavarier, Deepthi; Koster, Randal; Marshak, Jelena; Schubert, Siegfried; Molod, Andrea

2018-01-01

In this study, we examine the prediction skill and predictability of the Madden Julian Oscillation (MJO) in a recent version of the NASA GEOS-5 atmosphere-ocean coupled model run at at 1/2 degree horizontal resolution. The results are based on a suite of hindcasts produced as part of the NOAA SubX project, consisting of seven ensemble members initialized every 5 days for the period 1999-2015. The atmospheric initial conditions were taken from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), and the ocean and the sea ice were taken from a GMAO ocean analysis. The land states were initialized from the MERRA-2 land output, which is based on observation-corrected precipitation fields. We investigated the MJO prediction skill in terms of the bivariate correlation coefficient for the real-time multivariate MJO (RMM) indices. The correlation coefficient stays at or above 0.5 out to forecast lead times of 26-36 days, with a pronounced increase in skill for forecasts initialized from phase 3, when the MJO convective anomaly is located in the central tropical Indian Ocean. A corresponding estimate of the upper limit of the predictability is calculated by considering a single ensemble member as the truth and verifying the ensemble mean of the remaining members against that. The predictability estimates fall between 35-37 days (taken as forecast lead when the correlation reaches 0.5) and are rather insensitive to the initial MJO phase. The model shows slightly higher skill when the initial conditions contain strong MJO events compared to weak events, although the difference in skill is evident only from lead 1 to 20. Similar to other models, the RMM-index-based skill arises mostly from the circulation components of the index. The skill of the convective component of the index drops to 0.5 by day 20 as opposed to day 30 for circulation fields. The propagation of the MJO anomalies over the Maritime Continent does not appear problematic in the GEOS-5 hindcasts implying that the Maritime Continent predictability barrier may not be a major concern in this model. Finally, the MJO prediction skill in this version of GEOS-5 is superior to that of the current seasonal prediction system at the GMAO; this could be partly attributed to a slightly better representation of the MJO in the free running version of this model and partly to the improved atmospheric initialization from MERRA-2.

Development of the statistical ARIMA model: an application for predicting the upcoming of MJO index

NASA Astrophysics Data System (ADS)

Hermawan, Eddy; Nurani Ruchjana, Budi; Setiawan Abdullah, Atje; Gede Nyoman Mindra Jaya, I.; Berliana Sipayung, Sinta; Rustiana, Shailla

2017-10-01

This study is mainly concerned in development one of the most important equatorial atmospheric phenomena that we call as the Madden Julian Oscillation (MJO) which having strong impacts to the extreme rainfall anomalies over the Indonesian Maritime Continent (IMC). In this study, we focused to the big floods over Jakarta and surrounded area that suspecting caused by the impacts of MJO. We concentrated to develop the MJO index using the statistical model that we call as Box-Jenkis (ARIMA) ini 1996, 2002, and 2007, respectively. They are the RMM (Real Multivariate MJO) index as represented by RMM1 and RMM2, respectively. There are some steps to develop that model, starting from identification of data, estimated, determined model, before finally we applied that model for investigation some big floods that occurred at Jakarta in 1996, 2002, and 2007 respectively. We found the best of estimated model for the RMM1 and RMM2 prediction is ARIMA (2,1,2). Detailed steps how that model can be extracted and applying to predict the rainfall anomalies over Jakarta for 3 to 6 months later is discussed at this paper.

A simple model of intraseasonal oscillations

NASA Astrophysics Data System (ADS)

Fuchs, Željka; Raymond, David J.

2017-06-01

The intraseasonal oscillations and in particular the MJO have been and still remain a "holy grail" of today's atmospheric science research. Why does the MJO propagate eastward? What makes it unstable? What is the scaling for the MJO, i.e., why does it prefer long wavelengths or planetary wave numbers 1-3? What is the westward moving component of the intraseasonal oscillation? Though linear WISHE has long been discounted as a plausible model for intraseasonal oscillations and the MJO, the version we have developed explains many of the observed features of those phenomena, in particular, the preference for large zonal scale. In this model version, the moisture budget and the increase of precipitation with tropospheric humidity lead to a "moisture mode." The destabilization of the large-scale moisture mode occurs via WISHE only and there is no need to postulate large-scale radiatively induced instability or negative effective gross moist stability. Our WISHE-moisture theory leads to a large-scale unstable eastward propagating mode in n = -1 case and a large-scale unstable westward propagating mode in n = 1 case. We suggest that the n = -1 case might be connected to the MJO and the observed westward moving disturbance to the observed equatorial Rossby mode.

The Waves to Weather Challenge: Do Large-Scale Equatorial Waves Modulate Regional Rainfall in Southern Vietnam?

NASA Astrophysics Data System (ADS)

Fink, A. H.; van der Linden, R.; Phan-Van, T.; Pinto, J. G.

2014-12-01

About 85% of the annual precipitation in southern Vietnam (ca. 8-12°N, 104-110°E) occurs during the southwest monsoon season (June to October). Large-scale equatorial waves like the Madden-Julian Oscillation (MJO) and Convectively Coupled Equatorial Waves (CCEWs) are known to modulate the large-scale convective activity, often indicated by variations in (filtered) satellite-observed outgoing longwave radiation (OLR) anomalies. The present contribution analyses and quantifies the role of the MJO and CCEWs for rainfall not only in southern and central Vietnam as a whole, but also for smaller climatological sub-regions. Using circum-equatorial NOAA OLR (15°S-15°N), prominent spectral peaks are identified in wavenumber-frequency diagrams along the dispersion curves for the solutions of the shallow water equations. They are interpreted as CCEWs. Meridionally averaged wave-filtered OLR and its time derivatives are used to define phases and amplitudes of CCEWs. This will allow determining active and inactive phases of CCEWs in the vicinity of Vietnam. Eastward propagating deep convection is also related to the 30-90-day MJO. The OLR MJO Index (OMI) is used for the definition of convectively active and inactive phases of the MJO. TRMM 3B42 V7, APHRODITE MA V1101 data, and rain gauge measurements are used to investigate the relation between tropical wave phases and amplitudes and precipitation in southern and central Vietnam and adjacent regions. Results using the OMI are compared with those using the Real-time Multivariate MJO (RMM) Index. The major findings are: (a) Precipitation amounts in southern Vietnam are higher during convectively active phases of the MJO and CCEWs. The waves differ in terms of their relative importance for rainfall enhancement. (b) For increasing CCEW amplitudes, the difference between area-averaged precipitation during inactive and active phases increases. We provide evidence that precipitation amounts are higher when multiple wave types are in their convectively active phases over the Vietnam region.

Convective Cold Pool Structure and Boundary Layer Recovery in DYNAMO

NASA Astrophysics Data System (ADS)

Savarin, A.; Chen, S. S.; Kerns, B. W.; Lee, C.; Jorgensen, D. P.

2012-12-01

One of the key factors controlling convective cloud systems in the Madden-Julian Oscillation (MJO) over the tropical Indian Ocean is the property of the atmospheric boundary layer. Convective downdrafts and precipitation from the cloud systems produce cold pools in the boundary layer, which can inhibit subsequent development of convection. The recovery time is the time it takes for the boundary layer to return to pre convective conditions. It may affect the variability of the convection on various time scales during the initiation of MJO. This study examines the convective cold pool structure and boundary layer recovery using the NOAA WP-3D aircraft observations, include the flight-level, Doppler radar, and GPS dropsonde data, collected during the Dynamics of MJO (DYNAMO) field campaign from November-December 2011. The depth and strength of convective cold pools are defined by the negative buoyancy, which can be computed from the dropsonde data. Convective downdraft can be affected by environmental water vapor due to entrainment. Mid-level dry air observed during the convectively suppressed phase of MJO seems to enhance convective downdraft, making the cold pools stronger and deeper. Recovery of the cold pools in the boundary layer is determined by the strength and depth of the cold pools and also the air-sea heat and moisture fluxes. Given that the water vapor and surface winds are distinct for the convectively active and suppressed phases of MJO over the Indian Ocean, the aircraft data are stratified by the two different large-scale regimes of MJO. Preliminary results show that the strength and depth of the cold pools are inversely correlated with the surrounding mid-level moisture. During the convectively suppressed phase, the recovery time is ~5-20 hours in relative weak wind condition with small air-sea fluxes. The recovery time is generally less than 6 hours during the active phase of MJO with moist mid-levels and stronger surface wind and air-sea fluxes.

The Madden-Julian Oscillation and the Indo-Pacific Warm Pool

NASA Astrophysics Data System (ADS)

Raymond, David J.; Fuchs, Željka

2018-04-01

A minimal model of the interaction of the Madden-Julian oscillation (MJO) with the Indo-Pacific warm pool is presented. This model is based on the linear superposition of the flow associated with a highly simplified treatment of the MJO plus the flow induced by the warm pool itself. Both of these components parameterize rainfall as proportional to the column water vapor, which in turn is governed by a linearized moisture equation in which WISHE (wind induced surface heat exchange) plays a governing role. The MJO component has maximum growth rate for planetary wavenumber 1 and is equatorially trapped with purely zonal winds. The warm pool component exhibits a complex flow pattern, differing significantly from the classical Gill model as a result of the mean easterly flow. The combination of the two produce a flow that reproduces many aspects of the observed global flow associated with the MJO.

Evidence of organized intraseasonal convection linked to ocean dynamics in the Seychelles-Chagos thermocline ridge

NASA Astrophysics Data System (ADS)

D'Addezio, Joseph M.; Subrahmanyam, Bulusu

2018-01-01

The Madden-Julian oscillation (MJO) is the dominant driver of intraseasonal variability across the equatorial domain of the global ocean with alternating wet and dry bands that propagate eastward primarily between 5°N and 5°S. Past research has shown that MJOs impact the surface and subsurface variability of the Seychelles-Chagos thermocline ridge (SCTR) (55°E-65°E, 5°S-12°S) located in the southwest tropical Indian Ocean (SWTIO), but investigations of how SWTIO internal dynamics may play an important role in producing MJO events remain limited. This study uses Argo, in conjunction with several remote sensing and reanalysis products, to demonstrate that SWTIO oceanic dynamics, particularly barrier layer formation and near surface heat buildup, may be associated with MJO genesis between August and December of most years between 2005 and 2013. A total of eight SWTIO specific MJO events are observed, all occurring between August and December. Four of the eight events are correlated with positive SWTIO total heat content (THC) and barrier layer thickness (BLT) interannual anomalies. Two others formed over the SWTIO during times when only one of the variables was at or above their seasonal average, while two additional events occurred when both variables experienced negative interannual anomalies. Lacking complete 1:1 correlation between the hypothesized oceanic state and the identified SWTIO MJO events, we conclude that additional work is required to better understand when variability in key oceanic variables plays a primary role in regional MJO genesis or when other factors, such as atmospheric variability, are the dominate drivers.

Madden-Julian Oscillation: Western Pacific and Indian Ocean

NASA Astrophysics Data System (ADS)

Fuchs, Z.; Raymond, D. J.

2016-12-01

The MJO has been and still remains a "holy grail" of today's atmospheric science research. Why does the MJO propagate eastward? What makes it unstable? What is the scaling for the MJO, i.e. why does it prefer long wavelengths or planetary wavenumbers 1-3? The MJO has the strongest signal in the Indian ocean and in the West Pacific, but the average vertical structure is very different in each of those basins. We look at the reanalysis/analysis FNL, ERAI vertical structure of temperature and moisture as well as the surface zonal winds for two ocean basins. We also look at data from DYNAMO and TOGA_COARE in great detail (saturation fraction, temperature, entropy, surface zonal winds, gross moist stability, etc). The findings from observations and field projects for the two ocean basins are then compared to a linear WISHE model on an equatorial beta plane. Though linear WISHE has long been discounted as a plausible model for the MJO, the version we have developed explains many of the observed features of this phenomenon, in particular, the preference for large zonal scale, the eastward propagation, the westward group velocity, and the thermodynamic structure. There is no need to postulate large-scale negative gross moist stability, as destabilization occurs via WISHE at long wavelengths only. This differs from early WISHE models because we take a moisture adjustment time scale of order one day in comparison to the much shorter time scales assumed in earlier models. Linear modeling cannot capture all of the features of the MJO, so we are in the process of adding nonlinearity.

ARM Madden-Julian Oscillation Investigation Experiment

ScienceCinema

Long, Chuck

2018-06-06

Results of the ARM Madden-Julian Oscillation (MJO) Investigation Experiment (AMIE) field campaign are contributing significantly to concurrent national and international research efforts addressing questions about how the MJO initiates and changes as it passes phenomenon differs in observations versus models.

Thermodynamics in the Suppressed Phase of the Madden-Julian Oscillation Using a Multiplatform Strategy

NASA Technical Reports Server (NTRS)

Roberts, J. Brent; Robertson, Franklin R.; Clayson, Carol Anne; Taylor, Patrick

2014-01-01

The Madden-Julian Oscillation (MJO) represents a prominent mode of intraseasonal tropical variability. It is manifest by coherent large-scale changes in atmospheric circulation, convection, and thermodynamic processes. Preconditioning of the environment prior to the active phase of the MJO has been noted, but the balance of theorized mechanisms to accomplish this process remains unresolved. Further, there is a lack of consensus on the means by which primary initiation of an MJO event occurs. Observational and modeling efforts have recently been undertaken to advance our understanding of the physical underpinnings governing MJO development. However these intensive studies are often limited in space and/or time and are potentially subject to model deficiencies. Satellite observations, especially those providing vertical resolution of temperature and moisture, provide an opportunity to expand our knowledge of processes critical to MJO initiation and preconditioning. This work will provide an analysis of suppressed phase thermodynamics with an emphasis on the use of a complementary suite of satellite observations including AIRS/AMSU-A profiles, CERES radiative fluxes, and cloud properties observed by MODIS. Emphasis of this work will regard the distribution of cloud regimes, their radiative-convective effects, and their relationship to moist static energy during the recharge and suppressed stages of MJO initiation and eastward propagation. The analyses will make use of cloud regimes from MODIS observations to provide a compositing technique that enables the identification of systematic connections between different cloud regimes and the larger scale environment. Within these cloud regimes, the relationship between the associated cloud-radiative effects observed by CERES, vertically-resolved and vertically-integrated thermodynamics using AIRS/AMSU-A observations, and atmospheric boundary layer fluxes will be demonstrated.

Tropical Atlantic Dust and Smoke Aerosol Variations Related to the Madden-Julian Oscillation in MODIS and MISR Observations

NASA Technical Reports Server (NTRS)

Guo, Yanjuan; Tian, Baijun; Kahn, Ralph A.; Kalashnikova, Olga; Wong, Sun; Waliser, Duane E.

2013-01-01

In this study, Moderate Resolution Imaging Spectroradiometer (MODIS) fine mode fraction and Multi-angle Imaging SpectroRadiometer (MISR) nonspherical fraction data are used to derive dust and smoke aerosol optical thickness (T(sub dust) and T(sub smoke)) over the tropical Atlantic in a complementary way: due to its wider swath, MODIS has 3-4 times greater sampling than MISR, but MISR dust discrimination is based on particle shape retrievals, whereas an empirical scheme is used for MODIS. MODIS and MISR show very similar dust and smoke winter climatologies. T(sub dust) is the dominant aerosol component over the tropical Atlantic, accounting for 40-70 percent of the total aerosol optical thickness (AOT), whereas T(sub smoke) is significantly smaller than T(sub dust). The consistency and high correlation between these climatologies and their daily variations lends confidence to their use for investigating the relative dust and smoke contributions to the total AOT variation associated with the Madden-Julian Oscillation (MJO). The temporal evolution and spatial patterns of the tdus anomalies associated with the MJO are consistent between MODIS and MISR: the magnitude of MJO-realted T(sub dust) anomalies is comparable to or even larger than that of the total T, while the T(sub smoke) anomaly represents about 15 percent compared to the total, which is quite different from their relative magnitudes to the total T on the climatological time scale. This suggests that dust and smoke are not influenced by the MJO in the same way. Based on correlation analysis, dust is strongly influenced by the MJO-modulated trade wind and precipitation anomalies, and can last as long as one MJO phase, whereas smoke is less affected.

Physics Parameterization for Seasonal Prediction

DTIC Science & Technology

2013-09-30

particularly the Madden Julian Oscillation (MJO). We are continuing our participation in the project “Vertical Structure and Diabatic Processes of...Results are shown for: a) TRMM rainfall, b) NAVGEM 20-year run submitted for the YOTC/GEWEX project “Vertical Structure and Diabatic Processes of the MJO

Convective signals from surface measurements at ARM Tropical Western Pacific site: Manus

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

Wang, Yi; Long, Charles N.; Mather, James H.

2011-02-04

Madden-Julian Oscillation (MJO) signals have been detected using highly sampled observations from the U.S. DOE ARM Climate Research Facility located at the Tropical Western Pacific Manus site. Using downwelling shortwave radiative fluxes and derived shortwave fractional sky cover, and the statistical tools of wavelet, cross wavelet, and Fourier spectrum power, we report finding major convective signals and their phase change from surface observations spanning from 1996 to 2006. Our findings are confirmed with the satellite-gauge combined values of precipitation from the NASA Global Precipitation Climatology Project and the NOAA interpolated outgoing longwave radiation for the same location. We find thatmore » the Manus MJO signal is weakest during the strongest 1997-1998 El Nin˜o Southern Oscillation (ENSO) year. A significant 3-5-month lead in boreal winter is identified further between Manus MJO and NOAA NINO3.4 sea surface temperature (former leads latter). A striking inverse relationship is found also between the instantaneous synoptic and intraseasonal phenomena over Manus. To further study the interaction between intraseasonal and diurnal scale variability, we composite the diurnal cycle of cloudiness for 21-MJO events that have passed over Manus. Our diurnal composite analysis of shortwave and longwave fractional sky covers indicates that during the MJO peak (strong convection), the diurnal amplitude of cloudiness is reduced substantially, while the diurnal mean cloudiness reaches the highest value and there are no significant phase changes. We argue that the increasing diurnal mean and decreasing diurnal amplitude are caused by the systematic convective cloud formation that is associated with the wet phase of the MJO, while the diurnal phase is still regulated by the well-defined solar forcing. This confirms our previous finding of the anti-phase relationship between the synoptic and intraseasonal phenomena. The detection of theMJOover the Manus site provides further opportunities in using other ground-based remote sensing instruments to investigate the vertical distributions of clouds and radiative heatings of the MJO that currently is impossible from satellite observations.« less

Explicit Convection over the Western Pacific Warm Pool in the Community Atmospheric Model.

NASA Astrophysics Data System (ADS)

Ziemiaski, Micha Z.; Grabowski, Wojciech W.; Moncrieff, Mitchell W.

2005-05-01

This paper reports on the application of the cloud-resolving convection parameterization (CRCP) to the Community Atmospheric Model (CAM), the atmospheric component of the Community Climate System Model (CCSM). The cornerstone of CRCP is the use of a two-dimensional zonally oriented cloud-system-resolving model to represent processes on mesoscales at the subgrid scale of a climate model. Herein, CRCP is applied at each climate model column over the tropical western Pacific warm pool, in a domain spanning 10°S-10°N, 150°-170°E. Results from the CRCP simulation are compared with CAM in its standard configuration.The CRCP simulation shows significant improvements of the warm pool climate. The cloud condensate distribution is much improved as well as the bias of the tropopause height. More realistic structure of the intertropical convergence zone (ITCZ) during the boreal winter and better representation of the variability of convection are evident. In particular, the diurnal cycle of precipitation has phase and amplitude in good agreement with observations. Also improved is the large-scale organization of the tropical convection, especially superclusters associated with Madden-Julian oscillation (MJO)-like systems. Location and propagation characteristics, as well as lower-tropospheric cyclonic and upper-tropospheric anticyclonic gyres, are more realistic than in the standard CAM. Finally, the simulations support an analytic theory of dynamical coupling between organized convection and equatorial beta-plane vorticity dynamics associated with MJO-like systems.

