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Sample records for african easterly wave

  1. African Easterly Waves and Superparameterization

    NASA Astrophysics Data System (ADS)

    McCrary, Rachel; Randall, David; Stan, Cristiana

    2013-04-01

    This study examines the dynamics of African easterly wave (AEW) in the Superparameterized Community Climate System Model (SP-CCSM). Conventional general circulation models (GCMs) have difficulty representing AEW dynamics over West Africa. One reason is that the coarse resolution of these models limits their ability to represent the multi-scale interactions between the large-scale dynamics and individual convective systems, which are important for the origin and development of AEWs. The SP-CCSM has been designed to better simulate the interactions between small-scale circulations and large-scale dynamics, by replacing the conventional parameterizations with a 2D cloud resolving model embedded within each GCM grid column. With this approach we are able to capture the interactions between clouds and the global circulation of the atmosphere. The goal of our work is to improve our understanding of the multi-scale interactions that occur between AEWs and convection over West Africa. The implementation of the superparameterization into the CCSM improves the overall representation of monsoon precipitation over West Africa. Most notably, the region of maximum precipitation is shifted from the Gulf of Guinea in CCSM (not realistic), to over the continent in SP-CCSM. The biases found in precipitation for both models are thought to be linked to anomalously warm sea surface temperatures in the Gulf of Guinea and a misrepresentation of the equatorial Atlantic cold tongue (a common problem for coupled GCMs). AEWs and their relationship with convection are also improved in the SP-CCSM. In the standard model, little to no easterly wave activity is found over West Africa, and the relationship with convection is tenuous at best. SP-CCSM on the other hand produces strong AEWs over the region that exhibit similar horizontal and vertical structures to observations. The simulated waves are also shown to be strongly coupled to convection, and results suggest that barotropic and baroclinic

  2. African easterly wave energetics on intraseasonal timescales

    NASA Astrophysics Data System (ADS)

    Alaka, Ghassan J., Jr.

    African easterly waves (AEWs) are synoptic-scale eddies that dominate North African weather in boreal summer. AEWs propagate westward with a maximum amplitude near 700 hPa and a period of 2.5-6-days. AEWs and associated perturbation kinetic energy (PKE) exhibit significant intraseasonal variability in tropical North Africa during boreal summer, which directly impacts local agriculture and tropical cyclogenesis. This study performs a comprehensive analysis of the 30-90-day variability of AEWs and associated energetics using both reanalysis data and model output. Specifically, the PKE and perturbation available potential energy (PAPE) budgets are used to understand the factors that contribute to PKE maxima in West Africa and the extent to which these surges of AEW activity are modulated by the Madden-Julian oscillation (MJO). The role of the MJO in the intraseasonal variability of AEWs is assessed by comparing PKE sources as a function of an MJO index and a local 30-90-day West African PKE index. Since East Africa is an initiation zone for AEW activity and is modulated by the MJO, the relationship between this region and West Africa is a primary focus in this study. The intraseasonal variability of AEW energetics is first investigated in reanalysis products. While reanalysis data depicts a similar evolution of 30-90-day PKE anomalies in both the MJO and a local PKE index, the MJO index describes only a small (yet still significant) fraction of the local 30-90-day variance. In boreal summers with more significant MJO days, the correlation between the two indices is higher. Baroclinic energy conversions are important for the initiation of 30-90-day West African PKE events east of Lake Chad. In West Africa, both barotropic and baroclinic energy conversions maintain positive PKE anomalies before they propagate into the Atlantic. The primary role of diabatic heating is to destroy PAPE in a negative feedback to baroclinic energy conversions in West Africa. More frequent

  3. African easterly wave activity in a variable resolution GCM

    NASA Astrophysics Data System (ADS)

    Moustaoui, M.; Royer, J.-F.; Chauvin, F.

    2002-03-01

    The role of large-scale conditions on African easterly waves' variability and associated rainfall is investigated in simulations with the variable resolution version of the Arpege-Climat General Circulation Model (GCM). Easterly waves are identified from the 850 hPa meridional winds. The simulated waves' characteristics and their frequency response are compared with that in the reanalyses of the European Center for Medium-range Weather Forecasts (ECMWF) during summer 1992. The zonal wavelength of the simulated waves increases toward the equator. This increase, found also in previous works, is explained by the increase in 850-hPa mean zonal winds toward the equator as a result of low-level monsoon flow. A pronounced seasonal variability indicating a late summer enhancement of wave activity and related precipitation is found in both simulations and reanalyses. This feature, which has been found from observation campaigns, is explained by the variability of the large-scale circulation, which gives favorable conditions for the penetration of the easterly waves into the moist layer in the late summer. A shift of the spectra towards low frequencies is found in the simulated waves when compared to the reanalysis. The shift is explained by the relatively weak westward winds within the African Easterly Jet in the model, which tend to generate waves with low phase speed and frequency. We suggest that the weakness of the winds in the jet is caused by the strong eastward monsoon flow in the model, which may be due to surface condition parameterizations.

  4. Interactions between Oceanic Saharan Air Layer and African Easterly Jet- African Easterly Waves System

    NASA Astrophysics Data System (ADS)

    Hosseinpour, F.; Wilcox, E. M.

    2013-12-01

    Aerosols have robust influences on multi-scale climatic systems and variability. Non-linear aerosol-cloud-climate interactions depend on many parameters such as aerosol features, regional atmospheric dynamics and variability. Although there are remarkable modeling studies indicating that aerosols induce robust modifications in cloud properties, circulations and the hydrological cycle, many of the physical and dynamical processes involving in these complex interactions between aerosols and Earth's system are still poorly understood. Better understanding the contribution of aerosols with atmospheric phenomena and their transient changes are crucial for efforts to evaluate climate predictions by next generation climate models. This study provides strong evidence of mechanistic relationships between perturbations of the oceanic Saharan air layer (OSAL) and anomalies of atmospheric circulations over the eastern tropical Atlantic/Africa. These relationships are characterized using an ensemble of daily datasets including the Modern-Era Retrospective Analysis for Research and Applications (MERRA), the Moderate Resolution Imaging Spectro-radiometer (MODIS), and the Sea-viewing Wide Field-of-View Sensor (SeaWIFS) for the boreal summer season. The study is motivated by previous results suggesting that oceanic dust-induced large-scale to meso-scale climatic adjustments. Our hypothesis is that perturbations in OSAL significantly interact with regional climate variability through African Easterly Jet- African Easterly Waves (AEJ-AEW) system. Passive/ active phases of AEWs in the northern and southern-track wave packets are associated with dipole patterns of thermal/dynamical anomalies correlated with perturbations of aerosol optical depth (AOD) in OSAL. Enhanced (suppressed) dust AOD in OSAL are significantly correlated with convective re-circulation within subsidence region of Hadley cell as well as robust mid-level dipole vorticity disturbances downstream of the AEJ core

  5. Role of Easterly Waves in the Maintenance of the African Easterly Jet

    NASA Technical Reports Server (NTRS)

    Ferreira, Rosana Nieto; Suarez, Max; Bacmeister, Julio

    2000-01-01

    About fifty percent of all hurricanes in the Atlantic Ocean form within African easterly waves (AEW). Many previous studies have indicated that these waves result from combined barotropic-baroclinic instability of the African Easterly Jet (AEJ). The AEJ is in turn believed to be due to the strong temperature gradient between the very warm Sahara Desert and the cooler Sahel and Gulf of Guinea to the south. Zonally averaged latitude-pressure cross-sections of summertime zonal winds over Africa show the AEJ as a 8-12 m/s jet centered at 600-700 mb near 15 N. Such cross-sections also show a weaker southern hemisphere easterly jet near 5-150S, monsoonal westerlies centered beneath the AEJ, and upper tropospheric features such as the Tropical Easterly Jet (TEJ) near 30N and the subtropical westerly jet near 35ON . Thomcroft and Blackburn performed zonally symmetric simulations that showed that the effect of thermal wind balance over the observed low level meridional temperature gradient over northern Africa is particularly important in the formation of the AEJ. They also found that in order to reproduce some of the other aforementioned features of the summertime climatological wind field over Africa it is necessary to include the effects of Inter-Tropical Convergence Zone (ITCZ) convective heating. While the diabatic effects of Saharan and ITCZ heating tend to strengthen the AEJ, AEW remove energy from the AEJ, thereby weakening it. In this study we take the next step towards understanding the maintenance of the AEJ by including the effects of AEW.

  6. African Easterly Jet: Barotropic Instability, Waves, and Cyclogenesis

    NASA Technical Reports Server (NTRS)

    Wu, Man-Li C; Reale, Oreste; Schubert, Siegfried D.; Suarez, Max J.; Thorncroft, Chris D.

    2012-01-01

    This study investigates the structure of the African easterly jet, focusing on instability processes on a seasonal and subseasonal scale, with the goal of identifying features that could provide increased predictability of Atlantic tropical cyclogenesis. The Modern-Era Retrospective Analysis for Research and Applications (MERRA) is used as the main investigating tool. MERRA is compared with other reanalyses datasets from major operational centers around the world and was found to describe very effectively the circulation over the African monsoon region. In particular, a comparison with precipitation datasets from the Global Precipitation Climatology Project shows that MERRA realistically reproduces seasonal precipitation over that region. The verification of the generalized Kuo barotropic instability condition computed from seasonal means is found to have the interesting property of defining well the location where observed tropical storms are detected. This property does not appear to be an artifact of MERRA and is present also in the other adopted reanalysis datasets. Therefore, the fact that the areas where the mean flow is unstable seems to provide a more favorable environment for wave intensification, could be another factor to include-in addition to sea surface temperature, vertical shear, precipitation, the role of Saharan air, and others-among large-scale forcings affecting development and tropical cyclone frequency. In addition, two prominent modes of variability are found based on a spectral analysis that uses the Hilbert-Huang transform: a 2.5-6-day mode that corresponds well to the African easterly waves and also a 6-9-day mode that seems to be associated with tropical- extratropical interaction.

  7. Climatology of the African Easterly Jet and Subtropical Highs over North Africa and Arabian Peninsula and a Numerical Case Study of an Intense African Easterly Wave

    NASA Astrophysics Data System (ADS)

    Spinks, James D.

    North African climate is analyzed between 1979 and 2010 with an emphasis on August using the European Center for Medium Range Weather Forecast (ECMWF) global dataset to investigate the effects of the subtropical anticyclones over North Africa and the Arabian Peninsula on the Africa easterly jet (AEJ). It was found that the AEJ encloses a core with a local wind maximum (LWM) in both West and East Africa, in which the west LWM core has a higher zonal wind speed. The strength of both cores is distinctly different by way of thermal wind balance. The variability of these synoptic weather features is higher in East Africa. The most noticeable variability of intensity occurred with easterly waves. Maintenance of easterly waves from the Arabian Peninsula into East Africa is dependent on strong zonal gradients from the AEJ. These zonal gradients were induced by the strengthening of the subtropical highs and the presence of a westerly jet in Central Africa and south of the Arabian Peninsula. During positive ENSO periods, these systems are generally weaker while in negative periods are stronger. The origins of an intense African easterly wave (AEW) and mesoscale convective system (MCS) in August 2004 (A04) were traced back to the southern Arabian Peninsula, Asir Mountains, and Ethiopian Highlands using gridded satellite (GridSat) data, ERA-I, and the WRF-ARW model. A vorticity budget was developed to investigate the dynamics and mechanisms that contribute to the formation of A04's vorticity perturbation.

  8. Hurricane genesis: on the breaking African easterly waves and critical layers

    NASA Astrophysics Data System (ADS)

    Asaadi, Ali; Brunet, Gilbert; Yau, Peter

    2015-04-01

    This study bring new understanding on the decades-old hurricane genesis problem that starts with westward travelling African easterly waves that can evolve into coherent cyclonic vortices depending on their strength and other nonlinear wave breaking processes. In general, observations indicate that only a small fraction of the African easterly waves that occur in a single hurricane season contribute to tropical cyclogenesis. However, this small fraction includes a large portion of named storms. In addition, a recent study by Dunkerton et al. (2009) has shown that named storms in the Atlantic and eastern Pacific basins are almost all associated with a cyclonic Kelvin "cat's eye" of a tropical easterly wave typical of critical layers, located equatorward of the easterly jet axis. To better understand the dynamics involved in hurricane genesis, the flow characteristics and the physical and dynamical mechanisms by which easterly waves form cat's eyes are investigated with the help of atmospheric reanalyzes and numerical simulations. We perform a climatological study of developing easterly waves covering the 1998-2001 hurricane seasons using ERA-Interim 6-hourly reanalysis data. Composite analyses for all named storms show a monotonic potential vorticity (PV) profile with weak meridional PV gradient and a cyclonic (i.e., south of the easterly jet axis) critical line for time periods of several days preceding the cat's eye formation. In addition, the developing PV anomaly composite shows a statistically significant companion wave-packet of non-developing easterly waves. A barotropic shallow water model is used to study the initial value and forced problems of disturbances on a parabolic jet and realistic profiles associated with weak basic state meridional PV gradients, leading to Kelvin cat's eye formation around the jet axis. The results highlight the synergy of the dynamical mechanisms, including wave breaking and PV redistribution within the nonlinear critical layer

  9. African Easterly Waves and Their Association with Precipitation

    NASA Technical Reports Server (NTRS)

    Gu, Guo-Jun; Adler, Robert F.; Huffman, George J.; Curtis, Scott

    2003-01-01

    Summer tropical synoptic-scale waves over West Africa are quantified by the 850 mb meridional wind component from the NCEP/NCAR reanalysis project. Their relationships with surface precipitation patterns are further explored by applying the data from the Tropical Rainfall Measuring Mission (TRMM) satellite in combination with other satellite observations during 1998-2002. Evident wavelet spectral power peaks are seen within a period of 2.5 - 6 days in both meridional wind and precipitation. The most intense wave signals in meridional wind are concentrated along 15 deg N- 25 deg N. Wave signals in precipitation and corresponding wavelet cross-spectral signals between these two variables, however, are primarily located at 5 deg N- 15 deg N, the latitudes of major summer rain events. There is a tendency for the perturbations in meridional wind component to lag (lead) precipitation signals south (north) of 15 deg N. In some cases, either an in-phase or out-of-phase relationship can even be found between these two variables, suggesting a latitude-dependent horizontal structure for these waves and probably implying two distinct wave-convective coupling mechanisms. Moreover, the lagging relationship (and/or the out-of-phase tendency) is only observed south of 15 deg N during July-September, indicating a strong seasonal preference. This phase relationship is generally consistent with the horizontal wave structures from a composite analysis.

  10. African easterly waves and their association with precipitation

    NASA Astrophysics Data System (ADS)

    Gu, Guojun; Adler, Robert F.; Huffman, George J.; Curtis, Scott

    2004-02-01

    Summer tropical synoptic-scale waves over West Africa are quantified by the 850 mb meridional wind component from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis project. Their relationships with surface precipitation patterns are explored by applying the data from the Tropical Rainfall Measuring Mission satellite in combination with other satellite observations during 1998-2002. Evident wavelet spectral power peaks are seen within a period of 2.5-6 days in both meridional wind and precipitation. The most intense wave signals in meridional wind are concentrated along 15°N-25°N. Wave signals in precipitation and corresponding wavelet cross-spectral signals between these two variables, however, are primarily located at 5°N-15°N, the latitudes of major summer rain events. Southerly wind perturbations tend to lag (lead) precipitation signals south (north) of 15°N. In some cases either an in-phase or out-of-phase relationship can even be found, suggesting two distinct relationships between the waves and convection. Moreover, the lagging relationship (and/or the out-of-phase tendency) is only observed south of 15°N during July-September, indicating a strong seasonal preference. This phase relationship is generally consistent with the horizontal wave structures from a composite analysis.

  11. LASE Observations of Interactions Between African Easterly Waves and the Saharan Air Layer

    NASA Technical Reports Server (NTRS)

    Ismail, Syed; Ferrare, Richard; Browell, Edward; Kooi, Susan; Biswas, Mrinal; Krishnamurti, T. N.; Notari, Anthony; Heymsfield, Andrew; Butler, Carolyn; Burton, Sharon; Fenn, Marta; Dunion, Jason

    2010-01-01

    The Lidar Atmospheric Sensing Experiment (LASE) participated in the NASA African Monsoon Multidisciplinary Analyses (NAMMA) field experiment in 2006 that was conducted from Sal, Cape Verde to study the Saharan Air Layer (SAL) and its influence on the African Easterly Waves (AEWs) and Tropical Cyclones (TCs). During NAMMA, LASE collected simultaneous water vapor and aerosol lidar measurements from 14 flights onboard the NASA DC- 8. In this paper we present three examples of the interaction of the SAL and AEWs regarding: moistening of the SAL and transfer of latent heat; injection of dust in an updraft; and influence of dry air intrusion on an AEW. A brief discussion is also given on activities related to the refurbishment of LASE to enhance its operational performance and plans to participate in the next NASA hurricane field experiment in the summer of 2010.

  12. The Sensitivity of African Easterly Waves to Eastern Tropical Atlantic Sea-Surface Temperatures

    NASA Technical Reports Server (NTRS)

    Druyan, Leonard M.; Fulakeza, Matthew

    2011-01-01

    The results of two regional atmospheric model simulations are compared to assess the influence of the eastern tropical Atlantic sea-surface temperature maximum on local precipitation, transient easterly waves and the West African summer monsoon. Both model simulations were initialized with reanalysis 2 data (US National Center for Environmental Prediction and Department of Energy) on 15 May 2006 and extended through 6 October 2006, forced by synchronous reanalysis 2 lateral boundary conditions introduced four times daily. One simulation uses 2006 reanalysis 2 sea-surface temperatures, also updated four times daily, while the second simulation considers ocean forcing absent the sea-surface temperature maximum, achieved here by subtracting 3 K at every ocean grid point between 0 and 15 N during the entire simulation. The simulation with 2006 sea-surface temperature forcing produces a realistic distribution of June-September mean precipitation and realistic westward propagating swaths of maximum rainfall, based on validation against Tropical Rainfall Measuring Mission (TRMM) estimates. The simulation without the sea-surface temperature maximum produces only 57% of the control June-September total precipitation over the eastern tropical Atlantic and about 83% of the Sahel precipitation. The simulation with warmer ocean temperatures generates generally stronger circulation, which in turn enhances precipitation by increasing moisture convergence. Some local precipitation enhancement is also attributed to lower vertical thermal stability above the warm water. The study shows that the eastern tropical Atlantic sea-surface temperature maximum enhances the strength of transient easterly waves and broadens the spatial extent of associated precipitation. However, large-scale circulation and its interaction with the African continent, and not sea-surface temperatures, control the timing and trajectories of the waves.

  13. Interannual variability and predictability of African easterly waves in a GCM

    NASA Astrophysics Data System (ADS)

    Chauvin, Fabrice; Royer, Jean-François; Douville, Hervé

    2005-04-01

    The interannual variability of African Easterly Waves (AEWs) is assessed with the help of spatio-temporal spectral analysis (STSA) and complex empirical orthogonal functions methods applied to the results of ten-member multiyear ensemble simulations. Two sets of experiments were conducted with the Météo-France ARPEGE-Climat GCM, one with interactive soil moisture (control), and the other with soil moisture relaxed towards climatological monthly means calculated from the control. Composites of Soudano-Sahelian AEWs were constructed and associated physical processes and dynamics were studied in the frame of the waves. It is shown that the model is able to simulate realistically some interannual variability in the AEWs, and that this dynamical aspect of the West African climate is potentially predictable (i.e. signal can be extracted from boundary conditions relatively to internal error of the GCM), especially along the moist Guinean coast. Compared with ECMWF 15-year reanalysis (ERA15), the maximum activity of AEWs is located too far to the South and is somewhat too zonal, but the main characteristics of the waves are well represented. The major impact of soil moisture relaxation in the GCM experiments is to reduce the seasonal potential predictability of AEWs over land by enhancing their internal variability.

  14. 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

  15. Radiative Effects of Saharan Mineral Dust Aerosols on the Structure of African Easterly Waves

    NASA Astrophysics Data System (ADS)

    Bercos-Hickey, E.; Nathan, T. R.; Chen, S. H.

    2014-12-01

    How Saharan mineral dust affects the structure of African easterly waves (AEWs) is an outstanding scientific question. Addressing this question is important because AEWs often serve as precursors to the development of tropical storms off of West Africa. In this study, the Weather Research and Forecasting Dust (WRFD) model is used to examine the radiative effects of Saharan dust on the structure of AEWs that occurred in July 1995. Two numerical experiments are conducted. The first (control) experiment uses the standard WRF model in the absence of dust. The second experiment is identical to the first, but includes the transport and radiative effects of dust. Dust is modeled by 12 continuity equations for dust-sized particles that represent the spectrum of mineral dust in the atmosphere. Analysis and comparison of the no-dust and dust experiments show that Saharan dust significantly affects the structure of AEWs. For example, a spectral density analysis of the AEWs shows that dust causes higher peak power during the 3 to 6 day period at 700mb. For the meridional wind over Dakar in West Africa, the dust causes the power to increase by about 82% and to shift to a lower frequency by about a half day. Covariance plots show spatial shifts, structural changes and magnitude differences in the AEWs between the dust and no dust experiments. Calculations show that the dust causes the maximum in momentum flux to increase by about 4%. The African easterly jet (AEJ) also shows changes between the dust and no dust experiments. Ongoing work includes quantifying the structural changes of AEWs and the AEJ.

  16. LASE Observations of Saharan Air Layer and African Easterly Waves During NAMMA

    NASA Astrophysics Data System (ADS)

    Ismail, S.; Ferrare, R. A.; Browell, E. V.; Kooi, S.; Dunion, J.; Heymsfield, G. M.; Notari, A.; Butler, C. F.; Burton, S. P.; Fenn, M. A.; Krishnamurti, T. N.; Biswas, M.; Chen, G.; Anderson, B.

    2009-12-01

    The Lidar Atmospheric Sensing Experiment (LASE) on the NASA DC-8 aircraft provided the first simultaneous measurements of water vapor and aerosol distributions to study the thermodynamic characteristics of the Saharan Air Layer (SAL) and its impact on African Easterly Waves (AEWs) during the NASA African Monsoon Multidisciplinary Analyses (NAMMA) campaign. LASE data were used to derive profiles of aerosol scattering ratios, aerosol extinction coefficients, aerosol optical thickness, water vapor mixing ratios, and relative humidity (RH). LASE measurements and temperature profiles from the GPS dropsondes were used to characterize the SAL, convection, and clear air regions. Three case studies were selected for detailed analysis: 1) a vertically stratified SAL, with high-resolution layering (unlike a vertically well-mixed SAL), 2) a SAL with high RH, and 3) a SAL surrounded by dry air intrusions. The average extinction-to-backscatter ratios derived from LASE measurements over the dust layers varied from 35±5 to 45±5, which are well within the range of values determined by other lidar systems. LASE aerosol extinction and water vapor profiles were validated by comparison with onboard in situ aerosol measurements and dropsonde water vapor soundings, respectively. An analysis of LASE data suggests that the SAL suppresses low-altitude convection. A summary of latitudinal and longitudinal distributions of aerosol and water vapor distribution in SAL and non-SAL events is also presented.

  17. The Influence of Superparameterization on the Representation of African Easterly Waves

    NASA Astrophysics Data System (ADS)

    McCrary, R. R.; Randall, D. A.

    2012-12-01

    This study examines African easterly wave (AEW) dynamics in the Superparameterized Community Climate System Model (SP-CCSM). Conventional general circulation models (GCMs) typically have difficulty representing AEW dynamics over West Africa. One reason is that the coarse resolution of these models limits their ability to represent the multi-scale interactions between the large-scale dynamics and individual convective systems, which are important for the origin and development of AEWs. The SP-CCSM has been designed to better simulate the interactions between small-scale circulations and large-scale dynamics, by replacing the conventional parameterizations with a 2D cloud resolving model embedded within each GCM grid column. With this approach we are able to capture the interactions between clouds and the global circulation of the atmosphere. The goal of our work is to improve our understanding of the multi-scale interactions that occur between AEWs and convection over West Africa. The implementation of the superparameterization into the CCSM improves the overall representation of monsoon precipitation over West Africa. Most notably, the region of maximum precipitation is shifted from the Gulf of Guinea in CCSM (not realistic), to over the continent in SP-CCSM. The biases found in precipitation for both models are thought to be linked to anomalously warm sea surface temperatures in the Gulf of Guinea and a misrepresentation of the equatorial Atlantic cold tongue (a common problem for coupled GCMs). AEWs and their relationship with convection are also improved in the SP-CCSM. In the standard model, little to no easterly wave activity is found over West Africa, and the relationship with convection is tenuous at best. SP-CCSM on the other hand produces strong AEWs over the region that exhibit similar horizontal and vertical structures to observations. The simulated waves are also shown to be strongly coupled to convection, and results suggest that barotropic and

  18. The Role of Energy Dispersion in the Genesis and Life Cycle of African Easterly Waves

    NASA Astrophysics Data System (ADS)

    Diaz, Michael

    This dissertation uses energy dispersion and wave packet concepts to provide a better conceptual model of the genesis and life cycle of African Easterly Waves and to better understand the instability of the African Easterly Jet (AEJ). The existence of an upstream (eastward) group velocity for AEWs is shown based on single-point lag regressions using gridded reanalysis data from 1990 to 2010. The eastward energy dispersion is consistent with the direction of ageostrophic geopotential flux vectors. A local eddy kinetic energy (EKE) budget reveals that, early in the life cycle of AEWs, growth rate due to geopotential flux convergence exceeds baroclinic and barotropic growth rates. Later in the life cycle, EKE decay due to geopotential flux divergence cancels or exceeds baroclinic and barotropic growth. A potential vorticity (PV) budget is used to diagnose tendencies related to group propagation. Although both upstream and downstream group speeds are possible because of the reversal in the mean meridional PV gradient, upstream propagation associated with the positive poleward PV gradient dominates wave packet evolution. Analogous to the concept of downstream development of midlatitude baroclinic waves, new AEWs develop preferentially upstream of the older ones, thus providing a mechanism for seeding new waves. The usefulness of upstream development as a genesis mechanism for AEWs is demonstrated by performing a case study of the AEW which ultimately produced hurricane Alberto (2000). The case study uses the ERA-interim reanalysis combined with surface observations and TRMM data. Using a local EKE budget, we attribute its genesis to energy dispersion from a preceding AEW. After genesis, baroclinic and barotropic conversion dominated the energetics of this AEW. Some strengths and weaknesses of upstream development as a paradigm for AEW genesis are discussed with respect to other potential mechanisms. The stability of the AEJ is examined applying the concept of absolute

  19. Projected changes in African easterly wave intensity and track in response to greenhouse forcing

    PubMed Central

    Skinner, Christopher Bryan; Diffenbaugh, Noah S.

    2014-01-01

    Synoptic-scale African easterly waves (AEWs) impact weather throughout the greater Atlantic basin. Over the African continent, AEWs are instrumental in initiating and organizing precipitation in the drought-vulnerable Sahel region. AEWs also serve as the precursors to the most intense Atlantic hurricanes, and contribute to the global transport of Saharan dust. Given the relevance of AEWs for the climate of the greater Atlantic basin, we investigate the response of AEWs to increasing greenhouse gas concentrations. Using an ensemble of general circulation models, we find a robust increase in the strength of the winds associated with AEWs along the Intertropical Front in West Africa by the late 21st century of the representative concentration pathway 8.5. AEW energy increases directly due to an increase in baroclinicity associated with an enhanced meridional temperature gradient between the Sahara and Guinea Coast. Further, the pattern of low-level warming supports AEW development by enhancing monsoon flow, resulting in greater convergence and uplift along the Intertropical Front. These changes in energetics result in robust increases in the occurrence of conditions that currently produce AEWs. Given relationships observed in the current climate, such changes in the location of AEW tracks and the magnitude of AEW winds carry implications for the relationship between AEWs and precipitation in the Sahel, the mobilization of Saharan dust, and the likelihood of cyclogenesis in the Atlantic. Our results therefore suggest that changes in AEW characteristics could play a critical role in shaping the response of Atlantic basin climate to future increases in greenhouse gas concentrations. PMID:24778244

  20. Projected changes in African easterly wave intensity and track in response to greenhouse forcing.

    PubMed

    Skinner, Christopher Bryan; Diffenbaugh, Noah S

    2014-05-13

    Synoptic-scale African easterly waves (AEWs) impact weather throughout the greater Atlantic basin. Over the African continent, AEWs are instrumental in initiating and organizing precipitation in the drought-vulnerable Sahel region. AEWs also serve as the precursors to the most intense Atlantic hurricanes, and contribute to the global transport of Saharan dust. Given the relevance of AEWs for the climate of the greater Atlantic basin, we investigate the response of AEWs to increasing greenhouse gas concentrations. Using an ensemble of general circulation models, we find a robust increase in the strength of the winds associated with AEWs along the Intertropical Front in West Africa by the late 21st century of the representative concentration pathway 8.5. AEW energy increases directly due to an increase in baroclinicity associated with an enhanced meridional temperature gradient between the Sahara and Guinea Coast. Further, the pattern of low-level warming supports AEW development by enhancing monsoon flow, resulting in greater convergence and uplift along the Intertropical Front. These changes in energetics result in robust increases in the occurrence of conditions that currently produce AEWs. Given relationships observed in the current climate, such changes in the location of AEW tracks and the magnitude of AEW winds carry implications for the relationship between AEWs and precipitation in the Sahel, the mobilization of Saharan dust, and the likelihood of cyclogenesis in the Atlantic. Our results therefore suggest that changes in AEW characteristics could play a critical role in shaping the response of Atlantic basin climate to future increases in greenhouse gas concentrations. PMID:24778244

  1. African Easterly Waves in 30-day High-Resolution Global Simulations: A Case Study During the 2006 NAMMA Period

    NASA Technical Reports Server (NTRS)

    Shen, Bo-Wen; Tao, Wei-Kuo; Wu, Man-Li C.

    2010-01-01

    In this study, extended -range (30 -day) high-resolution simulations with the NASA global mesoscale model are conducted to simulate the initiation and propagation of six consecutive African easterly waves (AEWs) from late August to September 2006 and their association with hurricane formation. It is shown that the statistical characteristics of individual AEWs are realistically simulated with larger errors in the 5th and 6th AEWs. Remarkable simulations of a mean African easterly jet (AEJ) are also obtained. Nine additional 30 -day experiments suggest that although land surface processes might contribute to the predictability of the AEJ and AEWs, the initiation and detailed evolution of AEWs still depend on the accurate representation of dynamic and land surface initial conditions and their time -varying nonlinear interactions. 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.

  2. The Role of African Easterly Wave on Dust Transport and the Interaction Between Saharan Dust Layer and Atlantic ITCZ During Boreal Summer

    NASA Technical Reports Server (NTRS)

    Kim, Kyu-Myong; Lau, William K-M

    2011-01-01

    Saharan dust outbreaks not only transport large amount of dust to the northern Atlantic Ocean, but also alter African easterly jet and wave activities along the jet by changing north-south temperature gradient. Recent modeling and observational studies show that during periods of enhance outbreaks, rainfall on the northern part of ITCZ increases in conjunction with a northward shift of ITCZ toward the dust layer. In this paper, we study the radiative forcing of Saharan dust and its interactions with the Atlantic Inter-tropical Convergence Zone (ITCZ), through African easterly waves (AEW), African easterly jet (AEJ), using the Terra/Aqua observations as well as MERRA data. Using band pass filtered EOF analysis, we find that African easterly waves propagating westward along two principal tracks, centered at 15-25N and 5-10N respectively. The easterly waves in the northern track are slower, with propagation speed of 9 ms-1, and highly correlated with major dust outbreak over North Africa. On the other hand, easterly waves along the southern track are faster with propagating speed of 10 ms-1, and are closely tied to rainfall/cloud variations along the Atlantic ITCZ. Dust transport along the southern track leads rainfall/cloud anomalies in the same region by one or two days, suggesting the southern tracks of dust outbreak are regions of strong interaction between Saharan dust layer and Atlantic ITCZ. Possible linkage between two tracks of easterly waves, as well as the long-term change of easterly wave activities and dust outbreaks, are also discussed.

  3. Diagnosing GCM errors over West Africa using relaxation experiments. Part II: intraseasonal variability and African easterly waves

    NASA Astrophysics Data System (ADS)

    Pohl, Benjamin; Douville, Hervé

    2011-10-01

    A near-global grid-point nudging of the Arpege-Climat atmospheric General Circulation Model towards ECMWF reanalyses is used to diagnose the regional versus remote origin of the summer model biases and variability over West Africa. First part of this study revealed a limited impact on the monsoon climatology compared to a control experiment without nudging, but a significant improvement of interannual variability, although the amplitude of the seasonal anomalies remained underestimated. Focus is given here on intraseasonal variability of monsoon rainfall and dynamics. The reproducible part of these signals is investigated through 30-member ensemble experiments computed for the 1994 rainy season, a year abnormally wet over the Sahel but representative of the model systematic biases. In the control experiment, Arpege-Climat simulates too few rainy days that are associated with too low rainfall amounts over the central and western Sahel, in line with the seasonal dry biases. Nudging the model outside Africa tends to slightly increase the number of rainy days over the Sahel, but has little effect on associated rainfall amounts. However, results do indicate that a significant part of the monsoon intraseasonal variability simulated by Arpege-Climat is controlled by lateral boundary conditions. Parts of the wet/dry spells over the Sahel occur in phase in the 30 members of the nudging experiment, and are therefore embedded in larger-scale variability patterns. Inter-member spread is however not constant across the selected summer season. It is partly controlled by African Easterly Waves, which show dissimilar amplitude from one member to another, but a coherent phasing in all members. A lowpass filtering of the nudging fields suggests that low frequency variations in the lateral boundary conditions can lead to eastward extensions of the African Easterly Jet, creating a favorable environment for easterly waves, while high frequency perturbations seem to control their

  4. Analysis of the origins of east Pacific easterly waves

    NASA Astrophysics Data System (ADS)

    Findlay, E. W.; Rydbeck, A.; Maloney, E. D.

    2013-12-01

    The east Pacific Ocean is the second most active hurricane basin in the world. According to the National Hurricane Center, approximately 70% of tropical cyclones in the east Pacific are said to be seeded by African easterly waves. However, this statistic assumes continuous propagation of easterly waves from the Atlantic to the east Pacific. This study focuses on investigating the origins and tracks of easterly waves in the east Pacific during the months of June-November when EWs are most active. It is hypothesized in this study that most of the easterly waves (EWs) in the east Pacific are not linked to EWs originating in Africa but are initiated in-situ. The bight of Panama appears to be a climatologically favorable environment for the development of easterly waves due to the low-level cyclonic flow and precipitation maximum. Easterly waves are analyzed using lag correlation and composites plots of 2-10 day filtered meridional winds and precipitation from NCEP/NCAR reanalysis and TRMM, respectively. From these analyses, we compare the relationship between easterly waves in the Atlantic to those in the east Pacific. A limited WRF simulation was also utilized to compare the location and track of easterly waves to observations during August 2005. Composites and lag correlations of easterly waves support the idea that most easterly waves are generated in the east Pacific rather than initiating in Africa, as the analysis does not support the propagation of easterly waves across Central America and Mexico.

  5. Simulation of African Easterly Waves and its Projection in Response to Anthropogenic Greenhouse Forcing in a High Resolution AGCM

    NASA Astrophysics Data System (ADS)

    Kunhu Bangalth, Hamza; Raj, Jerry; Bhaskar Gunturu, Udaya; Stenchikov, Georgiy

    2016-04-01

    African Easterly Waves (AEWs) are the primary synoptic-scale disturbances over tropical Africa and Atlantic, which propagate westward from East Africa towards Atlantic during summer. AEWs have a pivotal role in the initiation and organization of the convective rainfall over this region and often act as the precursor for Atlantic tropical cyclones. Present study uses a high resolution AGCM, High Resolution Atmospheric Model (HiRAM) developed at GFDL, to investigate the projected changes in AEW characteristics in response to anthropogenic greenhouse forcing. Ensembles of simulations are conducted at a spatial resolution of ~ 25 km, with observed SST and SSTs from two coarse resolution Earth System Models (ESM2M and ESM2G) developed at GFDL, in the history period (1975-2004). Future projections (till 2050) are also conducted for two Representative Concentration Pathways (RCPs), RCP4.5 and RCP8.5. To test the ability of HiRAM to properly simulate the three dimensional structure and the space-time variability of AEW, the simulations in the history period are compared against two reanalysis products, ERA-Interim and MERRA, and against the parent ESMs. Space-time spectral analysis and complex empirical orthogonal function analysis have been conducted to investigate the dispersion characteristics and modes of variability, respectively. The representation of AEW in HiRAM is comparable to reanalyses and is improved in comparison with the coarse resolution parent ESMs.

  6. Direct Radiative Effect of Mineral Dust on the Development of African Easterly Waves in Late Summer, 2003-07

    SciTech Connect

    Ma, Po-Lun; Zhang, Kai; Shi, Jainn Jong; Matsui, Toshihisa; Arking, Albert

    2012-12-19

    Episodic events of both Saharan dust outbreaks and African easterly waves (AEWs) are observed to move westward over the eastern tropical Atlantic Ocean. The relationship between the warm, dry, and dusty Saharan air layer on the nearby storms has been the subject of considerable debate. In this study, the Weather Research and Forecasting model is used to investigate the radiative effect of dust on the development of AEWs during August and September, the months of maximumtropical cyclone activity, in years 2003–07. The simulations show that dust radiative forcing enhances the convective instability of the environment. As a result, mostAEWsintensify in the presence of a dust layer. The Lorenz energy cycle analysis reveals that the dust radiative forcing enhances the condensational heating, which elevates the zonal and eddy available potential energy. In turn, available potential energy is effectively converted to eddy kinetic energy, in which local convective overturning plays the primary role. The magnitude of the intensification effect depends on the initial environmental conditions, including moisture, baroclinity, and the depth of the boundary layer. The authors conclude that dust radiative forcing, albeit small, serves as a catalyst to promote local convection that facilitates AEW development.

  7. Direct Radiative Effect of Mineral Dust on the Development of African Easterly Wave in Late Summer, 2003-2007

    NASA Technical Reports Server (NTRS)

    Ma, Po-Lun; Zhang, Kai; Shi, Jainn Jong; Matsui, Toshihisa; Arking, Albert

    2012-01-01

    Episodic events of both Saharan dust outbreaks and African Easterly Waves (AEWs) are observed to move westward over the eastern tropical Atlantic Ocean. The relationship between the warm, dry, and dusty Saharan Air Layer (SAL) on the nearby storms has been the subject of considerable debate. In this study, the Weather Research and Forecasting (WRF) model is used to investigate the radiative effect of dust on the development of AEWs during August and September, the months of maximum tropical cyclone activity, in years 2003-2007. The simulations show that dust radiative forcing enhances the convective instability of the environment. As a result, most AEWs intensify in the presence of a dust layer. The Lorenz energy cycle analysis reveals that the dust radiative forcing enhances the condensational heating, which elevates the zonal and eddy available potential energy. In turn, available potential energy is effectively converted to eddy kinetic energy, in which local convective overturning plays the primary role. The magnitude of the intensification effect depends on the initial environmental conditions, including moisture, baroclinity, and the depth of the boundary layer. We conclude that dust radiative forcing, albeit small, serves as a catalyst to promote local convection that facilitates AEW development.

  8. The relationship between African easterly waves and daily rainfall over West Africa: observations and regional climate simulations

    NASA Astrophysics Data System (ADS)

    Crétat, Julien; Vizy, Edward K.; Cook, Kerry H.

    2015-01-01

    The relationship between summer African easterly waves (AEWs) and daily rainfall is assessed in West Africa for 1998-2008 using various reanalyses, satellite-derived rainfall products, and a regional climate model (RCM) run at 90- and 30-km resolutions. 3-5 and 6-9 day AEWs are extracted by filtering daily 700 hPa meridional wind time series at 1°W and 11.5°N, and 1°W and 17.5°N, respectively. Both observed and simulated rainfall anomalies are of larger magnitude over West Africa during 3-5-d than 6-9-d AEWs. The RCM simulates larger rainfall rates in phase with the 3-5-d wave trough instead of ahead, unlike the observations, and overestimates the intensity and spatial coverage of rainfall associated with 6-9-d AEWs. The observed and simulated co-variability between 3-5-d (6-9-d) AEW activity and daily rainfall is strong (weak) and mostly located south (north) of 15°N. However, the RCM overestimates the spatial coverage of the AEW-rainfall relationship in the longitudinal (latitudinal) direction in the case of 3-5-d (6-9-d) AEWs. Observed and simulated daily intense rainfall events, extracted using a percentile threshold approach, are mostly located south of 15°N during summer. The observed relationship between their frequency of occurrence and active 3-5-d AEWs is maximal west of 8°E, while extends up to southern Chad in both RCM simulations. Their magnitude is also largely overestimated by the RCM, indicating an exaggerated coupling between the wave activity and the convection. Finally, observed and simulated 3-5-d AEWs establish the most favorable synoptic conditions for the development of intense rainfall events over West Africa.

  9. The Impact of Projected Changes in Monsoon Season Circulation and African Easterly Waves on Saharan Dust Transport

    NASA Astrophysics Data System (ADS)

    Skinner, C. B.; Diffenbaugh, N. S.

    2013-12-01

    The Sahara is the largest source region of mineral dust in the world. Each year, an estimated 100 to 700 million tons of dust are transported from the Sahara through atmospheric processes. Roughly 30 - 50% of this dust travels westward into the North Atlantic where it impacts the regional radiative balance, atmospheric dynamics, and biogeochemical cycles. During the boreal summer season, dust emissions and dust transport over North Africa are largely controlled by westward propagating synoptic-scale and mesoscale systems such as African easterly waves (AEWs) and mesoscale convective systems (MCSs). In particular, strong low-level winds, vertical motion, and convection associated with these systems drive dust mobilization and vertical mixing throughout the atmosphere. In this work we utilize the CMIP5 ensemble of general circulation models to explore the projected impact of enhanced radiative forcing, consistent with a high emissions scenario (RCP8.5), on atmospheric processes that may influence the emission and transport of dust over West Africa. In particular we focus on the simulation of AEWs during the months of the West African monsoon (June - September). Results from the CMIP5 ensemble indicate a robust increase in low-level (850mb) AEW activity along the Sahel/Sahara border in response to increasing greenhouse gas concentrations by the end of the 21st century. Across the CMIP5 ensemble, AEWs exhibit the strongest increase in low-level winds directly over the observed prolific dust sources within Mali, Mauritania and Algeria in the western Sahara. Enhanced AEW activity in this region is consistent with projected increases in low-level baroclinicity and increased ascent associated with a deepening Saharan Heat Low and stronger convergence along the Intertropical Front. We use a variety of observed and modeled relationships between atmospheric processes and dust as well as output from the available CMIP5 dust modules to explore the impact of the projected

  10. Response of Seasonal Atlantic Tropical Cyclone Activity to Suppression of African Easterly Waves in a Regional Climate Model

    NASA Astrophysics Data System (ADS)

    Patricola, C. M.; Saravanan, R.; Chang, P.

    2014-12-01

    Atlantic tropical cyclones and African easterly waves (AEWs) are strongly linked on the synoptic timescale, with about 85% of observed major Atlantic hurricanes originating from AEWs (e.g., Landsea et al. 1993). However, the influence of variability in AEWs on seasonal Atlantic tropical cyclone activity is not fully understood; a positive correlation between AEW activity and Atlantic tropical cyclone activity exists on the interannual timescale during just some periods of the observational record (e.g., Thorncroft and Hodges, 2001; Hopsch et al. 2007). This study investigates the impact of AEWs on seasonal Atlantic tropical cyclone activity using regional climate model simulations in which AEWs were either prescribed or removed through the lateral boundary condition (LBC). The control simulation (10-member ensemble) was run at 27 km resolution and used 6-hourly LBCs from the NCEP CFS Reanalysis and daily NOAA Optimum Interpolation (OI) V2 sea surface temperature (SST) from the year 2005. In the experiment AEWs were suppressed by filtering 2-10 day variability over tropical latitudes from the eastern LBC, located along the west coast of the Sahel. The difference in Atlantic tropical cyclone frequency was insignificant between the simulations in which AEWs were prescribed versus suppressed, indicating that AEWs are not necessary to maintain climatological tropical cyclone frequency even though tropical cyclones readily originate from these features. This further implies that seasonal Atlantic tropical cyclone frequency is uninfluenced by variability in AEWs, and that the value of AEW variability as a predictor of Atlantic tropical cyclones is limited to the weekly timescale. However in response to filtering AEWs, accumulated cyclone energy significantly increased by about 15% of the control simulation mean and the spatial pattern of track density shifted in association with changes in steering winds. This suggests the importance of AEWs in impacting tropical cyclone

  11. The role of African easterly waves on Atlantic tropical cyclone variability

    NASA Astrophysics Data System (ADS)

    Hopsch, Susanna B.

    Coherent vorticity structures were identified at 850hPa over West Africa and the tropical Atlantic in the ERA40 reanalysis. The presence of two dominant source regions for stormtracks over the Atlantic was found. Results show that the southern stormtrack provides most storms that reach the MDR where most tropical cyclones develop. Marked seasonal variability in location and intensity of storms leaving the West African coast exists, which may influence the likelihood of downstream intensification and longevity. There exists considerable year-to-year variability in number of West African storms, both over land and continuing out over the tropical Atlantic Ocean. While the low-frequency variability is well correlated with Atlantic tropical cyclone activity, West African rainfall and SSTs, the interannual variability is found to be uncorrelated. In contrast, variance of 2-6-day-filtered meridional wind, which provides a synoptic-scale measure of AEW activity, shows a significant, positive correlation with TC activity at interannual timescales. The extent to which the nature of AEWs leaving the West African coast is important for influencing the probability of becoming named storms downstream was also explored. The ERA40 dataset has been analyzed for July through September from 1979-2001 to generate a climatology of AEWs leaving the West African coast. A composite view of the structure of the AEWs and their large-scale environment was obtained by identifying all AEWs that were associated with named storms over the MDR. This was compared to the composite of all disturbances that ultimately failed to develop. It is shown that substantial differences in structure and characteristics exist of AEWs that become associated with tropical cyclones and the ones that don't. The most important differences between developing and non-developing AEWs include: (1) Developing AEWs have a distinctive cold-core structure before reaching the West coast. (2) They transform towards more warm

  12. The relative role of ocean-atmosphere interaction and African easterly waves in the generation and development of Tropical cyclones in the North Atlantic

    NASA Astrophysics Data System (ADS)

    Cabos, William; Sein, Dmitry; Hodges, Kevin; Jacob, Daniela

    2016-04-01

    We use the regionally coupled ocean - atmosphere model ROM and its atmospheric component REMO in standalone configuration in order to assess the relative role of ocean feedbacks and the African easterly waves in the simulation of tropical cyclonic activity in the Atlantic ocean. To this end, a number of coupled and uncoupled simulations forced by ERA-Interim boundary conditions have been carried out. In one set of simulations, the atmospheric domain includes the Northern Africa land masses, where the easterly waves are formed. In a second set of simulations, the easterly waves are taken from the ERA Interim reanalysis, as atmospheric domain excludes explicitly the African land masses. We study the statistics of modeled tracks of the tropical cyclones in the simulations. We found that the coupling has a strong impact on the number of tropical cyclones generated in the Northern Tropical Atlantic. In the coupled run it was close to the observations, while in the uncoupled runs the number of tropical cyclones was strongly overestimated. The coupling also influences the simulated position of the ITCZ.

  13. The Role of African Easterly Wave on Dust Transport and the Interaction Between Saharan Dust Layer and Atlantic ITCZ During Boreal Summer

    NASA Technical Reports Server (NTRS)

    Lau, William K. M.; Kim, Kyu-Myong

    2012-01-01

    In this paper, we investigate the relationships among Saharan dust outbreak and transport, African easterly waves (AEW), African easterly jet (AEJ) and associated convective activities of Atlantic Intertropical Convergence Zone (ITCZ) using Cloudsat-Calipso, MODIS and MERRA data. We find that a major Saharan dust outbreak is associated with the formation of a westward propagating strong cyclone around 15-25N over the western part northern Saharan. The strong cyclonic flow mobilizes and lifts the dust from the desert surface to a high elevation. As the cyclone propagate westward, it transports a thick elevated dust layer between 900 -500 hPa from the African continent to the eastern Atlantic. Cloudiness is reduced within the warm, dry dusty layer, but enhanced underneath it, possibly due to the presence of a shallow inversion layer over the marine boundary layer. The dust outbreak is linked to enhanced deep convection in the northern part of Atlantic ITCZ, abutting the southern flank of the dust layer, and a strengthening of the northward flank of the AEJ. As the dust layer spreads westward, it loses elevation and becomes increasing diffused as it reaches the central and western Atlantic. Using band pass filtered EOF analysis of MERRA winds, we find that AEWs propagating westward along two principal tracks, centered at 15-25N and 5-10N respectively. The easterly waves in the northern track are highly correlated with major dust outbreak over North Africa and associated with slower moving systems, with a quasi-periodicity of 6-9 day. On the other hand, easterly waves along the southern track are faster, with quasi-periodicity of 3-5 days. These faster easterly waves are closely tied to rainfall/cloud variations along the Atlantic ITCZ. Dust transport along the southern track by the faster waves generally leads rainfall/cloud anomalies in the same region by one or two days, suggesting the southern tracks of dust outbreak are regions of strong interaction between

  14. Tropical cyclogenesis in Eastern Atlantique: Impact of earlier passage of African Easterly Wave trough on the evolution of Mesoscale Convective Systems and air-sea interaction

    NASA Astrophysics Data System (ADS)

    Lahat Dieng, Abdou; Eymard, Laurence; Moustapha Sall, Saidou; Lazar, Alban; Leduc-Leballeur, Marion

    2014-05-01

    A large part of Atlantic tropical depressions is generated in the Eastern basin in relation with the African Easterly Waves and the Mesoscale Convective Systems coming from the African continent. But initial surface oceanic and atmosphere conditions favoring such evolution are largely unknown. This study analyzes the structures of strengthening and dissipating MCSs evolving near the West African coast and evaluates the role of the surface oceanic condition on their evolutions. Satellite brightness temperature from Meteosat Second Generation over the summer season of 2006 and radar data for the same season between 1993 and 1999 are used to subjectively select fourteen cases of strengthening (dissipating) MCSs when they cross the Senegalese coast. With these observed MCSs locations, a lagged composite analysis is then performed using Era interim and CFSR reanalyses. Results show that the strengthening MCS composite is preceded by prior passage of an AEW near the West African coast. This first trough wave was associated with a cyclonic circulation in the low and middle troposphere and has enhanced southwest wind flow behind him feeding humidly to the strengthening MCS composite which was located in the vicinity of the second AEW trough. The contraction of the wave length associated with the two troughs was probably facilitated this supply in humidity. The Sea Surface Temperature seem contribute to the MCS enhancement through surface evaporation flux but this contribution is less important than humidity advection by the fist system. These conditions were not found in the dissipating MCS case which dissipated in a drying environment air dominated by subsidence and anticyclonic circulation. Key words: Mesoscale Convective System, African Easterly Wave, Sea Surface Temperature, tropical depression.

  15. Characteristics of African easterly waves associated with tropical cyclogenesis in the Cape Verde Islands region in July-August-September of 2004-2008

    NASA Astrophysics Data System (ADS)

    Arnault, Joël; Roux, Frank

    2011-04-01

    The most common synoptic-scale disturbances related to cyclogenesis over the tropical north Atlantic Ocean are African easterly waves (AEWs) that originated from the northern African continent. However, most of these waves do not evolve in tropical depressions, storms, or hurricanes. The reasons why only few AEWs develop and the necessary conditions for cyclogenetic evolution are still the subject of intense debate. Tropical cyclogenesis occurring near the Cape Verde Islands in the eastern tropical Atlantic is investigated here with five seasons (July-August-September of 2004-2008) of European Centre for Medium-Range Weather Forecasts analyses, Meteosat-9 images, and National Hurricane Center (National Oceanic and Atmospheric Administration, National Centers for Environmental Prediction) "best track" archives. The nine named storms that first reached tropical depression intensity east of 30°W, and two among six which developed between 30 and 40°W, during these five years evolved from intense AEW troughs, associated with low-level cyclonic circulation, weak mid-level anticyclonic Saharan flow to the east, and deep convection near the center of cyclonic vorticity. The cyclogenetic evolution of three AEW troughs, which verified these conditions but failed to develop into named storms, was probably inhibited by unusually dry environment and strong vertical wind shear. The fate of other AEW troughs, which did not satisfy the necessary conditions, is also discussed.

  16. Formation of African Easterly Waves and Mesoscale Convective Systems over Eastern Africa and its Implication to Tropical Cyclogenesis over Eastern Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Lin, Yuh-Lang

    2009-07-01

    The formation of African easterly waves and mesoscale convective systems in eastern North Africa and its impacts on the tropical cyclogenesis over the eastern Atlantic Ocean is studied. Based on numerical simulations, AEWs can be produced by vortex shedding from the EH. The lee vortex is generated mainly by the blocking of the EH and helped by the horizontal shear associated with the northeasterly wind and the jet passing through the Turkana channel. The MCS was originated from the moist convection over the EH triggered by diurnal sensible heating. When the MCS moved to the lee of the mountain, it merged with the lee vortex of the AEW train and formed the coupled AEW-MCS system. Numerical simulations of a regional climate model indicate that the simulated fields do possess the AEW characteristics and the convection was generated over the EH, and the pre-Alberto AEW-MCS system was generated near the lee of the EH. Finer-resolution numerical simulations demonstrate that the vortex generated on the lee and MCS over the mountain eventually merge and become an AEW-MCS system which might serve as a precursor of tropical cyclone.

  17. African Easterly Jet: Structure and Maintenance

    NASA Technical Reports Server (NTRS)

    Wu, Man-Li C.; Reale, Oreste; Schubert, Siegfried D.; Suarez, Max J.; Koster, Randy D.; Pegion, Philip J.

    2009-01-01

    This article investigates the African Easterly Jet (AEJ), its structure and the forcings contributing to its maintenance, critically revisiting previous work which attributed the maintenance of the jet to soil moisture gradients over tropical Africa. A state-of-the-art global model in a high-end computer framework is used to produce a 3-member 73-year ensemble run forced by observed SST to represent the Control run. The AEJ as produced by the Control is compared with the representation of the AEJ in the European Center for Medium Range Forecast Reanalyses (ERA-40) and other observational data sets and found very realistic. Five Experiments are then performed, each represented by sets of 3-member 22 year long (1980-2001) ensemble runs. The goal of the Experiments is to investigate the role of meridional soil moisture gradients, different land surface properties and orography. Unlike previous studies, which have suppressed soil moisture gradients within a highly idealized framework (i.e., the so-called bucket model), terrestrial evaporation control is here achieved with a highly sophisticated landsurface treatment and with an extensively tested and complex methodology. The results show that the AEJ is suppressed by a combination of absence of meridional evaporation gradients over Africa and constant vegetation, even if the individual forcings taken separately do not lead to the AEJ disappearance, but only its modification. Moreover, the suppression of orography also leads to a different circulation in which there is no AEJ. This work suggests that it is not just soil moisture gradients, but a unique combination of geographical features present only in northern tropical Africa, which causes and maintains the jet.

  18. Tropical Cyclogenesis in a Tropical Wave Critical Layer: Easterly Waves

    NASA Technical Reports Server (NTRS)

    Dunkerton, T. J.; Montgomery, M. T.; Wang, Z.

    2009-01-01

    The development of tropical depressions within tropical waves over the Atlantic and eastern Pacific is usually preceded by a "surface low along the wave" as if to suggest a hybrid wave-vortex structure in which flow streamlines not only undulate with the waves, but form a closed circulation in the lower troposphere surrounding the low. This structure, equatorward of the easterly jet axis, is identified herein as the familiar critical layer of waves in shear flow, a flow configuration which arguably provides the simplest conceptual framework for tropical cyclogenesis resulting from tropical waves, their interaction with the mean flow, and with diabatic processes associated with deep moist convection. The recirculating Kelvin cat's eye within the critical layer represents a sweet spot for tropical cyclogenesis in which a proto-vortex may form and grow within its parent wave. A common location for storm development is given by the intersection of the wave's critical latitude and trough axis at the center of the cat's eye, with analyzed vorticity centroid nearby. The wave and vortex live together for a time, and initially propagate at approximately the same speed. In most cases this coupled propagation continues for a few days after a tropical depression is identified. For easterly waves, as the name suggests, the propagation is westward. It is shown that in order to visualize optimally the associated Lagrangian motions, one should view the flow streamlines, or stream function, in a frame of reference translating horizontally with the phase propagation of the parent wave. In this co-moving frame, streamlines are approximately equivalent to particle trajectories. The closed circulation is quasi-stationary, and a dividing streamline separates air within the cat's eye from air outside.

  19. Tropical cyclogenesis in a tropical wave critical layer: easterly waves

    NASA Astrophysics Data System (ADS)

    Dunkerton, T. J.; Montgomery, M. T.; Wang, Z.

    2009-08-01

    The development of tropical depressions within tropical waves over the Atlantic and eastern Pacific is usually preceded by a "surface low along the wave" as if to suggest a hybrid wave-vortex structure in which flow streamlines not only undulate with the waves, but form a closed circulation in the lower troposphere surrounding the low. This structure, equatorward of the easterly jet axis, is identified herein as the familiar critical layer of waves in shear flow, a flow configuration which arguably provides the simplest conceptual framework for tropical cyclogenesis resulting from tropical waves, their interaction with the mean flow, and with diabatic processes associated with deep moist convection. The recirculating Kelvin cat's eye within the critical layer represents a sweet spot for tropical cyclogenesis in which a proto-vortex may form and grow within its parent wave. A common location for storm development is given by the intersection of the wave's critical latitude and trough axis at the center of the cat's eye, with analyzed vorticity centroid nearby. The wave and vortex live together for a time, and initially propagate at approximately the same speed. In most cases this coupled propagation continues for a few days after a tropical depression is identified. For easterly waves, as the name suggests, the propagation is westward. It is shown that in order to visualize optimally the associated Lagrangian motions, one should view the flow streamlines, or stream function, in a frame of reference translating horizontally with the phase propagation of the parent wave. In this co-moving frame, streamlines are approximately equivalent to particle trajectories. The closed circulation is quasi-stationary, and a dividing streamline separates air within the cat's eye from air outside. The critical layer equatorward of the easterly jet axis is important to tropical cyclogenesis because its cat's eye provides (i) a region of cyclonic vorticity and weak deformation by the

  20. Tropical cyclogenesis in a tropical wave critical layer: easterly waves

    NASA Astrophysics Data System (ADS)

    Dunkerton, T. J.; Montgomery, M. T.; Wang, Z.