A special MJO event with a double Kelvin wave structure

NASA Astrophysics Data System (ADS)

Zhu, Lili; Li, Tim

2017-04-01

The second Madden-Julian Oscillation (MJO) event during the field campaign of the Dynamics of the MJO/Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011 (DYNAMO/CINDY2011) exhibi ted an unusual double rainband structure. Using a wavenumber-frequency spectral filtering method, we unveil that this double rainband structure arises primarily from the Kelvin wave component. The zonal phase speed of the double rainbands is about 7.9 degree per day in the equatorial Indian Ocean, being in the range of convectively coupled Kelvin wave phase speeds. The convection and circulation anomalies associated with the Kelvin wave component are characterized by two anomalous convective cells, with low-level westerly (easterly) and high (low) pressure anomalies to the west (east) of the convective centers, and opposite wind and pressure anomalies in the upper troposphere. Such a zonal wind-pressure phase relationship is consistent with the equatorial free-wave dynamics. While the free-atmospheric circulation was dominated by the first baroclinic mode vertical structure, moisture and vertical motion in the boundary layer led the convection. The convection and circulation structures derived based on the conventional MJO filter show a different characteristic. For example, the phase speed is slower (about 5.9 degree per day), and there were no double convective branches. This suggests that MJO generally involves multi-scales and it is incomplete to extract its signals by using the conventional filtering technique.

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

Barnes, Hannah C.; Zuluaga, Manuel D.; Houze, Robert A.

We report the Tropical Rainfall Measurement Mission's (TRMM) Spectral Latent Heating algorithm shows the contributions of different forms of convection to the latent heating profiles of the Madden-Julian Oscillation over the central Indian and West Pacific Oceans. In both oceanic regions, storms containing broad stratiform regions produce increased upper level heating during active Madden-Julian Oscillation (MJO) phases. The largest differences between the central Indian and West Pacific Ocean heating are associated with heating produced by convective elements. Examination of the most extreme forms of convection shows that mesoscale organized convection often produces at least as much latent heat as youngmore » vigorous deep convection. Heating from nonextreme (often midlevel-topped) convection is an important component of the MJO heating in both regions in all stages of the MJO. Over the central Indian Ocean the heating profile changes from having a maximum at 2 km due to nonextreme convection to a profile during the active stage that has two maxima: one at 3 km due to nonextreme convection and 6 km owing to numerous mature mesoscale storms with broad stratiform precipitation components. Lastly, over the West Pacific, the maxima at 3 and 6 km are present in all MJO stages, but the magnitude of the 6 km maximum sharply increases in the active MJO stage due to an increase in the number of storms with broad stratiform precipitation areas.« less

Does the Madden-Julian Oscillation influence aerosol variability?

NASA Astrophysics Data System (ADS)

Tian, Baijun; Waliser, Duane E.; Kahn, Ralph A.; Li, Qinbin; Yung, Yuk L.; Tyranowski, Tomasz; Geogdzhayev, Igor V.; Mishchenko, Michael I.; Torres, Omar; Smirnov, Alexander

2008-06-01

We investigate the modulation of aerosols by the Madden-Julian Oscillation (MJO) using multiple, global satellite aerosol products: aerosol index (AI) from the Total Ozone Mapping Spectrometer (TOMS) on Nimbus-7, and aerosol optical thickness (AOT) from the Moderate Resolution Imaging Spectroradiometer (MODIS) on Terra and Aqua and the Advanced Very High Resolution Radiometer (AVHRR) on NOAA satellites. A composite MJO analysis indicates that large variations in the TOMS AI and MODIS/AVHRR AOT are found over the equatorial Indian and western Pacific Oceans where MJO convection is active, as well as the tropical Africa and Atlantic Ocean where MJO convection is weak but the background aerosol level is high. A strong inverse linear relationship between the TOMS AI and rainfall anomalies, but a weaker, less coherent positive correlation between the MODIS/AVHRR AOT and rainfall anomalies, were found. The MODIS/AVHRR pattern is consistent with ground-based Aerosol Robotic Network data. These results indicate that the MJO and its associated cloudiness, rainfall, and circulation variability systematically influence the variability in remote sensing aerosol retrieval results. Several physical and retrieval algorithmic factors that may contribute to the observed aerosol-rainfall relationships are discussed. Preliminary analysis indicates that cloud contamination in the aerosol retrievals is likely to be a major contributor to the observed relationships, although we cannot exclude possible contributions from other physical mechanisms. Future research is needed to fully understand these complex aerosol-rainfall relationships.

The Onset of the Madden-Julian Oscillation Within an Aquaplanet Model

NASA Technical Reports Server (NTRS)

Colon, Edward; Lindesay, James; Suarez, Max

1997-01-01

A series of numerical experiments using a two-level atmospheric general circulation model (AGCM) were performed for the purpose of investigating the coupling between sea surface temperature (SST) profile and the onset of the Madden-Julian Oscillation (MJO). The AGCM was modified to run as an aquaplane with all seasonal forcing removed. SST distributions based on the New Global Sea-Ice and Sea Surface Temperature (GISST) Data Set for 1903-1994 were generated then modified to vary the north-south gradient and tropical temperatures. It was found that the MJO signal did not depend on the SST temperature gradients but rather on the absolute temperature of the equatorial region, EOF analysis revealed that the SST distribution which generated the strongest MJO signal produced a periodic fluctuation in velocity potential at the 250 millibar level with a phase speed of 15 m/s, and a periodicity of 30 days which falls within the shortest limit of observed oscillations. This distribution also possessed the coolest equatorial SSTs which suggests that increased stability in the atmosphere favors the occurrence of organized MJO propagation.

NASA CYGNSS Tropical Cyclone Mission

NASA Astrophysics Data System (ADS)

Ruf, Chris; Atlas, Robert; Majumdar, Sharan; Ettammal, Suhas; Waliser, Duane

2017-04-01

The NASA Cyclone Global Navigation Satellite System (CYGNSS) mission consists of a constellation of eight microsatellites that were launched into low-Earth orbit on 15 December 2016. Each observatory carries a four-channel bistatic scatterometer receiver to measure near surface wind speed over the ocean. The transmitter half of the scatterometer is the constellation of GPS satellites. CYGNSS is designed to address the inadequacy in observations of the inner core of tropical cyclones (TCs) that result from two causes: 1) much of the TC inner core is obscured from conventional remote sensing instruments by intense precipitation in the eye wall and inner rain bands; and 2) the rapidly evolving (genesis and intensification) stages of the TC life cycle are poorly sampled in time by conventional polar-orbiting, wide-swath surface wind imagers. The retrieval of wind speed by CYGNSS in the presence of heavy precipitation is possible due to the long operating wavelength used by GPS (19 cm), at which scattering and attenuation by rain are negligible. Improved temporal sampling by CYGNSS is possible due to the use of eight spacecraft with 4 scatterometer channels on each one. Median and mean revisit times everywhere in the tropics are 3 and 7 hours, respectively. Wind speed referenced to 10m height above the ocean surface is retrieved from CYGNSS measurements of bistatic radar cross section in a manner roughly analogous to that of conventional ocean wind scatterometers. The technique has been demonstrated previously from space by the UK-DMC and UK-TDS missions. Wind speed is retrieved with 25 km spatial resolution and an uncertainty of 2 m/s at low wind speeds and 10% at wind speeds above 20 m/s. Extensive simulation studies conducted prior to launch indicate that there will be a significant positive impact on TC forecast skill for both track and intensity with CYGNSS measurements assimilated into HWRF numerical forecasts. Simulations of CYGNSS spatial and temporal sampling properties for observing the Madden-Julian Oscillation (MJO) and Convectively Coupled Equatorial Waves (CCEW) indicate that it will allow for improved characterization of MJO temporal variability and of the major CCEW modes. The EGU 2017 presentation will include an overview of the CYGNSS mission, a report on current mission status, and summaries of the simulation studies performed regarding TC forecasts and MJO and CCEW characterization.

ARM MJO Investigation Experiment on Gan Island (AMIE-Gan) Science Plan

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

Long, CL; Del Genio, A; Deng, M

2011-04-11

The overarching campaign, which includes the ARM Mobile Facility 2 (AMF2) deployment in conjunction with the Dynamics of the Madden-Julian Oscillation (DYNAMO) and the Cooperative Indian Ocean experiment on intraseasonal variability in the Year 2011 (CINDY2011) campaigns, is designed to test several current hypotheses regarding the mechanisms responsible for Madden-Julian Oscillation (MJO) initiation and propagation in the Indian Ocean area. The synergy between the proposed AMF2 deployment with DYNAMO/CINDY2011, and the corresponding funded experiment on Manus, combine for an overarching ARM MJO Investigation Experiment (AMIE) with two components: AMF2 on Gan Island in the Indian Ocean (AMIE-Gan), where the MJOmore » initiates and starts its eastward propagation; and the ARM Manus site (AMIE-Manus), which is in the general area where the MJO usually starts to weaken in climate models. AMIE-Gan will provide measurements of particular interest to Atmospheric System Research (ASR) researchers relevant to improving the representation of MJO initiation in climate models. The framework of DYNAMO/CINDY2011 includes two proposed island-based sites and two ship-based locations forming a square pattern with sonde profiles and scanning precipitation and cloud radars at both island and ship sites. These data will be used to produce a Variational Analysis data set coinciding with the one produced for AMIE-Manus. The synergy between AMIE-Manus and AMIE-Gan will allow studies of the initiation, propagation, and evolution of the convective cloud population within the framework of the MJO. As with AMIE-Manus, AMIE-Gan/DYNAMO also includes a significant modeling component geared toward improving the representation of MJO initiation and propagation in climate and forecast models. This campaign involves the deployment of the second, marine-capable, AMF; all of the included measurement systems; and especially the scanning and vertically pointing radars. The campaign will include sonde launches at a rate of eight per day for the duration of the deployment. The increased sonde launches for the entire period matches that of the AMIE-Manus campaign and makes possible a far more robust Variational Analysis forcing data set product for the entire campaign, and thus better capabilities for modeling studies and synergistic research using the data from both AMIE sites.« less

Scale Interactions in the Tropics from a Simple Multi-Cloud Model

NASA Astrophysics Data System (ADS)

Niu, X.; Biello, J. A.

2017-12-01

Our lack of a complete understanding of the interaction between the moisture convection and equatorial waves remains an impediment in the numerical simulation of large-scale organization, such as the Madden-Julian Oscillation (MJO). The aim of this project is to understand interactions across spatial scales in the tropics from a simplified framework for scale interactions while a using a simplified framework to describe the basic features of moist convection. Using multiple asymptotic scales, Biello and Majda[1] derived a multi-scale model of moist tropical dynamics (IMMD[1]), which separates three regimes: the planetary scale climatology, the synoptic scale waves, and the planetary scale anomalies regime. The scales and strength of the observed MJO would categorize it in the regime of planetary scale anomalies - which themselves are forced from non-linear upscale fluxes from the synoptic scales waves. In order to close this model and determine whether it provides a self-consistent theory of the MJO. A model for diabatic heating due to moist convection must be implemented along with the IMMD. The multi-cloud parameterization is a model proposed by Khouider and Majda[2] to describe the three basic cloud types (congestus, deep and stratiform) that are most responsible for tropical diabatic heating. We implement a simplified version of the multi-cloud model that is based on results derived from large eddy simulations of convection [3]. We present this simplified multi-cloud model and show results of numerical experiments beginning with a variety of convective forcing states. Preliminary results on upscale fluxes, from synoptic scales to planetary scale anomalies, will be presented. [1] Biello J A, Majda A J. Intraseasonal multi-scale moist dynamics of the tropical atmosphere[J]. Communications in Mathematical Sciences, 2010, 8(2): 519-540. [2] Khouider B, Majda A J. A simple multicloud parameterization for convectively coupled tropical waves. Part I: Linear analysis[J]. Journal of the atmospheric sciences, 2006, 63(4): 1308-1323. [3] Dorrestijn J, Crommelin D T, Biello J A, et al. A data-driven multi-cloud model for stochastic parametrization of deep convection[J]. Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences, 2013, 371(1991): 20120374.

Attributing Tropical Cyclogenesis to Equatorial Waves in the Western North Pacific

NASA Technical Reports Server (NTRS)

Schreck, Carl J., III; Molinari, John; Mohr, Karen I.

2009-01-01

The direct influences of equatorial waves on the genesis of tropical cyclones are evaluated. Tropical cyclogenesis is attributed to an equatorial wave when the filtered rainfall anomaly exceeds a threshold value at the genesis location. For an attribution threshold of 3 mm/day, 51% of warm season western North Pacific tropical cyclones are attributed to tropical depression (TD)-type disturbances, 29% to equatorial Rossby waves, 26% to mixed Rossby-Gravity waves, 23% to Kelvin waves, 13% to the Madden-Julian oscillation (MJO), and 19% are not attributed to any equatorial wave. The fraction of tropical cyclones attributed to TD-type disturbances is consistent with previous findings. Past studies have also demonstrated that the MJO significantly modulates tropical cyclogenesis, but fewer storms are attributed to the MJO than any other wave type. This disparity arises from the difference between attribution and modulation. The MJO produces broad regions of favorable conditions for cyclogenesis, but the MJO alone might not determine when and where a storm will develop within these regions. Tropical cyclones contribute less than 17% of the power in any portion of the equatorial wave spectrum because tropical cyclones are relatively uncommon equatorward of 15deg latitude. In regions where they are active, however, tropical cyclones can contribute more than 20% of the warm season rainfall and up to 50% of the total variance. Tropical cyclone-related anomalies can significantly contaminate wave-filtered precipitation at the location of genesis. To mitigate this effect, the tropical cyclone-related rainfall anomalies were removed before filtering in this study.

Extended-range ensemble forecasting of tropical cyclogenesis in the northern Indian Ocean: Modulation of Madden-Julian Oscillation

NASA Astrophysics Data System (ADS)

Fu, Xiouhua; Hsu, Pang-chi

2011-08-01

A conventional atmosphere-ocean coupled system initialized with NCEP FNL analysis has successfully predicted a tropical cyclogenesis event in the northern Indian Ocean with a lead time of two weeks. The coupled forecasting system reproduces the westerly wind bursts in the equatorial Indian Ocean associated with an eastward-propagating Madden-Julian Oscillation (MJO) event as well as the accompanying northward-propagating westerly and convective disturbances. After reaching the Bay of Bengal, this northward-propagating Intra-Seasonal Variability (ISV) fosters the tropical cyclogenesis. The present finding demonstrates that a realistic MJO/ISV prediction will make the extended-range forecasting of tropical cyclogenesis possible and also calls for improved representation of the MJO/ISV in contemporary weather and climate forecast models.

Propagation Dynamics of Successive, Circumnavigating MJO Events in MERRA2 Reanalysis

NASA Astrophysics Data System (ADS)

Powell, Scott

2017-04-01

Propagation speeds of strong circumnavigating successive MJO events are investigated in MERRA2 reanalysis. Coherent, statistically significant circumnavigating signals in parameterized latent heating and modeled adiabatic cooling associated with large-scale vertical motion are detected and tracked. The signals appear to be associated with propagation of a first baroclinic Kelvin wave, but they obviously moved at a rate much slower than the theoretical phase speed for a dry first baroclinic Kelvin wave. ( 45-50 m/s). The goal is to determine what factors primarily control the variable propagation speed of the MJO signal as a function of longitude. Following theory of Neelin and Held (1987) and Emanuel et al. (1994), the climatological offset (i.e. cancellation) between column integrated diabatic heating and adiabatic cooling in MERRA2 is used to the estimate the wave propagation speed if a reduction of "effective static stability" governed the phase speed. The offset is robust from year to year at all longitudes. A first baroclinic mode based on applying the theory to reanalysis output would propagate between 20-25 m/s over much of the Western Hemisphere, between 20-35 m/s over the eastern Atlantic and Africa, and between 5-20 m/s over the tropical warm pool. The theoretically predicted velocities closely match the propagation speed of the circumnavigating convective signal seen in reanalysis over regions of the tropics where the weak temperature gradient (WTG) approximation is apparently inapplicable (i.e. where deep convection is not prevalent and the offset between diabatic heating and adiabatic cooling is small enough to allow a non-negligible temperature tendency). However, in places where deep convection is prevalent and the offset is large (greater than about 0.9), such as over the warm pool, the theory greatly overestimates propagation speed of the MJO signal. Rather, the moisture wave theory of Adames and Kim (2016), which assumes a WTG, accurately predicts the speed of the MJO signal. Thus, two distinct dynamic regimes, one in which gravity waves dominate and another in which moisture wave dynamics are more applicable, govern MJO propagation depending on where the signal is located. In the East Pacific, the offset has seasonal dependence. It is small (about 0.7) during boreal winter, and a reduction of effective static stability adequately describes propagation of the MJO signal. During boreal summer, the offset approaches 0.9, meaning that the WTG dynamic regime is prevalent like over the warm pool. However, no known theory for MJO propagation can explain the propagation speed of the signal, 8-9 m/s. In the East Pacific, convection tends to have a second baroclinic vertical structure, and it is centered off the equator. This highlights the need for extension of moisture wave/moisture mode theories to incorporate the second convective vertical mode and convection that is not centered latitudinally at the equator.

Background Noises Versus Intraseasonal Variation Signals: Small vs. Large Convective Cloud Objects From CERES Aqua Observations

NASA Technical Reports Server (NTRS)

Xu, Kuan-Man

2015-01-01

During inactive phases of Madden-Julian Oscillation (MJO), there are plenty of deep but small convective systems and far fewer deep and large ones. During active phases of MJO, a manifestation of an increase in the occurrence of large and deep cloud clusters results from an amplification of large-scale motions by stronger convective heating. This study is designed to quantitatively examine the roles of small and large cloud clusters during the MJO life cycle. We analyze the cloud object data from Aqua CERES (Clouds and the Earth's Radiant Energy System) observations between July 2006 and June 2010 for tropical deep convective (DC) and cirrostratus (CS) cloud object types according to the real-time multivariate MJO index, which assigns the tropics to one of the eight MJO phases each day. The cloud object is a contiguous region of the earth with a single dominant cloud-system type. The criteria for defining these cloud types are overcast footprints and cloud top pressures less than 400 hPa, but DC has higher cloud optical depths (=10) than those of CS (<10). The size distributions, defined as the footprint numbers as a function of cloud object diameters, for particular MJO phases depart greatly from the combined (8-phase) distribution at large cloud-object diameters due to the reduced/increased numbers of cloud objects related to changes in the large-scale environments. The medium diameter corresponding to the combined distribution is determined and used to partition all cloud objects into "small" and "large" groups of a particular phase. The two groups corresponding to the combined distribution have nearly equal numbers of footprints. The medium diameters are 502 km for DC and 310 km for cirrostratus. The range of the variation between two extreme phases (typically, the most active and depressed phases) for the small group is 6-11% in terms of the numbers of cloud objects and the total footprint numbers. The corresponding range for the large group is 19-44%. In terms of the probability density functions of radiative and cloud physical properties, there are virtually no differences between the MJO phases for the small group, but there are significant differences for the large groups for both DC and CS types. These results suggest that the intreseasonal variation signals reside at the large cloud clusters while the small cloud clusters represent the background noises resulting from various types of the tropical waves with different wavenumbers and propagation speeds/directions.

Coupled Ocean-Atmosphere Dynamics and Predictability of MJO’s

DTIC Science & Technology

2012-09-30

chlorophyll modulation by the MJO Previous studies analyzed ocean color satellite data and suggested that the primary mechanism of surface...information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and...maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of

Coupled Ocean-Atmosphere Dynamics and Predictability of MJO’s

DTIC Science & Technology

2012-09-30

mechanisms of surface chlorophyll modulation by the MJO Previous studies analyzed ocean color satellite data and suggested that the primary mechanism of...estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the... data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this

Role of equatorial waves in tropical cyclogenesis

NASA Astrophysics Data System (ADS)

Schreck, Carl J., III

Tropical cyclones typically form within preexisting wavelike disturbances that couple with convection. Using Tropical Rainfall Measuring Mission (TRMM) multisatellite rainfall estimates, this study determines the relative number of tropical cyclones that can be attributed to various wave types, including the Madden--Julian oscillation (MJO), Kelvin waves, equatorial Rossby (ER) waves, mixed Rossby--gravity (MRG) waves, and tropical depression (TD)-type disturbances. Tropical cyclogenesis is attributed to an equatorial wave's convection when the filtered rainfall anomaly exceeds a threshold value at the genesis location. More storms are attributed to TD-type disturbances than to any other wave type in all of the Northern Hemisphere basins. In the Southern Hemisphere, however, ER waves and TD-type disturbances are equally important as precursors. Fewer storms are attributed to MRG waves, Kelvin waves, and the MJO in every basin. Although relatively few storms are attributed to the MJO, tropical cyclogenesis is 2.6 times more likely in its convective phase compared with its suppressed phase. This modulation arises in part because each equatorial wave type is amplified within MJO's convective phase. The amplification significantly increases the probability that these waves will act as tropical cyclone precursors. A case study from June 2002 illustrates the effects of a series of Kelvin waves on two tropical cyclone formations. These waves were embedded in the convective phase of the MJO. Together, the MJO and the Kelvin waves preconditioned the low-level environment for cyclogenesis. The first Kelvin wave weakened the trade easterlies, while the subsequent waves created monsoon westerlies near the equator. These westerlies provided the background cyclonic vorticity within which both storms developed. The effects of tropical cyclone-related rainfall anomalies are also investigated. In the wavenumber--frequency spectrum for rainfall, tropical cyclones can inflate the power for shorter wavelength westward propagating waves by up to 27%. This spectrum contains signals from all longitudes, but the greatest contamination occurs in regions like the Philippines where tropical cyclones are most frequent. Here, tropical cyclones contribute more than 40% of the rainfall variance in each filter band. To mitigate these effects, tropical cyclone-related anomalies were removed before filtering in this study.

Small vs. Large Convective Cloud Objects from CERES Aqua Observations: Where are the Intraseasonal Variation Signals?

NASA Technical Reports Server (NTRS)

Xu, Kuan-Man

2016-01-01

During inactive phases of Madden-Julian oscillation (MJO), there are plenty of deep but small convective systems and far fewer deep and large ones. During active phases of MJO, a manifestation of an increase in the occurrence of large and deep cloud clusters results from an amplification of large-scale motions by stronger convective heating. This study is designed to quantitatively examine the roles of small and large cloud clusters during the MJO life cycle. We analyze the cloud object data from Aqua CERES observations for tropical deep convective (DC) and cirrostratus (CS) cloud object types according to the real-time multivariate MJO index. The cloud object is a contiguous region of the earth with a single dominant cloud-system type. The size distributions, defined as the footprint numbers as a function of cloud object diameters, for particular MJO phases depart greatly from the combined (8-phase) distribution at large cloud-object diameters due to the reduced/increased numbers of cloud objects related to changes in the large-scale environments. The medium diameter corresponding to the combined distribution is determined and used to partition all cloud objects into "small" and "large" groups of a particular phase. The two groups corresponding to the combined distribution have nearly equal numbers of footprints. The medium diameters are 502 km for DC and 310 km for cirrostratus. The range of the variation between two extreme phases (typically, the most active and depressed phases) for the small group is 6-11% in terms of the numbers of cloud objects and the total footprint numbers. The corresponding range for the large group is 19-44%. In terms of the probability density functions of radiative and cloud physical properties, there are virtually no differences between the MJO phases for the small group, but there are significant differences for the large groups for both DC and CS types. These results suggest that the intreseasonal variation signals reside at the large cloud clusters while the small cloud clusters represent the background noises resulting from various types of the tropical waves with different wavenumbers and propagation directions/speeds.

Sounding-Based Thermodynamic Budgets from Dynamo/Cindy/Amie

NASA Astrophysics Data System (ADS)

Johnson, R. H.; Ciesielski, P. E.; Ruppert, J. H.; Katsumata, M.

2014-12-01

The DYNAMO/CINDY/AMIE field campaign, conducted over the Indian Ocean from October 2011 to March 2012, was designed to study the initiation of the Madden-Julian Oscillation (MJO). Two prominent MJOs occurred in the experimental domain during the Special Observing Period in October and November. Data from a northern and a southern sounding array (NSA and SSA, respectively) have been used to investigate the apparent heat sources and sinks (Q1 and Q2) and radiative heating rates QR throughout the life cycles of the two MJO events. The MJO signal was far stronger in the NSA than the SSA, so attention is focused on results for the NSA. Time series of Q1, Q2, and the vertical eddy flux of moist static energy reveal an evolution of cloud systems for both MJOs consistent with prior studies: shallow, non-precipitating cumulus during the suppressed phase, followed by cumulus congestus, then deep convection during the active phase, and finally stratiform precipitation. However, the duration of these phases was shorter for the November MJO than for the October event. The profiles of Q1 and Q2 for the two arrays indicate a greater stratiform rain fraction for the NSA than the SSA, a finding supported by TRMM measurements. Surface rainfall rates and column-integrated QR determined as residuals from the budgets show good agreement with satellite-based estimates. The column-integrated QR anomaly was nearly 20% of the net-tropospheric convective heating anomaly for the October MJO, approaching the proposed condition for radiative-convective instability. The ratio was far less for the November event, further emphasizing important distinctions between the two MJOs.

Observational and Modeling Studies of Radiative, Chemical, and Dynamical Interactions in the Earth''s Atmosphere

NASA Technical Reports Server (NTRS)

Salby, Murry

1998-01-01

A 3-dimensional model was developed to support mechanistic studies. The model solves the global primitive equations in isentropic coordinates, which directly characterize diabatic processes forcing the Brewer-Dobson circulation of the middle atmosphere. It's numerical formulation is based on Hough harmonics, which partition horizontal motion into its rotational and divergent components. These computational features, along with others, enable 3D integrations to be performed practically on RISC computer architecture, on which they can be iterated to support mechanistic studies. The model conserves potential vorticity quite accurately under adiabatic conditions. Forced by observed tropospheric structure, in which integrations are anchored, the model generates a diabatic circulation that is consistent with satellite observations of tracer behavior and diabatic cooling rates. The model includes a basic but fairly complete treatment of gas-phase photochemistry that represents some 20 chemical species and 50 governing reactions with diurnally-varying shortwave absorption. The model thus provides a reliable framework to study transport and underlying diabatic processes, which can then be compared against chemical and dynamical structure observed and in GCM integrations. Integrations with the Langley GCM were performed to diagnose feedback between simulated convection and the tropical circulation. These were studied in relation to tropospheric properties controlling moisture convergence and environmental conditions supporting deep convection, for comparison against mechanistic integrations of wave CISK that successfully reproduce the Madden-Julian Oscillation (MJO) of the tropical circulation. These comparisons were aimed at identifying and ultimately improving aspects of the convective simulation, with the objective of recovering a successful simulation of the MJO in the Langley GCM, behavior that should be important to budgets of upper-tropospheric water vapor and chemical species.

The Influence of Atmosphere-Ocean Interaction on MJO Development and Propagation

DTIC Science & Technology

2012-09-30

atmosphere-ocean feedbacks and their influence on MJO development, and for forecasting of air sea interaction in the Indian Ocean basin and its influence...black line indicating precipitation maximum over the DYNAMO area and the red line indicating the precipitation anomaly west of Sumatra . The... basin in December. Similar EOF decomposition of the precipitation associated with Kelvin waves (not shown here) indicates strong Kelvin wave anomaly

Evaluation of Model Performance over the Maritime Continent

NASA Astrophysics Data System (ADS)

Reynolds, C. A.; Barton, N. P.; Chen, S.; Flatau, M. K.; Ridout, J. A.; Janiga, M.; Jensen, T.; Richman, J. G.; Metzger, E. J.; Baranowski, D.

2017-12-01

The introduction of high-resolution global coupled models holds promise for extended-range (subseasonal to seasonal) prediction of high-impact weather. While forecast models have shown considerable improvement in the prediction of tropical phenomena on these timescales, specifically in the simulation and prediction of the Madden-Julian Oscillation (MJO), obstacles remain. In particular, many models still have difficulty accurately simulating the propagation of the MJO over the maritime continent. This has been hypothesized, at least in part, to be related to deficiencies in simulating the diurnal cycle over this region, which in turn is dependent on accurate representation of fine-scale atmosphere-ocean-land interactions, orography, and atmospheric convection. These issues have motivated the international Year of Maritime Continent (YMC) effort and the Office of Naval Research Propagation of Intra-Seasonal Tropical Oscillations (PISTON) initiative. In preparation for YMC and PISTON, we closely evaluate the performance of the Navy Earth System Model (NESM), a coupled global forecast model, in representing the diurnal cycle and other prominent phenomena in the maritime continent region. NESM performance is compared with stand-alone atmospheric simulations with prescribed fixed and analyzed sea surface temperatures (SSTs). Initial results from the Dynamics of the Madden-Julian Oscillation field phase (Fall 2011) period indicate that NESM is able to capture the precipitation day-time maximum over land and night-time maximum over ocean, but day-time precipitation over Borneo, Sumatra and the Malay Peninsula is too strong as compared to TRMM observations. The simulation of low-level winds qualitatively captures sea and land breeze patterns as compared with ERA-Interim analysis, with quantitative biases varying by island. The fully-coupled system and the stand-alone atmospheric model simulations are more similar to each other than to the observations, indicating that active ocean coupling is not the most prominent issue contributing to biases in these simulations. The performance of NESM will be more thoroughly evaluated and compared to other forecast systems using the 45-day forecasts currently being produced four times per week for the 1999-2015 time period under the NOAA SubX project.

Aircraft Measurements for Understanding Air-Sea Coupling and Improving Coupled Model Predictions

DTIC Science & Technology

2014-09-30

layer thermodynamic properties across the DYNAMO domain during the suppressed and active phase of MJO; and 3) variability and distribution of upper ocean...structure during suppressed, active and restoring phase of MJO. One of the unique aspects of LASP/ DYNAMO WP-3D project was to supplement the point...observations by probing the atmospheric and oceanic variability across the DYNAMO domain. Adhering to this aspect, vertical cross section of lower

Predictability of the 1997 and 1998 South Asian Summer Monsoons

NASA Technical Reports Server (NTRS)

Schubert, Siegfred D.; Wu, Man Li

2000-01-01

The predictability of the 1997 and 1998 south Asian summer monsoon winds is examined from an ensemble of 10 Atmospheric General Circulation Model (AGCM) simulations with prescribed sea surface temperatures (SSTs) and soil moisture, The simulations are started in September 1996 so that they have lost all memory of the atmospheric initial conditions for the periods of interest. The model simulations show that the 1998 monsoon is considerably more predictable than the 1997 monsoon. During May and June of 1998 the predictability of the low-level wind anomalies is largely associated with a local response to anomalously warm Indian Ocean SSTs. Predictability increases late in the season (July and August) as a result of the strengthening of the anomalous Walker circulation and the associated development of easterly low level wind anomalies that extend westward across India and the Arabian Sea. During these months the model is also the most skillful with the observations showing a similar late-season westward extension of the easterly CD wind anomalies. The model shows little predictability or skill in the low level winds over southeast Asia during, 1997. Predictable wind anomalies do occur over the western Indian Ocean and Indonesia, however, over the Indian Ocean they are a response to SST anomalies that were wind driven and they show no skill. The reduced predictability in the low level winds during 1997 appears to be the result of a weaker (compared with 1998) simulated anomalous Walker circulation, while the reduced skill is associated with pronounced intraseasonal activity that is not well captured by the model. Remarkably, the model does produce an ensemble mean Madden-Julian Oscillation (MJO) response that is approximately in phase with (though weaker than) the observed MJ0 anomalies. This is consistent with the idea that SST coupling may play an important role in the MJO.

Vertical Moist Thermodynamic Structure and Spatial-Temporal Evolution of the MJO in AIRS Observations

NASA Technical Reports Server (NTRS)

Tian, Baijun; Waliser, Duane E.; Fetzer, Eric J.; Lambrigtsen, Bjorn H.; Yung, Yuk L.; Wang, Bin

2006-01-01

The atmospheric moisture and temperature profiles from the Atmospheric Infrared Sounder (AIRS)/Advanced Microwave Sounding Unit on the NASA Aqua mission, in combination with the precipitation from the Tropical Rainfall Measuring Mission (TRMM), are employed to study the vertical moist thermodynamic structure and spatial-temporal evolution of the Madden-Julian oscillation (MJO). The AIRS data indicate that, in the Indian Ocean and western Pacific, the temperature anomaly exhibits a trimodal vertical structure: a warm (cold) anomaly in the free troposphere (800-250 hPa) and a cold (warm) anomaly near the tropopause (above 250 hPa) and in the lower troposphere (below 800 hPa) associated with enhanced (suppressed) convection. The AIRS moisture anomaly also shows markedly different vertical structures as a function of longitude and the strength of convection anomaly. Most significantly, the AIRS data demonstrate that, over the Indian Ocean and western Pacific, the enhanced (suppressed) convection is generally preceded in both time and space by a low-level warm and moist (cold and dry) anomaly and followed by a low-level cold and dry (warm and moist) anomaly. The MJO vertical moist thermodynamic structure from the AIRS data is in general agreement, particularly in the free troposphere, with previous studies based on global reanalysis and limited radiosonde data. However, major differences in the lower-troposphere moisture and temperature structure between the AIRS observations and the NCEP reanalysis are found over the Indian and Pacific Oceans, where there are very few conventional data to constrain the reanalysis. Specifically, the anomalous lower-troposphere temperature structure is much less well defined in NCEP than in AIRS for the western Pacific, and even has the opposite sign anomalies compared to AIRS relative to the wet/dry phase of the MJO in the Indian Ocean. Moreover, there are well-defined eastward-tilting variations of moisture with height in AIRS over the central and eastern Pacific that are less well defined, and in some cases absent, in NCEP. In addition, the correlation between MJO-related mid-tropospheric water vapor anomalies and TRMM precipitation anomalies is considerably more robust in AIRS than in NCEP, especially over the Indian Ocean. Overall, the AIRS results are quite consistent with those predicted by the frictional Kelvin-Rossby wave/conditional instability of the second kind (CISK) theory for the MJO.

Intraseasonal oscillation features of the South China Sea summer monsoon and its response to abnormal MJO in the tropical Indian Ocean

NASA Astrophysics Data System (ADS)

Li, Ting

2014-05-01

This paper analyzes Intraseasonal Oscillation (ISO) features and inter-annual differences of the South China Sea (SCS) Summer Monsoon (SCSSM), evolution of its Low Frequency (LF) circulation and convection fields and precipitation anomalies, and path of ISO propagation, as well as impact of MJO in tropical Indian Ocean on SCSSM ISO during 1979-2008. It is found that (1) The SCSSM ISO goes through six phases (exclusive of the weak phase) at every complete fluctuation: developing, strongest, weakening, restraining, weakest and recovering phase. Due to tropical LF convection propagating eastward and northward, the LF convection and circulation in the 1st-3rd and 4th-6th phases present the anti-phase in the Arabian Sea-West Pacific zonal band. Its corresponding rainy bands also present anti-phase roughly. The rainy band moves eastward with LF convection mainly in tropical regions in the south of 20° N, while moves northward in East Asia subtropical regions in the north of 20° N. (2) The SCSSM ISO intensity presents significant inter-annual difference. There are three stronger ISO in the stronger SCSSM ISO years. The first two oscillations propagates from the tropical Indian Ocean to the Bay of Bengal firstly, and then to SCS along the 10° -20° N zonal direction, stimulates the ISO to propagate to South China, forming a relay propagation path in meridional-zonal direction. Moreover, in the weaker SCSSM ISO years, the ISO weakens greatly and irregularly. In averaged conditions, the ISO propagates from tropical Indian Ocean to the SCS by about 20 days (one half ISO periods). (3) MJO1 (the first modal of MJO index provided by the Climate Prediction Center) averaged value in the 1st-2nd pentads of April has the negative correlation with the SCSSM ISO intensity. When MJO in tropical Indian Ocean is more active in the 1st-2nd pentads of April, it is stronger in the subsequent May to August, and the ISO also propagates strongly to the SCS, so that the SCSSM ISO strengthens. Conversely, the SCSSM ISO weakens. The abnormal MJO in the 1st-2nd pentads of April contributes to a certain theory basis to predict the subsequent SCSSM ISO intensity and analyze the abnormal rainfall in related regions.

Intraseasonal sea surface warming in the western Indian Ocean by oceanic equatorial Rossby waves

DTIC Science & Technology

2017-05-09

using observational and reanalysis products , respectively. In the heat budget, horizontal advection is the leading contributor to warming, in part due to...warming and cooling in these studies . SST is observed to maximize just ahead of MJO convection. After convection begins, SST rapidly cools and reaches a...minimum ~5 days later. However, several studies have observed a certain class of MJO events that deviate from the previously observed relationship of

Tropical warm pool rainfall variability and impact on upper ocean variability throughout the Madden-Julian oscillation

NASA Astrophysics Data System (ADS)

Thompson, Elizabeth J.

Heating and rain freshening often stabilize the upper tropical ocean, bringing the ocean mixed layer depth to the sea surface. Thin mixed layer depths concentrate subsequent fluxes of heat, momentum, and freshwater in a thin layer. Rapid heating and cooling of the tropical sea surface is important for controlling or triggering atmospheric convection. Ocean mixed layer depth and SST variability due to rainfall events have not been as comprehensively explored as the ocean's response to heating or momentum fluxes, but are very important to understand in the tropical warm pool where precipitation exceeds evaporation and many climate phenomena such as ENSO and the MJO (Madden Julian Oscillation) originate. The first part of the dissertation investigates tropical, oceanic convective and stratiform rainfall variability and determines how to most accurately estimate rainfall accumulation with radar from each rain type. The second, main part of the dissertation uses central Indian Ocean salinity and temperature microstructure measurements and surrounding radar-derived rainfall maps throughout two DYNAMO MJO events to determine the impact of precipitating systems on upper-ocean mixed layer depth and resulting SST variability. The ocean mixed layer was as shallow as 0-5 m during 528/1071 observation hours throughout 2 MJOs (54% of the data record). Out of 43 observation days, thirty-eight near-surface mixed layer depth events were attributed to freshwater stabilization, called rain-formed mixed layers (RFLs). Thirty other mixed layer stratification events were classified as diurnal warm layers (DWLs) due to stable temperature stratification by daytime heating. RFLs and DWLs were observed to interact in two ways: 1) RFLs fill preexisting DWLs and add to total near-surface mixed layer stratification, which occurred ten times; 2) RFLs last long enough to heat, creating a new DWL on top of the RFL, which happened nine times. These combination stratification events were responsible for the highest SST warming rates and some of the highest SSTs leading up to the most active precipitation and wind stage of the each MJO. DWLs without RFL interaction helped produce the highest SSTs in suppressed MJO conditions. As storm intensity, frequency, duration, and the ability of storms to maintain stratiform rain areas increased, RFLS became more common in the disturbed and active MJO phases. Along with the barrier layer, DWL and RFL stratification events helped suppress wind-mixing, cooling, and mixed layer deepening throughout the MJO. We hypothesize that both salinity and temperature stratification events, and their interactions, are important for controlling SST variability and therefore MJO initiation in the Indian Ocean. Most RFLs were caused by submesoscale and mesoscale convective systems with stratiform rain components and local rain accumulations above 10 mm but with winds mostly below 8 m s-1. We hypothesize that the stratiform rain components of storms helped stratify the ocean by providing weak but widespread, steady, long-lived freshwater fluxes. Although generally limited to rain rates ≤ 10 mm hr-1, it is demonstrated that stratiform rain can exert a strong buoyancy flux into the ocean, i.e. as high as maximum daytime solar heating. Storm morphology and the preexisting vertical structure of ocean stability were critical in determining ocean mixed layer depth variability in the presence of rain. Therefore, we suggest that high spatial and temporal resolution coupled ocean-atmosphere models that can parameterize or resolve storm morphology as well as ocean mixed layer and barrier layer evolution are needed to reproduce the diurnal and intraseasonal SST variability documented throughout the MJO.