    2008-06-01

    The development of tropical depressions within tropical waves over the Atlantic and eastern Pacific is usually preceded by a "surface low along the wave" as if to suggest a hybrid wave-vortex structure in which flow streamlines not only undulate with the waves, but form a closed circulation in the lower troposphere surrounding the low. This structure, equatorward of the easterly jet axis, resembles the familiar critical layer of waves in shear flow, a flow configuration which arguably provides the simplest conceptual framework for tropical cyclogenesis resulting from tropical waves, their interaction with the mean flow, and with diabatic processes associated with deep moist convection. The critical layer represents a sweet spot for tropical cyclogenesis in which a proto-vortex may form and grow within its parent wave. A common location for storm development within the critical layer is given by the intersection of the wave's critical latitude and trough axis, with analyzed vorticity centroid nearby. The wave and vortex live together for a time, and initially propagate at approximately the same speed. In most cases this coupled propagation continues for a few days after a tropical depression is identified. For easterly waves, as the name suggests, the propagation is westward. It is shown that in order to visualize optimally this "marsupial paradigm" one should view the flow streamlines, or stream function, in a frame of reference translating horizontally with the phase propagation of the parent wave. This translation requires an appropriate "gauge" that renders translating streamlines and isopleths of translating stream function approximately equivalent to flow trajectories. In the translating frame, the closed circulation is stationary, and a dividing streamline effectively separates air within the critical layer from air outside. The critical layer equatorward of the easterly jet axis is important to tropical cyclogenesis because it provides (i) a region of

  1. Initiation and intensification of east Pacific easterly waves

    NASA Astrophysics Data System (ADS)

    Rydbeck, Adam V.

    The background atmospheric state of the east Pacific (EPAC) warm pool in which easterly waves (EWs) develop varies dramatically on intraseasonal time scales. EPAC intraseasonal variability is well known to modulate local convective and circulation patterns. Westerly intraseasonal phases are associated with westerly low-level wind and positive convective anomalies and easterly intraseasonal phases are associated with easterly low-level wind and negative convective anomalies. This study first investigates the perturbation available potential energy (PAPE) and perturbation kinetic energy (PKE) budgets of easterly waves composited during westerly, easterly, and neutral intraseasonal phases, respectively. During neutral and westerly intraseasonal phases, the generation of PAPE associated with perturbation diabatic heating that is subsequently converted to PKE is enhanced and is the dominant energy source for EWs. EWs draw energy from low-level barotropic conversion, regardless of phase. A novel and previously unrecognized result is the detection of strong barotropic generation of PKE at midlevels during westerly intraseasonal phases. This previously unidentified source of PKE at midlevels is in part due to strong intraseasonal modulation of the background midlevel winds. Processes associated with the local amplification of EWs in the EPAC warm pool are then explored. Developing EWs favor convection in the southwest and northeast quadrants of the disturbance. In nascent EWs, convection favors the southwest quadrant. In these quadrants, lower tropospheric vorticity is generated locally through vertical stretching that supports a horizontal tilt of the wave from the southwest to the northeast. EWs with such tilts are then able to draw energy via barotropic conversion from the background cyclonic zonal wind shear present in the east Pacific. EWs during westerly and neutral intraseasonal periods are associated with robust convection anomalies. Easterly intraseasonal periods

  2. Genesis of Pre-Hurricane Felix (2007). Part 1; The Role of the Easterly Wave Critical Layer

    NASA Technical Reports Server (NTRS)

    Wang, Zhuo; Montgomery, M. T.; Dunkerton, T. J.

    2010-01-01

    The formation of pre Hurricane Felix (2007) in a tropical easterly wave is examined in a two-part study using the Weather Research and Forecasting (WRF) model with a high-resolution nested grid configuration that permits the representation of cloud system processes. The simulation commences during the wave stage of the precursor African easterly-wave disturbance. Here the simulated and observed developments are compared, while in Part II of the study various large-scale analyses, physical parameterizations, and initialization times are explored to document model sensitivities. In this first part the authors focus on the wave/vortex morphology, its interaction with the adjacent intertropical convergence zone complex, and the vorticity balance in the neighborhood of the developing storm. Analysis of the model simulation points to a bottom-up development process within the wave critical layer and supports the three new hypotheses of tropical cyclone formation proposed recently by Dunkerton, Montgomery, and Wang. It is shown also that low-level convergence associated with the ITCZ helps to enhance the wave signal and extend the "wave pouch" from the jet level to the top of the atmospheric boundary layer. The region of a quasi-closed Lagrangian circulation within the wave pouch provides a focal point for diabatic merger of convective vortices and their vortical remnants. The wave pouch serves also to protect the moist air inside from dry air intrusion, providing a favorable environment for sustained deep convection. Consistent with the authors' earlier findings, the tropical storm forms near the center of the wave pouch via system-scale convergence in the lower troposphere and vorticity aggregation. Components of the vorticity balance are shown to be scale dependent, with the immediate effects of cloud processes confined more closely to the storm center than the overturning Eliassen circulation induced by diabatic heating, the influence of which extends to larger radii.

  3. Convectively coupled Kelvin and easterly waves in a regional climate simulation of the tropics

    NASA Astrophysics Data System (ADS)

    Tulich, Stefan N.; Kiladis, George N.; Suzuki-Parker, Asuka

    2011-01-01

    This study evaluates the performance of a regional climate model in simulating two types of synoptic tropical weather disturbances: convectively-coupled Kelvin and easterly waves. Interest in these two wave modes stems from their potential predictability out to several weeks in advance, as well as a strong observed linkage between easterly waves and tropical cyclogenesis. The model is a recent version of the weather research and forecast (WRF) system with 36-km horizontal grid spacing and convection parameterized using a scheme that accounts for key convective triggering and inhibition processes. The domain spans the entire tropical belt between 45°S and 45°N with periodic boundary conditions in the east-west direction, and conditions at the meridional/lower boundaries specified based on observations. The simulation covers 6 years from 2000 to 2005, which is long enough to establish a statistical depiction of the waves through space-time spectral filtering of rainfall data, together with simple lagged-linear regression. Results show that both the horizontal phase speeds and three-dimensional structures of the waves are qualitatively well captured by the model in comparison to observations. However, significant biases in wave activity are seen, with generally overactive easterly waves and underactive Kelvin waves. Evidence is presented to suggest that these biases in wave activity (which are also correlated with biases in time-mean rainfall, as well as biases in the model's tropical cyclone climatology) stem in part from convection in the model coupling too strongly to rotational circulation anomalies. Nevertheless, the model is seen to do a reasonable job at capturing the genesis of tropical cyclones from easterly waves, with evidence for both wave accumulation and critical layer processes being importantly involved.

  4. Radiation of inertial kinetic energy as near-inertial waves forced by tropical Pacific Easterly waves

    NASA Astrophysics Data System (ADS)

    Soares, S. M.; Richards, K. J.

    2013-05-01

    Easterly waves (EW) are low level tropical atmospheric disturbances able to resonantly force strong mixed layer inertial currents. Using data from two Tropical Atmosphere Ocean/Eastern Pacific Investigation of Climate Processes (TAO/EPIC) buoys located along 95°W and a multiparameterization one-dimensional turbulence model, we examine how the EW-forced surface inertial kinetic energy (IKE) loss is partitioned between turbulent dissipation and near-inertial wave (NIW) radiation. Several EW-forcing events are individually simulated with a version of the General Ocean Turbulence Model modified to include a linear damping coefficient to account for the NIW radiation energy sink. The kinetic energy budget of these simulations shows that NIW radiation accounted for typically 50-60% of the IKE loss and in some cases up to 80%. These empirically derived estimates of the contribution of the radiated NIWs to the loss of wind-induced surface IKE are substantially higher than recently published numerical estimates. Furthermore, the results indicate that the vertical NIW energy flux increases linearly with the wind input of IKE, an easily obtained quantity. The NIW vertical energy flux estimated for a single near-resonant event is comparable to extreme north Pacific wintertime-averaged fluxes, indicating the existence of important episodic sources of near-inertial energy available for mixing within and below the thermocline in the tropical region.

  5. Observational analyses and idealized numerical simulations of African wave dynamics

    NASA Astrophysics Data System (ADS)

    Smith, Travis Allen

    The role of the Tropical Easterly Jet (TEJ) in West African rainfall climatology has received little attention in the research community to date. Therefore, this dissertation will examine the instabilities and wave activity associated with the TEJ and their implications regarding interannual rainfall variability over western Africa. First, the instability of the TEJ is examined using potential vorticity (PV) concepts to contrast wet and dry years in West Africa. Analyses of the meridional PV gradient indicate an abrupt shift in both location and magnitude of the instability associated with the TEJ during the transition from wet to dry years in the Sahel. Additionally, the signs of the climatological anomalies of PV at the TEJ level strongly reflect the four primary modes (wet, dry, wet dipole, and dry dipole) of interannual rainfall variability in West Africa. Several examples of PV perturbation analyses at the TEJ level confirm that the upper-level development of African Easterly Waves (AEWs) differs considerably between the two periods. These results support recent observations and modeling studies that suggest that the interaction between the TEJ and the African Easterly Jet (AEJ) plays an important role in the development and structure of AEWs. In addition to the observational study, a multi-layer primitive equation model is utilized to examine easterly wave activity and vertical motion patterns based on the juxtaposition of the three primary jets located over western Africa. Idealized simulations based on the basic states of the low-level westerly jet (LLWJ), African Easterly Jet (AEJ), and the Tropical Easterly Jet (TEJ) for several anomalously wet and dry years in the Sahel are studied. Results are compared to several linearized GCM simulations that are initialized with NCEP observational data. Results show that the location, intensity, and scale of wave perturbations are sensitive to the position and intensity of the jets. Vertical motion patterns also

  6. Relation between tropical easterly wave convection and tropical cyclogenesis over the Atlantic and East Pacific

    NASA Astrophysics Data System (ADS)

    Leppert, Kenneth D., II

    The characteristics of tropical easterly wave convection and the possible implications of convective structure on tropical cyclogenesis and intensification over the Atlantic Ocean and East Pacific were investigated in this study. Easterly waves were partitioned into northerly, southerly, trough, and ridge phases based on 700-hPa meridional wind data. Waves were subsequently divided according to whether they did or did not develop tropical cyclones (i.e., developing waves [DWs] and non-developing waves [NDWs], respectively), and composites of synoptic-scale and convective-scale variables as a function of wave phase and category were created using Eulerian and Lagrangian frameworks. Results of both the Eulerian and Lagrangian composites indicate that the greatest difference between DWs and NDWs is observed for the fractional coverage by infrared brightness temperatures ≤ 240 K and ≤ 210 K. Indicators of convective intensity (e.g., lightning flash rates, mean convective reflectivity profiles) provide relatively few statistically significant differences between DWs and NDWs, except over the East Pacific. In addition, the Lagrangian composites suggest that as genesis is approached for DWs, the coverage by convection and cold cloudiness increases, while convective intensity decreases. In contrast, convective coverage and intensity both increase with time for NDWs. Thus, the results of both the Lagrangian and Eulerian frameworks suggest that the coverage by cold cloudiness/convection is generally more important than convective intensity for tropical cyclogenesis. In terms of large-scale variables, both types of composites suggest that enhanced upper-level (˜200 hPa) divergence and deep-layer moisture are particularly important for cyclogenesis and for distinguishing DWs from NDWs. The Eulerian composites also suggest that favorable large-scale conditions for cyclogenesis (e.g., significantly greater low-level [˜925 hPa] vorticity) occur for Atlantic DWs relative to

  7. Convection and Easterly Wave Structure Observed in the Eastern Pacific Warm-Pool during EPIC-2001

    NASA Technical Reports Server (NTRS)

    Peterson, Walter A.; Cifelli, R.; Boccippio, D.; Rutledge, S. A.; Fairall, C. W.; Arnold, James E. (Technical Monitor)

    2002-01-01

    During September-October 2001, the East Pacific Investigation of Climate Processes in the Coupled Ocean-Atmosphere System (EPIC-2001) ITCZ field campaign focused on studies of deep convection in the warm-pool region of the East Pacific. In addition to the TAO mooring array, observational platforms deployed during the field phase included the NOAA ship RN Ronald H. Brown, the NSF ship RN Horizon, and the NOAA P-3 and NCAR C-130 aircraft. This study combines C-band Doppler radar, rawinsonde, and surface heat flux data collected aboard the RN Brown to describe ITCZ convective structure and rainfall statistics in the eastern Pacific as a function of 3-5 day easterly wave phase. Three distinct easterly wave passages occurred during EPIC-2001. Wind and thermodynamic data reveal that the wave trough axes exhibited positively correlated U and V winds and a slight westward phase tilt with height. A relatively strong (weak) northeasterly deep tropospheric shear followed the trough (ridge) axis. Temperature and humidity perturbations exhibited mid-to upper level cooling (warming) and drying (moistening) in the northerly (trough and southerly) phase. At low levels warming (cooling) occurred in the northerly (southerly) phase with little change in the relative humidity, though mixed layer mixing ratios were larger during the northerly phase. When composited, radar, sounding, lightning and surface heat flux observations suggest the following systematic behavior as a function of wave phase: approximately zero to one quarter wavelength ahead of (behind) the wave trough in northerly (southerly) flow, larger (smaller) CAPE, lower (higher) CIN, weaker (stronger) tropospheric shear, higher (lower) conditional mean rain rates, higher (lower) lightning flash densities, and more (less) robust convective vertical structure occurred. Latent and sensible heat fluxes reached a minimum in the northerly phase and then increased through the trough, reaching a peak during the ridge phase

  8. Atlantic tropical cyclone formation: Pre-genesis evolution of tropical easterly waves and impacts of the middle to upper tropospheric dry air

    NASA Astrophysics Data System (ADS)

    Hankes, Isaac E.

    This study first provides an overview of the dynamic and thermodynamic evolution of tropical easterly waves (TEWs) for 164 named tropical storms over the Atlantic during 1989-2010 July-October. The evolution of precipitation and the low-level convergence suggests that convection begins to organize near the center of the wave critical layer about one day prior to genesis, along with the rapid intensification of vorticity. The composites derived from the ERA-Interim reanalysis reveal higher specific humidity and equivalent potential temperature near the center of the wave critical layer, especially in the middle troposphere within one day prior to genesis. The study then focuses on the formation of the Cape Verde storms over the East Atlantic. There are two groups of easterly waves over West Africa, one to the south and the other to the north of the African Easterly Jet (AEJ), which sometimes merge near the coast of West Africa. Three groups of waves are identified in order to determine the role of wave merger in tropical cyclogenesis over the East Atlantic: non-merger developers, merger developers, and merger non-developers. Relative to non-mergers, it is found that merger developers have a weaker circulation near the surface at the early stages but the merger of a southern wave with a northern wave leads to a stronger and deeper wave pouch, which is more conducive to tropical cyclogenesis. It is also found that dry air intrusion west of the wave trough in the middle and upper troposphere inhibits deep convection and leads to the nondevelopment of some mergers, but that boundary layer dry air in the northern waves moistens quickly over the ocean and does not impede development. The interannual variability of the middle and upper tropospheric dry air and its impacts on tropical cyclone activity over the Atlantic are further examined using the EOF analysis and composite analysis. It is found that the interannual variability of the upper-tropospheric (300-500 hPa) dry

  9. A Regional View of Easterly Waves over Pacific and Atlantic Ocean: Tropical Cyclogenesis Thresholds and Rainfall

    NASA Astrophysics Data System (ADS)

    Dominguez, C.; Done, J.; Bruyere, C. L.

    2015-12-01

    Tropical cyclones (TCs) are well known as important contributors to summer precipitation over Intra America Seas (IAS) and the Eastern Pacific Ocean (EPA). They contribute up to 30% in the Caribbean Region, Gulf of Mexico and Eastern Pacific during high active seasons. Although Easterly Waves (EWs) are considered high-impact weather phenomena, their regional importance in summer rainfall and regional differences in their development into TCs remains uncertain. This study quantifies the contribution of EWs to summer rainfall. We find that EWs contributed up to 50% of summer rainfall over IAS and EPA during the period 1980-2013. In addition, this study demonstrates regional dependency of the structure of EWs that develop into hurricanes and the thresholds of tropical cyclogenesis. Using ERA-Interim data, vorticity at three levels (850, 700 and 600), Column Integrated Heating, equivalent potential temperature, sea surface temperature, wind speed, stretching radius and integrated moisture flux were analyzed to investigate regional dependency of thresholds for tropical cyclogenesis during the 1980-2013 period. We found that tropical cyclogenesis occurred under different regional environments over Pacific and Atlantic Ocean and the structure of EWs changed depending on the basin. This research can be relevant to improve operational forecast of tropical cyclogenesis since thresholds are used to indicate where and when a TC formation can occur.

  10. Impact of Interactive Aerosol on the African Easterly Jet in the NASA GEOS-5 Global Forecasting System

    NASA Technical Reports Server (NTRS)

    Reale, O.; Lau, K. M.; da Silva, A.

    2010-01-01

    The real-time treatment of interactive realistically varying aerosol in a global operational forecasting system, as opposed to prescribed (fixed or climatologically varying) aerosols, is a very difficult challenge that only recently begins to be addressed. Experiment results from a recent version of the NASA GEOS-5 forecasting system, inclusive of interactive aerosol treatment, are presented in this work. Four sets of 30 5-day forecasts are initialized from a high quality set of analyses previously produced and documented to cover the period from 15 August to 16 September 2006, which corresponds to the NASA African Monsoon Multidisciplinary Analysis (NAMMA) observing campaign. The four forecast sets are at two different horizontal resolutions and with and without interactive aerosol treatment. The net impact of aerosol, at times in which there is a strong dust outbreak, is a temperature increase at the dust level and decrease in the near-surface levels, in complete agreement with previous observational and modeling studies. Moreover, forecasts in which interactive aerosols are included depict an African Easterly (AEJ) at slightly higher elevation, and slightly displace northward, with respect to the forecasts in which aerosols are not include. The shift in the AEJ position goes in the direction of observations and agrees with previous results.

  11. Mantle Flow Implications across Easter and Southern Africa from Shear Wave Splitting Measurements

    NASA Astrophysics Data System (ADS)

    Ramirez, C.; Nyblade, A.; Bagley, B. C.; Mulibo, G. D.; Tugume, F.; Wysession, M. E.; Wiens, D.; van der Meijde, M.

    2015-12-01

    In this study, we present new shear wave splitting results from broadband seismic stations in Botswana and Namibia, and combine them with previous results from stations in Kenya, Uganda, Tanzania, Malawi, Zambia, South Africa, Mozambique, Zimbabwe, and Angola to further examine the pattern of seismic anisotropy across southern Africa. The new results come from stations in northern Namibia and Botswana, which help to fill in large gaps in data coverage. Our preliminary results show that fast polarization directions overall trend in a NE orientation. The most noticeable measurements that deviate from this pattern are located around the Archean Tanzania Craton in eastern Africa. The general NE pattern of fast polarization directions is attributed to mantle flow linked to the African superplume. Smaller scale variations from this general direction can be explained by shape anisotropy in the lithosphere in magmatic regions in the East African rift system and to fossil anisotropy in the Precambrian lithosphere.

  12. Electrically-Active Convection in Tropical Easterly Waves and Implications for Tropical Cyclogenesis in the Atlantic and East Pacific

    NASA Technical Reports Server (NTRS)

    Leppert, Kenneth D., II; Petersen, Walter A.; Cecil, Daniel J.

    2012-01-01

    In this study, we investigate the characteristics of tropical easterly wave convection and the possible implications of convective structure on tropical cyclogenesis and intensification over the Atlantic Ocean and East Pacific using data from the Tropical Rainfall Measurement Mission Microwave Imager, Precipitation Radar (PR), and Lightning Imaging Sensor as well as infrared (IR) brightness temperature data from the NASA global-merged IR brightness temperature dataset. Easterly waves were partitioned into northerly, southerly, trough, and ridge phases based on the 700-hPa meridional wind from the NCEP-NCAR reanalysis dataset. Waves were subsequently divided according to whether they did or did not develop tropical cyclones (i.e., developing and nondeveloping, respectively), and developing waves were further subdivided according to development location. Finally, composites as a function of wave phase and category were created using the various datasets. Results suggest that the convective characteristics that best distinguish developing from nondeveloping waves vary according to where developing waves spawn tropical cyclones. For waves that developed a cyclone in the Atlantic basin, coverage by IR brightness temperatures .240 K and .210 K provide the best distinction between developing and nondeveloping waves. In contrast, several variables provide a significant distinction between nondeveloping waves and waves that develop cyclones over the East Pacific as these waves near their genesis location including IR threshold coverage, lightning flash rates, and low-level (<4.5 km) PR reflectivity. Results of this study may be used to help develop thresholds to better distinguish developing from nondeveloping waves and serve as another aid for tropical cyclogenesis forecasting.

  13. The genesis of Typhoon Nuri as observed during the Tropical Cyclone Structure 2008 (TCS-08) field experiment - Part 1: The role of the easterly wave critical layer

    NASA Astrophysics Data System (ADS)

    Montgomery, M. T.; Lussier, L. L., III; Moore, R. W.; Wang, Z.

    2010-10-01

    An observational and real-time model forecast study of the genesis of Typhoon Nuri during the Tropical Cyclone Structure 2008 (TCS-08) field campaign in the western North Pacific sector is presented. Analysis and observational data show that the surrounding base state is an easterly trade wind flow and the precursor disturbance to Typhoon Nuri is an easterly wave that originates in the ITCZ in the Central Pacific. This disturbance can be tracked more than 10 days prior to tropical storm formation. An overview of the field data is presented here using a newly proposed dynamical framework for tropical cyclone formation within the critical layer of an easterly wave. Despite propagating through a hostile environment ripe with strong vertical wind shear and relatively dry air, the easterly wave critical layer protects the proto-vortex and allows it to gestate until it reaches a more favorable environment. Within this protective "Kelvin cat's eye flow" located within the wave's critical layer existed a sweet spot, defined as the intersection between the wave trough and critical latitude, which is the preferred location for tropical cyclogenesis. Global Forecast System Final Analyses and IR satellite imagery, which shows convective bands wrapping around the sweet spot as genesis nears, confirm that this sweet spot is the location where Typhoon Nuri's dominant low-level circulation emerges. United States Air Force C130 and Naval Research Laboratory P3 research flights on 16 and 17 August collected flight-level, dropwindsonde, and Doppler radar data that allowed an evaluation of the dynamic and thermodynamic processes within the cat's eye circulation. The dropwindsonde analyses identifies the precursor easterly wave disturbance on 16 August and identifies an area of weak low-level cyclonic circulation on 17 August. Real-time forecasts were produced using operational global prediction model data to support scientific missions during TCS-08. These forecasts were found to be

  14. The genesis of Typhoon Nuri as observed during the Tropical Cyclone Structure 2008 (TCS-08) field experiment - Part 1: The role of the easterly wave critical layer

    NASA Astrophysics Data System (ADS)

    Montgomery, M. T.; Lussier, L. L., III; Moore, R. W.; Wang, Z.

    2009-09-01

    An observational and real-time model forecast study of the genesis of Typhoon Nuri during the Tropical Cyclone Structure 2008 (TCS-08) field campaign in the western North Pacific sector is presented. Analysis and observational data show that the surrounding base state flow was an easterly trade wind flow and the precursor disturbance to Typhoon Nuri was an easterly wave that originated in the ITCZ in the Central Pacific and can be tracked more than 10 days prior to tropical storm formation. An overview of the field data is presented here using a newly proposed dynamical framework for tropical cyclone formation within the critical layer of an easterly wave. Despite propagating through a hostile environment ripe with strong vertical wind shear and relatively dry air, the easterly wave critical layer protected the proto-vortex and allowed it to gestate until it reached a more favorable environment. Within this protective "Kelvin's cat's eye flow" located within the wave's critical layer existed a "sweet spot", defined as the intersection between the wave trough and critical latitude, which was the preferred location for tropical cyclogenesis. Global Forecast System Final Analyses and IR satellite imagery, which shows convective bands wrapping around the sweet spot as genesis nears, confirm that this sweet spot is the location where Typhoon Nuri's dominant low-level circulation emerges. United States Air Force C130 and Naval Research Laboratory P3 research flights on 16 and 17 August collected flight-level, dropwindsonde, and Doppler radar data that allowed an evaluation of the dynamic and thermodynamic processes within the cat's eye. The dropwindsonde analyses identified the precursor easterly wave disturbance on 16 August and identified an area of weak low-level cyclonic circulation on 17 August. During the TCS-08 experiment "real-time forecasts" were produced in real-time using operational global prediction model data to support scientific missions. These forecasts

  15. Archaeoastronomy of Easter Island

    NASA Astrophysics Data System (ADS)

    Edwards, Edmundo

    Astronomer priests or "skywatchers" on Easter Island lived in stone towers that were used as observatories and built stone markers in the periphery that indicated the heliacal rising of certain stars that served to indicate the arrival of marine birds, turtles, the offshore fishing season, and times for planting and harvest. Petroglyphs related to such sites depict outriggers, fishhooks, pelagic fish, and turtles and supposedly represented a star map. In this chapter, we analyze a set of such skywatchers dwellings, and stone markers located upon the North coast of Easter Island that have astronomic orientations, its related petroglyphs, and the relations between these directions with their yearly activities and their ritual calendar.

  16. 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.

  17. Studies of African wave disturbances with the GISS GCM

    NASA Technical Reports Server (NTRS)

    Druyan, Leonard M.; Hall, Timothy M.

    1994-01-01

    Simulations made with the general circulation model of the NASA/Goddard Institute for Space Studies (GISS GCM) run at 4 deg latitude by 5 deg longitude horizontal resolution are analyzed to determine the model's representation of African wave disturbances. Waves detected in the model's lower troposphere over northern Africa during the summer monsoon season exhibit realistic wavelengths of about 2200 km. However, power spectra of the meridional wind show that the waves propagate westward too slowly, with periods of 5-10 days, about twice the observed values. This sluggishness is most pronounced during August, consistent with simulated 600-mb zonal winds that are only about half the observed speeds of the midtropospheric jet. The modeled wave amplitudes are strongest over West Africa during the first half of the summer but decrease dramatically by September, contrary to observational evidence. Maximum amplitudes occur at realistic latitudes, 12 deg - 20 deg N, but not as observed near the Atlantic coast. Spectral analyses suggest some wave modulation of precipitation in the 5-8 day band, and compositing shows that precipitation is slightly enhanced east of the wave trough, coincident with southerly winds. Extrema of low-level convergence west of the wave troughs, coinciding with northerly winds, were not preferred areas for simulated precipitation, probably because of the drying effect of this advection, as waves were generally north of the humid zone. The documentation of African wave disturbances in the GISS GCM is a first step toward considering wave influences in future GCM studies of Sahel drought.

  18. Tectonics of the Easter plate

    NASA Technical Reports Server (NTRS)

    Engeln, J. F.; Stein, S.

    1984-01-01

    A new model for the Easter plate is presented in which rift propagation has resulted in the formation of a rigid plate between the propagating and dying ridges. The distribution of earthquakes, eleven new focal mechanisms, and existing bathymetric and magnetic data are used to describe the tectonics of this area. Both the Easter-Nazca and Easter-Pacific Euler poles are sufficiently close to the Easter plate to cause rapid changes in rates and directions of motion along the boundaries. The east and west boundaries are propagating and dying ridges; the southwest boundary is a slow-spreading ridge and the northern boundary is a complex zone of convergent and transform motion. The Easter plate may reflect the tectonics of rift propagation on a large scale, where rigid plate tectonics requires boundary reorientation. Simple schematic models to illustrate the general features and processes which occur at plates resulting from large-scale rift propagation are used.

  19. The Sensitivity of WRF Daily Summertime Simulations over West Africa to Alternative Parameterizations. Part 1: African Wave Circulation

    NASA Technical Reports Server (NTRS)

    Noble, Erik; Druyan, Leonard M.; Fulakeza, Matthew

    2014-01-01

    The performance of the NCAR Weather Research and Forecasting Model (WRF) as a West African regional-atmospheric model is evaluated. The study tests the sensitivity of WRF-simulated vorticity maxima associated with African easterly waves to 64 combinations of alternative parameterizations in a series of simulations in September. In all, 104 simulations of 12-day duration during 11 consecutive years are examined. The 64 combinations combine WRF parameterizations of cumulus convection, radiation transfer, surface hydrology, and PBL physics. Simulated daily and mean circulation results are validated against NASA's Modern-Era Retrospective Analysis for Research and Applications (MERRA) and NCEP/Department of Energy Global Reanalysis 2. Precipitation is considered in a second part of this two-part paper. A wide range of 700-hPa vorticity validation scores demonstrates the influence of alternative parameterizations. The best WRF performers achieve correlations against reanalysis of 0.40-0.60 and realistic amplitudes of spatiotemporal variability for the 2006 focus year while a parallel-benchmark simulation by the NASA Regional Model-3 (RM3) achieves higher correlations, but less realistic spatiotemporal variability. The largest favorable impact on WRF-vorticity validation is achieved by selecting the Grell-Devenyi cumulus convection scheme, resulting in higher correlations against reanalysis than simulations using the Kain-Fritch convection. Other parameterizations have less-obvious impact, although WRF configurations incorporating one surface model and PBL scheme consistently performed poorly. A comparison of reanalysis circulation against two NASA radiosonde stations confirms that both reanalyses represent observations well enough to validate the WRF results. Validation statistics for optimized WRF configurations simulating the parallel period during 10 additional years are less favorable than for 2006.