Heavy precipitation in the southwest of Iran: association with the Madden-Julian Oscillation and synoptic scale analysis

NASA Astrophysics Data System (ADS)

Jafar Nazemosadat, M.; Shahgholian, K.

2017-11-01

Some important characteristics of the November-April heavy precipitation in southwestern parts of Iran and their linkages to the Madden-Julian Oscillation (MJO) were assessed for the period of 1975-2011. Daily precipitation data in nine meteorological stations spread in various parts of the study area and the corresponding MJO indices were analyzed. For each station, precipitation data were sorted in descending order and those values that fell within 5% of the highest records were categorized as the heavy precipitation. Besides this, the 10% threshold was also analyzed as an axillary assessment. The considered heavy precipitation data (5% threshold) accounted from about 26-35% of total annual precipitation. About half of the heavy precipitation occurred during December-January period and the other half distributed within the months of March, February, November and April by about 17, 14, 13and 6%, respectively. The highest frequency of heavy precipitation was related to the MJO phase 8. After this, the more frequent precipitation events were respectively associated to the phases 2, 7, 1, 6, 5 and 4 of the MJO. For the phases 1, 2, 7 and 8 frequency of the heavy precipitation statistically increased when the MJO amplitude was greater than unity. In contrast, for phases 4 and 5, heavy precipitation was generally linked to the spells that the amplitude size was lower than unity. Formation of a strong north-south oriented cold front mainly in Saudi Arabia and west-east oriented warm fronts in the southwest of Iran were realized as the key elements for initiating heavy precipitation over the study area. Although development of the Mediterranean-based cyclonic circulation is essential for the formation of these fronts, moisture transport mostly originates from northern parts of the Arabian Sea, southern parts of the Red Sea and the Persian Gulf.

Low Frequency Oscillations in Assimilated Global Datasets Using TRMM Rainfall Observations

NASA Technical Reports Server (NTRS)

Tao, Li; Yang, Song; Zhang, Zhan; Hou, Arthur; Olson, William S.

2004-01-01

Global datasets for the period May-August 1998 from the Goddard Earth Observing System (GEOS) data assimilation system (DAS) with/without assimilated Tropical Rainfall Measuring Mission (TRMM) precipitation are analyzed against European Center for Medium-Range Weather Forecast (ECMWF) output, NOAA observed outgoing longwave radiation (OLR) data, and TRMM measured rainfall. The purpose of this study is to investigate the representation of the Madden-Julian Oscillation (MJO) in GEOS assimilated global datasets, noting the impact of TRMM observed rainfall on the MJO in GEOS data assimilations. A space-time analysis of the OLR data indicates that the observed OLR exhibits a spectral maximum for eastward-propagating wavenumber 1-3 disturbances with periods of 20-60 days in the 0deg-30degN latitude band. The assimilated OLR has a similar feature but with a smaller magnitude. However, OLR spectra from assimilations including TRMM rainfall data show better agreement with observed OLR spectra than spectra from assimilations without TRMM rainfall. Similar results are found for wavenumber 4-6 disturbances. There is a spectral peak for eastward-propagating wavenumber 4-6 disturbances with periods of 20-40 days near the equator, while for westward-moving disturbances, a spectral peak is noted for periods of 30-50 days near 25degN. To isolate the MJO, a 30-50 day band filter is selected for this study. It was found that the eastward-propagating waves from the band-filtered observed OLR between 10degs- 10degN are located in the eastern hemisphere. Similar patterns are evident in surface rainfall and the 850 hPa wind field. Assimilation of TRMM-observed rainfall reveals more distinct MJO features in the analysis than without rainfall assimilation. Similar analyses are also conducted over the Indian summer monsoon and East Asia summer monsoon regions, where the MJO is strongly related to the summer monsoon active-break patterns.

Ocean feedback to pulses of the Madden–Julian Oscillation in the equatorial Indian Ocean

PubMed Central

Moum, James N.; Pujiana, Kandaga; Lien, Ren-Chieh; Smyth, William D.

2016-01-01

Dynamical understanding of the Madden–Julian Oscillation (MJO) has been elusive, and predictive capabilities therefore limited. New measurements of the ocean's response to the intense surface winds and cooling by two successive MJO pulses, separated by several weeks, show persistent ocean currents and subsurface mixing after pulse passage, thereby reducing ocean heat energy available for later pulses by an amount significantly greater than via atmospheric surface cooling alone. This suggests that thermal mixing in the upper ocean from a particular pulse might affect the amplitude of the following pulse. Here we test this hypothesis by comparing 18 pulse pairs, each separated by <55 days, measured over a 33-year period. We find a significant tendency for weak (strong) pulses, associated with low (high) cooling rates, to be followed by stronger (weaker) pulses. We therefore propose that the ocean introduces a memory effect into the MJO, whereby each event is governed in part by the previous event. PMID:27759016

Bias Reduction as Guidance for Developing Convection and Cloud Parameterization in GFDL AM4/CM4

NASA Astrophysics Data System (ADS)

Zhao, M.; Held, I.; Golaz, C.

2016-12-01

The representations of moist convection and clouds are challenging in global climate models and they are known to be important to climate simulations at all spatial and temporal scales. Many climate simulation biases can be traced to deficiencies in convection and cloud parameterizations. I will present some key biases that we are concerned about and the efforts that we have made to reduce the biases during the development of NOAA's Geophysical Fluid Dynamics Laboratory (GFDL) new generation global climate model AM4/CM4. In particular, I will present a modified version of the moist convection scheme that is based on the University of Washington Shallow Cumulus scheme (UWShCu, Bretherton et. al 2004). The new scheme produces marked improvement in simulation of the Madden-Julian Oscillation (MJO) and the El Niño-Southern Oscillation (ENSO) compared to that used in AM3 and HIRAM. AM4/CM4 also produces high quality simulation of global distribution of cloud radiative effects and the precipitation with realistic mean climate state. This differs from models of improved MJO but with a much deteriorated mean state. The modifications to the UWShCu include an additional bulk plume for representing deep convection. The entrainment rate in the deep plume is parameterized to be a function of column-integrated relative humidity. The deep convective closure is based on relaxation of the convective available potential energy (CAPE) or cloud work function. The plumes' precipitation efficiency is optimized for better simulations of the cloud radiative effects. Precipitation re-evaporation is included in both shallow and deep plumes. In addition, a parameterization of convective gustiness is included with an energy source driven by cold pool derived from precipitation re-evaporation within the boundary layer and energy sink due to dissipation. I will present the motivations of these changes which are driven by reducing some aspects of the AM4/CM4 biases. Finally, I will also present the biases in current AM4/CM4 and challenges to further reduce them.

The effects of blocking in the subtropics on the phase speed of the MJO

NASA Astrophysics Data System (ADS)

Roundy, P. E.

2016-12-01

The phase speed of the MJO might be regulated by many different factors. Previous works have suggested that moist processes govern the phase speed, and our results show that intensification of convection is associated with reduction of phase speed down to about 5 ms-1. However, convection and rainfall decline with declining phase speeds below 5 ms-1. This presentation shows that increased Rossby wave breaking and blocking east of MJO deep convection is associated with reduced phase speed below about 6 ms-1. A wavelet filter is applied to extract time series characterized by selected zonal wavenumbers and frequencies at select equatorial base longitudes over the Indian and West Pacific Oceans. Results show that anomalies of active convection characterized by wavenumber 2 (the dominant scale of MJO convection over the warm pool) are associated with meridional potential vorticity (PV) gradients across the tropics to the east of the active convection that are near climatology for events moving east at 5 ms-1. These gradients are much weaker for slower events. The slowest phase speed events have almost no meridional PV gradients across the tropics between the mean latitudes of the subtropical jet streams, suggesting that jet exit regions occur immediately east of the deep convection, dumping mass in the upper troposphere over the region of suppressed convection. In the absence of PV gradients, synoptic to planetary scale waves moving into that environment break or cease to propagate linearly.

Use of Machine Learning Techniques for Identification of Robust Teleconnections to East African Rainfall Variability

NASA Technical Reports Server (NTRS)

Roberts, J. Brent; Robertson, F. R.; Funk, C.

2014-01-01

Hidden Markov models can be used to investigate structure of subseasonal variability. East African short rain variability has connections to large-scale tropical variability. MJO - Intraseasonal variations connected with appearance of "wet" and "dry" states. ENSO/IOZM SST and circulation anomalies are apparent during years of anomalous residence time in the subseasonal "wet" state. Similar results found in previous studies, but we can interpret this with respect to variations of subseasonal wet and dry modes. Reveal underlying connections between MJO/IOZM/ENSO with respect to East African rainfall.

A High-Resolution Merged Wind Dataset for DYNAMO: Progress and Future Plans

NASA Technical Reports Server (NTRS)

Lang, Timothy J.; Mecikalski, John; Li, Xuanli; Chronis, Themis; Castillo, Tyler; Hoover, Kacie; Brewer, Alan; Churnside, James; McCarty, Brandi; Hein, Paul;

Evaluation of the impacts of the Madden-Julian Oscillation on rainfall and hurricanes in Central and South America and the Atlantic Ocean using ICI-RAFT

NASA Astrophysics Data System (ADS)

Giovannettone, J. P.

2013-12-01

Based on the method of Regional Frequency Analysis (RFA) and L-moments (Hosking & Wallis, 1997), a tool was developed to estimate the frequency/intensity of a rainfall event of a particular duration using ground-based rainfall observations. Some of the code used to develop this tool was taken from the FORTRAN code provided by Hosking & Wallis and rewritten in Visual Basic 2010. This tool was developed at the International Center for Integrated Water Resources Management (ICIWaRM) and is referred to as the ICIWaRM Regional Analysis of Frequency Tool (ICI-RAFT) (Giovannettone & Wright, 2012). In order to study the effectiveness of ICI-RAFT, three case studies were selected for the analysis. The studies take place in selected regions within Argentina, Nicaragua, and Venezuela. Rainfall data were provided at locations throughout each country; total rainfall for specific periods were computed and analyzed with respect to several global climate indices using lag times ranging from 1 to 6 months. Each analysis attempts to identify a global climate index capable of predicting above or below average rainfall several months in advance, qualitatively and using an equation that is developed. The index that had the greatest impact was the MJO (Madden-Julian Oscillation), which is the focus of the current study. The MJO is considered the largest element of intra-seasonal (30 - 90 days) variability in the tropical atmosphere and, unlike other indices, is characterized by the eastward propagation of large areas of convective anomalies near the equator, propagating from the Indian Ocean east into the Pacific Ocean. The anomalies are monitored globally using ten different indices located on lines of longitude near the equator, with seven in the eastern hemisphere and three in the western hemisphere. It has been found in previous studies that the MJO is linked to summer rainfall in Southeast China (Zhang et al., 2009) and southern Africa (Pohl et al., 2007) and to rainfall patterns in Australia (Wheeler et al., 2009). The current study found that similar strong relationships between MJO activity over Africa and the western Indian Ocean and rainfall totals in central Argentina, Nicaragua, and northwestern Venezuela. For example, in Nicaragua, the 20-year event almost doubles depending on the phase of the MJO. A fourth case study attempts to develop a relationship between the annual number of hurricanes in the Atlantic Ocean and Caribbean during the hurricane season (July - October) and the average value of the Madden-Julian Oscillation over Africa during a period 3 - 4 months prior to the hurricane season. Similar work has been performed in the northern Atlantic by Villarini et al. (2010), except the authors focused on other indices, including tropical mean sea-surface temperatures (SST's), the North Atlantic Oscillation (NAO), and the Southern Oscillation Index (SOI). Even though the NAO and SOI show some correlation with hurricane activity, the results of the current study show that there is a stronger link between the MJO prior to hurricane season and the total number of hurricanes that form. The greatest correlation again comes from MJO activity over Africa.

Diurnal Cycle of ITCZ Convection during the MJO Suppressed Phase in DYNAMO

NASA Astrophysics Data System (ADS)

Ciesielski, P. E.; Johnson, R. H.; Schubert, W. H.

2017-12-01

During the special observing period of the Dynamics of the MJO (DYNAMO) experiment, conducted over the Indian Ocean from 1 October to 30 November 2011, two sounding arrays - one north and one south of the equator, referred to here as the NSA and SSA, respectively - took 4-8 soundings/day. We augment this 3-h dataset with observations of radiation and rainfall to investigate the diurnal cycle of convection during the suppressed phase of the October MJO. During this 14-day period when convection was suppressed over the NSA but prominent over the SSA, the circulation over the sounding arrays could be characterized as a local Hadley cell embedded within a monsoonal flow. Strong rising motion was present within the ITCZ and compensating subsidence over the NSA. A prominent diurnal pulsing of this cell was observed, impacting conditions on both sides of the equator, with the cell running strongest in the early morning hours (05-08 LT) and notably weakening later in the day (17-20LT). The reduction in evening subsidence over the NSA may have assisted the moistening of the low to mid-troposphere there during the pre-onset stage of the MJO. Apparent heating Q1 within the ITCZ exhibits a diurnal evolution from early morning bottom-heavy profiles to weaker daytime top-heavy profiles. Making use of the weak temperature gradient approximation, results suggest that direct radiative effects played a dominant role in controlling diurnal variations of vertical motion and convection within the ITCZ while non-radiative processes were more prominent over the NSA.

Effect of dry large-scale vertical motions on initial MJO convective onset

NASA Astrophysics Data System (ADS)

Powell, Scott W.; Houze, Robert A.

2015-05-01

Anomalies of eastward propagating large-scale vertical motion with ~30 day variability at Addu City, Maldives, move into the Indian Ocean from the west and are implicated in Madden-Julian Oscillation (MJO) convective onset. Using ground-based radar and large-scale forcing data derived from a sounding array, typical profiles of environmental heating, moisture sink, vertical motion, moisture advection, and Eulerian moisture tendency are computed for periods prior to those during which deep convection is prevalent and those during which moderately deep cumulonimbi do not form into deep clouds. Convection with 3-7 km tops is ubiquitous but present in greater numbers when tropospheric moistening occurs below 600 hPa. Vertical eddy convergence of moisture in shallow to moderately deep clouds is likely responsible for moistening during a 3-7 day long transition period between suppressed and active MJO conditions, although moistening via evaporation of cloud condensate detrained into the environment of such clouds may also be important. Reduction in large-scale subsidence, associated with a vertical velocity structure that travels with a dry eastward propagating zonal wavenumbers 1-1.5 structure in zonal wind, drives a steepening of the lapse rate below 700 hPa, which supports an increase in moderately deep moist convection. As the moderately deep cumulonimbi moisten the lower troposphere, more deep convection develops, which itself moistens the upper troposphere. Reduction in large-scale subsidence associated with the eastward propagating feature reinforces the upper tropospheric moistening, helping to then rapidly make the environment conducive to formation of large stratiform precipitation regions, whose heating is critical for MJO maintenance.

Improving synoptic and intraseasonal variability in CFSv2 via stochastic representation of organized convection

NASA Astrophysics Data System (ADS)

Goswami, B. B.; Khouider, B.; Phani, R.; Mukhopadhyay, P.; Majda, A.

2017-01-01

To better represent organized convection in the Climate Forecast System version 2 (CFSv2), a stochastic multicloud model (SMCM) parameterization is adopted and a 15 year climate run is made. The last 10 years of simulations are analyzed here. While retaining an equally good mean state (if not better) as the parent model, the CFS-SMCM simulation shows significant improvement in the synoptic and intraseasonal variability. The CFS-SMCM provides a better account of convectively coupled equatorial waves and the Madden-Julian oscillation. The CFS-SMCM exhibits improvements in northward and eastward propagation of intraseasonal oscillation of convection including the MJO propagation beyond the maritime continent barrier, which is the Achilles Heel for coarse-resolution global climate models (GCMs). The distribution of precipitation events is better simulated in CFSsmcm and spreads naturally toward high-precipitation events. Deterministic GCMs tend to simulate a narrow distribution with too much drizzling precipitation and too little high-precipitation events.

Equatorial Wave Activity during NOAA's 2016 El Niño Rapid Response Field Campaign

NASA Astrophysics Data System (ADS)

Kiladis, G. N.; Dias, J.; Gehne, M.; Mayer, K.

2016-12-01

The El Niño Rapid Response (ENRR) field campaign targeted equatorial Pacific atmospheric convective activity during January-March 2016 through enhanced observations using dropsondes from the NOAA G-IV aircraft and radiosonde observations from Kiritimati (Christmas) Island and the NOAA research ship the Ronald H. Brown. This presentation examines the equatorial wave activity observed during ENRR and its relationship to tropical convection, and compares this activity to observations of past large El Niño events. The 2015-16 El Niño had much in common with the events during 1982-83 and 1997-98, with similar amplitude sea surface temperature (SST) anomalies, but also differed in several key aspects. All of these episodes featured enhanced convectively coupled Kelvin wave activity crossing the entire Pacific basin, which is generally absent during the northern winter seasons of near normal or La Niña SSTs. Prior to the ENRR period during December 2015 a large amplitude Madden-Julian Oscillation (MJO) was observed, with a convective signal that propagated unusually far to the east ( 150W). This was associated with an eastward displacement of the North Pacific storm track and heavy precipitation along the west coast of North America, broadly matching the large scale behavior of MJO evolution in statistical composites during El Niño. A second MJO-like event occurred during the latter part of February, 2016, but despite a similar convective heating field, the basic state flow was much different than during December, with a well-developed "westerly duct" which favored the intrusion of extratropical Rossby wave energy into the equatorial eastern Pacific region, as can be seen in E Vector fields. This latter event was accompanied by a distinct lack of an extended storm track and associated precipitation along the west coast of North America. Based on the preliminary results of AMIP simulations using observed SSTs, these differences are difficult to reproduce, and are hypothesized to be due to a certain level of "internal variability" within the storm track itself that may have been overriding the large scale forcing by the tropical diabatic heating field.

Effect of the Barrier Layer on the Upper Ocean Response to MJO Forcing

NASA Astrophysics Data System (ADS)

Bulusu, S.

2014-12-01

Recently, attention has been given to an upper ocean feature known as the Barrier Layer, which has been shown to impact meteorological phenomena from ENSO to tropical cyclones by suppressing vertical mixing, which reduces sea surface cooling and enhances surface heat fluxes. The calculation defines the Barrier Layer as the difference between the Isothermal Layer Depth (ILD) and Mixed Layer Depth (MLD). Proper representation of these features relies on precise observations of SSS to attain accurate measurements of the MLD and subsequently, the BLT. Compared to the many available in situ SSS measurements, the NASA Aquarius salinity mission currently obtains the closest observations to the true SSS. The role of subsurface features will be better understood through increased accuracy of SSS measurements. In this study BLT estimates are derived from satellite measurements using a multilinear regression model (MRM) in the Indian Ocean. The MRM relates BLT to satellite derived SSS, sea surface temperature (SST) and sea surface height anomalies (SSHA). Besides being a variable that responds passively to atmospheric conditions, SSS significantly controls upper ocean density and therefore the MLD. The formation of a Barrier Layer can lead to possible feedbacks that impact the atmospheric component of the Madden-Julian Oscillation (MJO), as stated as one of the three major hypotheses of the DYNAMO field campaign. This layer produces a stable stratification, reducing vertical mixing, which influences surface heat fluxes and thus could possibly impact atmospheric conditions during the MJO. Establishing the magnitude and extent of SSS variations during the MJO will be a useful tool for data assimilation into models to correctly represent both oceanic thermodynamic characteristics and atmospheric processes during intraseasonal variations.

Tropical Atlantic Dust and Smoke Aerosol Variabilities Related to the Madden-Julian Oscillation in MODIS and MISR Observations

NASA Technical Reports Server (NTRS)

Guo, Yanjuan; Tian, Baijun; Kahn, Ralph A.; Kalashnikova, Olga; Wong, Sun; Waliser, Duane E.

2012-01-01

In this study, MODIS fine mode fraction and MISR non-spherical fraction are 2used to derive dust and smoke AOT components (tau(sub dust) and tau(sub smoke)) over the tropical Atlantic, and their variabilities related to the Madden-Julian Oscillation (MJO) are then investigated. Both MODIS and MISR show a very similar dust and smoke winter climatology. tau(sub dust) is found to be the dominant aerosol component over the tropical Atlantic while tau(sub smoke) is significantly smaller than tau(sub dust). The daily MODIS and MISR tau(sub dust) are overall highly correlated, with the correlation coefficients typically about 0.7 over the North Atlantic. The consistency between the MODIS and MISR dust and smoke aerosol climatology and daily variations give us confidence to use these two data sets to investigate their relative contributions to the total AOT variation associated with the MJO. However, unlike the MISR dust discrimination, which is based on particle shape retrievals, the smoke discrimination is less certain, based on assumed partitioning of maritime aerosol for both MISR and MODIS. The temporal evolution and spatial patterns of the tau(sub dust) anomalies associated with the MJO are consistent between MODIS and MISR. The tau(sub dust) anomalies are very similar to those of tau anomalies, and are of comparable magnitude. In contrast, the MJO-related tau(sub smoke) anomalies are rather small, and the tau(sub mar) anomalies are negligible. The consistency between the MODIS and MISR results suggests that dust aerosol is the dominant component on the intra-seasonal time scale over the tropical Atlantic Ocean.

Oceanic Feedback to the Madden-Julian Oscillation: Mixing's Critical Role

NASA Astrophysics Data System (ADS)

Moum, J. N.; Pujiana, K.; Lien, R. C.; Smyth, W.

2016-02-01

The Madden-Julian Oscillation (MJO) in the Indian Ocean is a large-scale, propagating atmospheric disturbance in the equatorial latitude band characterized by reduced outgoing longwave radiation due to deep atmospheric convection, and at the surface by intense westerly wind bursts and a change in sign of the net surface heat flux. The ocean response is the formation of a near-surface Yoshida-Wyrtki Jet, which accelerates almost in balance with the surface wind stress. High shear at the Jet's base drives intense turbulence, both of which continue long after the atmospheric disturbance has passed (Moum et al., 2014). The sequence of MJOs observed in the 2011-2012 DYNAMO experiment suggested the possibility that the greater mixing due to more intense MJO wind bursts might reduce SST recovery rates following MJO passage, thus reducing upper ocean heat content available to drive future atmospheric convection. We have tested this with a statistical analysis of less-complete historical observations of MJOs documenting 50 previous events. Our analysis shows that 1) SST increases more rapidly following weak MJOs than strong MJOs, and within a 60-day window, 2) weak MJOs follow strong MJOs (and do not follow weak MJOs), 3) strong MJOs follow weak MJOs (and do not follow strong MJOs). We hypothesize that these results are the consequence of Jet-forced variations in subsurface mixing on SST recovery rates, thereby providing direct feedback to subsequent MJOs. Moum, J.N., S.P. de Szoeke, W.D. Smyth, J.B. Edson, H.L. DeWitt, A.J. Moulin, E.J. Thompson, C.J. Zappa, S.A. Rutledge, R.H. Johnson and C.W. Fairall, 2014. Air-sea interactions from westerly wind bursts during the November 2011 MJO in the Indian Ocean. Bull.Am.Met.Soc., 95, 1185-1199.

Advancing Atmospheric River Forecasts into Subseasonal-to-Seasonal Timescales

NASA Astrophysics Data System (ADS)

Barnes, E. A.; Baggett, C.; Mundhenk, B. D.; Nardi, K.; Maloney, E. D.

2017-12-01

Atmospheric rivers can cause considerable mayhem along the west coast of North America - delivering flooding rains during periods of heightened activity and desiccating droughts during periods of reduced activity. The intrinsic chaos of the atmosphere makes the prediction of atmospheric rivers at subseasonal-to-seasonal (S2S) timescales ( 2 to 6 weeks) an inherently difficult task. We demonstrate here that the potential exists to advance forecast lead times of atmospheric rivers into S2S timescales through knowledge of two of the atmosphere's most prominent oscillations; the Madden-Julian oscillation (MJO) and the Quasi-biennial oscillation (QBO). The dynamical relationship between atmospheric rivers, the MJO and the QBO is hypothesized to occur through modulation of North Pacific blocking. We present an empirical prediction scheme for anomalous atmospheric river activity based solely on the MJO and QBO and demonstrate skillful subseasonal "forecasts of opportunity" 5+ weeks ahead. We conclude with a discussion of the ability of state-of-the-art NWP models to predict atmospheric river characteristics on S2S timescales. With the wide-ranging impacts associated with landfalling atmospheric rivers, even modest gains in the subseasonal prediction of anomalous atmospheric river activity may support early action decision making and benefit numerous sectors of society.

Boreal Summer ISO hindcast experiment: preliminary results from SNU

NASA Astrophysics Data System (ADS)

Heo, S.; Kang, I.; Kim, D.; Ham, Y.

2010-12-01

As a part of internationally coordinated research program, hindcast experiments with focus on boreal summer intraseasonal oscillation (ISO) have been done in Seoul National University (SNU). This study aims to show preliminary results from SNU’s efforts. The ISO prediction system used in the hindcast experiment consists of SNU coupled model and SNU initialization method. The SNU coupled model is an ocean-atmosphere coupled model which couples the SNU Atmospheric GCM (SNU AGCM) to the Modular Ocean Model ver.2.2 (MOM2.2) Ocean GCM developed at Geophysical Fluid Dynamics Laboratory (GFDL). In the SNU initialization method, both atmospheric and oceanic states are nudged toward reanalysis data (ERAinterim and GODAS) before prediction starting date. For the results here, 2 ensemble members are generated by using different nudging period, 8 and 9 days, respectively. The initial dates of 45-day predictions are the 1st, 11th, 21st of months during boreal summer season (May to October). Prediction skills and its dependency on the initial amplitude, the initial phase, and the number of ensemble members are investigated using the Real-time Multivariate MJO (RMM) index suggested by Wheeler and Hendon (2004). It is shown in our hindcast experiment that, after 13 forecast lead days (the forecast skill is about 0.7), the prediction skill does not depend on the strength of the initial state. Also, we found that the prediction skill has a phase dependency. The prediction skill is particularly low when the convective center related to the MJO is over the Indian Ocean (phase 2). The ensemble prediction has more improved correlation skill than each member. To better understand the phase dependency, we compared the observed and predicted behavior of the MJO that propagates from different starting phases. The phase speed of the prediction is slower than the observation. The MJO in the hindcast experiment propagates with weaker amplitudes than observed except for initial phase 3. Also investigated is the climatology and anomalies of precipitable water to understand the difference of the propagation. The difference between observed and predicted climatology shows strong dry bias over the eastern Indian Ocean, in where convective anomalies are not properly developed in hindcast data, especially those from initial phase 2. Our results suggest possible impacts of mean bias on prediction skills of the MJO.

Microphysical Analysis using Airborne 2-D Cloud and Precipitation Imaging Probe Data

NASA Astrophysics Data System (ADS)

Guy, N.; Jorgensen, D.; Witte, M.; Chuang, P. Y.; Black, R. A.

2013-12-01

The NOAA P-3 instrumented aircraft provided in-situ cloud and precipitation microphysical observations during the DYNAMO (Dynamics of the Madden-Julian Oscillation) field experiment. The Particle Measuring System 2D cloud (2D-C) and precipitation (2D-P) probes collected data for particles between 12.5 μm - 1.55 mm (25 μm resolution) and 100 μm - 6.2 mm (100 μm resolution), respectively. Spectra from each instrument were combined to provide a broad distribution of precipitation particle sizes. The 'method of moments' technique was used to analyze drop size distribution (DSD) spectra, which were modeled by fitting a three-parameter (slope, shape, and intercept) gamma distribution to the spectra. The characteristic shape of the mean spectrum compares to previous maritime measurements. DSD variability will be presented with respect to the temporal evolution of cloud populations during a Madden-Julian Oscillation (MJO) event, as well as in-situ aircraft vertical wind velocity measurements. Using the third and sixth moments, rainfall rate (R) and equivalent radar reflectivity factor (Z), respectively, were computed for each DSD. Linear regression was applied to establish a Z-R relationship for the data for the estimation of precipitation. The study indicated unique characteristics of microphysical processes for this region. These results are important to continue to define the cloud population characteristics in the climatological MJO region. Improved representation of the cloud characteristics on the microphysical scale will serve as a check to model parameterizations, helping to improve numerical simulations.

Shallow cloud statistics over Tropical Western Pacific: CAM5 versus ARM Comparison

NASA Astrophysics Data System (ADS)

Chandra, A.; Zhang, C.; Klein, S. A.; Ma, H. Y.; Kollias, P.; Xie, S.

2014-12-01

The role of shallow convection in the tropical convective cloud life cycle has received increasing interest because of its sensitivity to simulate large-scale tropical disturbances such as MJO. Though previous studies have proposed several hypotheses to explain the role of shallow clouds in the convective life cycle, our understanding on the role of shallow clouds is still premature. There are more questions needs to be addressed related to the role of different cloud population, conditions favorable for shallow to deep convection transitions, and their characteristics at different stages of the convective cloud life. The present study aims to improve the understanding of the shallow clouds by documenting the role of different shallow cloud population for the Year of Tropical Convection period using Atmospheric Radiation Measurement observations at the Tropical Western Pacific Manus site. The performance of the CAM5 model to simulate shallow clouds are tested using observed cloud statistics.

Intraseasonal Oscillations over South America: A Study with a Regional Climate Model

NASA Technical Reports Server (NTRS)

Chen, Baode; Chao, Winston

2003-01-01

The National Center for Atmospheric Research (NCAR) regional climate model version 2 (RegCM2) is used to investigate the observed characteristics of intraseasonal oscillations over South America. Our study is mainly concentrated on an intraseaonal mode, which is observed to account for a large portion of the intraseasonal variation, to have a standing feature and to be independent of the MJO. The NCEPDOE AMIP-II reanalysis is utilized to provide initial and lateral boundary conditions for the RegCM2 based upon the OOZ, 062, 122 and 182 data.Our results indicate that the intraseasonal oscillation still exists with time- averaged lateral boundary condition, which prevents the MJO and other outside disturbances from entering the model's domain, suggesting a locally forced oscillation responsible for ths intraseasonal mode independent of the MJO. Further experiments show that the annual and daily variabilities and a radiative-convective interaction are not essential to the locally forced intraseasonal oscillation. The intraseasonal oscillations over Amazon in our model essentially result from interactions among atmospheric continental- scale circulation, surface radiation, surface sensible and latent heat fluxes, and cumulus convection. The wavelet analyses of various surface energy fluxes and surface energy budget also verify that the primary cause of intraseasonal oscillation is the interaction of land surface processes with the atmosphere.

Climate extremes in Malaysia and the equatorial South China Sea

NASA Astrophysics Data System (ADS)

Salahuddin, Ahmed; Curtis, Scott

2011-08-01

The southern extent of the South China Sea (SCS) is an important natural resource epicenter for Malaysia which experiences climate extremes. This paper documents the variability of extremes in the equatorial SCS through selected ground-based observations of precipitation in Malaysia and ship-based observations of wind data in the Maritime Continent region, to elucidate the interrelationship between precipitation variability over Malaysia and wind variability over the ocean. The data have been carefully inspected and analyzed, and related to the real-time multivariate Madden-Julian Oscillation (MJO) time series. The analysis suggests that the northeast or boreal winter monsoon dominates extreme rainfall in eastern Malaysian cities. Further, the west coast of Peninsular Malaysia and Borneo Malaysia are affected by the MJO differently than the east coast of Peninsular Malaysia. From the wind analysis we found that average zonal wind is westerly from May to September and easterly from November to April. When the active (convective) phase of the MJO is centered over the Maritime Continent, the strong westerly wind bursts are more frequent in the South China Sea. While more investigation is needed, these results suggest that the status of the Madden-Julian Oscillation can be used to help forecast climate extremes in areas of Malaysia.

Addressing model error through atmospheric stochastic physical parametrizations: impact on the coupled ECMWF seasonal forecasting system

PubMed Central

Weisheimer, Antje; Corti, Susanna; Palmer, Tim; Vitart, Frederic

2014-01-01

The finite resolution of general circulation models of the coupled atmosphere–ocean system and the effects of sub-grid-scale variability present a major source of uncertainty in model simulations on all time scales. The European Centre for Medium-Range Weather Forecasts has been at the forefront of developing new approaches to account for these uncertainties. In particular, the stochastically perturbed physical tendency scheme and the stochastically perturbed backscatter algorithm for the atmosphere are now used routinely for global numerical weather prediction. The European Centre also performs long-range predictions of the coupled atmosphere–ocean climate system in operational forecast mode, and the latest seasonal forecasting system—System 4—has the stochastically perturbed tendency and backscatter schemes implemented in a similar way to that for the medium-range weather forecasts. Here, we present results of the impact of these schemes in System 4 by contrasting the operational performance on seasonal time scales during the retrospective forecast period 1981–2010 with comparable simulations that do not account for the representation of model uncertainty. We find that the stochastic tendency perturbation schemes helped to reduce excessively strong convective activity especially over the Maritime Continent and the tropical Western Pacific, leading to reduced biases of the outgoing longwave radiation (OLR), cloud cover, precipitation and near-surface winds. Positive impact was also found for the statistics of the Madden–Julian oscillation (MJO), showing an increase in the frequencies and amplitudes of MJO events. Further, the errors of El Niño southern oscillation forecasts become smaller, whereas increases in ensemble spread lead to a better calibrated system if the stochastic tendency is activated. The backscatter scheme has overall neutral impact. Finally, evidence for noise-activated regime transitions has been found in a cluster analysis of mid-latitude circulation regimes over the Pacific–North America region. PMID:24842026

Addressing model error through atmospheric stochastic physical parametrizations: impact on the coupled ECMWF seasonal forecasting system.

PubMed

Weisheimer, Antje; Corti, Susanna; Palmer, Tim; Vitart, Frederic

2014-06-28

The finite resolution of general circulation models of the coupled atmosphere-ocean system and the effects of sub-grid-scale variability present a major source of uncertainty in model simulations on all time scales. The European Centre for Medium-Range Weather Forecasts has been at the forefront of developing new approaches to account for these uncertainties. In particular, the stochastically perturbed physical tendency scheme and the stochastically perturbed backscatter algorithm for the atmosphere are now used routinely for global numerical weather prediction. The European Centre also performs long-range predictions of the coupled atmosphere-ocean climate system in operational forecast mode, and the latest seasonal forecasting system--System 4--has the stochastically perturbed tendency and backscatter schemes implemented in a similar way to that for the medium-range weather forecasts. Here, we present results of the impact of these schemes in System 4 by contrasting the operational performance on seasonal time scales during the retrospective forecast period 1981-2010 with comparable simulations that do not account for the representation of model uncertainty. We find that the stochastic tendency perturbation schemes helped to reduce excessively strong convective activity especially over the Maritime Continent and the tropical Western Pacific, leading to reduced biases of the outgoing longwave radiation (OLR), cloud cover, precipitation and near-surface winds. Positive impact was also found for the statistics of the Madden-Julian oscillation (MJO), showing an increase in the frequencies and amplitudes of MJO events. Further, the errors of El Niño southern oscillation forecasts become smaller, whereas increases in ensemble spread lead to a better calibrated system if the stochastic tendency is activated. The backscatter scheme has overall neutral impact. Finally, evidence for noise-activated regime transitions has been found in a cluster analysis of mid-latitude circulation regimes over the Pacific-North America region.

Trend analysis of tropical intraseasonal oscillations in the summer and winter during 1982-2009

NASA Astrophysics Data System (ADS)

Tao, Li; Zhao, Jiuwei; Li, Tim

2015-04-01

Based on the daily outgoing long-wave radiation (OLR) data of the National Oceanic and Atmospheric Administration (NOAA) from 1979 to 2012, we investigated the intensity changes of the 20-70-d boreal summer (June-September; JJAS) intra-seasonal oscillation (BSISO) and winter (December-February; DJF) intra-seasonal oscillation, also known as the Madden-Julian Oscillation (MJO). The results showed that the intensity of the BSISO has a significant intensifying trend during 1982-2009. On the other hand, little trend was found for boreal winter MJO during this period. The wavenumber-frequency analysis (Hayashi, 1982) was applied to separate ISO into westward propagation and eastward propagation parts. The significant intensified trend was observed over tropical Indian Ocean for the eastward-propagation BSISO. The weakened but not significant trend was observed over southern tropical Indian Ocean for the eastward-propagation MJO. To gain insight into the different ISO characteristics, the tendencies of sea surface temperature (SST) and the vertical shear of zonal wind were analyzed. The results showed that in both seasons from 1982 to 2009, the global SST trends were similar, and thus they could not be used to explain the BSISO upward trend. However, lower-tropospheric easterly shear in boreal summer over tropical Indian Ocean has a decreasing trend, while the easterly vertical shear over maritime continent was enhanced in winter. It is proposed that the reduced easterly vertical shear over tropical Indian Ocean favored the amplification of the eastward-propagating Kelvin wave, which led to the intensified eastward-propagating BSISO. The enhanced easterly vertical shear over maritime continent might be unfavorable to the amplification of the eastward-propagating Kelvin wave, but its impact was offset by the enhanced upward motion over maritime continent. As a result, there was little trend of the MJO in boreal winter. The hypothesis above was further verified by intermediate model results.

Madden-Julian Oscillation (MJO) Signal over Kototabang, West Sumatera Based on the Mini Automatic Weather Station (MAWS) Data Analysis Using the Wavelet Technique

NASA Astrophysics Data System (ADS)

Hermawan, E.

2018-04-01

This study is mainly concerned an application of Mini Automatic Weather Station (MAWS) at Kototabang, West Sumatera nearby the location of an Equatorial Atmosphere Radar (EAR) side. We are interest to use this data to investigate the propagation of the Madden-Julian Oscillation (MJO). We examined of daily MAWS data for 3 years observations started from January 2001 to Mei 2004. By applying wavelet analysis, we found the MJO at Kototabang have 32 days oscillations as shown in Fig.1 below. In this study, we concentrate just for local mechanis only. We will show in this paper that at the phase of the MJO with a dipole structure to the convection anomalies, there is enhanced tropical convection over the eastern Indian Ocean and reduced convection over the western Pacific. Over the equatorial western Indian Ocean, the equatorial Rossby wave response to the west of the enhanced convection includes a region of anomalous surface divergence associated with the anomalous surface westerlies and pressure ridge. This tends to suppress ascent in the boundary layer and shuts off the deep convection, eventually leading to a convective anomaly of the opposite sign. Over the Indonesian sector, the equatorial Kelvin wave response to the east of the enhanced convection includes a region of anomalous surface convergence into the anomalous equatorial surface easterlies and pressure trough, which will tend to favour convection in this region. The Indonesian sector is also influenced by an equatorial Rossby wave response (of opposite sign) to the west of the reduced convection over the western Pacific, which also has a region of anomalous surface convergence associated with its anomalous equatorial surface easterlies and pressure trough. Hence, convective anomalies of either sign tend to erode themselves from the west and initiate a convective anomaly of opposite sign via their equatorial Rossby wave response, and expand to the east via their equatorial Kelvin wave response.