  20. Aerosol interactions with African/Atlantic climate dynamics

    NASA Astrophysics Data System (ADS)

    Hosseinpour, F.; Wilcox, E. M.

    2014-07-01

    Mechanistic relationships exist between variability of dust in the oceanic Saharan air layer (OSAL) and transient changes in the dynamics of Western Africa and the tropical Atlantic Ocean. This study provides evidence of possible interactions between dust in the OSAL region and African easterly jet-African easterly wave (AEJ-AEW) system in the climatology of boreal summer, when easterly wave activity peaks. Synoptic-scale changes in instability and precipitation in the African/Atlantic intertropical convergence zone are correlated with enhanced aerosol optical depth (AOD) in the OSAL region in response to anomalous 3D overturning circulations and upstream/downstream thermal anomalies at above and below the mean-AEJ level. Upstream and downstream anomalies are referred to the daily thermal/dynamical changes over the West African monsoon region and the Eastern Atlantic Ocean, respectively. Our hypothesis is that AOD in the OSAL is positively correlated with the downstream AEWs and negatively correlated with the upstream waves from climatological perspective. The similarity between the 3D pattern of thermal/dynamical anomalies correlated with dust outbreaks and those of AEWs provides a mechanism for dust radiative heating in the atmosphere to reinforce AEW activity. We proposed that the interactions of OSAL dust with regional climate mainly occur through coupling of dust with the AEWs.

  1. Diurnal variations and modulation by easterly waves of the size distribution of convective cloud clusters over West Africa and the Atlantic Ocean

    SciTech Connect

    Machado, L.A.T.; Duvel, J.Ph.; Desbois, M. )

    1993-01-01

    Short time-scale fluctuations of the size distribution of tropical convective cloud clusters for July to September 1989 were studied using Meteosat data. A cluster at a given brightness-temperature threshold was defined as the area covered by adjacent cloudy pixels with brightness temperature lower than the threshold. The clusters were classified according to the area covered and the position of their center of mass. Over land regions of West Africa the size distribution underwent a coherent diurnal behavior with development of small cells between noon and 1500 LST. Over the Atlantic Ocean, the highest cloudiness had a weak maximum extent in early morning, while cloudiness at lower levels was more extended in the afternoon. This diurnal behavior was primarily due to large cloud clusters, suggesting that the diurnal variation over the ocean resulted from internal variations of large convective systems and not from the initiation of convection at a given hour of the day. This was confirmed by the analysis of 15 large convective systems propagating over the ocean. The authors have ascertained that the high cloud cover was maximized within the trough of eastrly waves. The cluster size was dependent upon the wave amplitude with a larger mean cluster size when the amplitude was largr. The trough phase of the wave was found to promote the development of large clusters more than it favored the initial stage of convection. 30 refs., 11 figs.

  2. Crustal thinning between the Ethiopian and East African Plateaus from modeling Rayleigh wave dispersion

    SciTech Connect

    Benoit, M H; Nyblade, A A; Pasyanos, M E

    2006-01-17

    The East African and Ethiopian Plateaus have long been recognized to be part of a much larger topographic anomaly on the African Plate called the African Superswell. One of the few places within the African Superswell that exhibit elevations of less than 1 km is southeastern Sudan and northern Kenya, an area containing both Mesozoic and Cenozoic rift basins. Crustal structure and uppermost mantle velocities are investigated in this area by modeling Rayleigh wave dispersion. Modeling results indicate an average crustal thickness of 25 {+-} 5 km, some 10-15 km thinner than the crust beneath the adjacent East African and Ethiopian Plateaus. The low elevations can therefore be readily attributed to an isostatic response from crustal thinning. Low Sn velocities of 4.1-4.3 km/s also characterize this region.

  3. Herbert Easterly auxiliary truck heater

    SciTech Connect

    Not Available

    1991-12-09

    The objective of this work was to continue the development of the Herbert Easterly heater apparatus for vehicles, such as semi-trailer tractors in order to fully establish its technical feasibility and provide the basis for its commercialization. This heater is auxiliary to the vehicle's primary heating system. With the engine off it heats both the vehicle engine to a temperature at which it starts easily and the vehicle passenger compartment. Specifically, this heater is automatically ignitable, operates directly from the vehicle diesel fuel supply and preheats the vehicle engine fuel prior to combustion. During the course of this work nine different versions of prototype heaters were designed, constructed and tested. All designs were based on the ideas and principles outlined in the Easterly patent. Each successive version incorporated design and fabrication improvements relative to the previous version. The final version, Prototype 9, utilized a multiple water jacket design to capture additional heat from the combustion gases prior to exhausting to the atmosphere. This final prototype exceeded the performance of a commercially available Webasto DBW-2010 using the same commercial burner as the one used in the Webasto unit. The time required to raise the heater fluid temperature by 120{degree}F was 23% less (20 minutes compared to 26 minutes) for Prototype 9 compared to the commercially available unit. In addition a prototype heat exchanger for preheating engine fuel was designed, fabricated and tested. It was also determined that the Prototype 9 auxiliary heater could operate at 85{degree}F for approximately 6 hours on a fully charged 12 volt marine battery rated to deliver 500 cold cranking amps.

  4. Seismic anisotropy across the east African plateau from shear wave splitting analysis

    NASA Astrophysics Data System (ADS)

    Bagley, B. C.; Nyblade, A.; Mulibo, G.; Tugume, F.

    2011-12-01

    Previous studies of the east African plateau reveal complicated patterns of seismic anisotropy that are not easily explained by a single mechanism. The pattern is defined by rift-parallel fast directions for stations within or near Cenozoic rift valleys, and near-null results in Precambrian terrains away from the rift. Data from 65 temporary Africa Array stations deployed between 2007 and 2011 are being used to make new shear wave splitting measurements. The stations span the east African plateau and cover both the eastern and western branches of the east African rift system, as well as unrifted Proterozoic and Archean terrains in Uganda, Kenya, Tanzania, and Zambia. Through analysis of shear wave splitting we will better constrain the distribution of seismic anisotropy, and and from it gain new insight into the tectonic evolution of east Africa.

  5. Lithospheric structure of the southern African subcontinent from surface wave tomography

    NASA Astrophysics Data System (ADS)

    Raveloson, A.; Nyblade, A.; Mulibo, G.; Mangongolo, A.; Tugume, F.

    2012-12-01

    In this study the lithospheric structure of the southern African subcontinent is examined using a new 3D shear wave velocity model. The lithospheric structure of Africa consists of several Archean cratons and Proterozoic mobile belts. Many intracratonic and rift basin are found within both the Archean and Protozoic terrains. We investigate the 3D shear wave velocity structure of the lithosphere by tomographically modeling Rayleigh wave dispersion curves. Rayleigh waves group velocities from 10 to 125 s period were determined by using multiple-filter and phase-matched techniques. We used seismic events with a magnitude greater than 4.5 and depth shallower than 100 km recorded from 1990 to 2011 on many stations belonging to temporary or permanent networks. We used events and stations within the African plate in an effort to minimize the contributions from outside structure. We constructed the 3D S wave model in two steps. In the first step we measured group velocities of fundamental mode Rayleigh waves. In the second stage we extracted a dispersion curve from the group velocity maps and inverted them to obtain 1D shear wave velocity models. The 1D models are then combined at a regular spatial interval to create a 3D shear wave velocity model. New features revealed in our model include a region of lower wave speeds beneath the cuvette central separating several Archean blocks of the Congo craton and a region of fast lithosphere in northern Mozambique associated with the Ruvuma microplate.

  6. Burns during Easter festivities in Greece.

    PubMed

    Pallantzas, A; Kourakos, P; Stampolidis, N; Papagianni, E; Balagoura, A; Stathopoulos, A; Polizoi, A; Emvalomata, A; Evaggelopoulou, M; Castana, O

    2012-12-31

    Easter is the most important holiday for the Greek Church. It is rich in traditions and rituals but during the Greek Easter festivities, especially at midnight Mass on Easter Saturday night, it is customary to throw fireworks around. These fireworks are not part of the true Easter tradition and they are potentially fatal. Unfortunately, in the past few years, the custom has become more and more popular in Greece. There are some local variations, mainly in the Aegean islands, where homemade rockets are used to have a "rocket war". The rockets consist of wooden sticks loaded with an explosive mixture containing gunpowder and launched from special platforms. Many severe injuries involving loss of sight and limbs as well as major burns are also caused by the use of illegal fireworks at Easter. Every year numerous burn victims are hospitalized. The most affected areas are the face, the upper extremities, and the chest, often in association with slight or severe wounds and injuries. This study presents our department's experience with incidents due to the use of fireworks during Easter festivities. PMID:23766749

  7. Topological description of Easter Islander palmar dermatoglyphics.

    PubMed

    Goodson, C S; Meier, R J

    1986-10-01

    A sample of 594 Easter Islander palms was analyzed according to the topological method. Some suggestions for clarification of the topological approach were made, including clearer definition of the palmar triradii and substitution of the term "profile" for "formula." The frequency of Easter Islander profiles was compared against British and Australian Aborigine samples (Loesch, 1974; 1983a,b) and found to be significantly different for two of the ten most common combinations. The individual pattern elements, pattern intensities, a-b count, A-line exit, and atd angle were described, with population comparisons made when they were available. PMID:3799825

  8. View of south boundary of Easter Hill project site, former ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View of south boundary of Easter Hill project site, former right of way for Hoffman Boulevard. Note reconstructed Easter Hill Building No. 6 at rear. Looking east - Easter Hill Village, Bordered by South Twenty-sixth Street, South Twenty-eighth Street, Hinkley Avenue, Foothill Avenue & Corto Square, Richmond, Contra Costa County, CA

  9. Seismic Anisotropy beneath the African Plate using Shear Wave Splitting Measurements from AfricaArray Stations

    NASA Astrophysics Data System (ADS)

    Nunley, M. E.; Weeraratne, D.; Nyblade, A.

    2011-12-01

    The African continental plate is made up of a series of cratons and fold belts with activation ages ranging from present to Archean. Recent studies have shown that this tectonic assemblage occurred over a long history of accretion and rifting cycles that likely left behind the complex crust and lithospheric fabric that we see today. Here we study seismic anisotropy beneath the African continent using a large array of permanent AfricaArray and Global Seismic Network seismic stations located throughout Africa. We supply shear wave splitting techniques to teleseismic earthquake events using the eigenvalue method where the second eigenvalue is minimized to determine anisotropy. Stations located in the Ethiopian rift zone yield a NE-SW fast direction with the largest delay times of 1.5s. One station (KOWA) located in the west African craton displays a NW-SE fast direction. Stations located near Cameroon, at the coastal edge of the central African shear zone, produce NW-SE fast directions oriented perpendicular to the shear zone axis. . A group of stations located on Archean crust in central Africa skirt the Congo craton and display consistent NNE fast directions and delay times of 1.0s. Two stations, LSZ and TEZI are located in the Damara suture belt between the Congo and Kaapvaal cratons display a NE-SW fast direction parallel to the suture axis. In the Kaapvaal craton region the average anisotropic direction is NNE with a 1.0s delay time. New stations available south of the Kaapvaal craton reveal a NE fast direction with delay times that vary from 0.5 to 1.3 s. Several splitting measurements are made for the southern station HVD which display backazimuth dependence producing NW-SE fast directions for ray paths coming from the east and are consistent with observations at GRM located east of HVD. These results show that seismic anisotropy across the continent is not uniform and shows significant variation between tectonic regions. While mantle flow and lithospheric

  10. Organization of rainfall by an unstable jet with an application to African waves

    NASA Technical Reports Server (NTRS)

    Miller, R. L.; Lindzen, R. S.

    1992-01-01

    It is hypothesized that a shear instability can organize rainfall if it converges sufficient amounts of moisture. This convergence is calculated by specifying the amplitude of a downgoing wave just beneath the jet and calculating the ascent induced below as a function of the zonal wind. Data obtained question whether a jet can organize rainfall from an arbitrary large distance above the moist layer. While in the absence of shear, a wave can reach the moist layer with undiminished amplitude, the induced ascent is small - less than the estimated ascent during phase I of the GARP Atlantic Tropical Experiment (GATE) when rainfall remained unorganized. It is suggested that organization can occur only if the unstable jet is within a few kilometers of the moist and separated by large shear. A wind profile resembling the observed 600-mb African jet is considered as an example. The waves are found to be closer to the moist layer during the later summer, causing larger ascent at this time.

  11. Segmented African Lithosphere Beneath Anatolia Imaged by Teleseismic P-Wave Tomography

    NASA Astrophysics Data System (ADS)

    Biryol, Cemal; Zandt, George; Beck, Susan; Ozacar, Atilla

    2010-05-01

    Anatolia, a part of the Alpine-Himalayan orogenic belt, is shaped by a variety of complex tectonic processes that define the major tectonic provinces across which different deformation regimes exist. Collision related plateau formation dominates the present lithospheric deformation to the east and slab roll-back related back-arc extension takes place in the west. The two zones are connected at the northern part of the region by strike-slip faulting along the right-lateral North Anatolian Fault Zone. Recent seismological studies show that the Eastern Anatolian Plateau (EAP) is supported by hot asthenosphereric material that was emplaced beneath the plateau following the detachment of subducted Arabian lithosphere. The westward continuation of the deeper structure of Anatolia was previously less well constrained due to the lack of geophysical observations. In order to study the deeper lithosphere and mantle structure beneath Anatolia, we used teleseismic P-wave tomography and data from several temporary and permanent seismic networks deployed in the region. A major part of the data comes from the North Anatolian Fault passive seismic experiment (NAF) that consists of 39 broadband seismic stations operated at the north central part of Anatolia between 2005 and 2008. We also used data collected from permanent seismic stations of the National Earthquake Monitoring Center (NEMC) and stations from the Eastern Turkey Seismic Experiment (ETSE). Approximately 34,000 P-wave travel time residuals, measured in multiple frequency bands, are inverted using approximate finite-frequency sensitivity kernels. Our tomograms reveal a fast anomaly that corresponds to the subducted portion of the African lithosphere along the Cyprean Arc. This fast anomaly dips northward beneath central Anatolia with an angle of approximately 45 degrees. However, the anomaly disappears rather sharply to the east beneath the western margin of the EAP and to the west beneath the Isparta Angle. The western

  12. The P and S wave velocity structure of the mantle beneath eastern Africa and the African superplume anomaly

    NASA Astrophysics Data System (ADS)

    Mulibo, Gabriel D.; Nyblade, Andrew A.

    2013-08-01

    P and S relative arrival time residuals from teleseismic earthquakes recorded on over 60 temporary AfricaArray broadband seismic stations deployed in Uganda, Tanzania, and Zambia between 2007 and 2011 have been inverted, together with relative arrival time residuals from earthquakes recorded by previous deployments, for a tomographic image of mantle wave speed variations extending to a depth of 1200 km beneath eastern Africa. The image shows a low-wave speed anomaly (LWA) well developed at shallow depths (100-200 km) beneath the Eastern and Western branches of the Cenozoic East African rift system and northwestern Zambia, and a fast wave speed anomaly at depths ≤ 350 km beneath the central and northern parts of the East African Plateau and the eastern and central parts of Zambia. At depths ≥350 km the LWA is most prominent under the central and southern parts of the East African Plateau and dips to the southwest beneath northern Zambia, extending to a depth of at least 900 km. The amplitude of the LWA is consistent with a ˜150-300 K thermal perturbation, and its depth extent indicates that the African superplume, originally identified as a lower mantle anomaly, is likely a whole mantle structure. A superplume extending from the core-mantle boundary to the surface implies an origin for the Cenozoic extension, volcanism, and plateau uplift in eastern Africa rooted in the dynamics of the lower mantle.

  13. View of south boundary of Easter Hill project site for ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View of south boundary of Easter Hill project site for right of way for Hoffman Boulevard. Buildings No. 11 and 14 at right in trees. Looking west - Easter Hill Village, Bordered by South Twenty-sixth Street, South Twenty-eighth Street, Hinkley Avenue, Foothill Avenue & Corto Square, Richmond, Contra Costa County, CA

  14. Easter School Guidance. The National Literacy and Numeracy Strategies.

    ERIC Educational Resources Information Center

    Department for Education and Skills, London (England).

    This booklet explains the goals of Easter Schools, part of England's National Literacy and Numeracy Strategies. Easter Schools should be planned to cover four half-days and include four literacy and four mathematics lessons each covering the equivalent of at least an hour. The booklet addresses the following issues: why funding has been made…

  15. View of sports field and Easter Hill at west side ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View of sports field and Easter Hill at west side of project site. Looking southwest - Easter Hill Village, Bordered by South Twenty-sixth Street, South Twenty-eighth Street, Hinkley Avenue, Foothill Avenue & Corto Square, Richmond, Contra Costa County, CA

  16. View of sports field and Easter Hill at west side ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View of sports field and Easter Hill at west side of project site. Looking west - Easter Hill Village, Bordered by South Twenty-sixth Street, South Twenty-eighth Street, Hinkley Avenue, Foothill Avenue & Corto Square, Richmond, Contra Costa County, CA

  17. View of sports field from Easter Hill looking at intersection ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View of sports field from Easter Hill looking at intersection of South Twenty-Sixth Street and Foothill Avenue at left center rear. Buildings No. 36, 35, 25, 27, and 29, from left to right. Looking northeast - Easter Hill Village, Bordered by South Twenty-sixth Street, South Twenty-eighth Street, Hinkley Avenue, Foothill Avenue & Corto Square, Richmond, Contra Costa County, CA

  18. Anisotropic structure of the African upper mantle from Rayleigh and Love wave tomography

    NASA Astrophysics Data System (ADS)

    Sebai, Amal; Stutzmann, Eléonore; Montagner, Jean-Paul; Sicilia, Déborah; Beucler, Eric

    2006-04-01

    The geodynamics of the mantle below Africa is not well understood and anisotropy tomography can provide new insight into the coupling between the African plate and the underlying mantle convection. In order to study the anisotropic structure of the upper mantle beneath Africa, we have measured phase velocities of 2900 Rayleigh and 1050 Love waves using the roller-coaster algorithm [Beucler, E., Stutzmann, E., Montagner, J.-P., 2003. Surface-wave higher mode phase velocity measurments, using a roller-coaster type algorithm. Geophys. J. Int. 155 (1), 289-307]. These phase velocities have been inverted to obtain a new tomographic model that gives access to isotropic S V-wave velocity perturbations, azimuthal and radial anisotropies. Isotropic S V-wave velocity maps have a lateral resolution of 500 km. Anisotropy parameters have a lateral resolution of 1000 km which is uniform over Africa for azimuthal anisotropy but decreases at the West and South of Africa for radial anisotropy. At shallow depth, azimuthal anisotropy varies over horizontal distances much smaller than the continent scale. At 280 km depth, azimuthal anisotropy is roughly N-S, except in the Afar area, which might indicate differential motion between the African plate and the underlying mantle. The three cratons of West Africa, Congo and Kalahari are associated with fast velocities and transverse anisotropy that decrease very gradually down to 300 km depth. On the other hand, we observe a significant change in the direction and amplitude of azimuthal anisotropy at about 180 km depth, which could be the signature of the root of these cratons. The Tanzania craton is a shallower structure than the other African cratons and the slow velocities (-2%) observed on the maps at 180 and 280 km depth could be the signature of hot material such as a plume head below the craton. This slow velocity anomaly extends toward the Afar and azimuthal anisotropy fast directions are N-S at 180 km depth, indicating a possible

  19. Regional analysis of convective systems during the West African monsoon

    NASA Astrophysics Data System (ADS)

    Guy, Bradley Nicholas

    The West African monsoon (WAM) occurs during the boreal summer and is responsible for a majority of precipitation in the northern portion of West Africa. A distinct shift of precipitation, often driven by large propagating mesoscale convective systems, is indicated from satellite observations. Excepting the coarser satellite observations, sparse data across the continent has prevented understanding of mesoscale variability of these important systems. The interaction between synoptic and mesoscale features appears to be an important part of the WAM system. Without an understanding of the mesoscale properties of precipitating systems, improved understanding of the feedback mechanism between spatial scales cannot be attained. Convective and microphysical characteristics of West African convective systems are explored using various observational data sets. Focus is directed toward meso -alpha and -beta scale convective systems to improve our understanding of characteristics at this spatial scale and contextualize their interaction with the larger-scale. Ground-based radar observations at three distinct geographical locations in West Africa along a common latitudinal band (Niamey, Niger [continental], Kawsara, Senegal [coastal], and Praia, Republic of Cape Verde [maritime]) are analyzed to determine convective system characteristics in each domain during a 29 day period in 2006. Ancillary datasets provided by the African Monsoon Multidisciplinary Analyses (AMMA) and NASA-AMMA (NAMMA) field campaigns are also used to place the radar observations in context. Results show that the total precipitation is dominated by propagating mesoscale convective systems. Convective characteristics vary according to environmental properties, such as vertical shear, CAPE, and the degree of synoptic forcing. Data are bifurcated based on the presence or absence of African easterly waves. In general, African easterly waves appear to enhance mesoscale convective system strength

  20. Characteristics of large-scale wave structure observed from African and Southeast Asian longitudinal sectors

    NASA Astrophysics Data System (ADS)

    Tulasi Ram, S.; Yamamoto, M.; Tsunoda, R. T.; Chau, H. D.; Hoang, T. L.; Damtie, B.; Wassaie, M.; Yatini, C. Y.; Manik, T.; Tsugawa, T.

    2014-03-01

    The spatial large-scale wave structure (LSWS) at the base of F layer is the earliest manifestation of seed perturbation for Rayleigh-Taylor instability, hence, found to play a deterministic role in the development of Equatorial Plasma Bubbles (EPBs). Except for a few case studies, a comprehensive investigation has not been conducted on the characteristics of LSWS because of the complexity involved in detecting the LSWS, particularly, in spatial domain. In this scenario, a comprehensive study is carried out, for the first time, on the spatial and temporal characteristics of LSWS observed in spatial domain over African and Southeast Asian longitudinal sectors during the year 2011. The observations indicate that these wave structures can be detected a few degrees west of E region sunset terminator and found to grow significantly at longitudes past the sunset terminator. The phase fronts of these spatial structures are found to align with the geomagnetic field (B→) lines over a latitudinal belt for at least 5-6° (~500-600 km) centered on dip equator. The zonal wavelengths of these structures are found to vary from 100 to 700 km, which is consistent with the earlier reports, and the EPBs were consistently observed when the amplitudes of LSWS were grown to sufficient strengths. These results would provide better insights on the underlying physical processes involved in excitation of LSWS in terms of important roles being played by E region electrical loading and polarization electric fields induced via spatially varying dynamo current due to neutral wind perturbations associated with atmospheric gravity waves.

  1. An Energetic Perspective on Aerosol Radiative Forcing and Interactions with Atmospheric Wave Activity

    NASA Astrophysics Data System (ADS)

    Hosseinpour, F.; Wilcox, E. M.; Colarco, P. R.

    2014-12-01

    Aerosols have the capability to alter regional-scale atmospheric circulations. A better understanding of the contribution of aerosols to multi-scale atmospheric phenomena and their transient changes is crucial for efforts to evaluate climate predictions using next generation climate models. In this study we address the following questions: (1) Is there a mechanistic relationship between variability of oceanic dust aerosol forcing and transient changes in the African easterly jet- African easterly wave (AEJ-AEW) system? (2) What are the long-term impacts of possible aerosol-wave interactions on climate dynamics of eastern tropical Atlantic Ocean and western African monsoon (WAM) region during boreal summer seasons? Our hypothesis is that aerosol radiative forcing may act as additional energy source to fuel the development of African easterly waves on the northern and southern sides of the AEJ. Evidence in support of this hypothesis is presented based on analysis of an ensemble of NASA satellite data sets, including aerosol optical thickness (AOT) observations from the Moderate Resolution Imaging Spectro-radiometer (MODIS) and the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS), as well as an atmospheric reanalysis from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) and a simulation of global aerosol distributions made with the Goddard Earth Observing System Model version 5 (GEOS-5) Earth system model with meteorology constrained by MERRA and an assimilation of MODIS AOT (MERRAero). We propose that the impacts of Saharan aerosols on the regional climate dynamics occur through contributions to the eddy energy of waves with 2—7-day and 7—11-day variability.

  2. Eastern Termination of the Subducting African Lithosphere Beneath Anatolia Imaged by Teleseismic P-Wave Tomography

    NASA Astrophysics Data System (ADS)

    Biryol, C. B.; Zandt, G.; Beck, S. L.; Ozacar, A.; Schmandt, B.

    2009-12-01

    A variety of complex tectonic processes are active in Anatolia. Collision related plateau formation dominates the present lithospheric deformation toward the east and slab roll-back related back-arc extension takes place toward the west. The two zones are connected at the northern part of the region by strike-slip faulting along the right-lateral North Anatolian Fault. Recent seismological studies show that the Eastern Anatolian Plateau (EAP) is supported by hot asthenosphereric material that was emplaced beneath the plateau following the detachment of subducted Arabian lithosphere. The westward continuation of the deeper structure of Anatolia is less well constrained due to the lack of geophysical observations. In order to study how the deeper lithosphere and mantle structure evolves spatially from east to west, we used teleseismic P-wave tomography and data from several temporary and permanent seismic networks deployed in the region. A major part of the data comes from the North Anatolian Fault passive seismic experiment (NAF) that consists of 39 broadband seismic stations operated at the north central part of Anatolia between 2005 - 2008. We also used data collected from permanent seismic stations of the National Earthquake Monitoring Center (NEMC) and stations from the Eastern Turkey Seismic Experiment (ETSE). Approximately 15,000 P-wave travel time residuals, measured in multiple frequency bands, are inverted using approximate finite-frequency sensitivity kernels. Our tomographic model reveals a fast anomaly that corresponds to the subducted portion of the African lithosphere along the Cyprean Arc. This fast anomaly dips northward beneath central Anatolia with an angle of approximately 45 degrees. However, the anomaly disappears rather sharply east of 36 degree longitude. This eastern edge of the slab also marks the western boundary of the EAP and Arabia-Eurasia collision zone. Beneath EAP our model reveals distributed slow anomalies down to 400 km and upper

  3. Regional Climate Modeling of West African Summer Monsoon Climate: Impact of Historical Boundary Forcing

    NASA Astrophysics Data System (ADS)

    Kebe, I.

    2015-12-01

    In this paper, we analyze and intercompare the performance of an ensemble of three Regional Climate Models (RCMs) driven by three set of Global Climate Models (GCMs), in reproducing seasonal mean climatologies with their annual cycle and the key features of West African summer monsoon over 20 years period (1985-2004) during the present day. The results show that errors in lateral boundary conditions from the GCM members, have an unexpected way on the skill of the RCMs in reproducing regional climate features such as the West African Monsoon features and the annual cycle of precipitation and temperature in terms of outperforming the GCM simulation. It also shows the occurrence of the West African Monsoon jump, the intensification and northward shift of the Saharan Heat Low (SHL) as expressed in some RCMs than the GCMs. Most RCMs also capture the mean annual cycle of precipitation and temperature, including, single and double-peaked during the summer months, in terms of events and amplitude. In a series of RCMs and GCMs experiments between the Sahara region and equatorial Africa, the presence of strong positive meridional temperature gradients at the surface and a strong meridional gradients in the potential temperatures near the surface are obvious, indicating the region of strong vertical shear development enough to establish easterly flow such as the African easterly jet. In addition, the isentropic potential vorticity (IPV) gradient decreases northward in the lower troposphere across northern Africa, with the maximum reversal on the 315-K surface. The region with negative IPV gradient favors the potential instability which has been associated with the growth of easterly waves.

  4. From Easter Island to coated coronary stents: a remarkable saga.

    PubMed

    Cantwell, John D

    2008-01-01

    Easter Island, even though it's in the middle of nowhere, is indeed a piece of the continent, as John Donne alluded to. In addition to contributing rapamycin to the medical field, the island is an example to the whole world of the consequences of affluent lifestyles, tribal wars, and ignorance of ecology. Jared Diamond expressed these thoughts best in his book, "Collapse:" The parallels between Easter Island and the whole modern world are chillingly obvious... All countries on earth today share resources and affect each other just as did Easter's dozen clans. Polynesian Easter Island was as isolated in the Pacific Ocean as the Earth is today in space. People see the collapse of Easter Island 's society as a metaphor; a worst-case scenario, for what may lie ahead for us in our own future. Some veteran Easter Island archaeologists like Claudio Cristina feel that Diamond's views are overly simplistic, commenting that he only spent a week on the island (versus 30 years for Cristina). Predatory Polynesian rats, earthquakes, tsunamis, variations in rainfall, diseases introduced by European sailing ships, could all have contributed to the near-demise of Easter Island. Tribal wars certainly didn't help, nor did slave-raiding parties from Peru. Only the eyes of the moai (Fig. 5) have seen it all, but the statues remain silent, as they have for over 1,000 years. PMID:18839797

  5. Q c and Q S wave attenuation of South African earthquakes

    NASA Astrophysics Data System (ADS)

    Brandt, Martin B. C.