Sub-seasonal prediction of significant wave heights over the Western Pacific and Indian Oceans, part II: The impact of ENSO and MJO

NASA Astrophysics Data System (ADS)

Shukla, Ravi P.; Kinter, James L.; Shin, Chul-Su

2018-03-01

This study evaluates the effect of El Niño and the Southern Oscillation (ENSO) and Madden Julian Oscillation (MJO) events on 14-day mean significant wave height (SWH) at 3 weeks lead time (Wk34) over the Western Pacific and Indian Oceans using the National Centers for Environmental Prediction (NCEP) Climate Forecast System, version 2 (CFSv2). The WAVEWATCH-3 (WW3) model is forced with daily 10m-winds predicted by a modified version of CFSv2 that is initialized with multiple ocean analyses in both January and May for 1979-2008. A significant anomaly correlation of predicted and observed SWH anomalies (SWHA) at Wk34 lead-time is found over portions of the domain, including the central western Pacific, South China Sea (SCS), Bay of Bengal (BOB) and southern Indian Ocean (IO) in January cases, and over BOB, equatorial western Pacific, the Maritime Continent and southern IO in May cases. The model successfully predicts almost all the important features of the observed composite SWHA during El Niño events in January, including negative SWHA in the central IO where westerly wind anomalies act on an easterly mean state, and positive SWHA over the southern Ocean (SO) where westerly wind anomalies act on a westerly mean state. The model successfully predicts the sign and magnitude of SWHA at Wk34 lead-time in May over the BOB and SCS in composites of combined phases-2-3 and phases-6-7 of MJO. The observed leading mode of SWHA in May and the third mode of SWHA in January are influenced by the combined effects of ENSO and MJO. Based on spatial and temporal correlations, the spatial patterns of SWHA in the model at Wk34 in both January and May are in good agreement with the observations over the equatorial western Pacific, equatorial and southern IO, and SO.

Tropical Intraseasonal Variability in Version 3 of the GFDL Atmosphere Model

NASA Astrophysics Data System (ADS)

Benedict, J. J.; Maloney, E. D.; Sobel, A. H.; Frierson, D. M.; Donner, L.

2012-12-01

Tropical intraseasonal variability is examined in version 3 of the Geophysical Fluid Dynamics Laboratory Atmosphere Model (AM3). Compared to its predecessor AM2, AM3 uses a new treatment of deep and shallow cumulus convection and mesoscale clouds. The AM3 cumulus parameterization is a mass flux-based scheme but also, unlike that in AM2, incorporates subgrid-scale vertical velocities; these play a key role in cumulus microphysical processes. The AM3 convection scheme allows multi-phase water substance produced in deep cumuli to be transported directly into mesoscale clouds, which strongly influence large-scale moisture and radiation fields. We examine four AM3 simulations, using a control model and three versions with different modifications to the deep convection scheme. In the control AM3, using a convective closure based on CAPE relaxation, both the MJO and Kelvin waves are weak compared to those in observations. By modifying the convective closure and trigger assumptions to inhibit deep cumuli, AM3 produces reasonable intraseasonal variability but a degraded mean state. MJO-like disturbances in the modified AM3 propagate eastward at roughly the observed speed in the Indian Ocean but up to twice the observed speed in the West Pacific. Distinct differences in intraseasonal convective organization and propagation exist among the modified AM3 versions. Differences in vertical diabatic heating profiles associated with the MJO are also found. The two AM3 versions with the strongest intraseasonal signals have a more prominent "bottom-heavy" heating profile leading the disturbance center and "top-heavy" heating profile following the disturbance. The more realistic heating structures are associated with an improved depiction of moisture convergence and intraseasonal convective organization in AM3.ag correlations of 850 hPa zonal wind with precipitation at (left column) 90°E and (right column) 150°E. Both fields are bandpass filtered (20-100 days) and averaged between 15°S-15°N. Solid (dashed) contours represent positive (negative) correlations that are shaded dark (light) gray if they exceed the 95% statistical significance level. We use ERAI and TRMM for the observed wind and rainfall fields. In the left panels, index reference longitudes and the 5 m/s phase speed are marked by vertical and slanted thick lines, respectively. Right panels also contain the 10 m/s phase speed line.

Easterly and westerly wind events in the equatorial Pacific ocean and their oceanic response

NASA Astrophysics Data System (ADS)

Puy, martin; Lengaigne, matthieu; Vialard, jerome; Guilyardi, eric

2014-05-01

Intraseasonal wind variability is known to influence the onset and evolution of the El Niño Southern Oscillation (ENSO), in particular through the occurrence of Westerly Wind Events (WWEs) in the western Equatorial Pacific. For predictability purposes, it is important to identify the large scale atmospheric controls of the occurrences of those WWEs. We hence carefully assess the link between equatorial WWEs and large-scale atmospheric waves. We find that WWEs preferably occur during convectively active phases associated to equatorial atmospheric Rossby waves (74% against 15% if the distribution was random) and to the MJO (60% against 15%). We also find that WWEs that occur in relation with those atmospheric waves tend to be stronger. The results also show that WWEs that occur in relation with the MJO tend to be longer than others, and tend to have a larger impact on SST, both on the eastern edge of the warm pool and in the eastern Pacific. We further show that the central and eastern equatorial Pacific is home to frequent easterly wind events (EWEs). These EWEs are further shown to be influenced by atmospheric Rossby waves and the MJO, but to a lesser extent than WWEs. We will discuss the potential influence of EWEs on the ENSO cycle, and propose a modeling strategy to test the influence of these EWEs / WWEs on the ENSO evolution.

Convectively-coupled Kelvin waves over the tropical Atlantic and African regions and their influence on Atlantic tropical cyclogenesis

NASA Astrophysics Data System (ADS)

Ventrice, Michael J.

High-amplitude convectively coupled atmospheric Kelvin waves (CCKWs) are explored over the tropical Atlantic during the boreal summer. Atlantic tropical cyclogenesis is found to be more frequent during the passage of the convectively active phase of the CCKW, and most frequent two days after its passage. CCKWs impact convection within the mean latitude of the inter-tropical convergence zone over the northern tropical Atlantic. In addition to convection, CCKWs also impact the large scale environment that favors Atlantic tropical cyclogenesis (i.e., deep vertical wind shear, moisture, and low-level relative vorticity). African easterly waves (AEWs) are known to be the main precursors for Atlantic tropical cyclones. Therefore, the relationship between CCKWs and AEW activity during boreal summer is explored. AEW activity is found to increase over the Guinea Highlands and Darfur Mountains during and after the passage of the convectively active phase of the CCKW. First, CCKWs increase the number of convective triggers for AEW genesis. Secondly, the associated zonal wind structure of the CCKW is found to affect the horizontal shear on the equatorward side of the African easterly jet (AEJ), such that the jet becomes more unstable during and after the passage of the convectively active phase of the CCKW. The more unstable AEJ is assumed to play a role with increased AEW growth. Through the increased number of AEWs propagating over the tropical Atlantic, as well as from the direct impact on convection and the large-scale environment over the tropical Atlantic, CCKWs are recommended to be used as a means for medium-range predictability of Atlantic tropical cyclones. In addition to modulating tropical cyclone activity over the tropical Atlantic, CCKWs might impact the intensification processes of tropical cyclones. A case study highlighting two August 2010 tropical cyclones (Danielle and Earl) is explored for potential CCKW-tropical cyclone interactions. While predicted to intensify by most model guidance, both Danielle and Earl struggled to do so. It is shown that Danielle and Earl interacted with the convectively suppressed phase of an eastward propagating CCKW during the time they were predicted to intensify. Composite analysis shows that during and after the passage of the convectively suppressed phase of the CCKW over the Atlantic, large-scale vertical wind shear increases as a result of anomalous upper-level westerlies collocated with anomalous lower-level easterlies. Large-scale subsidence associated with the convectively suppressed phase of the CCKW causes the atmosphere to dry. Further, when the upper-level westerly wind anomalies associated with the CCKW are located over the equatorial Atlantic, a tropical upper-tropospheric trough (TUTT) develops over the northern tropical Atlantic. TUTTs are upper-level disturbances known to negatively impact the intensity of tropical cyclones. CCKWs over the tropical Atlantic tend to occur during preferable locations of the Madden-Julian Oscillation (MJO). Results show that the MJO significantly modulates Atlantic tropical cyclogenesis using real-time multivariate MJO indices. Like CCKWs, AEW activity is found to vary coherently with MJO passages. Furthermore, the MJO also impacts the large-scale environment that favors for Atlantic tropical cyclogenesis. Therefore in addition to CCKWs, the state of the MJO should be used for Atlantic tropical cyclogenesis medium-range predictability.

Coastal heavy rainband formed along Sumatera Island, Indonesia, observed with X-band Doppler radars during HARIMAU2011 campaign

NASA Astrophysics Data System (ADS)

Mori, Shuichi; Jun-Ichi, Hamada; Hattori, Miki; Kamimera, Hideyuki; Wu, Peiming; Arbain, Ardhi A.; Lestari, Sopia; Syamsudin, Fadli; Yamanaka, Manabu D.

2013-04-01

Coastal heavy rainbands (CHeRs) are widely identified over Asian monsoon region (e.g., Western Ghats, Bay of Bengal, Gulf of Thailand, and western Philippines) by satellite observations. Some of them are explained by synoptic wind-terrain interaction (Xie et al., 2006 JC) because they are anchored along mountain ranges face to southwest direction and predominant during boreal summer southwesterly monsoon season. Most Asian megacities are located in coastal regions, thus they have much chance to be suffered from torrential rainfall embedded in CHeRs which may cause flash floods in downtown cities and landslides in mountainous regions. Moreover, rainfall amount over the coastal land varies quite largely if those CHeRs change their lateral location a little, therefore water resource management for social community is seriously sensitive to their variability. Satellite observations show that CHeRs are modified by various kinds of environmental variations, e.g., diurnal, intraseasonal, monsoonal, ENSO, and IOD. However, climatology, structure, and mechanism of CHeRs have not been examined in detail from mesoscale points of view because there are quite few studies based on ground based radar observations. Previous studies (e.g., Mori et al. 2004 MWR; Yamanaka et al. 2008 JDR; Wu et al. 2007 SOLA) showed most CHeRs in Indonesia are identified along coastlines where convective diurnal variation is predominant, and coastal heavy rain are brought mainly in the nighttime observed with a radar-profiler network deployed by Hydrometeorological ARray for Intraseasonal variation (ISV) - Monsoon AUtomonitoring (HARIMAU) project. In addition, they are confirmed even in the seasons when the wind-terrain interaction cannot explain them well. These results suggest that CHeRs are formed by not only the synoptic wind-terrain effect but also mesoscale convections which developed nocturnally everyday along coastlines. We carried out the HARIMAU2011 campaign observation over Sumatera Island, Indonesia, during 01-31 December 2011 in collaboration with CINDY and DYNAMO to study the CHeR formed along the southwestern coastline of Sumatera Island by using X-band Doppler and dual polarimetric (DP) radars, intensive soundings at two stations, disdrometers, and surface observation network. Two MJOs (MJO-2 and -3) were identified which passed over Sumatera Island during the campaign period. We divided the period into four phases: MJO-2 active (phase-I), MJO inactive (phase-II), MJO-3 active (phase-III), and MJO inactive (phase IV). CHeRs organized by a lot of mesoscale convections were observed throughout the period, however, those convections developed mainly over the coastal sea, coastal land, and both coastal sea and land, during phase-I, -II, and -III, respectively. Diurnal cycle of convections was not clear during the phase-I and -II. Whereas, that during the phase-III was clearly observed and a lot of convections were identified which migrated from the coastal land to sea during the night. Radar observations showed CHeRs were formed by both convections, a) generated originally over the coastal land in the evening and developed in the night after migrated into the sea, b) generated over the coastal sea in the night and developed independently. Environmental conditions including MJO activity and local circulations were also examined in terms of CHeR formation process.

Dynamics of the Seychelles-Chagos Thermocline Ridge

NASA Astrophysics Data System (ADS)

Bulusu, S.

2016-02-01

The southwest tropical Indian Ocean (SWTIO) features a unique, seasonal upwelling of the thermocline also known as the Seychelles-Chagos Thermocline Ridge (SCTR). More recently, this ridge or "dome"-like feature in the thermocline depth at (55°E-65°E, 5°S-12°S) in the SWTIO has been linked to interannual variability in the semi-annual Indian Ocean monsoon seasons as well as the Madden-Julian Oscillation (MJO) and El Niño Southern Oscillation (ENSO). The SCTR is a region where the MJO is associated with strong SST variability. Normally more cyclones are found generated in this SCTR region when the thermocline is deeper, which has a positive relation to the arrival of a downwelling Rossby wave from the southeast tropical Indian Ocean. Previous studies have focused their efforts solely on sea surface temperature (SST) because they determined salinity variability to be low, but with the Soil Moisture and Ocean Salinity (SMOS), and Aquarius salinity missions new insight can be shed on the effects that the seasonal upwelling of the thermocline has on Sea Surface Salinity (SSS). Seasonal SSS anomalies these missions will reveal the magnitude of seasonal SSS variability, while Argo depth profiles will show the link between changes in subsurface salinity and temperature structure. A seasonal increase in SST and a decrease in SSS associated with the downwelling of the thermocline have also been shown to occasionally generate MJO events, an extremely important part of climate variability in the Indian ocean. Satellite derives salinity and Argo data can help link changes in surface and subsurface salinity structure to the generation of the important MJO events. This study uses satellite derived salinity from Soil Moisture and Ocean Salinity (SMOS), and Aquarius to see if these satellites can yield new information on seasonal and interannual surface variability. In this study barrier layer thickness (BLT) estimates will be derived from satellite measurements using a multilinear regression model (MRM). This study will help to improve monsoon modeling and forecasting, two areas that remain highly inaccurate after decades of research work.

Simulation of monsoon intraseasonal oscillations in a coarse-resolution aquaplanet GCM

NASA Astrophysics Data System (ADS)

Ajayamohan, R. S.; Khouider, Boualem; Majda, Andrew J.

2014-08-01

The skill of the global climate models (GCMs) to realistically simulate the monsoon intraseasonal oscillations (MISOs) is related to the sensitivity of their convective parameterization schemes. Here we show that by coupling a simple multicloud parameterization to a coarse-resolution aquaplanet GCM, realistic MISOs can be simulated. We conduct three different simulations with a fixed nonhomogeneous sea surface temperature mimicking the Indian Ocean/western Pacific warm pool (WP) centered at the three latitudes 5°N, 10°N, and 15°N, respectively, to replicate the seasonal migration of the Tropical Convergence Zone (TCZ). This results in the generation of mean circulation resembling the monsoonal flow pattern in boreal summer. Succession of eastward propagating Madden-Julian Oscillation (MJO) disturbances with phase speed, amplitude, and structure similar to summer MJOs are simulated when the WP is at 5°N. When the WP is located over 10°N, northward and eastward propagating MISOs are simulated. This case captures the meridional seesaw of convection between continental and oceanic TCZ observed during boreal summer over South Asia. Westward propagating Rossby wave-like disturbances are simulated when the WP is over 15°N congruous with the synoptic disturbances seen over the monsoon trough. The initiation of intraseasonal oscillations in the model can occur internally through organization of convective events above the WP associated with internal dynamics.

Rain Hampers Tsunami Relief Efforts

NASA Technical Reports Server (NTRS)

2005-01-01

The cleanup and relief efforts from the recent tsunamis continue in coastal communities that were ravaged by the waves all across the Indian Ocean. Heavy rains have further complicated the matter and added to the misery in parts of eastern Sri Lanka. Between December 28, 2004, and January 5, 2005, up to 10 to 15 inches of rain may have fallen along the southeast coast of the island, and as much as 20 inches (red areas) fell just offshore. This rainfall map was created by the TRMM-based, near-real time Multi-satellite Precipitation Analysis (MPA) at the NASA Goddard Space Flight Center, which monitors rainfall over the global tropics. The map shows that many other regions around the Indian Ocean were also affected by the rains, including Malaysia and parts of Sumatra. The heaviest rains fell on December 31 and January 4. The rains were likely the result of a combination of the northeast monsoon interacting with the topography and an active phase of what is known as the Madden-Julian Oscillation (MJO) (or 30-60 day oscillation). The MJO is a large-scale disturbance that propagates eastward from the Indian Ocean into the West Pacific Ocean, bringing extended periods of unsettled weather with it. Individual convective complexes within the MJO can last on the order of a day. TRMM is a joint mission between NASA and the Japanese space agency JAXA. NASA image produced by Hal Pierce (SSAI/NASA GSFC) and caption by Steve Lang (SSAI/NASA GSFC).

Stochasticity and organization of tropical convection: Role of stratiform heating in the simulation of MJO in an aquaplanet coarse resolution GCM using a stochastic multicloud parameterization

NASA Astrophysics Data System (ADS)

Khouider, B.; Majda, A.; Deng, Q.; Ravindran, A. M.

2015-12-01

Global climate models (GCMs) are large computer codes based on the discretization of the equations of atmospheric and oceanic motions coupled to various processes of transfer of heat, moisture and other constituents between land, atmosphere, and oceans. Because of computing power limitations, typical GCM grid resolution is on the order of 100 km and the effects of many physical processes, occurring on smaller scales, on the climate system are represented through various closure recipes known as parameterizations. The parameterization of convective motions and many processes associated with cumulus clouds such as the exchange of latent heat and cloud radiative forcing are believed to be behind much of uncertainty in GCMs. Based on a lattice particle interacting system, the stochastic multicloud model (SMCM) provide a novel and efficient representation of the unresolved variability in GCMs due to organized tropical convection and the cloud cover. It is widely recognized that stratiform heating contributes significantly to tropical rainfall and to the dynamics of tropical convective systems by inducing a front-to-rear tilt in the heating profile. Stratiform anvils forming in the wake of deep convection play a central role in the dynamics of tropical mesoscale convective systems. Here, aquaplanet simulations with a warm pool like surface forcing, based on a coarse-resolution GCM , of ˜170 km grid mesh, coupled with SMCM, are used to demonstrate the importance of stratiform heating for the organization of convection on planetary and intraseasonal scales. When some key model parameters are set to produce higher stratiform heating fractions, the model produces low-frequency and planetary-scale Madden Julian oscillation (MJO)-like wave disturbances while lower to moderate stratiform heating fractions yield mainly synoptic-scale convectively coupled Kelvin-like waves. Rooted from the stratiform instability, it is conjectured here that the strength and extent of stratiform downdrafts are key contributors to the scale selection of convective organizations perhaps with mechanisms that are in essence similar to those of mesoscale convective systems.

Evidence of an Intrinsic Intraseasonal Oscillation over Tropical South America During Austral Summer

NASA Technical Reports Server (NTRS)

Zhou, Jiayu; Lau, William K.-M.

2002-01-01

The intraseasonal variation (ISV) in the 30-60 day band, also known as Madden-Julian oscillation (MJO), has been studied for decades. Madden and Julian showed that the oscillation originated from the western Indian Ocean, propagated eastward, got enhanced over the maritime continent and weakened after passing over the dateline. Composite studies showed evidences of a signal in upper and lower level zonal wind propagating around the globe during an oscillation. Theoretical studies pointed out that the interaction with the warm ocean surface and the coupling with the convective and radiative processes in the atmosphere could manifest the oscillation, which propagates eastward via mutual feedbacks between the wave motions and the cumulus heating. Over tropical South America, no independent 30-60 day oscillation has been reported so far, despite that Amazon is the most distinct tropical convection center over the western hemisphere and the fluxes from its surface of tropical rainforests are close to that from the warm tropical ocean. Liebmann et al. showed a distinct spectral peak of 40-50 day oscillation in outgoing longwave radiation (OLR) over tropical South America and considered that was manifested by the MJO propagation. Nogues-Paegle et al. (2000) focused on a dipole pattern of the OLR anomaly with centers of action over the South Atlantic Convergence Zone (SACZ) and the subtropical plain. They used the regional 10-90 day filtered data and demonstrated this pattern could be represented by the fifth mode of the rotated empirical orthogonal function. Its principal component was further analyzed using the singular spectrum analysis. Their result showed two oscillatory modes with periods of 36-40 days and 22-28 days, of which the former was related to the MJO influence and the latter linked to the remote forcing over southwest of Australia, which produced a wave train propagating southeastward, rounding the southern tip of South America and returning back toward the northeast. The 22-28 day mode has distinct impact on SACZ, responsible for the regional seesaw pattern of alternating dry and wet conditions. In this study we will focus on the 30-60-day spectral band and investigate whether the independent oscillation source over tropical South America is existed. First, we will show the seasonal dependence of the tropical South American ISV in Section 3. Then, the leading principal modes of 30-60 day bandpass filtered 850-hPa velocity potential (VP850) will be computed to distinguish the stationary ISV over tropical South America (SISA) from the propagating MJO in the austral summertime in Section 4. The importance of SISA in representing the regional ISV over South America will be discussed. In Section 5, we will demonstrate the mass oscillation regime of SISA, which is well separated from that of MJO by the Andes, and the convective coupling with rainfall. The dynamical response of SISA and the impact on the South American summer monsoon (SASM) will be presented. Finally, we will give the concluding remarks.

Precipitation Anomalies in the Tropical Indian Ocean and Possible Links to the Initiation of El Nino

NASA Technical Reports Server (NTRS)

Curtis, Scott; Adler, Robert F.; Huffman, George J.; Starr, David OC. (Technical Monitor)

2001-01-01

A pattern of variability in precipitation and 1000mb zonal winds for the tropical Indian Ocean during, 1979 to 1999 (AtmIO mode) is described using EOFs. The AtmIO mode consists of a cross-equatorial gradient of precipitation anomalies and equatorial wind anomalies of alternating signs on the Equator. The positive phase is defined as enhanced precipitation to the In "n south of the equator, suppressed precipitation to the north, and anomalous westerlies centered on the island of Sumatra. In September-October 1981, February-March 1990, and October-December 1996 the AtmIO mod-, was positive and there was a significant 30-60 day variability in the gradient of precipitation anomalies. These cases coincided with moderate to heavy ,activity in the Madden-Jullan Oscillation (MJO). Links between the AtmIO, MJO, and El Nino are discussed.

Advancing atmospheric river forecasts into subseasonal-to-seasonal time scales

NASA Astrophysics Data System (ADS)

Baggett, Cory F.; Barnes, Elizabeth A.; Maloney, Eric D.; Mundhenk, Bryan D.

2017-07-01

Atmospheric rivers are elongated plumes of intense moisture transport that are capable of producing extreme and impactful weather. Along the West Coast of North America, they occasionally cause considerable mayhem—delivering flooding rains during periods of heightened activity and desiccating droughts during periods of reduced activity. The intrinsic chaos of the atmosphere makes the prediction of atmospheric rivers at subseasonal-to-seasonal time scales (3 to 5 weeks) an inherently difficult task. We demonstrate here that the potential exists to advance forecast lead times of atmospheric rivers into subseasonal-to-seasonal time scales through knowledge of two of the atmosphere's most prominent oscillations, the Madden-Julian oscillation (MJO) and the quasi-biennial oscillation (QBO). Strong MJO and QBO activity modulates the frequency at which atmospheric rivers strike—offering an opportunity to improve subseasonal-to-seasonal forecast models and thereby skillfully predict atmospheric river activity up to 5 weeks in advance.

Vertical structure and physical processes of the Madden-Julian Oscillation: Biases and uncertainties at short range

NASA Astrophysics Data System (ADS)

Xavier, Prince K.; Petch, Jon C.; Klingaman, Nicholas P.; Woolnough, Steve J.; Jiang, Xianan; Waliser, Duane E.; Caian, Mihaela; Cole, Jason; Hagos, Samson M.; Hannay, Cecile; Kim, Daehyun; Miyakawa, Tomoki; Pritchard, Michael S.; Roehrig, Romain; Shindo, Eiki; Vitart, Frederic; Wang, Hailan

2015-05-01

An analysis of diabatic heating and moistening processes from 12 to 36 h lead time forecasts from 12 Global Circulation Models are presented as part of the "Vertical structure and physical processes of the Madden-Julian Oscillation (MJO)" project. A lead time of 12-36 h is chosen to constrain the large-scale dynamics and thermodynamics to be close to observations while avoiding being too close to the initial spin-up of the models as they adjust to being driven from the Years of Tropical Convection (YOTC) analysis. A comparison of the vertical velocity and rainfall with the observations and YOTC analysis suggests that the phases of convection associated with the MJO are constrained in most models at this lead time although the rainfall in the suppressed phase is typically overestimated. Although the large-scale dynamics is reasonably constrained, moistening and heating profiles have large intermodel spread. In particular, there are large spreads in convective heating and moistening at midlevels during the transition to active convection. Radiative heating and cloud parameters have the largest relative spread across models at upper levels during the active phase. A detailed analysis of time step behavior shows that some models show strong intermittency in rainfall and differences in the precipitation and dynamics relationship between models. The wealth of model outputs archived during this project is a very valuable resource for model developers beyond the study of the MJO. In addition, the findings of this study can inform the design of process model experiments, and inform the priorities for field experiments and future observing systems.

Impact of DYNAMO observations on NASA GEOS-5 reanalyses and the representation of MJO initiation

NASA Astrophysics Data System (ADS)

Achuthavarier, D.; Wang, H.; Schubert, S. D.; Sienkiewicz, M.

2017-01-01

This study examines the impact of the Dynamics of the Madden-Julian Oscillation (DYNAMO) campaign in situ observations on NASA Goddard Earth Observing System version 5 (GEOS-5) reanalyses and the improvements gained thereby in the representation of the Madden-Julian Oscillation (MJO) initiation processes. To this end, we produced a global, high-resolution (1/4° spatially) reanalysis that assimilates the level-4, quality-controlled DYNAMO upper air soundings from about 87 stations in the equatorial Indian Ocean region along with a companion data-denied control reanalysis. The DYNAMO reanalysis produces a more realistic vertical structure of the temperature and moisture in the central tropical Indian Ocean by correcting the model biases, namely, the cold and dry biases in the lower troposphere and warm bias in the upper troposphere. The reanalysis horizontal winds are substantially improved, in that, the westerly acceleration and vertical shear of the zonal wind are enhanced. The DYNAMO reanalysis shows enhanced low-level diabatic heating, moisture anomalies and vertical velocity during the MJO initiation. Due to the warmer lower troposphere, the deep convection is invigorated, which is evident in convective cloud fraction. The GEOS-5 atmospheric general circulation model (AGCM) employed in the reanalysis is overall successful in assimilating the additional DYNAMO observations, except for an erroneous model response for medium rain rates, between 700 and 600 hPa, reminiscent of a bias in earlier versions of the AGCM. The moist heating profile shows a sharp decrease there due to the excessive convective rain re-evaporation, which is partly offset by the temperature increment produced by the analysis.

Effects of Cloud-Microphysics on Tropical Atmospheric Hydrologic Processes in the GEOS GCM

NASA Technical Reports Server (NTRS)

Lau, K. M.; Wu, H. T.; Sud, Y. C.; Walker, G. K.

2004-01-01

The sensitivity of tropical atmospheric hydrologic processes to cloud-microphysics is investigated using the NASA GEOS GCM. Results show that a faster autoconversion - rate produces more warm rain and less clouds at all levels. Fewer clouds enhances longwave cooling and reduces shortwave heating in the upper troposphere, while more warm rain produces increased condensation heating in the lower troposphere. This vertical heating differential destablizes the tropical atmosphere, producing a positive feedback resulting in more rain over the tropics. The feedback is maintained via a two-cell secondary circulation. The lower cell is capped by horizontal divergence and maximum cloud detrainment near the melting/freezing, with rising motion in the warm rain region connected to descending motion in the cold rain region. The upper cell is found above the freezing/melting level, with longwave-induced subsidence in the warm rain and dry regions, coupled to forced ascent in the deep convection region. The tropical large scale circulation is found to be very sensitive to the radiative-dynamic effects induced by changes in autoconversion rate. Reduced cloud-radiation processes feedback due to a faster autoconversion rate results in intermittent but more energetic eastward propagating Madden and Julian Oscillations (MJO). Conversely,-a slower autconversion rate, with increased cloud radiation produces MJO's with more realistic westward propagating transients, resembling a supercloud cluster structure. Results suggests that warm rain and associated low and mid level clouds, i.e., cumulus congestus, may play a critical role in regulating the time-intervals of deep convections and hence the fundamental time scales of the MJO.

Predictability of CFSv2 in the tropical Indo-Pacific region, at daily and subseasonal time scales

NASA Astrophysics Data System (ADS)

Krishnamurthy, V.

2018-06-01

The predictability of a coupled climate model is evaluated at daily and intraseasonal time scales in the tropical Indo-Pacific region during boreal summer and winter. This study has assessed the daily retrospective forecasts of the Climate Forecast System version 2 from the National Centers of Environmental Prediction for the period 1982-2010. The growth of errors in the forecasts of daily precipitation, monsoon intraseasonal oscillation (MISO) and the Madden-Julian oscillation (MJO) is studied. The seasonal cycle of the daily climatology of precipitation is reasonably well predicted except for the underestimation during the peak of summer. The anomalies follow the typical pattern of error growth in nonlinear systems and show no difference between summer and winter. The initial errors in all the cases are found to be in the nonlinear phase of the error growth. The doubling time of small errors is estimated by applying Lorenz error formula. For summer and winter, the doubling time of the forecast errors is in the range of 4-7 and 5-14 days while the doubling time of the predictability errors is 6-8 and 8-14 days, respectively. The doubling time in MISO during the summer and MJO during the winter is in the range of 12-14 days, indicating higher predictability and providing optimism for long-range prediction. There is no significant difference in the growth of forecasts errors originating from different phases of MISO and MJO, although the prediction of the active phase seems to be slightly better.

Understanding the temporal characteristics of the Madden-Julian Oscillation

NASA Astrophysics Data System (ADS)

Toma, V. E.; Webster, P. J.; Stephens, G. L.; Johnson, R. H.

2012-12-01

One of the great mysteries existing in the climate of the tropics is the background physics that define the 20-60 day period band of intraseasonal variability and the variance that occurs within it. Although the modal structure of the oscillations appears to match some of the spatial characteristics of normal modes of the tropics, there is no match between theoretical temporal structure and that which is observed. A previous paper (Stephens et al. 2004) defined the MJO as a self-regulating oscillator with three distinct phases: destabilization, convective and restoring. Whereas these three phases appear endemic among the variety of intraseasonal oscillations observed in the tropics, the theory provides little information about the temporal structure of the MJO or its variation within the observed range. We extend the exploration of the thermodynamic self-regulation of the MJO by including an ocean-atmosphere interaction component. We use a semi-empirical ocean -atmosphere coupled model (developed initially by Agudelo 2007) consisting of the Kantha-Clayson single column ocean layer model coupled to an empirical atmospheric model comprised of empirically derived linear relationships between atmospheric variables and SST. The result is a broad spectrum of OLR and surface winds in the 20-60 day range supporting the hypothesis that local coupling between the ocean and the atmosphere. Specifically, the time-scale of the self-regulation is mainly due to feedbacks between SST and both convective activity and surface wind speed control that the evolution of the surface radiative and latent heat fluxes in the model. The sensitivity of the response to imposed ocean-mixed layer depth suggests why intraseasonal variability has specific genesis locations with the tropics. The implications of these results for the prediction of the MJO and the interpretation of the DYNAMO results are discussed. Agudelo, P. A., 2007: Role of local thermodynamic coupling in the life cycle of the intraseasonal oscillation in the indo-pacific warm pool, PhD. Dissertation, School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Stephens, G. L., P. J. Webster, R. H. Johnson, R. Engelen and T. L'Ecuyer, 2004: Observational Evidence for the Mutual Regulation of the Tropical Hydrological Cycle and Tropical Sea Surface Temperatures. J. Climate: 17(11), 2213-2224.

Cloud statistics over the Indonesian Maritime Continent during the first and second CPEA campaigns

NASA Astrophysics Data System (ADS)

Marzuki; Vonnisa, Mutya; Rahayu, Aulya; Hashiguchi, Hiroyuki

2017-06-01

Improvement of precipitation prediction requires an understanding of the organization mechanism, such as the initiation and evolution of organized convective systems. This paper is a follow-up of a previous study on cloud propagation over the Indonesian Maritime Continent (IMC). Here, the infrared blackbody brightness temperature data is analyzed. A comprehensive cloud statistics model, including span, speed, duration, all possible directions, and size was estimated by applying the modified tracking reflectivity echoes by correlation (TREC) method to time-latitude-longitude space. Comparisons were made to cloud statistics during the first and second campaigns of Coupling Processes in the Equatorial Atmosphere, hereinafter called CPEA-I and CPEA-II. Although the two campaigns were conducted in different monsoon seasons, the cloud propagation directions during each campaign were similar. The cloud systems moved in most directions, except north and east, and preferred southwestward, westward and northwestward movements. Thus, westward-moving clouds were more dominant than eastward-moving clouds, in agreement with previous studies. This feature is consistent with the prevailing easterly wind in the middle and upper troposphere despite the difference in low-level wind during each campaign. The two campaign periods were different due to the phase of the Madden-Julian Oscillation (MJO). CPEA-I took place over the active MJO phase, with larger-sized clouds than CPEA-II. Thus, the MJO had an enormous impact on cloud size, but such an impact was not significantly observed in the speed, lifetime, span and direction of propagation. In the two campaigns, clouds moved with a speed of 3-30 m s-1 and in duration from a few hours to longer than one day. Clouds with long spans and high speeds were generally observed during the strong vertical shear of horizontal winds. In contrast, clouds with short spans and low speeds were found in the more varied environment of the IMC, but were dominant over land, which may have been associated with the diurnal heating cycle. Finally, the present results showed more complex behavior than a previous study in the Bay of Bengal, indicating precipitation mechanisms over the IMC including interactions between large-scale atmospheric phenomena (e.g., monsoon and MJO) with the diurnal precipitation cycles.

Simulation of the Intraseasonal Variability over the Eastern Pacific ITCZ in Climate Models

NASA Technical Reports Server (NTRS)

Jiang, Xianan; Waliser, Duane E.; Kim, Daehyun; Zhao, Ming; Sperber, Kenneth R.; Stern, W. F.; Schubert, Siegfried D.; Zhang, Guang J.; Wang, Wanqiu; Khairoutdinov, Marat;

The variability of tropical ice cloud properties as a function of the large-scale context from ground-based radar-lidar observations over Darwin, Australia

NASA Astrophysics Data System (ADS)

Protat, A.; Delanoë, J.; May, P. T.; Haynes, J.; Jakob, C.; O'Connor, E.; Pope, M.; Wheeler, M. C.

2011-08-01

The high complexity of cloud parameterizations now held in models puts more pressure on observational studies to provide useful means to evaluate them. One approach to the problem put forth in the modelling community is to evaluate under what atmospheric conditions the parameterizations fail to simulate the cloud properties and under what conditions they do a good job. It is the ambition of this paper to characterize the variability of the statistical properties of tropical ice clouds in different tropical "regimes" recently identified in the literature to aid the development of better process-oriented parameterizations in models. For this purpose, the statistical properties of non-precipitating tropical ice clouds over Darwin, Australia are characterized using ground-based radar-lidar observations from the Atmospheric Radiation Measurement (ARM) Program. The ice cloud properties analysed are the frequency of ice cloud occurrence, the morphological properties (cloud top height and thickness), and the microphysical and radiative properties (ice water content, visible extinction, effective radius, and total concentration). The variability of these tropical ice cloud properties is then studied as a function of the large-scale cloud regimes derived from the International Satellite Cloud Climatology Project (ISCCP), the amplitude and phase of the Madden-Julian Oscillation (MJO), and the large-scale atmospheric regime as derived from a long-term record of radiosonde observations over Darwin. The vertical variability of ice cloud occurrence and microphysical properties is largest in all regimes (1.5 order of magnitude for ice water content and extinction, a factor 3 in effective radius, and three orders of magnitude in concentration, typically). 98 % of ice clouds in our dataset are characterized by either a small cloud fraction (smaller than 0.3) or a very large cloud fraction (larger than 0.9). In the ice part of the troposphere three distinct layers characterized by different statistically-dominant microphysical processes are identified. The variability of the ice cloud properties as a function of the large-scale atmospheric regime, cloud regime, and MJO phase is large, producing mean differences of up to a factor 8 in the frequency of ice cloud occurrence between large-scale atmospheric regimes and mean differences of a factor 2 typically in all microphysical properties. Finally, the diurnal cycle of the frequency of occurrence of ice clouds is also very different between regimes and MJO phases, with diurnal amplitudes of the vertically-integrated frequency of ice cloud occurrence ranging from as low as 0.2 (weak diurnal amplitude) to values in excess of 2.0 (very large diurnal amplitude). Modellers should now use these results to check if their model cloud parameterizations are capable of translating a given atmospheric forcing into the correct statistical ice cloud properties.

Lower Boundary Forcing related to the Occurrence of Rain in the Tropical Western Pacific

NASA Astrophysics Data System (ADS)

Li, Y.; Carbone, R. E.

2013-12-01

Global weather and climate models have a long and somewhat tortured history with respect to simulation and prediction of tropical rainfall in the relative absence of balanced flow in the geostrophic sense. An important correlate with tropical rainfall is sea surface temperature (SST). The introduction of SST information to convective rainfall parameterization in global models has improved model climatologies of tropical oceanic rainfall. Nevertheless, large systematic errors have persisted, several of which are common to most atmospheric models. Models have evolved to the point where increased spatial resolution demands representation of the SST field at compatible temporal and spatial scales, leading to common usage of monthly SST fields at scales of 10-100 km. While large systematic errors persist, significant skill has been realized from various atmospheric and coupled ocean models, including assimilation of weekly or even daily SST fields, as tested by the European Center for Medium Range Weather Forecasting. A few investigators have explored the role of SST gradients in relation to the occurrence of precipitation. Some of this research has focused on large scale gradients, mainly associated with surface ocean-atmosphere climatology. These studies conclude that lower boundary atmospheric convergence, under some conditions, could be substantially enhanced over SST gradients, destabilizing the atmosphere, and thereby enabling moist convection. While the concept has a firm theoretical foundation, it has not gained a sizeable following far beyond the realm of western boundary currents. Li and Carbone 2012 examined the role of transient mesoscale (~ 100 km) SST gradients in the western Pacific warm pool by means of GHRSST and CMORPH rainfall data. They found that excitation of deep moist convection was strongly associated with the Laplacian of SST (LSST). Specifically, -LSST is associated with rainfall onset in 75% of 10,000 events over 4 years, whereas the background ocean is symmetric about zero Laplacian. This finding is fully consistent with theory for gradients of order ~1degC in low mean wind conditions, capable of inducing atmospheric convergence of N x 10-5s-1. We will present new findings resulting from the application of a Madden-Julian oscillation (MJO) passband filter to GHRSST/CMORPH data. It shows that the -LSST field organizes at scales of 1000-2000 km and can persist for periods of two weeks to 3 months. Such -LSST anomalies are in quadrature with MJO rainfall, tracking and leading the wet phase of the MJO by 10-14 days, from the Indian Ocean to the dateline. More generally, an evaluation of SST structure in rainfall production will be presented, which represents a decidedly alternative view to conventional wisdom. Li, Yanping, and R.E. Carbone, 2012: Excitation of Rainfall over the Tropical Western Pacific, J. Atmos. Sci., 69, 2983-2994.