    2016-04-01

    Quality factor Q, which describes the attenuation of seismic waves with distance, was determined for South Africa using data recorded by the South African National Seismograph Network. Because of an objective paucity of seismicity in South Africa and modernisation of the seismograph network only in 2007, I carried out a coda wave decay analysis on only 13 tectonic earthquakes and 7 mine-related events for the magnitude range 3.6 ≤ M L ≤ 4.4. Up to five seismograph stations were utilised to determine Q c for frequencies at 2, 4, 8 and 16 Hz resulting in 84 individual measurements. The constants Q 0 and α were determined for the attenuation relation Q c( f) = Q 0 f α . The result was Q 0 = 396 ± 29 and α = 0.72 ± 0.04 for a lapse time of 1.9*( t s - t 0) (time from origin time t 0 to the start of coda analysis window is 1.9 times the S-travel time, t s) and a coda window length of 80 s. This lapse time and coda window length were found to fit the most individual frequencies for a signal-to-noise ratio of at least 3 and a minimum absolute correlation coefficient for the envelope of 0.5. For a positive correlation coefficient, the envelope amplitude increases with time and Q c was not calculated. The derived Q c was verified using the spectral ratio method on a smaller data set consisting of nine earthquakes and one mine-related event recorded by up to four seismograph stations. Since the spectral ratio method requires absolute amplitudes in its calculations, site response tests were performed to select four appropriate stations without soil amplification and/or signal distortion. The result obtained for Q S was Q 0 = 391 ± 130 and α = 0.60 ± 0.16, which agrees well with the coda Q c result.

  6. 2015 Easter bolide over North Hungary

    NASA Astrophysics Data System (ADS)

    Hegedüs, T.; Csizmadia, S.; Zelkó, Z.; Kereszty, Z.; Bíró, Z.

    2015-01-01

    On Easter Monday, April 6, 2015, at UTC 17h31m (near sunset) there was a bright (peak magnitude -12 ~ -14) bolide which also produced a sonic boom, over North Hungary, close to Miskolc, above the Bükk mountains. The event was witnessed by many people, and recorded by several car dashboard-, meteorological and all sky cameras from as far away as Farád (North-West Hungary) and Görbeháza (North-East Hungary). Unfortunately, with the event having occurred only a few minutes after sunset, the sky was still bright and therefore the Hungarian Video meteor network cameras were not yet operating. Our team has collected and re-calibrated as much video and photo material as possible. Since there were very few direct images of the bolide itself, but more photos and videos of the persistent train left behind, these latter images were also used, in certain circumstances, in our calculations. The deduced final atmospheric path and heliocentric orbit are presented, along with the estimation of the errors.

  7. Effects of isolation and fishing on the marine ecosystems of Easter Island and Salas y Gómez, Chile

    USGS Publications Warehouse

    Friedlander, Alan M.; Ballesteros, Enric; Beets, Jim; Berkenpas, Eric; Gaymer, Carlos F.; Gorny, Matthias; Sala, Enric

    2013-01-01

    1. An expedition to Salas y Gómez and Easter islands was conducted to develop a comprehensive baseline of the nearshore marine ecosystem, to survey seamounts of the recently created Motu Motiro Hiva Marine Park (MMHMP) – a no-take marine reserve of 150 000 km2 – and to compare these results with Easter Island where the marine ecosystem is similar but has no marine protection. 2. Live coral cover was surprisingly high at both Easter Island (53%) and Salas y Gómez (44%), especially considering their sub-tropical location, high wave energy environments, and geographic isolation. 3. Endemic and regionally-endemic species comprised 77% of the fish abundance at Easter Island and 73% at Salas y Gómez. Fish biomass at Salas y Gómez was relatively high (1.2 t ha-1) and included a large proportion of apex predators (43%), whereas at Easter Island it was almost three times lower (0.45 t ha-1) with large predators accounting for less than 2% of the biomass, despite good habitat quality. 4. The large cohort of small sharks and the absence of larger sharks at Salas y Gómez suggest mesopredator release consistent with recent shark fishing. The fish fauna at the seamounts between Easter Island and Salas y Gómez, outside of MMHMP, harboured 46% endemic species, including a new species of damselfish (Chromis sp. nov.) and probably a new species of Chimaera (Hydrolagus). Numerous seamounts adjacent to Salas y Gómez are currently not included in the MMHMP. 5. This expedition highlights the high biodiversity value of this remote part of the Pacific owing to the uniqueness (endemicity) of the fauna, large apex predator biomass, and geographic isolation.

  8. 6. VIEW FROM SOUTHERN FOOT BRIDGE ABOVE INTAKE STRUCTURE EASTERLY ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    6. VIEW FROM SOUTHERN FOOT BRIDGE ABOVE INTAKE STRUCTURE EASTERLY TOWARD UPSTREAM SIDE OF SPILLWAY - Upper Doughty Dam, 200 feet west of Garden State Parkway, 1.7 miles west of Absecon, Egg Harbor City, Atlantic County, NJ

  9. 16. VIEW EASTERLY ALONG THE UPSTREAM SIDE OF THE OGEE ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    16. VIEW EASTERLY ALONG THE UPSTREAM SIDE OF THE OGEE SECTION OF THE SPILLWAY.... Volume XVIII, No. 13, January 29, 1940. - Prado Dam, Spillway, Santa Ana River near junction of State Highways 71 & 91, Corona, Riverside County, CA

  10. 18. EASTERLY VIEW ALONG THE SPILLWAY BUCKET, SHOWING CONSTRUCTION OPERATIONS....

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    18. EASTERLY VIEW ALONG THE SPILLWAY BUCKET, SHOWING CONSTRUCTION OPERATIONS.... Volume XX, No. 5, September 5, 1940. - Prado Dam, Spillway, Santa Ana River near junction of State Highways 71 & 91, Corona, Riverside County, CA

  11. 6. EASTERLY AERIAL VIEW SHOWING THE RIGHT ABUTMENT AND OUTLET ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    6. EASTERLY AERIAL VIEW SHOWING THE RIGHT ABUTMENT AND OUTLET CONTROL WORKS IN THE FOREGROUND.... Volume XX, No. 8, September 9, 1940. - Prado Dam, Santa Ana River near junction of State Highways 71 & 91, Corona, Riverside County, CA

  12. A Lesson in Complexity: Seabed Minerals and Easter Island.

    ERIC Educational Resources Information Center

    Druker, Kristen

    1984-01-01

    This high school-level classroom activity presents a hypothetical situation based on scientific fact concerning the likelihood that seabed mineral deposits lie off Easter Island. Activity goals, instructional strategies, and instructions for students are included. (JN)

  13. Satellite Witnesses Developing U.S. Nor'easter

    NASA Video Gallery

    National Weather Service forecasters have been tracking a low pressure area that moved from the Midwest into the Atlantic Ocean Jan. 26, 2015, and is expected to become a strong nor'easter that wil...

  14. GPM Sees Nor'easter Dump Snow on New England

    NASA Video Gallery

    At 5:05 p.m. EST Monday, Jan. 26, 2015, the Global Precipitation Measurement mission's Core Observatory flew over the Nor'easter that dumped snow on New England. This satellite image shows the rate...

  15. Gauß and beyond: the making of Easter algorithms

    NASA Astrophysics Data System (ADS)

    Bien, Reinhold

    2004-07-01

    It is amazing to see how many webpages are devoted to the art of finding the date of Easter Sunday. Just for illustration, the reader may search for terms such as Gregorian calendar, date of Easter, or Easter algorithm. Sophisticated essays as well as less enlightening contributions are presented, and many a doubt is expressed about the reliability of some results obtained with some Easter algorithms. In short, there is still a great interest in those problems. Gregorian Easter algorithms exist for two centuries (or more?), but most of their history is rather obscure. Some reasons may be that some important sources are written in Latin or in the German of Goethe's time, or they are difficult to discover. Without being complete, the following paper is intended to shed light on how those techniques emerged and evolved. Like a microcosm, the history of Easter algorithms resembles the history of any science: it is a story of trials, errors, and successes, and, last but not least, a story of offended pride. A number of articles, published before 1910, are cited in: A. Fraenkel, Die Berechnung des Osterfestes. Journal für die reine und angewandte Mathematik, Volume 138 (1910), 133-146.

  16. The Dependence of the Low-Level Equatorial Easterly Jet on Hadley and Walker Circulations.

    NASA Astrophysics Data System (ADS)

    Battisti, David S.; Ovens, David D.

    1995-11-01

    How the time-mean Hadley and Walker circulations affect the formation of a low-level equatorial easterly jet is investigated. Experiments are conducted for equinoctial conditions using a general circulation model, the Community Climate Model (CCM1), that includes a Kuo convective scheme and a lower boundary that is specified to be water at a fixed sea surface temperature (SST). Several zonally symmetric SST forcings are used to determine how various Hadley circulations affect the tropical zonal wind field. A zonal wavenumber one equatorial SST anomaly superimposed on a zonally symmetric SST distribution forces a wind field that includes both Hadley and Walker circulations.The Hadley circulation experiments produce equatorial easterlies and low-level jets on the poleward sides of the intertropical convergence zone (ITCZ) 10° to 15° from the equator. In an experiment with a single, dominant off-equatorial ITCZ in the Northern Hemisphere, the Southern Hemisphere jet moves to within 7.5° of the equator; yet none of the Hadley circulation cases produce a low-level easterly jet on the equator because they lack a mechanism to vertically confine the flow.The experiment that includes a zonally overturning cell on the equator produces a low-level equatorial easterly jet in the cold tongue region that is similar to the observed jet over the central to eastern Pacific. That case shows that east of the equatorial warm pool the Walker circulation and its induced Kelvin wave response provide the necessary upper-level westerly flow and subsidence to vertically confine the low-level easterlies into a jet. Spring and fall climatological runs of the CCMI with land surfaces, seasonally varying SSTs and insolation, and a moist convective adjustment scheme support the hypothesis that the Walker circulation provides the vertical confinement necessary to form a low-level equatorial easterly jet in the region east of the equatorial convective center, regardless of the Hadley circulation

  17. Upper mantle structure beneath southern African cratons from seismic finite-frequency P- and S-body wave tomography

    NASA Astrophysics Data System (ADS)

    Youssof, M.; Thybo, H.; Artemieva, I. M.; Levander, A.

    2015-06-01

    We present a 3D high-resolution seismic model of the southern African cratonic region from teleseismic tomographic inversion of the P- and S-body wave dataset recorded by the Southern African Seismic Experiment (SASE). Utilizing 3D sensitivity kernels, we invert traveltime residuals of teleseismic body waves to calculate velocity anomalies in the upper mantle down to a 700 km depth with respect to the ak135 reference model. Various resolution tests allow evaluation of the extent of smearing effects and help defining the optimum inversion parameters (i.e., damping and smoothness) for regularizing the inversion calculations. The fast lithospheric keels of the Kaapvaal and Zimbabwe cratons reach depths of 300-350 km and 200-250 km, respectively. The paleo-orogenic Limpopo Belt is represented by negative velocity perturbations down to a depth of ˜ 250 km, implying the presence of chemically fertile material with anomalously low wave speeds. The Bushveld Complex has low velocity down to ˜ 150 km, which is attributed to chemical modification of the cratonic mantle. In the present model, the finite-frequency sensitivity kernels allow to resolve relatively small-scale anomalies, such as the Colesberg Magnetic Lineament in the suture zone between the eastern and western blocks of the Kaapvaal Craton, and a small northern block of the Kaapvaal Craton, located between the Limpopo Belt and the Bushveld Complex.

  18. Shear wave velocity structure of the southern African upper mantle with implications for the uplift of southern Africa

    NASA Astrophysics Data System (ADS)

    Adams, Aubreya; Nyblade, Andrew

    2011-08-01

    Broad-band seismic data from the southern African seismic experiment and the AfricaArray network are used to investigate the seismic velocity structure of the upper mantle beneath southern Africa, and in particular beneath the Kaapvaal Craton. A two-plane approximation method that includes a finite frequency sensitivity kernel is employed to measure Rayleigh wave phase velocities, which are inverted to obtain a quasi-3-D shear wave velocity model of the upper mantle. We find phase velocities for the Kaapvaal Craton and surrounding mobile belts that are comparable to those reported by previous studies, and we find little evidence for variation from east to west across the Namaqua-Natal Belt, a region not well imaged in previous studies. A high-velocity upper-mantle lid is found beneath the Kaapvaal Craton and most of southern Africa. For the Kaapvaal Craton, the thickness of the lid (˜150-200 km) is consistent with the lid thicknesses reported in many previous studies. The cratonic lid is underlain by a ˜100-km thick low-velocity zone with a 3.9 per cent maximum velocity reduction. By comparing the velocity model to those published for other Archean cratons, we find few differences, and therefore conclude that there is little evidence in the shear wave velocity structure of the mantle to indicate that the southern African plateau is supported by an upper-mantle thermal anomaly.

  19. Seasonal Evolution and Variability Associated with the West African Monsoon System

    NASA Technical Reports Server (NTRS)

    Gu, Guojun; Adler, Robert F.

    2003-01-01

    In this study, we investigate the seasonal variations in surface rainfall and associated large-scale processes in the tropical eastern Atlantic and West African region. The 5-yr (1998-2002) high-quality TRMM rainfall, sea surface temperature (SST), water vapor and cloud liquid water observations are applied along with the NCEP/NCAR reanalysis wind components and a 3-yr (2000-2002) Quickscat satellite-observed surface wind product. Major mean rainfall over West Africa tends to be concentrated in two regions and is observed in two different seasons, manifesting an abrupt shift of the mean rainfall zone during June-July. (i) Near the Gulf of Guinea (about 5 degN), intense convection and rainfall are seen during April-June and roughly follow the seasonality of SST in the tropical eastern Atlantic. (ii) Along the latitudes of about 10 deg. N over the interior West African continent, a second intense rain belt begins to develop from July and remains there during the later summer season. This belt co-exists with a northwardmoved African Easterly Jet (AEJ) and its accompanying horizonal and vertical shear zones, the appearance and intensification of an upper tropospheric Tropical Easterly Jet (TEJ), and a strong low-level westerly flow. Westward-propagating wave signals [ i e . , African easterly waves (AEWs)] dominate the synoptic-scale variability during July-September, in contrast to the evident eastward-propagating wave signals during May- June. The abrupt shift of mean rainfall zone thus turns out to be a combination of two different physical processes: (i) Evident seasonal cycles in the tropical eastern Atlantic ocean which modulate convection and rainfall in the Gulf of Guinea by means of SST thermal forcing and SST-related meridional gradient; (ii) The interaction among the AEJ, TEJ, low-level westerly flow, moist convection and AEWs during July-September which modulates rainfall variability in the interior West Africa, primarily within the ITCZ rain band. Evident

  20. Coastal flooding in Scituate (MA): A FVCOM study of the 27 December 2010 nor'easter

    NASA Astrophysics Data System (ADS)

    Beardsley, Robert C.; Chen, Changsheng; Xu, Qichun

    2013-11-01

    A nested Finite-Volume Coastal Ocean Model (FVCOM) inundation forecast model has been developed for Scituate (MA) as part of the Northeast Coastal Ocean Forecast System (NECOFS). Scituate Harbor is a small coastal lagoon oriented north-south with a narrow entrance (with opposing breakwaters) opening eastward onto Massachusetts Bay and the Gulf of Maine. On 27 December 2010, a classic nor'easter produced a ˜0.9 m high surge, which when added to the ˜1.5 m high tide and seasonal higher mean water level, produced significant inundation in Scituate. The Scituate FVCOM inundation model includes flooding/drying, seawall/breakwater, and wave-current interaction capabilities, and was driven by one-way nesting with NECOFS. Hindcasts of the 27 December nor'easter event were made with two different resolution Scituate FVCOM grids with and without inclusion of wave-current interaction to examine the influence of spatial resolution and model dynamics on the predicted flooding. In all simulations, a wind-driven coastal current flowed southward across the harbor entrance, with an attached separation eddy forming downstream of the northern breakwater and rapid decrease in wave energy entering the harbor. With wave-current interaction, the southward coastal current was strongly enhanced and currents within the separation eddy increased to more than 1 m/s, making it highly nonlinear with large lateral shears. Comparisons of the model water elevation time series with harbor tide station measurements showed that inclusion of wave-current interaction increased the peak model surge by ˜8 cm, in closer agreement with the observed peak.

  1. 5. GENERAL VIEW OF EASTERLY ELEVATION OF SPILLWAY; VIEW TO ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. GENERAL VIEW OF EASTERLY ELEVATION OF SPILLWAY; VIEW TO SOUTHWEST ACROSS CANAL PRISM, FROM ROUTE 146 EMBANKMENT. - Blackstone Canal Millbury Segment, Beginning northwest of State Route 146 & McCracken Road, running along west side of Route 146, Millbury, Worcester County, MA

  2. CACTUS (Calculator and Computer Technology User Service): Some Easter Mathematics

    ERIC Educational Resources Information Center

    Hyde, Hartley

    2007-01-01

    In the Western Gregorian Calendar, the date of Easter Sunday is defined as the Sunday following the ecclesiastical Full Moon that falls on or next after March 21. While the pattern of dates so defined usually repeats each 19 years, there is a 0.08 day difference between the cycles. More accurately, the system has a period of 70 499 183 lunations…

  3. 17. VIEW EASTERLY ALONG DOWNSTREAM END OF THE SPILLWAY, SHOWING ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    17. VIEW EASTERLY ALONG DOWNSTREAM END OF THE SPILLWAY, SHOWING CELL WALL CONSTRUCTION IN THE CRIB CUTOFF.... Volume XX, No. 4, August 3, 1940. - Prado Dam, Spillway, Santa Ana River near junction of State Highways 71 & 91, Corona, Riverside County, CA

  4. Christmas and Easter Art Programs in Elementary School.

    ERIC Educational Resources Information Center

    Duncum, Paul

    2000-01-01

    Describes art programs that were given at several elementary Australian schools focusing on Christmas and Easter. Explains that the programs are based on the accounts of the birth and death of Jesus given in the Bible. States that the programs integrate studio art, art criticism, and art history. (CMK)

  5. MTR BUILDING AND BALCONY FLOORS. CAMERA FACING EASTERLY. PHOTOGRAPHER DID ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    MTR BUILDING AND BALCONY FLOORS. CAMERA FACING EASTERLY. PHOTOGRAPHER DID NOT EXPLAIN DARK CLOUD. MTR WING WILL ATTACH TO GROUND FLOOR. INL NEGATIVE NO. 1567. Unknown Photographer, 2/28/1951 - Idaho National Engineering Laboratory, Test Reactor Area, Materials & Engineering Test Reactors, Scoville, Butte County, ID

  6. Do West African thunderstorms predict the intensity of Atlantic hurricanes?

    NASA Astrophysics Data System (ADS)

    Price, Colin; Reicher, Naama; Yair, Yoav

    2015-04-01

    Since 85% of all major Atlantic hurricanes originate as thunderstorm clusters in equatorial Africa, we have investigated the connection between these African thunderstorms and the consequent development of these disturbances into tropical storms. We have analyzed Meteosat infrared cloud top temperature data to determine the areal coverage of cold cloud tops over a 6 year period from 2005 to 2010. In addition, hurricane statistics from the same period (intensity, date of generation, location, and maximum winds) were obtained from the National Hurricane Center database. We first show that the areal coverage of cold clouds (with brightness temperatures Tb < -50°C) in tropical Africa is a good indicator of the monthly number of African Easterly Waves (AEWs) leaving the west coast of tropical Africa. Furthermore, the AEWs that develop into tropical storms have a significantly larger area covered by cold cloud tops compared with nondeveloping waves. Finally, we show that on a storm-by-storm basis, the cold cloud coverage in West Africa is positively correlated (r = 0.57) with the accumulated cyclone energy of the future tropical cyclones that develop out of these waves.

  7. Do West African Thunderstorms Predict the Intensity of Atlantic Hurricanes?

    NASA Astrophysics Data System (ADS)

    Price, Colin; Reicher, Naama; Yair, Yoav

    2015-04-01

    Since 85% of all major Atlantic hurricanes originate as thunderstorm clusters in equatorial Africa, we have investigated the connection between these African thunderstorms and the consequent development of these disturbances into tropical storms. We have analyzed METEOSAT infrared cloud-top temperature data to determine the areal coverage of cold cloud tops over a six year period from 2005-2010. In addition, hurricane statistics from the same period (intensity, date of generation, location, maximum winds) were obtained from the National Hurricane Center (NHC) data base. We first show that the areal coverage of cold clouds (with brightness temperatures Tb<-50oC) in tropical Africa is a good indicator of the monthly number of African Easterly Waves (AEWs) leaving the west coast of tropical Africa. Furthermore, the AEWs that develop into tropical storms have a significantly larger area covered by cold cloud tops compared with non-developing waves. Finally, we show that on a storm-by-storm basis, the cold cloud coverage in West Africa is positively correlated (r=0.57) with the accumulated cyclone energy (ACE) of the future tropical cyclones that develop out of these waves.

  8. Study of the dynamics of the corona using July 11, 2010 eclipse data recorded from Easter Island

    NASA Astrophysics Data System (ADS)

    Samanta, Tanmoy

    Spectroscopic observations of the solar corona were performed during the total solar eclipse of 11 July 2010 in the green line at 5303 Å [Fe XIV] and the red line at 6374 Å [Fe X] from Easter Island, Chile. The data is analyzed to study the periodic variations in the intensity, line width and doppler velocity using wavelet analysis at all pixels within our field of view. We have found that there are few locations where significant oscillations are present. These oscillations can be interpreted in terms of the presence of magnetoacoustic waves or Alfvén waves in the corona.

  9. Multiple mantle upwellings beneath the Northern East-African Rift System from relative P- and S-wave traveltime tomography

    NASA Astrophysics Data System (ADS)

    Civiero, Chiara; Hammond, James; Goes, Saskia; Fishwick, Stewart; Ahmed, Abdulhakim; Ayele, Atalay; Doubre, Cecile; Goitom, Berhe; Keir, Derek; Kendall, Mike; Leroy, Sylvie; Ogubazghi, Ghebrebrhan; Rumpker, Georg; Stuart, Graham

    2015-04-01

    Mantle plumes have been invoked as the likely cause of East African Rift volcanism and extension. However, the nature of mantle upwelling is debated, with proposed configurations ranging from a single broad plume, the African Superplume, connected to the LLSVP beneath Southern Africa, to one or more distinct lower-mantle sources along the rift. We present a new relative travel-time tomography model that images detailed P- and S- wave velocities from P,S and SKS phases below the northern East-African, Red Sea and Gulf of Aden rift. Data comes from stations that cover the area from Tanzania to Saudi Arabia. The aperture of the integrated dataset allows us to image for the first time structures of ~100 km length scale down to depths of 900 km beneath this region. Our images provide evidence of at least two low-velocity structures with a diameter of ~200 km that continue through the transition zone and into the lower mantle: the first extends to at least 900 km beneath Afar, and a second reaching at least 750 km depth just west of the Main Ethiopian Rift, a region with off-rift volcanism. Taking into account seismic sensitivity to temperature and thermally controlled phase boundary topography, we interpret these features as multiple focused upwellings from below the transition zone with excess temperatures of 100±50 K. The scale of the upwellings is smaller than any of the previously proposed lower mantle plume sources. This suggests the ponding or flow of deep-plume material below the transition zone may be spawning smaller upper-mantle upwellings.

  10. Ocean internal waves off the North American and African coasts from ERTS-1

    NASA Technical Reports Server (NTRS)

    Apel, J. R.; Charnell, R. L.

    1974-01-01

    Periodic features observed in the ocean portions of certain ERTS-1 images have been identified with reasonable certainty as surface manifestations of oceanic internal gravity waves. A series of images taken over the New York Bight, commencing with the 16 July 1972 overpass and continuing on into autumn of 1973, has shown the internal waves to be present when summer solar heating stratifies the water sufficiently well to support such oscillations. When fall and winter wind action mixes the shelf water down to the bottom, the waves no longer appear. In the Bight, the wavelengths range from approximately 400 to 1000 m, with the wave field being most sharply delineated near the edges of the continental shelf, at the mouth of the Hudson Canyon. They appear in packets consisting of several waves separated by 10-15 km, which propagate up on the shelf and disappear.

  11. Impact of GCM boundary forcing on regional climate modeling of West African summer monsoon precipitation and circulation features

    NASA Astrophysics Data System (ADS)

    Kebe, Ibourahima; Sylla, Mouhamadou Bamba; Omotosho, Jerome Adebayo; Nikiema, Pinghouinde Michel; Gibba, Peter; Giorgi, Filippo

    2016-05-01

    In this study, the latest version of the International Centre for Theoretical Physics Regional Climate Model (RegCM4) driven by three CMIP5 Global Climate Models (GCMs) is used at 25 km grid spacing over West Africa to investigate the impact of lateral boundary forcings on the simulation of monsoon precipitation and its relationship with regional circulation features. We find that the RegCM4 experiments along with their multimodel ensemble generally reproduce the location of the main precipitation characteristics over the region and improve upon the corresponding driving GCMs. However, the provision of different forcing boundary conditions leads to substantially different precipitation magnitudes and spatial patterns. For instance, while RegCM4 nested within GFDL-ESM-2M and HadGEM2-ES exhibits some underestimations of precipitation and an excessively narrow Intertropical Convergence Zone, the MPI-ESM-MR driven run produces precipitation spatial distribution and magnitudes more similar to observations. Such a superior performance originates from a much better simulation of the interactions between baroclinicity, temperature gradient and African Easterly Jet along with an improved connection between the Isentropic Potential Vorticity, its gradient and the African Easterly Waves dynamics. We conclude that a good performing GCM in terms of monsoon dynamical features (in this case MPI-ESM-MR) is needed to drive RCMs in order to achieve a better representation of the West Africa summer monsoon precipitation.

  12. Hindcasting coastal flooding in Scituate (MA) during the Dec. 27, 2010 Nor'easter

    NASA Astrophysics Data System (ADS)

    Beardsley, R. C.; Chen, C.; Xu, Q.; Qi, J.; Lin, H.

    2012-12-01

    As part of the Northeast Coastal Ocean Forecast System (NECOFS) and in collaboration with the Taunton NWS Weather Forecast Office, we have built a nested inundation forecast model system for Scituate (MA). Here we have used this system to hindcast the coastal flooding in Scituate during the Dec. 26-27 2010 Nor'easter. This classic storm started as a large extratropical low pressure system centered off North Carolina on Dec. 26 and strengthen into a gale as it approached Cape Cod and southeastern Massachusetts the next day. By 06 GMT Dec. 27, barometric pressure in Scituate had dropped 42 mb in 21 hrs, northeast winds had increased to 22 m/s, and waves offshore increased to 7.5 m. NECOFS uses a regional mesoscale weather model (WRF) to drive an unstructured-grid ocean model (FVCOM) and surface wave model (SWAVE) to produce hindcast/forecasts of total water level, currents, and waves on a Northeast regional (GOM3) grid. The Scituate FVCOM inundation model includes flooding/drying, seawall/dike, and wave-current interaction capabilities, and is driven by one-way nesting with NECOFS. Hindcasts were made with two grids, a base grid with resolution varying from 10 m to 100 m within the harbor and a second more refined grid with resolution down to 2 m. The Dec. 27 Nor'easter simulations made with a base grid indicate that inundation predicted within the harbor was realistic and agreed well with tidal measurements. Increasing the grid resolution within the harbor produced greater flooding in several shallow areas but did not change the maximum water level in the main harbor significantly. The inundation model system did not predict significant flooding caused by the wind-wave-current-driven overtopping of the exposed northern seawall. This "splash-over" process is not included in the Scituate inundation forecast system at present but work has started on including this in the future. The computational effort and efficiency to product timely inundation forecasts with this

  13. Galapagos and Easter: A Tale of Two Hotspots

    NASA Astrophysics Data System (ADS)

    Harpp, K.; Hall, P. S.; Jackson, M. G.

    2012-12-01

    Spatial asymmetry in the isotopic composition of volcanic rocks has been identified at several Pacific hotspots, including Hawaii, the Marquesas, and Samoa (Weis, 2011; Huang et al., 2011); the volcanoes are arranged in two chains that define distinct, sub-parallel fields in isotopic space. For these hotspots, lavas from the northern chains have a more depleted signature (higher ɛNd, lower 87Sr/86Sr, lower 208Pb*/206Pb*) than the corresponding southern chains. All 3 hotspots are located near the northern margin of the Large Low Shear Velocity Province (LLSVP) beneath the Pacific. Previous workers have proposed that the asymmetry may reflect bilateral compositional zonation in the plume created by an azimuthal distribution of heterogeneities about the base of the plume conduit, related to material in the LLSVP. This distribution is preserved in filaments from the lower mantle (e.g., Farnetani and Hofmann, 2009). Recently, Payne et al. (in press) showed that rocks from the Societies have an isotopic asymmetry that is the mirror image of Hawaii, with the northern lavas enriched relative to the southern chain. This is consistent with the Societies hotspot's location near the southern, rather than the northern margin of the LLSVP. We present data from two additional hotspots that exhibit spatial asymmetry in the isotopic characteristics of their lavas: the Galapagos and Easter hotspots, both on the Nazca Plate. Despite lacking two distinct volcanic chains, Galapagos lavas define a pattern similar to Hawaii, with enriched isotopic signatures in the southern and western archipelago and more depleted material in the north and east; the boundary dividing the compositional fields defines a NW-SE line parallel to the edge of the LLSVP. In contrast, the Easter Island chain resembles the Societies, in that the enriched lavas are erupted from the northern volcanoes, a mirror image of the Galapagos and coincident with the southern boundary of the LLSVP. Several important

  14. View of South TwentyEighth Street from south boundary of Easter ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View of South Twenty-Eighth Street from south boundary of Easter Hill project site. Buildings No. 15, 16, 41, 46, 45, and 48 from left to right. Church Building at right foreground is not an element of Easter Hill object site. Looking north - Easter Hill Village, Bordered by South Twenty-sixth Street, South Twenty-eighth Street, Hinkley Avenue, Foothill Avenue & Corto Square, Richmond, Contra Costa County, CA

  15. Predictable waves of sequential forest degradation and biodiversity loss spreading from an African city

    PubMed Central

    Burgess, Neil D.; Milledge, Simon A. H.; Bulling, Mark T.; Fisher, Brendan; Smart, James C. R.; Clarke, G. Philip; Mhoro, Boniface E.; Lewis, Simon L.