Prediction of Significant Wave Heights in the Tropics at Sub-seasonal Time Scales

NASA Astrophysics Data System (ADS)

Kinter, J. L.; Shukla, R. P.; Shin, C. S.

2017-12-01

Skillfully predicting the 14-day mean significant wave height (SWH) forecasts at 3 weeks lead-time over the Western Pacific and Indian Oceans has been demonstrated using the WAVEWATCH-3 (WW3) model coupled to a modified version of the National Centers for Environmental Prediction (NCEP) Climate Forecast System, version 2 (CFSv2). In this paper, we present results on the effect of the Madden Julian Oscillation (MJO) events and El Niño and the Southern Oscillation (ENSO) on such predictions. Forecasts initialized with multiple ocean analyses in both January and May for 1979-2008 are evaluated. A significant anomaly correlation of predicted and observed SWH anomalies (SWHA) at 3 weeks lead-time is found over portions of the domain in both January and May cases. The model successfully predicts almost all the important features of the observed SWHA during El Niño events in January, including negative SWHA in the central Indian Ocean and northern western tropical Pacific, and positive SWHA over the southern Ocean and western Pacific. The model also reproduces the spatial pattern of the inverse relationship between SWHA and sea level pressure anomalies during both composite El Niño and La Niña events at 3 weeks lead-time. The model successfully predicts the sign and magnitude of SWHA in May over the Bay of Bengal and South China Sea in composites of phases 2 and 6 of MJO. The observed leading mode of SWHA in May and the third mode of SWHA in January are influenced by the combined effects of MJO and ENSO. Analysis of the mechanisms for these relationships is described.

Constructing a Merged Cloud-Precipitation Radar Dataset for Tropical Convective Clouds during the DYNAMO/AMIE Experiment at Addu Atoll

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

Feng, Zhe; McFarlane, Sally A.; Schumacher, Courtney

2014-05-16

To improve understanding of the convective processes key to the Madden-Julian-Oscillation (MJO) initiation, the Dynamics of the MJO (DYNAMO) and Atmospheric Radiation Measurement MJO Investigation Experiment (AMIE) collected four months of observations from three radars, the S-band Polarization Radar (S-Pol), the C-band Shared Mobile Atmospheric Research & Teaching Radar (SMART-R), and Ka-band Zenith Radar (KAZR) on Addu Atoll in the tropical Indian Ocean. This study compares the measurements from the S-Pol and SMART-R to those from the more sensitive KAZR in order to characterize the hydrometeor detection capabilities of the two scanning precipitation radars. Frequency comparisons for precipitating convective cloudsmore » and non-precipitating high clouds agree much better than non-precipitating low clouds for both scanning radars due to issues in ground clutter. On average, SMART-R underestimates convective and high cloud tops by 0.3 to 1.1 km, while S-Pol underestimates cloud tops by less than 0.4 km for these cloud types. S-Pol shows excellent dynamic range in detecting various types of clouds and therefore its data are well suited for characterizing the evolution of the 3D cloud structures, complementing the profiling KAZR measurements. For detecting non-precipitating low clouds and thin cirrus clouds, KAZR remains the most reliable instrument. However, KAZR is attenuated in heavy precipitation and underestimates cloud top height due to rainfall attenuation 4.3% of the time during DYNAMO/AMIE. An empirical method to correct the KAZR cloud top heights is described, and a merged radar dataset is produced to provide improved cloud boundary estimates, microphysics and radiative heating retrievals.« less

Decadal modulation of the relationship between intraseasonal tropical variability and ENSO

NASA Astrophysics Data System (ADS)

Gushchina, Daria; Dewitte, Boris

2018-05-01

The El Niño Southern Oscillation (ENSO) amplitude is modulated at decadal timescales, which, over the last decades, has been related to the low-frequency changes in the frequency of occurrence of the two types of El Niño events, that is the Eastern Pacific (EP) and Central Pacific (CP) El Niños. Meanwhile ENSO is tightly linked to the intraseasonal tropical variability (ITV) that is generally enhanced prior to El Niño development and can act as a trigger of the event. Here we revisit the ITV/ENSO relationship taking into account changes in ENSO properties over the last six decades. The focus is on two main components of ITV, the Madden-Julian Oscillation (MJO) and convectively coupled equatorial Rossby waves (ER). We show that the ITV/ENSO relationship exhibits a decadal modulation that is not related in a straight-forward manner to the change in occurrence of El Niño types and Pacific decadal modes. While enhanced MJO activity associated to EP El Niño development mostly took place over the period 1985-2000, the ER activity is enhanced prior to El Niño development over the whole period with a tendency to relate more to CP El Niño than to EP El Niño. In particular the relationship between ER activity and ENSO was particularly strong for the period 2000-2015, which results in a significant positive long-term trend of the predictive value of ER activity. The statistics of the MJO and ER activity is consistent with the hypothesis that they can be considered a state-dependent noise for ENSO linked to distinct lower frequency climate modes.

Variability of Oceanic Mesoscale Convective System Vertical Structures Observed by CloudSat in Indo-Pacific Regions Associated with the Madden-Julian Oscillation

NASA Astrophysics Data System (ADS)

Yuan, J.

2016-12-01

Vertical structures of mesoscale convective systems (MCSs) during the Madden-Julian-Oscillation (MJO) are investigated using 2006-2011 CloudSat radar measurements for Indo-Pacific oceanic areas. In active phases of the MJO relatively more large MCSs and connected MCSs occur. The frequency of occurrence of connected MCSs peaks in the onset phase, a phase earlier than separated MCSs. Compared to separated MCSs, connected MCSs in all sizes have weaker reflectivity above 8 km in their deep precipitating portions and thick anvil clouds closely linked to them, suggesting more "stratiform" physics associated with them. Separated MCSs and connected MCSs together produce relatively the least anvil clouds in the onset phase while their deep precipitating portions show stronger/weaker reflectivity above 8 km before/after the onset phase. Thus after the onset phase of the MJO, MCSs shift toward more "convective" organization because separated MCSs maximize after the onset, while their internal structures appear more "stratiform" because internally they have weaker reflectivity above 8km. Connected MCSs coincide with a more humid middle troposphere spatially, even at the same places a few days before they occur. Middle-tropospheric moistening peaks in the onset phase. Moistening of the free troposphere around deep convective systems shows relatively stronger moistening/drying below the 700 hPa before/after the onset phase compared to domain-mean averages. Lower-topped clouds occur most frequently around CMCSs and in active phases, consistent with the presence of a moister free troposphere. Coexistence of these phenomena suggests that the role of middle troposphere moisture in the formation of CMCSs needs to be better understood.

Variability of oceanic deep convective system vertical structures observed by CloudSat in Indo-Pacific regions associated with the Madden-Julian oscillation

NASA Astrophysics Data System (ADS)

Yuan, Jian

2016-09-01

Vertical structures of deep convective systems during the Madden-Julian oscillation (MJO) are investigated using CloudSat radar measurements in Indo-Pacific oceanic areas. In active phases of the MJO, relatively more large systems and connected mesoscale convective systems (CMCSs) occur. The occurrence frequency of CMCSs peaks in the onset phase, a phase earlier than separated mesoscale convective systems (SMCSs). Compared with SMCSs, CMCSs of all sizes have weaker reflectivity above 8 km in their deep precipitating portions and thick anvil clouds closely linked to them, suggesting more "stratiform" physics associated with them. SMCSs and CMCSs together produce relatively the least anvil clouds in the onset phase, while their deep precipitating portions show stronger/weaker reflectivity above 8 km before/after the onset phase. Thus, after the onset phase of the MJO, mesoscale convective systems shift toward a more "convective" organization because SMCSs maximize after the onset, while their internal structures appear more stratiform because internally they have weaker reflectivity above 8 km. CMCSs coincide with a more humid middle troposphere spatially, even at the same locations a few days before they occur. Middle-tropospheric moistening peaks in the onset phase. Moistening of the free troposphere around deep convective systems shows relatively stronger moistening/drying below 700 hPa before/after the onset phase than domain-mean averages. Low-topped clouds occur most frequently around CMCSs and in active phases, consistent with the presence of a moister free troposphere. Coexistence of these phenomena suggests that the role of middle troposphere moisture in the formation of CMCSs should be better understood.

Vertical structure and physical processes of the Madden-Julian Oscillation: Biases and uncertainties at short range

DOE PAGES

Xavier, Prince K.; Petch, Jon C.; Klingaman, Nicholas P.; ...

2015-05-26

We present an analysis of diabatic heating and moistening processes from 12 to 36 h lead time forecasts from 12 Global Circulation Models as part of the “Vertical structure and physical processes of the Madden-Julian Oscillation (MJO)” project. A lead time of 12–36 h is chosen to constrain the large-scale dynamics and thermodynamics to be close to observations while avoiding being too close to the initial spin-up of the models as they adjust to being driven from the Years of Tropical Convection (YOTC) analysis. A comparison of the vertical velocity and rainfall with the observations and YOTC analysis suggests thatmore » the phases of convection associated with the MJO are constrained in most models at this lead time although the rainfall in the suppressed phase is typically overestimated. Although the large-scale dynamics is reasonably constrained, moistening and heating profiles have large intermodel spread. In particular, there are large spreads in convective heating and moistening at midlevels during the transition to active convection. Radiative heating and cloud parameters have the largest relative spread across models at upper levels during the active phase. A detailed analysis of time step behavior shows that some models show strong intermittency in rainfall and differences in the precipitation and dynamics relationship between models. In conclusion, the wealth of model outputs archived during this project is a very valuable resource for model developers beyond the study of the MJO. Additionally, the findings of this study can inform the design of process model experiments, and inform the priorities for field experiments and future observing systems.« less

Intra-seasonal Characteristics of Wintertime Extreme Cold Events over South Korea

NASA Astrophysics Data System (ADS)

Park, Taewon; Jeong, Jeehoon; Choi, Jahyun

2017-04-01

The present study reveals the changes in the characteristics of extreme cold events over South Korea for boreal winter (November to March) in terms of the intra-seasonal variability of frequency, duration, and atmospheric circulation pattern. Influences of large-scale variabilities such as the Siberian High activity, the Arctic Oscillation (AO), and the Madden-Julian Oscillation (MJO) on extreme cold events are also investigated. In the early and the late of the winter during November and March, the upper-tropospheric wave-train for a life-cycle of the extreme cold events tends to pass quickly over East Asia. In addition, compared with the other months, the intensity of the Siberian High is weaker and the occurrences of strong negative AO are less frequent. It lead to events with weak amplitude and short duration. On the other hand, the amplified Siberian High and the strong negative AO occur more frequently in the mid of the winter from December to February. The extreme cold events are mainly characterized by a well-organized anticyclonic blocking around the Ural Mountain and the Subarctic. These large-scale circulation makes the extreme cold events for the midwinter last long with strong amplitude. The MJO phases 2-3 which provide a suitable condition for the amplification of extreme cold events occur frequently for November to January when the frequencies are more than twice those for February and March. While the extreme cold events during March have the least frequency, the weakest amplitude, and the shortest duration due to weak impacts of the abovementioned factors, the strong activities of the factors for January force the extreme cold events to be the most frequent, the strongest, and the longest among the boreal winter. Keywords extreme cold event, wave-train, blocking, Siberian High, AO, MJO

Effects of the diurnal cycle in solar radiation on the tropical Indian Ocean mixed layer variability during wintertime Madden-Julian Oscillations

NASA Astrophysics Data System (ADS)

Li, Yuanlong; Han, Weiqing; Shinoda, Toshiaki; Wang, Chunzai; Lien, Ren-Chieh; Moum, James N.; Wang, Jih-Wang

2013-10-01

The effects of solar radiation diurnal cycle on intraseasonal mixed layer variability in the tropical Indian Ocean during boreal wintertime Madden-Julian Oscillation (MJO) events are examined using the HYbrid Coordinate Ocean Model. Two parallel experiments, the main run and the experimental run, are performed for the period of 2005-2011 with daily atmospheric forcing except that an idealized hourly shortwave radiation diurnal cycle is included in the main run. The results show that the diurnal cycle of solar radiation generally warms the Indian Ocean sea surface temperature (SST) north of 10°S, particularly during the calm phase of the MJO when sea surface wind is weak, mixed layer is thin, and the SST diurnal cycle amplitude (dSST) is large. The diurnal cycle enhances the MJO-forced intraseasonal SST variability by about 20% in key regions like the Seychelles-Chagos Thermocline Ridge (SCTR; 55°-70°E, 12°-4°S) and the central equatorial Indian Ocean (CEIO; 65°-95°E, 3°S-3°N) primarily through nonlinear rectification. The model also well reproduced the upper-ocean variations monitored by the CINDY/DYNAMO field campaign between September-November 2011. During this period, dSST reaches 0.7°C in the CEIO region, and intraseasonal SST variability is significantly amplified. In the SCTR region where mean easterly winds are strong during this period, diurnal SST variation and its impact on intraseasonal ocean variability are much weaker. In both regions, the diurnal cycle also has a large impact on the upward surface turbulent heat flux QT and induces diurnal variation of QT with a peak-to-peak difference of O(10 W m-2).

Revisiting the Processes That Determine Wintertime Intraseasonal SST Variability in the Thermocline Ridge of the Tropical South Indian Ocean

NASA Astrophysics Data System (ADS)

Han, W.; Li, Y.; Shinoda, T.; Wang, C.; Ravichandran, M.; Wang, J. W.

2014-12-01

Intraseasonal sea surface temperature (SST) variability over the Seychelles-Chagos thermocline ridge (SCTR) induced by boreal wintertime Madden-Julian oscillations (MJOs) is investigated by performing a series of OGCM experiments with improved model configuration and the recently available high quality satellite forcing fields. The impact of the ocean interannual variation of the thermocline depth -represented by the depth of 20C isotherm (D20) - in the SCTR is also assessed. The OGCM main run solution agrees well with the observations. The results show that for the 2001-2011 period, surface shortwave radiation (SWR), turbulent heat fluxes associated with wind speed, and wind stress-driven ocean dynamical processes are all important in causing the MJO-related intraseasonal SST variability in the SCTR region. Overall, forcing by SWR contributes ~31%, and forcing by winds (via both surface turbulent heat flux and ocean dynamics) contributes ~62%. The contribution of turbulent heat flux associated with wind speed is ~39% and that of wind-stress driven ocean dynamics is ~23%. The contribution of ocean dynamics, however, is considerably larger during strong ("prime") MJO events under "strong" thermocline condition. The overall effect of interannual variability of D20 on intraseasonal SST during 2001-2011 is significant in the eastern part of the SCTR (70E-85E), where the intraseasonal SST amplitudes are strengthened by about 20%. In general, a shallower/deeper SCTR favors larger/smaller SST responses to the MJO forcing. In the eastern SCTR, both the heat flux forcing and entrainment are greatly amplified under the strong SCTR condition, but only slightly suppressed under the weak SCTR condition, leading to an overall strengthening effect on intraseasonal SST variability.

The Impacts of Multiple Simultaneous Climate Variations

DTIC Science & Technology

2016-12-01

MULTIPLE SIMULTANEOUS CLIMATE VARIATIONS by Richard E. Ilczuk Jr. December 2016 Thesis Advisor: Tom Murphree Co-Advisor: Megan Hutchins......13. ABSTRACT (maximum 200 words) Climate variations—such as El Niño–La Niña (ENLN), the Madden–Julian Oscillation (MJO), and the Arctic

DDS: The Dental Diagnostic Simulation System.

ERIC Educational Resources Information Center

Tira, Daniel E.

The Dental Diagnostic Simulation (DDS) System provides an alternative to simulation systems which represent diagnostic case studies of relatively limited scope. It may be used to generate simulated case studies in all of the dental specialty areas with case materials progressing through the gamut of the diagnostic process. The generation of a…

Intraseasonal to interannual variations in the tropical wave activity revealed in reanalyses and their potential impact on the QBO

NASA Astrophysics Data System (ADS)

Kim, Young-Ha; Yoo, Changhyun

2017-04-01

We investigate activities of tropical waves represented in reanalysis products. The wave activities are quantified by the Eliassen-Palm (EP) flux at 100 hPa, after decomposed into the following four components: equatorially trapped Kelvin waves and mixed Rossby-gravity waves, gravity waves, and Rossby waves. Monthly EP fluxes of the four waves exhibit considerable temporal variations at intraseasonal and interannual, along with seasonal, time scales. These variations are discussed with the tropical large-scale variabilities, including the Madden-Julian Oscillation (MJO), the El Ninõ-Southern Oscillation, and the stratospheric quasi-biennial oscillation (QBO). We find that during boreal winter, the interannual variation of Kelvin wave activity is in phase with that of the MJO amplitude, while such a simultaneous variation cannot be seen in other seasons. The gravity wave is dominated by a semi-annual cycle, while the departure from its semi-annual cycle is largely correlated with the QBO phase in the stratosphere. Potential impacts of the variations in the wave activity upon the QBO properties will be assessed using a simple one-dimensional QBO model.

Predicting Tropical Cyclogenesis with a Global Mesoscale Model: Preliminary Results with Very Severe Cyclonic Storm Nargis (2008)

NASA Astrophysics Data System (ADS)

Shen, B.; Tao, W.; Atlas, R.

2008-12-01

Very Severe Cyclonic Storm Nargis, the deadliest named tropical cyclone (TC) in the North Indian Ocean Basin, devastated Burma (Myanmar) in May 2008, causing tremendous damage and numerous fatalities. An increased lead time in the prediction of TC Nargis would have increased the warning time and may therefore have saved lives and reduced economic damage. Recent advances in high-resolution global models and supercomputers have shown the potential for improving TC track and intensity forecasts, presumably by improving multi-scale simulations. The key but challenging questions to be answered include: (1) if and how realistic, in terms of timing, location and TC general structure, the global mesoscale model (GMM) can simulate TC genesis and (2) under what conditions can the model extend the lead time of TC genesis forecasts. In this study, we focus on genesis prediction for TCs in the Indian Ocean with the GMM. Preliminary real-data simulations show that the initial formation and intensity variations of TC Nargis can be realistically predicted at a lead time of up to 5 days. These simulations also suggest that the accurate representations of a westerly wind burst (WWB) and an equatorial trough, associated with monsoon circulations and/or a Madden-Julian Oscillation (MJO), are important for predicting the formation of this kind of TC. In addition to the WWB and equatorial trough, other favorable environmental conditions will be examined, which include enhanced monsoonal circulation, upper-level outflow, low- and middle-level moistening, and surface fluxes.

Ensemble superparameterization versus stochastic parameterization: A comparison of model uncertainty representation in tropical weather prediction

NASA Astrophysics Data System (ADS)

Subramanian, Aneesh C.; Palmer, Tim N.

2017-06-01

Stochastic schemes to represent model uncertainty in the European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble prediction system has helped improve its probabilistic forecast skill over the past decade by both improving its reliability and reducing the ensemble mean error. The largest uncertainties in the model arise from the model physics parameterizations. In the tropics, the parameterization of moist convection presents a major challenge for the accurate prediction of weather and climate. Superparameterization is a promising alternative strategy for including the effects of moist convection through explicit turbulent fluxes calculated from a cloud-resolving model (CRM) embedded within a global climate model (GCM). In this paper, we compare the impact of initial random perturbations in embedded CRMs, within the ECMWF ensemble prediction system, with stochastically perturbed physical tendency (SPPT) scheme as a way to represent model uncertainty in medium-range tropical weather forecasts. We especially focus on forecasts of tropical convection and dynamics during MJO events in October-November 2011. These are well-studied events for MJO dynamics as they were also heavily observed during the DYNAMO field campaign. We show that a multiscale ensemble modeling approach helps improve forecasts of certain aspects of tropical convection during the MJO events, while it also tends to deteriorate certain large-scale dynamic fields with respect to stochastically perturbed physical tendencies approach that is used operationally at ECMWF.