    2010-01-01

    Tropical forest degradation emits carbon at a rate of ~0.5 Pg·y−1, reduces biodiversity, and facilitates forest clearance. Understanding degradation drivers and patterns is therefore crucial to managing forests to mitigate climate change and reduce biodiversity loss. Putative patterns of degradation affecting forest stocks, carbon, and biodiversity have variously been described previously, but these have not been quantitatively assessed together or tested systematically. Economic theory predicts a systematic allocation of land to its highest use value in response to distance from centers of demand. We tested this theory to see if forest exploitation would expand through time and space as concentric waves, with each wave targeting lower value products. We used forest data along a transect from 10 to 220 km from Dar es Salaam (DES), Tanzania, collected at two points in time (1991 and 2005). Our predictions were confirmed: high-value logging expanded 9 km·y−1, and an inner wave of lower value charcoal production 2 km·y−1. This resource utilization is shown to reduce the public goods of carbon storage and species richness, which significantly increased with each kilometer from DES [carbon, 0.2 Mg·ha−1; 0.1 species per sample area (0.4 ha)]. Our study suggests that tropical forest degradation can be modeled and predicted, with its attendant loss of some public goods. In sub-Saharan Africa, an area experiencing the highest rate of urban migration worldwide, coupled with a high dependence on forest-based resources, predicting the spatiotemporal patterns of degradation can inform policies designed to extract resources without unsustainably reducing carbon storage and biodiversity. PMID:20679200

  16. Predictable waves of sequential forest degradation and biodiversity loss spreading from an African city.

    PubMed

    Ahrends, Antje; Burgess, Neil D; Milledge, Simon A H; Bulling, Mark T; Fisher, Brendan; Smart, James C R; Clarke, G Philip; Mhoro, Boniface E; Lewis, Simon L

    2010-08-17

    Tropical forest degradation emits carbon at a rate of approximately 0.5 Pgxy(-1), reduces biodiversity, and facilitates forest clearance. Understanding degradation drivers and patterns is therefore crucial to managing forests to mitigate climate change and reduce biodiversity loss. Putative patterns of degradation affecting forest stocks, carbon, and biodiversity have variously been described previously, but these have not been quantitatively assessed together or tested systematically. Economic theory predicts a systematic allocation of land to its highest use value in response to distance from centers of demand. We tested this theory to see if forest exploitation would expand through time and space as concentric waves, with each wave targeting lower value products. We used forest data along a transect from 10 to 220 km from Dar es Salaam (DES), Tanzania, collected at two points in time (1991 and 2005). Our predictions were confirmed: high-value logging expanded 9 kmxy(-1), and an inner wave of lower value charcoal production 2 kmxy(-1). This resource utilization is shown to reduce the public goods of carbon storage and species richness, which significantly increased with each kilometer from DES [carbon, 0.2 Mgxha(-1); 0.1 species per sample area (0.4 ha)]. Our study suggests that tropical forest degradation can be modeled and predicted, with its attendant loss of some public goods. In sub-Saharan Africa, an area experiencing the highest rate of urban migration worldwide, coupled with a high dependence on forest-based resources, predicting the spatiotemporal patterns of degradation can inform policies designed to extract resources without unsustainably reducing carbon storage and biodiversity. PMID:20679200

  17. Role of inertial instability in the West African monsoon jump

    NASA Astrophysics Data System (ADS)

    Cook, Kerry H.

    2015-04-01

    The West African monsoon jump is a sudden shift in the latitude of the West African precipitation maximum from the Guinean coast near 4°N into Sahel near 12°N in late June or early July. An examination of reanalyses and observations indicates that the Sahel rainy season develops smoothly and the monsoon jump occurs because of an abrupt decrease in Guinean coast rainfall. We show that this abrupt end of the coastal rainy season occurs when inertial instability develops over the region, 1 month later than it develops in the vicinity of the marine Atlantic Intertropical Convergence Zone. The reason for this delay is the presence of the African easterly jet, which places strong negative meridional zonal wind gradients over the coast to preserve the inertially stable environment. When the African easterly jet moves farther north due to the seasonal solar forcing, these gradients weaken and then reverse to satisfy the threshold condition for inertial instability; the rapid end of the Guinean coast rainy season follows. The northward movement and intensity of the African easterly jet are controlled by the seasonal development of strong meridional land surface temperature gradients and are independent of the formation of the Atlantic cold tongue. This explanation for the West African monsoon jump relates the phenomenon to the shape and location of the African continent, including the low-latitude position of the Guinean coast and the large expanse of the continent to the north.

  18. The second wave of violence scholarship: South African synergies with a global research agenda.

    PubMed

    Bowman, Brett; Stevens, Garth; Eagle, Gillian; Langa, Malose; Kramer, Sherianne; Kiguwa, Peace; Nduna, Mzikazi

    2015-12-01

    Violence is a serious public health and human rights challenge with global psychosocial impacts across the human lifespan. As a middle-income country (MIC), South Africa experiences high levels of interpersonal, self-directed and collective violence, taking physical, sexual and/or psychological forms. Careful epidemiological research has consistently shown that complex causal pathways bind the social fabric of structural inequality, socio-cultural tolerance of violence, militarized masculinity, disrupted community and family life, and erosion of social capital, to individual-level biological, developmental and personality-related risk factors to produce this polymorphic profile of violence in the country. Engaging with a concern that violence studies may have reached something of a theoretical impasse, 'second wave' violence scholars have argued that the future of violence research may not lie primarily in merely amassing more data on risk but rather in better theorizing the mechanisms that translate risk into enactment, and that mobilize individual and collective aspects of subjectivity within these enactments. With reference to several illustrative forms of violence in South Africa, in this article we suggest revisiting two conceptual orientations to violence, arguing that this may be useful in developing thinking in line with this new global agenda. Firstly, the definition of our object of enquiry requires revisiting to fully capture its complexity. Secondly, we advocate for the utility of specific incident analyses/case studies of violent encounters to explore the mechanisms of translation and mobilization of multiple interactive factors in enactments of violence. We argue that addressing some of the moral and methodological challenges highlighted in revisiting these orientations requires integrating critical social science theory with insights derived from epidemiology and, that combining these approaches may take us further in understanding and addressing the

  19. View of South TwentySixth Street entrance to Easter Hill housing ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    View of South Twenty-Sixth Street entrance to Easter Hill housing project at intersection with Cutting Boulevard, looking south - Easter Hill Village, Bordered by South Twenty-sixth Street, South Twenty-eighth Street, Hinkley Avenue, Foothill Avenue & Corto Square, Richmond, Contra Costa County, CA

  20. Upper-tropospheric inversion and easterly jet in the tropics

    NASA Astrophysics Data System (ADS)

    Fujiwara, M.; Xie, S.-P.; Shiotani, M.; Hashizume, H.; Hasebe, F.; VöMel, H.; Oltmans, S. J.; Watanabe, T.

    2003-12-01

    Shipboard radiosonde measurements revealed a persistent temperature inversion layer with a thickness of ˜200 m at 12-13 km in a nonconvective region over the tropical eastern Pacific, along 2°N, in September 1999. Simultaneous relative humidity measurements indicated that the thin inversion layer was located at the top of a very wet layer with a thickness of 3-4 km, which was found to originate from the intertropical convergence zone (ITCZ) to the north. Radiative transfer calculations suggested that this upper tropospheric inversion (UTI) was produced and maintained by strong longwave cooling in this wet layer. A strong easterly jet stream was also observed at 12-13 km, centered around 4°-5°N. This easterly jet was in the thermal wind balance, with meridional temperature gradients produced by the cloud and radiative processes in the ITCZ and the wet outflow. Furthermore, the jet, in turn, acted to spread inversions further downstream through the transport of radiatively active water vapor. This feedback mechanism may explain the omnipresence of temperature inversions and layering structures in trace gases in the tropical troposphere. Examination of high-resolution radiosonde data at other sites in the tropical Pacific indicates that similar UTIs often appear around 12-15 km. The UTI around 12-15 km may thus be characterized as one of the "climatological" inversions in the tropical troposphere, forming the lower boundary of the so-called tropical tropopause layer, where the tropospheric air is processed photochemically and microphysically before entering the stratosphere.

  1. Morphology and distribution of seamounts surrounding Easter Island

    USGS Publications Warehouse

    Rappaport, Y.; Naar, D.F.; Barton, C.C.; Liu, Z.-J.; Hey, R.N.

    1997-01-01

    We investigate the morphology and distribution of a seamount population on a section of seafloor influenced by both superfast seafloor spreading and hotspot volcanism. The population under investigation is part of a broad chain of seamounts extending eastward from the East Pacific Rise, near Easter Island. In order to define the morphological variability of the seamounts, basal shape, cross-sectional area, volume, flatness, and flank slope are plotted against height for 383 seamounts with heights greater than 200 m, based on bathymetry data collected by GLORI-B and SeaBeam 2000, during three cruises onboard the R/V Melville in the spring of 1993. Nearly complete swath mapping coverage of the seamounts is available for the analysis of size and shape distribution. We quantitatively describe the seamount population of this active region, in which seamounts cover ???27% of the seafloor, and account for ???4.2% of the total crustal volume. Over 50% of the total volume (61,000 km3) of seamounts used in this study is made up by the 14 largest seamounts, and the remaining volume is made up by the 369 smaller seamounts (>200 m in height). Our analysis indicates there are at least two seamount populations in the Easter Island-Salas y Gomez Island (25??-29??S, 113??-104??W) study area. One population of seamounts is composed of short seamounts (1200 m), shield-like, pointy cones (flatness ???1200 m) originate exclusively from a hotspot source, but only a portion of the smaller volcanoes (

  2. Herbert Easterly auxiliary truck heater. Final technical report

    SciTech Connect

    Not Available

    1991-12-09

    The objective of this work was to continue the development of the Herbert Easterly heater apparatus for vehicles, such as semi-trailer tractors in order to fully establish its technical feasibility and provide the basis for its commercialization. This heater is auxiliary to the vehicle`s primary heating system. With the engine off it heats both the vehicle engine to a temperature at which it starts easily and the vehicle passenger compartment. Specifically, this heater is automatically ignitable, operates directly from the vehicle diesel fuel supply and preheats the vehicle engine fuel prior to combustion. During the course of this work nine different versions of prototype heaters were designed, constructed and tested. All designs were based on the ideas and principles outlined in the Easterly patent. Each successive version incorporated design and fabrication improvements relative to the previous version. The final version, Prototype 9, utilized a multiple water jacket design to capture additional heat from the combustion gases prior to exhausting to the atmosphere. This final prototype exceeded the performance of a commercially available Webasto DBW-2010 using the same commercial burner as the one used in the Webasto unit. The time required to raise the heater fluid temperature by 120{degree}F was 23% less (20 minutes compared to 26 minutes) for Prototype 9 compared to the commercially available unit. In addition a prototype heat exchanger for preheating engine fuel was designed, fabricated and tested. It was also determined that the Prototype 9 auxiliary heater could operate at 85{degree}F for approximately 6 hours on a fully charged 12 volt marine battery rated to deliver 500 cold cranking amps.

  3. Examining Intraseasonal Variability in the West African Monsoon Using the Superparameterized Community Climate System Model

    NASA Astrophysics Data System (ADS)

    McCrary, Rachel; Randall, David; Stan, Cristiana

    2013-04-01

    In West Africa, the ability to predict intraseasonal variations in rainfall would have important social and economic impacts for local populations. In particular, such predictions might be useful for estimating the timing of the monsoon onset and break periods in monsoon rains. Current theory suggests that on 25-90 day timescales, the West African monsoon (WAM) is influenced by intraseasonal variations in the Indo-Pacific region, namely the Madden Julian Oscillation (MJO) and the Asian summer monsoon. Unfortunately, most general circulation models (GCMs) show weak skill in simulating the seasonal variations in the WAM as well as intraseasonal variability in the Indo-Pacific. These model limitations make it difficult to study the dynamical links in variability across the tropics. Unlike traditional GCMs, models that have implemented the superparameterization (where traditional convective parameterizations are replaced by embedding a two dimensional cloud resolving model in each grid box) have been shown to be able to represent the WAM, the MJO and the Asian Summer Monsoon with reasonable fidelity. These model advances may allow us to study the teleconnections between the Indo-Pacific and West Africa in more detail. This study examines the intraseasonal variability of the WAM in the Superparameterized Community Climate System model (SP-CCSM). Results from the SP-CCSM are consistent with observations where intraseasonal variability accounts for 15-20% of the total variability in rainfall over West Africa during the monsoon season. We also show that on 25-90 day timescales, increases in precipitation over West Africa correspond with a northward shift of the African easterly jet and an increase in African easterly wave activity. Lag-composite analysis indicates that intraseasonal variations in WAM precipitation correspond with the North-South propagation of the MJO during boreal summer as well as the active and breaking phases of the Asian summer monsoon. Preliminary

  4. Management Options for Pratylenchus penetrans in Easter Lily

    PubMed Central

    Westerdahl, B. B.; Giraud, D.; Etter, S.; Riddle, L. J.; Radewald, J. D.; Anderson, C. A.; Darso, J.

    2003-01-01

    Alternatives to reduce or modify nematicide use for minimizing groundwater contamination in Easter lily were explored in two field trials. Alternatives to standard 1,3-dichloropropene (1,3-D) plus phorate injection in the first trial were: (i) delaying applications until after winter rains, (ii) removing roots from planting stock, (iii) 1,3-D via drip irrigation, (iv) a chitin-urea soil amendment, (v) the registered insecticide disulfoton, and (vi) several nonregistered nematicides. None of the treatments equaled the standard treatment. In the second trial, potential benefits of adding a systemic nematicide, oxamyl (OX), or a fungicide, metalaxyl (MX), to the standard treatment were explored. Preplant drip irrigation applications of metam sodium (MS), sodium tetrathiocarbonate (ST), and emulsifiable 1,3-D were evaluated alone and in combination with postplant applications of OX and MX. Several drip-applied treatments performed comparably to the standard treatment with respect to the most important criteria of crop quality, bulb circumference. Metam-sodium in combination with either or both OX and MX, 1,3-D plus OX and MX, and ST plus OX and MX provided the best results. PMID:19262778

  5. Development of West African Rainy Seasons (Invited)

    NASA Astrophysics Data System (ADS)

    Cook, K. H.

    2013-12-01

    The development of West African rainy seasons in the observed climatology can be understood in terms of two factors: continentality, i.e., the shape and placement of the African continent, and solar forcing. First, the observed features of the West African spring and summer precipitation climatology that distinguish it from the precipitation climatology of the tropical Atlantic to the east and Central/Eastern Africa to the west are presented. These include a lingering of the precipitation maximum along the Guinean coast in June and the apparent sudden movement of the precipitation maximum into the Sahel in early July. Then, these distinguishing features of the West Africa precipitation climatology are explained in terms of the regional dynamics and, finally, related to continentality and solar forcing through the roles of the African easterly jet, land surface temperature, and seasonally-varying SSTs.

  6. Magmatic evolution of the Easter microplate-Crough Seamount region (South East Pacific)

    USGS Publications Warehouse

    Hekinian, R.; Stoffers, P.; Akermand, D.; Binard, N.; Francheteau, Jean; Devey, C.; Garbe-Schonberg, D.

    1995-01-01

    The Easter microplate-Crough Seamount region located between 25?? S-116?? W and 25?? S-122?? W consists of a chain of seamounts forming isolated volcanoes and elongated (100-200 km in length) en echelon volcanic ridges oriented obliquely NE (N 065??), to the present day general spreading direction (N 100??) of the Pacific-Nazca plates. The extension of this seamount chain into the southwestern edge of the Easter microplate near 26??30??? S-115?? W was surveyed and sampled. The southern boundary including the Orongo fracture zone and other shallow ridges ( 0.25) MORBs which are similar in composition to other more recent basalts from the Southwest and East Rifts spreading axes of the Easter microplate. Incompatible element ratios normalized to chondrite values [(Ce/Yb)N = 1-2.5}, {(La/Sm)N = 0.4-1.2} and {(Zr/Y)N = 0.7-2.5} of the basalts are also similar to present day volcanism found in the Easter microplate. The volcanics from the Easter microplate-Crough region are unrelated to other known South Pacific intraplate magmatism (i.e. Society, Pitcairn, and Salas y Gomez Islands). Instead their range in incompatible element ratios is comparable to the submarine basalts from the recently investigated Ahu and Umu volcanic field (Easter hotspot) (Scientific Party SO80, 1993) and centered at about 80 km west of Easter Island. The oblique ridges and their associated seamounts are likely to represent ancient leaky transform faults created during the initial stage of the Easter microplate formation (??? 5 Ma). It appears that volcanic activity on seamounts overlying the oblique volcanic ridges has continued during their westward drift from the microplate as shown by the presence of relatively fresh lava observed on one of these structures, namely the first Oblique Volcanic Ridge near 25?? S-118?? W at about 160 km west of the Easter microplate West Rift. Based on a reconstruction of the Easter microplate, it is suggested that the Crough seamount (< 800 m depth) was formed

  7. An Investigation of Anatolian-African Subduction Zone in Southwestern Aegean:Lithospheric Structure Beneath Isparta Angle(IA)and the Surroundings from Surface Wave Tomography

    NASA Astrophysics Data System (ADS)

    Teoman, U. M.; Sandvol, E. A.; Turkelli, N.

    2009-12-01

    Our primary objective is to obtain the lithospheric structure of Anatolian-African Subduction zone and the surroundings including the Isparta Angle(IA) from Phase velocity inversion of Rayleigh waves. IA is seismically active and formed by the intersection of two very different subduction zones: The Hellenic arc to the west and the Cyprian arc to the east. The Hellenic arc is characterized by relatively steep, retreating subduction, whereas the Cyprus arc appears to involve a shallower subduction. The Geometric difference between Hellenic Arc and Cyprus Arc might indicate a tear in the subducting African Lithosphere beneath the Anatolian Plate responsible for the active deformation. A temporary seismic network consisting of 10 3-component BB stations were installed in August 2006 with the support from University of Missouri and 9 more stations in March 2007 in addition to the 21 existing permanent stations of Kandilli Observatory and Earthquake Research Institute(KOERI) and two from Süleyman Demirel University(SDU). 8 stations from Geofon Network were also included in the data to extend the station coverage. We used earthquakes in a distance range of 30-120 degrees with body wave magnitude larger than 5.5. Signal to noise ratio, azimuthal coverage of events, and coherence from station to station were considered during event selection.80 events provided high-quality data for our analysis. The distribution of events shows a good azimuthal coverage, which is important for resolving both lateral heterogeneity and azimuthal anisotropy. We adopted a two-plane-wave inversion technique of Forsyth and Li(2003) to simultaneously solve for the incoming wave field and phase velocity. The wave field is represented by the sum of two plane waves with initially unknown phase, amplitude and propagation direction.This relatively simpler representation of a more complex wavefield provided the pattern of amplitude variations effectively in many cases.This method will also help us

  8. DEVELOPING AND EXPLOITING A UNIQUE SEISMIC DATA SET FROM SOUTH AFRICAN GOLD MINES FOR SOURCE CHARACTERIZATION AND WAVE PROPAGATION

    SciTech Connect

    Julia, J; Nyblade, A A; Gok, R; Walter, W R; Linzer, L; Durrheim, R

    2008-07-08

    In this project, we are developing and exploiting a unique seismic data set to address the characteristics of small seismic events and the associated seismic signals observed at local (< 200 km) and regional (< 2000 km) distances. The dataset is being developed using mining-induced events from 3 deep gold mines in South Africa recorded on inmine networks (< 1 km) comprised of tens of high-frequency sensors, a network of 4 broadband stations installed as part of this project at the surface around the mines (1-10 km), and a network of existing broadband seismic stations at local/regional distances (50-1000 km) from the mines. After 1 year of seismic monitoring of mine activity (2007), over 10,000 events in the range -3.4 < ML < 4.4 have been catalogued and recorded by the in-mine networks. Events with positive magnitudes are generally well recorded by the surface-mine stations, while magnitudes 3.0 and larger are seen at regional distances (up to {approx}600 km) in high-pass filtered recordings. We have analyzed in-mine recordings in detail at one of the South African mines (Savuka) to (i) improve on reported hypocentral locations, (ii) verify sensor orientations, and (iii) determine full moment tensor solutions. Hypocentral relocations on all catalogued events have been obtained from P- and S-wave travel-times reported by the mine network operator through an automated procedure that selects travel-times falling on Wadati lines with slopes in the 0.6-0.7 range; sensor orientations have been verified and, when possible, corrected by correlating P-, SV-, and SH-waveforms obtained from theoretical and empirical (polarization filter) rotation angles; full moment tensor solutions have been obtained by inverting P-, SV-, and SH- spectral amplitudes measured on the theoretically rotated waveforms with visually assigned polarities. The relocation procedure has revealed that origin times often necessitate a negative correction of a few tenths of second and that hypocentral

  9. Multiple mantle upwellings in the transition zone beneath the northern East-African Rift system from relative P-wave travel-time tomography

    NASA Astrophysics Data System (ADS)

    Civiero, Chiara; Hammond, James O. S.; Goes, Saskia; Fishwick, Stewart; Ahmed, Abdulhakim; Ayele, Atalay; Doubre, Cecile; Goitom, Berhe; Keir, Derek; Kendall, J.-Michael; Leroy, Sylvie; Ogubazghi, Ghebrebrhan; Rümpker, Georg; Stuart, Graham W.

    2015-09-01

    Mantle plumes and consequent plate extension have been invoked as the likely cause of East African Rift volcanism. However, the nature of mantle upwelling is debated, with proposed configurations ranging from a single broad plume connected to the large low-shear-velocity province beneath Southern Africa, the so-called African Superplume, to multiple lower-mantle sources along the rift. We present a new P-wave travel-time tomography model below the northern East-African, Red Sea, and Gulf of Aden rifts and surrounding areas. Data are from stations that span an area from Madagascar to Saudi Arabia. The aperture of the integrated data set allows us to image structures of ˜100 km length-scale down to depths of 700-800 km beneath the study region. Our images provide evidence of two clusters of low-velocity structures consisting of features with diameter of 100-200 km that extend through the transition zone, the first beneath Afar and a second just west of the Main Ethiopian Rift, a region with off-rift volcanism. Considering seismic sensitivity to temperature, we interpret these features as upwellings with excess temperatures of 100 ± 50 K. The scale of the upwellings is smaller than expected for lower mantle plume sources. This, together with the change in pattern of the low-velocity anomalies across the base of the transition zone, suggests that ponding or flow of deep-plume material below the transition zone may be spawning these upper mantle upwellings. This article was corrected on 28 SEP 2015. See the end of the full text for details.

  10. Vigorous venting and biology at Pito Seamount, Easter microplate

    NASA Astrophysics Data System (ADS)

    Naar, D. F.; Hekinian, R.; Segonzac, M.; Francheteau, J.; Armijo, R.; Cogne, J.-P.; Constantin, M.; Girardeau, J.; Hey, R. N.; Searle, R. C.

    A Nautile submersible investigation of Pito Seamount documents vigorous hydrothermal venting at 23°19.65'S, 111°38.41'W and at a depth of 2270 m. The data indicate the volcano is young and recently active, as predicted from analyses of SeaMARC II side-scan and swath bathymetry, and geophysical data. Pito Seamount lies near Pito Deep (5980 m), which marks the tip of the northwestward propagating East rift of the Easter microplate. Bathymetry surrounding Pito Seamount consists of a series of ridges and valleys with relief up to ˜4 km. The 4-km submersible-transect to the summit of Pito Seamount crossed areas of very glassy basalt with little or no sediment cover, suggesting the lava flows are very young. Most of the lava samples from Pito Seamount are depleted normal MORB (mid-ocean ridge basalt). Lava samples associated with active and dead hydrothermal vents consist of phyric and aphyric transitional and enriched MORB. Sulfides consist primarily of sphalerite and pyrite, with traces of chalcopyrite. The active hydrothermal chimney on Pito Seamount has a small, undiversified biological community similar to northern East Pacific Rise vent sites (alvinellid worms, bythograeid crabs and bythitid fishes) and western Pacific back-arc basin sites (alvinocaridid shrimps). No vestimentiferan worms were observed. Previous geophysical data, and new geochemical data and visual observations, suggest that the vigorous black smoker is a result of deep, extensive crosscutting faults formed by extensive tectonic thinning of Pito Deep, and a very robust magmatic supply being supplied from upwelling asthenosphere. Although no biological or vent fluid samples were obtained, geological and biological observations, such as the large number of inactive chimneys, old hydrothermal deposits, and starfish, as well as the occurrence of dead mollusks (gastropod and mussels), suggest a recent waning of hydrothermal activity near the summit. The speculative interpretation that Pito Seamount

  11. Contrasting a non-developing African mesoscale convective system with the precursor to Hurricane Helene (2006)

    NASA Astrophysics Data System (ADS)

    Rivera, G.; Fuentes, J. D.; Evans, J. L.; Hamilton, H. L.

    2015-12-01

    Mesoscale convective systems (MCSs) in West Africa traverse strong thermodynamic gradients during their westward propagation from land to ocean. Some of the systems continue to develop after crossing the coastline and may ultimately develop into tropical cyclones, while others do not. Understanding the lifecycle behavior of these convective systems and the factors that contribute to their continuous development as they transition from a continental environment to a marine environment poses a challenge. We examine the difference between two MCSs, one that continued to develop when it crossed the West African coast and one that did not, using European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA Interim) and Tropical Rainfall Measurement Mission (TRMM) 3B42 data. The non-developing MCS that intensified briefly while over land, weakened as soon as it crossed the coast. Preliminary results show that the developing MCS interacted with two cyclonic vortices, one associated with an African Easterly Wave that was propagating towards the coast and the other vortex generated by the topography near the coast.

  12. Summer Synoptic-Scale Waves over Tropical West Africa Observed by TRMM

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

    A 5-year daily rainfall dataset (3B42) from TRMM (Tropical Rainfall Measuring Mission) is used to investigate the activity and properties of westward-propagating synoptic-scale waves over tropical West Africa. Evident wave signals appearing in wavenumber-frequency space show their modulations on the surface rainfall pattern during the boreal summer. Interannual variability exists in both their intensity and spectral properties, i. e., dominant frequency and wavenumber ranges. These variabilities can be partly ascribed to year-to-year variations of their embedded large-scale environment, especially the status of mid-tropospheric African easterly jet (AEJ). Generally, a stronger (weaker) AEJ indicates more (less) instability energy yielding a stronger (weaker) wave activity season. Seasonal mean rainfall has shown an impact on these waves in some years. However, the impact is not as clear and consistent as AEJ, implying the complexity of their relationship with large-scale environment. To fully understand interannual variability of synoptic-scale waves over tropical West Africa, including the variability in their preferred frequencies and wavenumbers, it is therefore necessary to examine possible intra-seasonal variations existing in both wave activity and large-scale fields, in addition to their structure, propagation, and associated convection.

  13. Sustainability in a differential equations course: a case study of Easter Island

    NASA Astrophysics Data System (ADS)

    Koss, Lorelei

    2011-06-01

    Easter Island is a fascinating example of resource depletion and population collapse, and its relatively short period of human habitation combined with its isolation lends itself well to investigation by students in a first-semester ordinary differential equations course. This article describes curricular materials for a semester-long case study into environmental and sustainability issues in the history of Easter Island. Using results that appeared in recent journal articles, students investigate the date of arrival of early settlers, the impact they had on natural resources through population growth as well as through the introduction of non-native species, and the effect of European diseases on the population.

  14. Mutual interaction between the West African Monsoon on the summer Mediterranean climate

    NASA Astrophysics Data System (ADS)

    Gaetani, M.; Baldi, M.; Dalu, G. A.

    2009-04-01

    Many studies have show that the West African Monsoon (WAM) is teleconnected with neighbouring regions, as the Mediterranean (Med) basin and the Tropical Atlantic, but also it is sensitive to the perturbations occurring even in remote regions, as the Indian sub-continent and the Tropical Pacific, these teleconnections being active on several time-scales, from intraseasonal to multidecadal. The WAM plays also an active role in the regional atmospheric circulation, inducing significant changes in rainfall, moisture, temperature, and wind distribution up to the North Africa. Within this framework, recent works were focused on the teleconnection between WAM and Med. WAM is strengthened by the north-easterly advection of moisture from the Med Sea, and, since the subsiding monsoonal air often invades the Med, there is a 2-way interaction between WAM and Med summer circulation. We study these interactions, applying SVD analysis to global NCEP Reanalysis and to rainfall data from CMAP, during the extended monsoonal season from May to October, on interannual and on intraseasonal time-scale. Dynamical features are explored using composite analysis, focusing on the role of this connection in the heat waves occurrence in the Med. We find that a strong WAM intensifies the Hadley meridional circulation, with a strengthening of the north Atlantic anticyclone and a weakening, even blocking, of the westerly flow in the Med. A deep inland penetration of WAM produces a northern shift of the Libyan anticyclone, with subsidence and high pressure affecting mainly the western Med. The positive feedback is due to the intensification of north-easterly flow from the eastern Med, which, reaching the Sahara desert, intensifies the intertropical front, favouring abundant monsoonal precipitation because of the added moist air.

  15. The Great Easter Egg Hunt: The Void's Incredible Richness

    NASA Astrophysics Data System (ADS)

    2006-04-01

    An image made of about 300 million pixels is being released by ESO, based on more than 64 hours of observations with the Wide-Field Camera on the 2.2m telescope at La Silla (Chile). The image covers an 'empty' region of the sky five times the size of the full moon, opening an exceptionally clear view towards the most distant part of our universe. It reveals objects that are 100 million times fainter than what the unaided eye can see. Easter is in many countries a time of great excitement for children who are on the big hunt for chocolate eggs, hidden all about the places. Astronomers, however, do not need to wait this special day to get such an excitement: it is indeed daily that they look for faraway objects concealed in deep images of the sky. And as with chocolate eggs, deep sky objects, such as galaxies, quasars or gravitational lenses, come in the wildest variety of colours and shapes. ESO PR Photo 11/06 ESO PR Photo 14a/06 The Deep 3 'Empty' Field The image presented here is one of such very deep image of the sky. It is the combination of 714 frames for a total exposure time of 64.5 hours obtained through four different filters (B, V, R, and I)! It consists of four adjacent Wide-Field Camera pointings (each 33x34 arcmin), covering a total area larger than one square degree. Yet, if you were to look at this large portion of the firmament with the unaided eye, you would just see... nothing. The area, named Deep 3, was indeed chosen to be a random but empty, high galactic latitude field, positioned in such a way that it can be observed from the La Silla observatory all over the year. Together with two other regions, Deep 1 and Deep 2, Deep 3 is part of the Deep Public Survey (DPS), based on ideas submitted by the ESO community and covering a total sky area of 3 square degrees. Deep 1 and Deep 2 were selected because they overlapped with regions of other scientific interest. For instance, Deep 1 was chosen to complement the deep ATESP radio survey carried out

  16. Shear Wave Velocity Structure of Southern African Crust: Evidence for Compositional Heterogeneity within Archaean and Proterozoic Terrains

    SciTech Connect

    Kgaswane, E M; Nyblade, A A; Julia, J; Dirks, P H H M; Durrheim, R J; Pasyanos, M E

    2008-11-11

    Crustal structure in southern Africa has been investigated by jointly inverting receiver functions and Rayleigh wave group velocities for 89 broadband seismic stations spanning much of the Precambrian shield of southern Africa. 1-D shear wave velocity profiles obtained from the inversion yield Moho depths that are similar to those reported in previous studies and show considerable variability in the shear wave velocity structure of the lower part of the crust between some terrains. For many of the Archaean and Proterozoic terrains in the shield, S velocities reach 4.0 km/s or higher over a substantial part of the lower crust. However, for most of the Kimberley terrain and adjacent parts of the Kheis Province and Witwatersrand terrain, as well as for the western part of the Tokwe terrain, mean shear wave velocities of {le} 3.9 km/s characterize the lower part of the crust along with slightly ({approx}5 km) thinner crust. These findings indicate that the lower crust across much of the shield has a predominantly mafic composition, except for the southwest portion of the Kaapvaal Craton and western portion of the Zimbabwe Craton, where the lower crust is intermediate-to-felsic in composition. The parts of the Kaapvaal Craton underlain by intermediate-to-felsic lower crust coincide with regions where Ventersdorp rocks have been preserved, and thus we suggest that the intermediate-to-felsic composition of the lower crust and the shallower Moho may have resulted from crustal melting during the Ventersdorp tectonomagmatic event at c. 2.7 Ga and concomitant crustal thinning caused by rifting.

  17. Hopping into Economics: First Graders Learn about Economics through an Easter Theme.

    ERIC Educational Resources Information Center

    Davis, Gaylene

    A 3-month study unit introducing first grade students to economics through an Easter theme is outlined in five sections. Sections 1 and 2 describe rationale, goals, and learning objectives. Section 3 provides learning activities. A wide range of instructional strategies is used to teach the basic economic concepts of want, need, scarcity,…

  18. Sustainability in a Differential Equations Course: A Case Study of Easter Island

    ERIC Educational Resources Information Center

    Koss, Lorelei

    2011-01-01

    Easter Island is a fascinating example of resource depletion and population collapse, and its relatively short period of human habitation combined with its isolation lends itself well to investigation by students in a first-semester ordinary differential equations course. This article describes curricular materials for a semester-long case study…

  19. The Easter Seal Directory of Resident Camps for Persons with Special Health Needs.

    ERIC Educational Resources Information Center

    National Easter Seal Society for Crippled Children and Adults, Chicago, IL.

    The directory describes approximately 260 resident camps in 44 states and Canada for children and adults with physical, mental, social, and/or emotional handicaps which have been compiled by the National Easter Seal Society for Crippled Children and Adults. Organized alphabetically by state, each camp listing includes information on impairments…

  20. The Easter Seal Directory of Resident Camps for Persons with Special Health Needs.

    ERIC Educational Resources Information Center

    National Easter Seal Society for Crippled Children and Adults, Chicago, IL.

    The directory of resident camps is designed for persons with special health needs (children and adults with physical, mental, social, or emotional handicaps). Published by the National Easter Seal Society for Crippled Children and Adults, the listing contains residential facilities only (day care camp program information is not included). Listed…

  1. Carbohydrate changes during flower senescence of the Easter Lily (Lilium Longiflorum Thunb.)

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This research was initiated to examine changes in ethanol soluble carbohydrates and cell wall neutral sugar composition in various floral organs of cut Lilium longiflorum Thunb. (Easter lily) flowers. Fresh weight of anthers decreased sharply, reaching a minimum level 3 days post-anthesis (DPA). T...

  2. Bias reduction in decadal predictions of West African monsoon rainfall using regional climate models

    NASA Astrophysics Data System (ADS)

    Paxian, A.; Sein, D.; Panitz, H.-J.; Warscher, M.; Breil, M.; Engel, T.; Tödter, J.; Krause, A.; Cabos Narvaez, W. D.; Fink, A. H.; Ahrens, B.; Kunstmann, H.; Jacob, D.; Paeth, H.

    2016-02-01

    The West African monsoon rainfall is essential for regional food production, and decadal predictions are necessary for policy makers and farmers. However, predictions with global climate models reveal precipitation biases. This study addresses the hypotheses that global prediction biases can be reduced by dynamical downscaling with a multimodel ensemble of three regional climate models (RCMs), a RCM coupled to a global ocean model and a RCM applying more realistic soil initialization and boundary conditions, i.e., aerosols, sea surface temperatures (SSTs), vegetation, and land cover. Numerous RCM predictions have been performed with REMO, COSMO-CLM (CCLM), and Weather Research and Forecasting (WRF) in various versions and for different decades. Global predictions reveal typical positive and negative biases over the Guinea Coast and the Sahel, respectively, related to a southward shifted Intertropical Convergence Zone (ITCZ) and a positive tropical Atlantic SST bias. These rainfall biases are reduced by some regional predictions in the Sahel but aggravated by all RCMs over the Guinea Coast, resulting from the inherited SST bias, increased westerlies and evaporation over the tropical Atlantic and shifted African easterly waves. The coupled regional predictions simulate high-resolution atmosphere-ocean interactions strongly improving the SST bias, the ITCZ shift and the Guinea Coast and Central Sahel precipitation biases. Some added values in rainfall bias are found for more realistic SST and land cover boundary conditions over the Guinea Coast and improved vegetation in the Central Sahel. Thus, the ability of RCMs and improved boundary conditions to reduce rainfall biases for climate impact research depends on the considered West African region.

  3. Attribution of variations in the quasi-biennial oscillation period from the duration of easterly and westerly phases

    NASA Astrophysics Data System (ADS)

    Yang, Mengmiao; Yu, Yueyue

    2015-12-01

    This study reports the main features of quasi-biennial oscillation (QBO) period variability at stratospheric levels from 70 to 10 hPa and its attribution from the duration variability of westerly and easterly phases using monthly mean zonal wind data from August 1956 to July 2013, archived by Free University of Berlin. A total of 24 QBO events have been distinguished based on the zonal wind field and wavelet analysis for it. The QBO period varies in phase at various stratospheric levels and shows no significant long-term trend but decadal to multi-decadal variability. The noted case-to-case variations in QBO period are due to variations in durations of the westerly and easterly phases at the same level. The highly coupled variability of the easterly duration in the upper levels above 30 hPa and westerly durations in the lower levels below, which manifests the stalling or accelerating of the descent rate of easterly wind regimes around 30 hPa, is found to be the dominant variability of the easterly and westerly durations at various stratospheric levels. Accordingly, the period of QBO in the lower levels below 40 hPa/upper levels above 20 hPa is determined by the westerly/easterly durations there in about 75 % of the 24 QBO events; and at 30 hPa, variations in the durations of both easterly and westerly phases contribute to the QBO period variability. On the contrary, in only 4 out of 24 QBO events, the variations of the westerly/easterly durations in the upper/lower levels are greater than the variations of the easterly/westerly durations in the upper/lower levels, making deterministic contributions to the QBO period variability.

  4. DEVELOPING AND EXPLOITING A UNIQUE DATASET FROM SOUTH AFRICAN GOLD MINES FOR SOURCE CHARACTERIZATION AND WAVE PROPAGATION

    SciTech Connect

    Julia, J; Nyblade, A; Gok, R; Walter, W; Linzer, L; Durrheim, R

    2009-07-06

    In this project, we are developing and exploiting a unique seismic dataset to address the characteristics of small seismic events and the associated seismic signals observed at local (< 200 km) and regional (< 2000 km) distances. The dataset is being developed using mining-induced events from three deep gold mines in South Africa recorded on in-mine networks (< 1 km) composed of tens of high-frequency sensors, a network of four broadband stations installed as part of this project at the surface around the mines (1-10 km), and a network of existing broadband seismic stations at local/regional distances (50-1000 km) from the mines. Data acquisition has now been completed and includes: (1) {approx}2 years (2007 and 2008) of continuous recording by the surface broadband array, and (2) tens of thousands of mine tremors in the -3.4 < ML < 4.4 local magnitude range. Events with positive magnitudes are generally well recorded by the surface-mine stations, while magnitudes of 3.0 and larger are seen at regional distances (up to {approx} 600 km) in high-pass filtered recordings. We have now completed the quality control of the in-mine data gathered at the three gold mines included in this project. The quality control consisted of: (1) identification and analysis of outliers among the P- and S-wave travel-time picks reported by the in-mine network operator and (2) verification of sensor orientations. The outliers have been identified through a 'Wadati filter' that searches for the largest subset of P- and S-wave travel-time picks consistent with a medium of uniform wave-speed. They have observed that outliers are generally picked at a few select stations. They have also detected that trigger times were mistakenly reported as origin times by the in-mine network operator, and corrections have been obtained from the intercept times in the Wadati diagrams. Sensor orientations have been verified through rotations into the local ray-coordinate system and, when possible, corrected

  5. A New Look to Interactions of Saharan Dust with Waves in the Tropical Atlantic Storm Track

    NASA Astrophysics Data System (ADS)

    Hosseinpour, F.; Wilcox, E. M.; Colarco, P. R.

    2015-12-01

    This study addresses mechanisms of the interactions between light-absorbing aerosols and transient atmospheric waves, including their feedback onto the mean-circulation in one of the most meteorologically sensitive areas of the world: the tropical western African/eastern Atlantic Ocean. Evidence of these interactions are presented based on analyses of an ensemble of NASA satellite data sets, including aerosol optical thickness (AOT) observations from the Moderate Resolution Imaging Spectro-radiometer (MODIS) and the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS), as well as an atmospheric reanalysis from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) and a simulation of The Goddard Chemistry Aerosol Radiation and Transport (GOCART) model. We analyzed the components of the rate of change of eddy kinetic energy (EKE) to explore the possible role of dust aerosol radiative forcing on reinforcing energetic terms associated with the African easterly waves (AEWs) during boreal summer seasons when the activity of AEWs peaks. This study shows that the anomalous perturbations in concentration of dust in the oceanic Saharan Air Layer (OSAL) precede amplified growth and decay of the subsequent waves compared to waves occurring prior to dust outbreaks. The amplified EKE associated with dust outbreaks are followed by seeding of new wave packets through enhanced divergence and convergence of ageostrophic geopotential height fluxes in the tropical Atlantic storm track. Meanwhile, the enhanced forcing of the mean-circulation associated with the increased momentum fluxes of the high frequency eddies at the northern track of AEWs occurs with a time-lag after the peak of dust concentration in the OSAL. We suggest that dust radiative heating in the OSAL may act as an additional energy source to amplify the thermal/mechanical activity of eddies in the northern track of the AEWs.

  6. Is ENSO related to 2015 Easter Star Capsized on the Yangtze River of China?

    NASA Astrophysics Data System (ADS)

    Xie, P.

    2015-12-01

    Natural disasters have profound effects on community security and economic damage of China's Hubei province. In June 1st, 2015, a cruise ship, Easter Star, capsized on Yangtze River in Hubei province with 442 died. What reason gives rise to such strong convection causing ship sunk? Based on the wind disasters of Hubei province happened in 1963-2015, this study analyzes their features bytime-series regression, and correlates them to global El Niño/Southern Oscillation (ENSO) events. The compared results demonstrated that the wind disasters shown an increasing tendency. There are two peaks corresponding to the strongest ENSO peaks during the past 50 years; each peak lasts two-three years. The facts demonstrated an essential linear relation between the ENSO phenomena and wind disasters in Hubei province. 2015 Easter Star capsized happened at current El Niño event in 2014-2015. We also observed that the historical wind disasters appeared in seasonal variation. Over 90% events concentrated in spring and summer; very few events happened in autumn and winter. Moreover, the disasters depend on the geographic conditions. Most disasters concentrated in four zones, named as Xingshan-Baokang, Xuanen, Wufeng-Yichang, Jingzhou-Gongan, in which Xingshan and Changyang are the two most density of zones. Yangtze River provides an air flowing conduct for strong convective winds. It can be concluded that the strong convection causing 2015 Easter Star capsized is related to current global ENSO phenomenon.Keywords: ENSO, wind disaster, time-series regression analysis, Easter Star, Yangtze River, Hubei Province,

  7. A report on the outbreak of Zika virus on Easter Island, South Pacific, 2014.

    PubMed

    Tognarelli, J; Ulloa, S; Villagra, E; Lagos, J; Aguayo, C; Fasce, R; Parra, B; Mora, J; Becerra, N; Lagos, N; Vera, L; Olivares, B; Vilches, M; Fernández, J

    2016-03-01

    Zika virus (ZIKV) is an emerging mosquito-borne flavivirus circulating in Asia and Africa. In 2013, a large outbreak was reported on the archipelago of French Polynesia. In this study, we report the detection and molecular characterization of Zika virus for the first time in Chile from an outbreak among the inhabitants of Easter Island. A total of 89 samples from patients suspected of having ZIKV infection were collected between the period from January to May, 2014. Molecular diagnosis of the virus was performed by RT-PCR followed by the sequencing of the region containing the NS5 gene. A comparison of the viral nucleic acid sequence with those of other strains of ZIKA virus was performed using the MEGA software. Fifty-one samples were found positive for ZIKV by RT-PCR analysis. Further analysis of the NS5 gene revealed that the ZIKV strains identified in Easter Island were most closely related to those found in French Polynesia (99.8 to 99.9% nt and 100% aa sequence identity). These results strongly suggest that the transmission pathway leading to the introduction of Zika virus on Easter Island has its origin in French Polynesia. PMID:26611910

  8. Endemism and long distance dispersal in the waterfleas of Easter Island.

    PubMed

    Damme, Kay Van

    2016-01-01

    Easter Island is known for a depauperate terrestrial and aquatic biota. The discovery of new taxa is unusual, even among the island's micro-invertebrates. A new cladoceran, Ovalona pascua sp. nov. (Crustacea: Cladocera: Anomopoda: Chydoridae), is described from freshwater environments. The chydorid, the only known extant cladoceran on the island, is the dominant aquatic invertebrate in the surface waters. Based on detailed morphological comparison, including a character similarity matrix applied across the species in the genus (12 characters/17 spp), the new taxon is proposed here as an insular endemic with affinities in the East (New World). The revision challenges the theory that invasive zooplankton species were introduced from the subantarctic islands during the 18th century. Human introduction is not the main mechanism through which cladocerans could have arrived on Easter Island. Late Pleistocene - Early Holocene fossils in Cañellas-Boltà et al. (2012) from cores in Rano Raraku Lake are identified here as Daphnia O.F. Müller, 1785 (subgenus Ctenodaphnia Dybowski & Grochowski, 1895). The establishment of Daphnia before human colonization on Easter Island provides strong proof of successful long distance dispersal by ephippia over thousands of kilometers of open sea. PMID:27615838

  9. Exceptionally strong easterly wind burst stalling El Niño of 2014.

    PubMed

    Hu, Shineng; Fedorov, Alexey V

    2016-02-23

    Intraseasonal wind bursts in the tropical Pacific are believed to affect the evolution and diversity of El Niño events. In particular, the occurrence of two strong westerly wind bursts (WWBs) in early 2014 apparently pushed the ocean-atmosphere system toward a moderate to strong El Niño--potentially an extreme event according to some climate models. However, the event's progression quickly stalled, and the warming remained very weak throughout the year. Here, we find that the occurrence of an unusually strong basin-wide easterly wind burst (EWB) in June was a key factor that impeded the El Niño development. It was shortly after this EWB that all major Niño indices fell rapidly to near-normal values; a modest growth resumed only later in the year. The easterly burst and the weakness of subsequent WWBs resulted in the persistence of two separate warming centers in the central and eastern equatorial Pacific, suppressing the positive Bjerknes feedback critical for El Niño. Experiments with a climate model with superimposed wind bursts support these conclusions, pointing to inherent limits in El Niño predictability. Furthermore, we show that the spatial structure of the easterly burst matches that of the observed decadal trend in wind stress in the tropical Pacific, suggesting potential links between intraseasonal wind bursts and decadal climate variations. PMID:26858437

  10. Climate windows for Polynesian voyaging to New Zealand and Easter Island.

    PubMed

    Goodwin, Ian D; Browning, Stuart A; Anderson, Atholl J

    2014-10-14

    Debate about initial human migration across the immense area of East Polynesia has focused upon seafaring technology, both of navigation and canoe capabilities, while temporal variation in sailing conditions, notably through climate change, has received less attention. One model of Polynesian voyaging observes that as tradewind easterlies are currently dominant in the central Pacific, prehistoric colonization canoes voyaging eastward to and through central East Polynesia (CEP: Society, Tuamotu, Marquesas, Gambier, Southern Cook, and Austral Islands) and to Easter Island probably had a windward capacity. Similar arguments have been applied to voyaging from CEP to New Zealand against prevailing westerlies. An alternative view is that migration required reliable off-wind sailing routes. We investigate the marine climate and potential voyaging routes during the Medieval Climate Anomaly (MCA), A.D. 800-1300, when the initial colonization of CEP and New Zealand occurred. Paleoclimate data assimilation is used to reconstruct Pacific sea level pressure and wind field patterns at bidecadal resolution during the MCA. We argue here that changing wind field patterns associated with the MCA provided conditions in which voyaging to and from the most isolated East Polynesian islands, New Zealand, and Easter Island was readily possible by off-wind sailing. The intensification and poleward expansion of the Pacific subtropical anticyclone culminating in A.D. 1140-1260 opened an anomalous climate window for off-wind sailing routes to New Zealand from the Southern Austral Islands, the Southern Cook Islands, and Tonga/Fiji Islands. PMID:25267611

  11. Climate windows for Polynesian voyaging to New Zealand and Easter Island

    PubMed Central

    Goodwin, Ian D.; Browning, Stuart A.; Anderson, Atholl J.

    2014-01-01

    Debate about initial human migration across the immense area of East Polynesia has focused upon seafaring technology, both of navigation and canoe capabilities, while temporal variation in sailing conditions, notably through climate change, has received less attention. One model of Polynesian voyaging observes that as tradewind easterlies are currently dominant in the central Pacific, prehistoric colonization canoes voyaging eastward to and through central East Polynesia (CEP: Society, Tuamotu, Marquesas, Gambier, Southern Cook, and Austral Islands) and to Easter Island probably had a windward capacity. Similar arguments have been applied to voyaging from CEP to New Zealand against prevailing westerlies. An alternative view is that migration required reliable off-wind sailing routes. We investigate the marine climate and potential voyaging routes during the Medieval Climate Anomaly (MCA), A.D. 800–1300, when the initial colonization of CEP and New Zealand occurred. Paleoclimate data assimilation is used to reconstruct Pacific sea level pressure and wind field patterns at bidecadal resolution during the MCA. We argue here that changing wind field patterns associated with the MCA provided conditions in which voyaging to and from the most isolated East Polynesian islands, New Zealand, and Easter Island was readily possible by off-wind sailing. The intensification and poleward expansion of the Pacific subtropical anticyclone culminating in A.D. 1140–1260 opened an anomalous climate window for off-wind sailing routes to New Zealand from the Southern Austral Islands, the Southern Cook Islands, and Tonga/Fiji Islands. PMID:25267611

  12. Exceptionally strong easterly wind burst stalling El Niño of 2014

    PubMed Central

    Hu, Shineng; Fedorov, Alexey V.

    2016-01-01

    Intraseasonal wind bursts in the tropical Pacific are believed to affect the evolution and diversity of El Niño events. In particular, the occurrence of two strong westerly wind bursts (WWBs) in early 2014 apparently pushed the ocean–atmosphere system toward a moderate to strong El Niño—potentially an extreme event according to some climate models. However, the event’s progression quickly stalled, and the warming remained very weak throughout the year. Here, we find that the occurrence of an unusually strong basin-wide easterly wind burst (EWB) in June was a key factor that impeded the El Niño development. It was shortly after this EWB that all major Niño indices fell rapidly to near-normal values; a modest growth resumed only later in the year. The easterly burst and the weakness of subsequent WWBs resulted in the persistence of two separate warming centers in the central and eastern equatorial Pacific, suppressing the positive Bjerknes feedback critical for El Niño. Experiments with a climate model with superimposed wind bursts support these conclusions, pointing to inherent limits in El Niño predictability. Furthermore, we show that the spatial structure of the easterly burst matches that of the observed decadal trend in wind stress in the tropical Pacific, suggesting potential links between intraseasonal wind bursts and decadal climate variations. PMID:26858437

  13. The Polynesian gene pool: an early contribution by Amerindians to Easter Island

    PubMed Central

    Thorsby, Erik

    2012-01-01

    It is now generally accepted that Polynesia was first settled by peoples from southeast Asia. An alternative that eastern parts of Polynesia were first inhabited by Amerindians has found little support. There are, however, many indications of a ‘prehistoric’ (i.e. before Polynesia was discovered by Europeans) contact between Polynesia and the Americas, but genetic evidence of a prehistoric Amerindian contribution to the Polynesian gene pool has been lacking. We recently carried out genomic HLA (human leucocyte antigen) typing as well as typing for mitochondrial DNA (mtDNA) and Y chromosome markers of blood samples collected in 1971 and 2008 from reputedly non-admixed Easter Islanders. All individuals carried HLA alleles and mtDNA types previously found in Polynesia, and most of the males carried Y chromosome markers of Polynesian origin (a few had European Y chromosome markers), further supporting an initial Polynesian population on Easter Island. The HLA investigations revealed, however, that some individuals also carried HLA alleles which have previously almost only been found in Amerindians. We could trace the introduction of these Amerindian alleles to before the Peruvian slave trades, i.e. before the 1860s, and provide suggestive evidence that they were introduced already in prehistoric time. Our results demonstrate an early Amerindian contribution to the Polynesian gene pool on Easter Island, and illustrate the usefulness of typing for immunogenetic markers such as HLA to complement mtDNA and Y chromosome analyses in anthropological investigations. PMID:22312048

  14. Observational analyses and numerical simulations of the transition of a tropical wave critical layer to a tropical depression

    NASA Astrophysics Data System (ADS)

    Montgomery, M. T.

    2009-04-01

    In recent research my collaborators and I have hypothesized that tropical cyclones in the deep Atlantic and eastern Pacific basins develop from the cyclonic Kelvin Cat's eye of a tropical easterly wave critical layer located equatorward of the easterly jet axis that typifies the trade wind belt. The genesis sequence is likened to the development of a marsupial infant in its mother's pouch, and for this reason has been dubbed the "Marsupial Paradigm". In this talk I will summarize our previous observational findings using the ERA-40, TRMM and best-track data sets and then report on our first multi-scale numerical test of the Marsupial Paradigm that revisits the enigmatic problem of the transformation of an idealized African easterly wave-like disturbance into a tropical storm vortex. The results are found to support key elements of the Marsupial Paradigm by demonstrating the existence of a vorticity dominant region with minimal strain within the critical layer pouch that contains strong cyclonic vorticity and high saturation fraction. This localized region within the pouch serves as the "attractor" for an upscale "bottom up" development process while the wave and pouch move together. As part of the research, I will also report on our findings concerning the evolution of stratiform vs. convective precipitation within the Cat's eye. It is shown that moist deep convection is sustained near the center of the Cat's eye. The convergence profile within the Cat's eye is found to become dominantly convective with persistent convection. Low-level convergence plays a key role in establishing and intensifying the near-surface circulation, while the non-advective vorticity flux and the mid-level convergence associated with stratiform precipitation help to increase the mid-level circulation and build a tropospheric-deep vortex. Implications of these findings are discussed in relation to a newly proposed field experiment for the most active period of the Atlantic hurricane season

  15. Recent changes in air temperature, heat waves occurrences, and atmospheric circulation in Northern Africa

    NASA Astrophysics Data System (ADS)

    Fontaine, Bernard; Janicot, Serge; Monerie, Paul-Arthur

    2013-08-01

    study documents the time evolution of air temperature and heat waves occurrences over Northern Africa for the period 1979-2011. A significant warming (1°-3°C), appearing by the mid-1960s over Sahara and Sahel, is associated with higher/lesser frequency of warm/cold temperatures, as with longer duration and higher occurrences of heat waves. Heat waves episodes of at least 4 day duration have been examined after removing the long-term evolution. These episodes are associated with specific anomalies: (i) in spring, positive low-level temperature anomalies over the Sahel and Sahara; low and midlevel cyclonic rotation over Morocco associated with a Rossby wave pattern, lessening the Harmattan; more/less atmospheric moisture westward/eastward to 0°; upward/downward anomalies above the western/eastern regions associated with the Rossby wave pattern; (ii) in summer, a similar but weaker positive low-level temperature anomaly (up to 3°C); less moisture westward to 10°W, a cyclonic anomaly in central Sahel favoring the monsoon eastward to 0° and a midlevel anticyclonic anomaly over the Western Sahara, increasing southward the flux divergence associated with the African Easterly Jet. In March-May, two to three heat waves propagate eastward. They are preceded by an abnormal warm cell over Libya and southwesterlies over the West Sahara. A large trough stands over North Atlantic while midtropospheric subsidence and anticyclonic rotation reinforce over the continent, then migrates toward the Arabian peninsula in breaking up. These signals are spatially coherent and might suggest the role of short Rossby waves with an eastward group velocity and a baroclinic mode, possibly associated with jet stream deformation.

  16. Quantification of Dune Response over the Course of a 6-Day Nor'Easter, Outer Banks, NC

    NASA Astrophysics Data System (ADS)

    Brodie, K. L.; Spore, N.; Swann, C.

    2014-12-01

    The amount and type of foredune morphologic change during a storm event primarily scales with the level of inundation during that event. Specifically, external hydrodynamic forcing (total water level) can be compared with antecedent beach and foredune morphology to predict an impact regime that relates to the type of expected morphologic evolution of the system. For example, when total water levels are above the dune toe, but below the dune crest, the impact regime is classified as "collision" and the expected morphology response is slumping or scarping of the dune face. While the amount of dune retreat scales largely with the duration of wave attack to the dune face, characteristics of the dune other than its crest or toe elevation may also enhance or impede rates of morphologic change. The aftermath of Hurricane Sandy provided a unique opportunity to observe alongshore variations in dune response to a 6-day Nor'Easter (Hs >4 m in 6 m depth), as a variety of dunes were constructed (or not) by individual home owners in preparation for the winter storm season. Daily terrestrial lidar scans were conducted along 20 km of coastline in Duck, NC using Coastal Lidar And Radar Imaging System (CLARIS) during the first dune collision event following Sandy. Foredunes were grouped by their pre-storm form (e.g. vegetated, pushed, scarped, etc) using automated feature extraction tools based on surface curvature and slope, and daily rates of morphologic volume change were calculated. The highest dune retreat rates were focused along a 1.5 km region where cross-shore erosion of recently pushed, un-vegetated dunes reached 2 m/day. Variations in dune response were analyzed in relation to their pre-storm morphology, with care taken to normalize for alongshore variations in hydrodynamic forcing. Ongoing research is focused on identifying specific metrics that can be easily extracted from topographic DEMs to aid in dune retreat predictions.

  17. Cloud-Resolving Model Simulations of LBA Convective Systems: Easterly and Westerly Regimes

    NASA Technical Reports Server (NTRS)

    Lang, Stephen E.; Tao, Wei-Kuo

    2002-01-01

    The 3D Goddard Cumulus Ensemble (GCE) model was used to simulate convection that occurred during the TRMM LBA field experiment in Brazil. Convection in this region can be categorized into two different regimes. Low-level easterly flow results in moderate to high CAPE and a drier environment. Convection is more intense like that seen over continents. Low-level westerly flow results in low CAPE and a moist environment. Convection is weaker and more widespread characteristic of oceanic or monsoon-like systems. The GCE model has been used to study both regimes in order to provide cloud data sets that are representative of both environments in support of TRMM rainfall and heating algorithm development. Two different case are presented: Jan 26,1999, an easterly regime case, and Feb 23,1999, a westerly regime case. The Jan 26 case is an organized squall line and is initialized with a standard cold pool. The sensitivity to mid-level sounding moisture and wind shear will also be shown. The Feb 23 case is less-organized with only transient lines and is initialized with either warm bubbles or prescribed surface fluxes. Heating profiles, rainfall statistics and storm characteristics are compared and validated for the two cases against observations collected during the experiment.

  18. Vesicular-arbuscular mycorrhizae of Easter lily in the northwestern United States.

    PubMed

    Ames, R N; Linderman, R G

    1977-12-01

    The vesicular-arbuscular (VA) mycorrhizal fungi of commercially grown Easter lily (Lilium longiflorum Thunb.) were studied. Soil and root samples were collected monthly from March through September 1975 from five fields in the coastal area of southern Oregon and northern California. Soil seivings were inoculated onto clover, onion, and lily to cause infections resulting in the production of many new mycorrhizal spores facilitating identification. Four VA mycorrhizal species were found: Acaulospora trappei, A. elegans, Glomus monosporus, and G. fasciculatus. All four VA species infected Easter lily, clover, and onion. Acaulospora trappei and G. fasciculatus were the most commonly isolated species from all five fields. Mycorrhizal infections in roots of field-grown lilies were sparse and presumably young in March and gradually increased in size and number until September when bulbs were harvested. Over 75% of each root system became infected with mycorrhizae in fields with all four fungal species, and those levels were reached by July. In fields with only two mycorrhizal species, usually 50% or less of each root system was infected, even by the end of the growing season. PMID:597791

  19. Patterns of recurrent evolution and geographic parthenogenesis within apomictic polyploid Easter daises (Townsendia hookeri).

    PubMed

    Thompson, Stacey Lee; Whitton, Jeannette

    2006-10-01

    Geographic patterns of parthenogenesis and the number of transitions from sexual diploidy to asexual (apomictic) autopolyploidy were examined for 40 populations of the Easter daisy, Townsendia hookeri. Analyses of pollen diameter and stainability characterized 15 sexual diploid and 25 apomictic polyploid populations from throughout the plant's western North American range. Sexual diploids were restricted to two Wisconsin refugia: Colorado/Wyoming, south of the ice sheets, and northern Yukon/Beringia. Chloroplast DNA sequencing uncovered 17 polymorphisms within the ndhF gene and trnK intron, yielding 10 haplotypes. Phylogenetic analyses indicated that five exclusively polyploid haplotypes were derived from four haplotypes that are shared among ploidies, conservatively inferring a minimum of four origins of apomictic polyploidy. Three of these apomictic polyploid origins were derived from southern sexual diploids, while the fourth origin was derived from northern sexual diploids. Analyses of regional diversity were suggestive of a formerly broad distribution for sexual diploids that has become subsequently fragmented, possibly due to the last round of glaciation. As sexual diploids were exclusively found north and south of the glacial maximum, while formerly glaciated areas were exclusively inhabited by asexual polyploids derived from both northern and southern sexual lineages, it is more likely that patterns of glaciation, as opposed to a particular latitudinal trend, played a causal role in the establishment of the observed pattern of geographic parthenogenesis in Easter daisies. PMID:16968277

  20. African Equatorial and Subtropical Ozone Plumes: Recurrences Timescales of the Brown Cloud Trans-African Plumes and Other Plumes

    NASA Technical Reports Server (NTRS)

    Chatfield, Robert B.; Thompson, Anne M.; Guan, Hong; Witte, Jacquelyn C.

    2004-01-01

    We have found repeated illustrations in the maps of Total Tropospheric Ozone (TTO) of apparent transport of ozone from the Indian Ocean to the Equatorial Atlantic Ocean. Most interesting are examples that coincide with the INDOEX observations of late northern winter, 1999. Three soundings associated with the SHADOZ (Southern Hemisphere Additional Ozonesondes) network help confirm and quantify degree of influence of pollution, lightning, and stratospheric sources, suggesting that perhaps 40% of increased Atlantic ozone could be Asian pollution during periods of maximum identified in the TTO maps. We outline recurrent periods of apparent ozone transport from Indian to Atlantic Ocean regions both during and outside the late-winter period. These are placed in the context of some general observations about factors controlling recurrence timescales for the expression of both equatorial and subtropical plumes. Low-level subtropical plumes are often controlled by frontal systems approaching the Namib coast; these direct mid-level air into either easterly equatorial plumes or westerly mid- troposphere plumes. Equatorial plumes of ozone cross Africa on an easterly path due to the occasional coincidence of two phenomena: (1) lofting of ozone to mid and upper levels, often in the Western Indian Ocean, and (2) the eastward extension of an Equatorial African easterly jet.

  1. The role of easterly wind surges in La Niña and El Niño events

    NASA Astrophysics Data System (ADS)

    Chiodi, A. M.; Harrison, D.

    2015-12-01

    The processes responsible for the onset of La Niña events have not received the same attention as those responsible for the onset of El Niño events, for which Westerly Wind Events (WWEs) in the tropical Pacific have been identified as important contributors. We have previously shown that equatorial Pacific WWE wind stress composites in the years following the large El Niño event of 1997/98 are very like their pre-97-98 counterparts except that they also include an easterly anomaly element over the cold tongue. We have argued that this easterly component modifies the oceanic response so that warming is concentrated in the central equatorial Pacific. This significant change in forced SST anomaly results from the fact that a relatively small increase in easterly wind speed, acting on top of the background easterly trade winds, is sufficient to produce a stress anomaly comparable in magnitude to that of the westerly wind event and thereby produce current anomalies to balance out most of the cold tongue warming that would otherwise be driven by the WWE wind stresses. Motivated by the large effect of these "Easterly Wind Surges" (EWSs) we have examined their occurrence statistics and effects on ENSO-related sea surface temperature anomalies (SSTAs) in the period over which the TAO/TRITON buoy wind observations are available for verification. We find that EWSs are a prominent component of equatorial Pacific wind stress variability and play an important role in the onset and development of La Niña events akin to the role that Westerly Wind Events play in El Niño events. EWSs also help shape amplitude and pattern development of El Niño SSTAs. We examine how well recent ENSO-related sea surface temperature development can be accounted for by paying attention to the occurrence of each year's westerly and easterly wind events.

  2. Impact of four WRF modifications upon eight nor'easter simulations

    NASA Astrophysics Data System (ADS)

    Nicholls, Stephen David

    This dissertation investigated the impact of four modifications to the Weather Research and Forecasting Model (WRF) model during eight nor'easter simulations. Specifically these modification include: 1) Different WRF model versions, 2) Usage of different bulk microphysics schemes created between 1983-2011, 3) Assimilation of radio occultation data, and 4) Fully coupling WRF to a dynamic ocean model. Model simulations were conducted for 180 hours, starting roughly 72 hours prior to the first precipitation impacts in the highly populated Mid-Atlantic US and associated cyclogenesis. Simulation accuracy was assessed by comparing each simulation to Global Forecasting System model analysis. Despite various updates, errors in both storm track and simulated storm intensity were highest in the newest WRF version and were strongly associated with mid-tropospheric heat release. Error analysis of WRF-version simulations revealed the newest WRF model version (WRF 3.3) had worst overall simulation accuracy due to errors in simulated winds, mid-tropospheric latent heat release and similar dynamical fields, whereas WRF 3.2 was best. Comparison of simulations using different microphysics parameterization revealed both storm tracks and maximum cyclone intensity revealed little to no variation between schemes due to their common programming heritage. Error analysis of the local storm environment revealed simulations little impact from the inclusion of graupel, however the newer microphysics parameterization tended to be more accurate. In contrast, for the entire environment (nor'easter and background) the newest BMPS scheme only performed on-par with the oldest BMPS within the inner most model domains. Improvements to both storm track and overall nor'easter simulation accuracy were typically inversely proportional to the data assimilation period length and was strongly sensitive to cyclone-to-sounding distance and stratospheric data assimilation errors. Simulation accuracy however

  3. Automated recognition of spikes in 1 Hz data recorded at the Easter Island magnetic observatory

    NASA Astrophysics Data System (ADS)

    Soloviev, Anatoly; Chulliat, Arnaud; Bogoutdinov, Shamil; Gvishiani, Alexei; Agayan, Sergey; Peltier, Aline; Heumez, Benoit

    2012-09-01

    In the present paper we apply a recently developed pattern recognition algorithm SPs to the problem of automated detection of artificial disturbances in one-second magnetic observatory data. The SPs algorithm relies on the theory of discrete mathematical analysis, which has been developed by some of the authors for more than 10 years. It continues the authors' research in the morphological analysis of time series using fuzzy logic techniques. We show that, after a learning phase, this algorithm is able to recognize artificial spikes uniformly with low probabilities of target miss and false alarm. In particular, a 94% spike recognition rate and a 6% false alarm rate were achieved as a result of the algorithm application to raw one-second data acquired at the Easter Island magnetic observatory. This capability is critical and opens the possibility to use the SPs algorithm in an operational environment.

  4. The terrestrial Isopoda (Crustacea, Oniscidea) of Rapa Nui (Easter Island), with descriptions of two new species

    PubMed Central

    Taiti, Stefano; Wynne, J. Judson

    2015-01-01

    Abstract Nine species of terrestrial isopods are reported for the Polynesian island of Rapa Nui (Easter Island) based upon museum materials and recent collections from field sampling. Most of these animals are non-native species, but two are new to science: Styloniscus manuvaka sp. n. and Hawaiioscia rapui sp. n. Of these, the former is believed to be a Polynesian endemic as it has been recorded from Rapa Iti, Austral Islands, while the latter is identified as a Rapa Nui island endemic. Both of these new species are considered ‘disturbance relicts’ and appear restricted to the cave environment on Rapa Nui. A short key to all the oniscidean species presently recorded from Rapa Nui is provided. We also offered conservation and management recommendations for the two new isopod species. PMID:26261438

  5. The terrestrial Isopoda (Crustacea, Oniscidea) of Rapa Nui (Easter Island), with descriptions of two new species.

    PubMed

    Taiti, Stefano; Wynne, J Judson

    2015-01-01

    Nine species of terrestrial isopods are reported for the Polynesian island of Rapa Nui (Easter Island) based upon museum materials and recent collections from field sampling. Most of these animals are non-native species, but two are new to science: Styloniscusmanuvaka sp. n. and Hawaiiosciarapui sp. n. Of these, the former is believed to be a Polynesian endemic as it has been recorded from Rapa Iti, Austral Islands, while the latter is identified as a Rapa Nui island endemic. Both of these new species are considered 'disturbance relicts' and appear restricted to the cave environment on Rapa Nui. A short key to all the oniscidean species presently recorded from Rapa Nui is provided. We also offered conservation and management recommendations for the two new isopod species. PMID:26261438

  6. Kelvin waves and ozone Kelvin waves in the quasi-biennial oscillation and semiannual oscillation: A simulation by a high-resolution chemistry-coupled general circulation model

    NASA Astrophysics Data System (ADS)

    Watanabe, Shingo; Takahashi, Masaaki

    2005-09-01

    Equatorial Kelvin waves and ozone Kelvin waves were simulated by a T63L250 chemistry-coupled general circulation model with a high vertical resolution (300 m). The model produces a realistic quasi-biennial oscillation (QBO) and a semiannual oscillation (SAO) in the equatorial stratosphere. The QBO has a period slightly longer than 2 years, and the SAO shows rapid reversals from westerly to easterly regimes and gradual descents of westerlies. Results for the zonal wave number 1 slow and fast Kelvin waves are discussed. Structure of the waves and phase relationships between temperature and ozone perturbations coincide well with satellite observations made by LIMS, CLAES, and MLS. They are generally in phase (antiphase) in the lower (upper) stratosphere as theoretically expected. The fast Kelvin waves in the temperature and ozone are dominant in the upper stratosphere because the slow Kelvin waves are effectively filtered by the QBO westerly. In this simulation, the fast Kelvin waves encounter their critical levels in the upper stratosphere when zonal asymmetry of the SAO westerly is enhanced by an intrusion of the extratropical planetary waves. In addition to the critical level filtering effect, modulations of wave properties by background winds are evident near easterly and westerly shears associated with the QBO and SAO. Enhancement of wave amplitude in the QBO westerly shear is well coincident with radiosonde observations. Increase/decrease of vertical wavelength in the QBO easterly/westerly is obvious in this simulation, which is consistent with the linear wave theory. Shortening of wave period due to the descending QBO westerly shear zone is demonstrated for the first time. Moreover, dominant periods during the QBO westerly phase are longer than those during the QBO easterly phase for both the slow and fast Kelvin waves.

  7. West African monsoon intraseasonal activity and its daily precipitation indices in regional climate models: diagnostics and challenges

    NASA Astrophysics Data System (ADS)

    Poan, E. D.; Gachon, P.; Dueymes, G.; Diaconescu, E.; Laprise, R.; Seidou Sanda, I.

    2016-02-01

    The West African monsoon intraseasonal variability has huge socio-economic impacts on local populations but understanding and predicting it still remains a challenge for the weather prediction and climate scientific community. This paper analyses an ensemble of simulations from six regional climate models (RCMs) taking part in the coordinated regional downscaling experiment, the ECMWF ERA-Interim reanalysis (ERAI) and three satellite-based and observationally-constrained daily precipitation datasets, to assess the performance of the RCMs with regard to the intraseasonal variability. A joint analysis of seasonal-mean precipitation and the total column water vapor (also called precipitable water—PW) suggests the existence of important links at different timescales between these two variables over the Sahel and highlights the relevance of using PW to follow the monsoon seasonal cycle. RCMs that fail to represent the seasonal-mean position and amplitude of the meridional gradient of PW show the largest discrepancies with respect to seasonal-mean observed precipitation. For both ERAI and RCMs, spectral decompositions of daily PW as well as rainfall show an overestimation of low-frequency activity (at timescales longer than 10 days) at the expense of the synoptic (timescales shorter than 10 days) activity. Consequently, the effects of the African Easterly Waves and the associated mesoscale convective systems are substantially underestimated, especially over continental regions. Finally, the study investigates the skill of the models with respect to hydro-climatic indices related to the occurrence, intensity and frequency of precipitation events at the intraseasonal scale. Although most of these indices are generally better reproduced with RCMs than reanalysis products, this study indicates that RCMs still need to be improved (especially with respect to their subgrid-scale parameterization schemes) to be able to reproduce the intraseasonal variance spectrum adequately.

  8. African Aesthetics

    ERIC Educational Resources Information Center

    Abiodun, Rowland

    2001-01-01

    No single traditional discipline can adequately supply answers to the many unresolved questions in African art history. Because of the aesthetic, cultural, historical, and, not infrequently, political biases, already built into the conception and development of Western art history, the discipline of art history as defined and practiced in the West…

  9. Barotropic, baroclinic, and inertial instabilities of the easterly Gaussian jet on the equatorial β-plane in rotating shallow water model

    NASA Astrophysics Data System (ADS)

    Ribstein, Bruno; Zeitlin, Vladimir; Tissier, Ann-Sophie

    2014-05-01

    A detailed linear stability analysis of an easterly barotropic Gaussian jet centered at the equator is performed in the long-wave sector in the framework of one- and two-layer shallow-water models on the equatorial β-plane. It is shown that the dominant instability of the jet is due to phase-locking and resonance between Yanai waves, although the standard barotropic and baroclinic instabilities due to the resonance between Rossby waves are also present. In the one-layer case, this dominant instability has non-zero growth rate at zero wavenumber for high enough Rossby and low enough Burger numbers, thus reproducing the classical symmetric inertial instability. Yet its asymmetric counterpart has the highest growth rate. In the two-layer case, the dominant instability may be barotropic or baroclinic, the latter being stronger, with the maximum of the growth rate shifting towards smaller downstream wavenumbers as Rossby number increases at fixed Burger number, and given thickness and density ratios. At large enough Rossby numbers this instability has a non-zero growth rate limit at zero wavenumber, giving the baroclinic symmetric inertial instability. Again, the maximal growth rate is achieved at small but non-zero wavenumbers, corresponding to the asymmetric inertial instability. At high enough Rossby number and low enough Burger number not only the baroclinic, but also the barotropic symmetric instability appears, as well as higher meridional modes of the baroclinic symmetric instability. Still, all of them are dominated by their asymmetric counterparts. Direct numerical simulations of the saturation of the leading instabilities are performed, showing that the barotropic species of the instability saturates by forming a double vortex street subject to nonlinear oscillations, while the baroclinic, the most vigorous one, saturates by producing strong vertical shears and related dissipation and mixing.

  10. Wave evolution across the Louisiana shelf

    NASA Astrophysics Data System (ADS)

    Engelstad, Anita; Janssen, Tim; Herbers, T. H. C.; van Vledder, Gerbrant; Elgar, Steve; Raubenheimer, Britt; Trainor, Lincoln; Garcia-Garcia, Ana

    2013-01-01

    Observations and third-generation wave model hindcasts of ocean surface gravity waves propagating across the Louisiana shelf show that the effects of the mud environment on wave evolution are complex and episodic. Whereas low-frequency waves (0.04-0.20 Hz) show a consistent decay similar to earlier studies, the presence of mud also appears to suppress the development of short waves (0.20-0.25 Hz) under fetch-limited growth conditions. Significant suppression of wave development under wind-forced conditions is found to occur almost exclusively during easterly winds when satellite images show the Atchafalaya mud plume extends into the study area. These results suggest that episodic sediment suspension events with high mud concentrations in the upper water column can affect the evolution of wind waves.

  11. Quantitative Analysis of Phenylpropanoid Glycerol Glucosides in Different Organs of Easter Lily (Lilium longiflorum Thunb.).

    PubMed

    Munafo, John P; Gianfagna, Thomas J

    2015-05-20

    The Easter lily (Lilium longiflorum Thunb.) is esteemed worldwide as an attractive ornamental plant, and the flower buds and bulbs are used for both culinary and medicinal purposes in many parts of the world. L. longiflorum contains significant amounts of phenylpropanoid glycerol glucosides, a group of compounds that may contribute to plant pathogen defense, ultraviolet/high-intensity visible light (UV/high light) protection, and the purported medicinal uses of lilies. To define the natural distribution of these compounds within the plant, a liquid chromatography-mass spectrometry (LC-MS) method performed in selected ion monitoring (SIM) mode was employed for the quantitative analysis of five phenylpropanoid glycerol glucosides, namely, (2S)-1-O-caffeoyl-2-O-β-D-glucopyranosylglycerol, 1; (2R)-1-O-β-D-glucopyranosyl-2-O-p-coumaroylglycerol, 2; (2S)-1-O-p-coumaroyl-2-O-β-D-glucopyranosylglycerol, 3; (2S)-1-O-caffeoyl-2-O-β-D-glucopyranosyl-3-O-acetylglycerol, 4; and (2S)-1-O-p-coumaroyl-2-O-β-D-glucopyranosyl-3-O-acetylglycerol, 5, in the different organs of L. longiflorum. The p-coumaroyl-based 3 and its acetylated derivative 5 were determined to be the most abundant of the phenylpropanoid glycerol glucosides found in Easter lily bulbs, at 776.3 ± 8.4 and 650.7 ± 32.6 μg/g dry weight, respectively. The acetylated p-coumaroyl- and caffeoyl-based derivatives, 5 and 4, accumulated to the highest concentration in the closed flower buds, at 4925.2 ± 512.8 and 3216.8 ± 406.4 μg/g dry weight, respectively. Compound 4, followed by 5 and 1, proved to be the most abundant in the mature flowers, occurring at 6006.2 ± 625.8, 2160.3 ± 556.5, and 1535.8 ± 174.1 μg/g dry weight, respectively. Total concentrations of the phenylpropanoid glycerol glucosides were 10-100-fold higher in the above-ground plant organs as compared to the bulbs and fleshy roots. Two of the five compounds, 1 and 2, were identified in L. longiflorum for the first time. The quantitative

  12. West African crude production diversifies

    SciTech Connect

    Aalund, L.

    1983-06-01

    Nigeria, with its seven crude-oil export streams, dominated West African production and accounted for over 70% of the depressed 1.8 million b/d output from the region last year. However, during the 1970s a flurry of new producing fields, primarily off the African coast, diversified production among a number of countries and touched off a wave of oil activity. The Journal takes a close look at the quality of West African oil in this installment of assays on world export crudes. This issue covers, in alphabetical order, Bonny Light (Nigeria) to Espoir (Ivory Coast). A following issue will wrap up West Africa by presenting assays on crudes from Forcados Blend (Nigeria) to Zaire Crude (Zaire).

  13. How the July 2014 easterly wind burst gave the 2015-2016 El Niño a head start

    NASA Astrophysics Data System (ADS)

    Levine, Aaron F. Z.; McPhaden, Michael J.

    2016-06-01

    Following strong westerly wind bursts in boreal winter and spring of 2014, both the scientific community and the popular press were abuzz with the possibility of a major El Niño developing. However, during the boreal summer of 2014, the Bjerknes feedback failed to kick in, aided and abetted by a strong easterly wind burst. The widely anticipated major 2014-2015 El Niño event failed to materialize and even failed to qualify as an El Niño by conventional definitions. However, the boreal summer easterly wind burst had the effect of not only inhibiting the growth of the El Niño event but also preventing and then reversing the discharge of the equatorial heat content that typically occurs during the course of an El Niño event. This head start of equatorial heat content helped push the 2015-2016 El Niño event to extreme magnitude.

  14. Ecological Catastrophes and Disturbance Relicts: A Case Study from Easter Island

    NASA Astrophysics Data System (ADS)

    Wynne, J.

    2014-12-01

    Caves are often considered buffered environments in terms of their ability to sustain near constant microclimatic conditions. However, environments within cave entrances are expected to respond most quickly to changing surface conditions. We cataloged a relict assemblage of at least 10 endemic arthropods likely restricted to caves and occurring primarily within cave entranceways. Of these animals, eight were considered new undescribed species. These endemic arthropods have persisted in Rapa Nui (Easter Island) caves despite a catastrophic ecological shift induced by island-wide deforestation, fire intolerance, and drought, as well as intensive livestock grazing and surface ecosystems dominated by invasive species. We consider these animals to be "disturbance relicts" - species whose distributions are now limited to areas that experienced minimal human disturbance historically. Today, these species represent one-third of the Rapa Nui's known endemic arthropods. Given the island's severely depauperate native fauna, these arthropods should be considered among the highest priority targets for biological conservation. In other regions globally, epigean examples of imperiled disturbance relicts persisting within narrow distributional ranges have been documented. As human activity intensifies, and habitat loss and fragmentation continues worldwide, additional disturbance relicts will be identified. We expect extinction debts, global climate change and interactions with invasive species will challenge the persistence of both hypogean and epigean disturbance relict species.

  15. Flowering pathway is regulated by bulb size in Lilium longiflorum (Easter lily).

    PubMed

    Lazare, S; Zaccai, M

    2016-07-01

    Lilium longiflorum (Easter lily) vegetative propagation occurs through production of underground bulbs containing apical and axillary meristems. In addition, sexual reproduction is achieved by flowering of elongated shoots above the bulb. It is generally accepted that L. longiflorum has an obligatory requirement for vernalisation and that long day (LD) regime hastens flowering. However, the effect of bulb size and origin, with respect to axillary or apical meristems on flowering, as well as the interactions between these meristems are largely unknown. The aim of this study was to explore the effect of bulb size, vernalisation and photoperiod on L. longiflorum flowering. To this end, we applied vernalisation and photoperiod treatments to the different bulb sizes and used a system of constant ambient temperature of 25 °C, above vernalisation spectrum, to avoid cold-dependent floral induction during plant growth. Vernalisation and LD hasten flowering in all bulbs. Large, non-vernalised bulbs invariably remained at a vegetative stage. However, small non-vernalised bulbs flowered under LD conditions. These results demonstrate for the first time that cold exposure is not an obligatory prerequisite for L. longiflorum flowering, and that an alternative flowering pathway can bypass vernalisation in small bulbs. We suggest that apical dominance interactions determine the distinct flowering pathways of the apical and axillary meristems. Similar floral induction is achieved in propagated bulblets from scaling. These innovative findings in the field of geophyte floral induction represent valuable applicative knowledge for lily production. PMID:26833779

  16. Collembola of Rapa Nui (Easter Island) with descriptions of five endemic cave-restricted species.

    PubMed

    Bernard, Ernest C; Soto-Adames, Felipe N; Wynne, J Judson

    2015-01-01

    Eight species of Collembola are reported from recent collections made in caves on the Polynesian island of Rapa Nui (Easter Island). Five of these species are new to science and apparently endemic to the island: Coecobrya aitorererere n. sp., Cyphoderus manuneru n. sp., Entomobrya manuhoko n. sp., Pseudosinella hahoteana n. sp. and Seira manukio n. sp. The Hawaiian species Lepidocyrtus olena Christiansen & Bellinger and the cosmopolitan species Folsomia candida Willem also were collected from one or more caves. Coecobrya kennethi Jordana & Baquero, recently described from Rapa Nui and identified as endemic, was collected in sympatric association with C. aitorererere n.sp. With the exception of F. candida, all species are endemic to Rapa Nui or greater Polynesia and appear to be restricted to the cave environment on Rapa Nui. A key is provided to separate Collembola species reported from Rapa Nui. We provide recommendations to aid in the conservation and management of these new Collembola, as well as the other presumed cave-restricted arthropods. PMID:25947805

  17. Simulated Radar Characteristics of LBA Convective Systems: Easterly and Westerly Regimes

    NASA Technical Reports Server (NTRS)

    Lang, Stephen E.; Tao, Wei-Kuo; Simpson, Joanne

    2003-01-01

    The 3D Goddard Cumulus Ensemble (GCE) model was used to simulate convection that occurred during the TRMM LBA field experiment in Brazil. Convection in this region can be categorized into two different regimes. Low-level easterly flow results in moderate to high CAPE and a drier environment. Convection is more intense like that seen over continents. Low-level westerly flow results in low CAPE and a moist environment. Convection is weaker and more widespread characteristic of oceanic or monsoon-like systems. The GCE model has been used to study both regimes n order to provide cloud datasets that are representative of both environments in support of TRMM rainfall and heating algorithm development. Two different cases are analyzed: Jan 26, 1999, an eastely regime case, and Feb 23, 1999, a westerly regime case. The Jan 26 case is an organized squall line, while the Feb 23 case is less organized with only transient lines. Radar signatures, including CFADs, from the two simulated cases are compared to each other and with observations. The microphysical processes simulated in the model are also compared between the two cases.

  18. Obesity and African Americans

    MedlinePlus

    ... Data > Minority Population Profiles > Black/African American > Obesity Obesity and African Americans African American women have the ... ss6304.pdf [PDF | 3.38MB] HEALTH IMPACT OF OBESITY More than 80 percent of people with type ...

  19. Potential landslide activity affecting the archaeological site of Orongo (Easter Island-Chile): preliminary analysis

    NASA Astrophysics Data System (ADS)

    Margottini, C.; Delmonaco, G.; Spizzichino, D.; Pandolfi, O.; Crisostomo, R.; Nohe, S.

    2009-04-01

    Easter Island forms part of the Easter Line, a continuous latitudinal chain of volcanic seamounts and islands in the Pacific Sea. The island's roughly triangular shape is determined by the merging of lava flows produced by its three main volcanoes (Rano Kau, Terevaka, Poike) which form its main mass. The Rano Kau volcano, sited in the SW vertex of the island, is made up of numerous basaltic lava flows and has been reduced in size by faulting and marine erosion. Its crater (1.4 km wide) is a small caldera that collapsed after a late, large explosive phase, as attested by the presence of breccia deposits around the eastern rim of the crater. The archaeological stone village of Orongo is located above the inner wall of the crater at an altitude of ca. 300m a.s.l. Prominent historical remains are the numerous petroglyphs that represent the ancient ceremonial of the birdman cult (tangata manu). Rano Kau is mainly composed of sequences of basaltic and intermediate lavas and pyroclastics. Most of the of the original caldera area, especially in the southern flank, has been disrupted by marine erosion. This has caused a dramatic change of the original morphology, resulting in a sub-vertical cliff and steep slopes, especially in the middle-low portions. In the upper part of the slopes weathered soils and regolith are outcropping. Topographical and geomorphological analysis of the area conducted by a direct field surveys in January and July 2008 have provided clear evidences of slope instability along the southern external flank of the caldera. Different landslide areas have been detected. The most active area is located at east of the village in correspondence of the crest zone of Rano Kau where a debris slide/fall has recently occurred. The analysis of photos taken in Nov. 2007 in the same area evidences that the landslide crown area was originated at an elevation of ca. 200m a.s.l. along a probable contact between basaltic layers on the top and weathered lava. Other minor

  20. The impact of latent heating on the location and strength of the tropical easterly jet

    NASA Astrophysics Data System (ADS)

    Rao, Samrat; Srinivasan, Jayaraman

    2016-04-01

    The tropical easterly jet (TEJ) is a prominent atmospheric circulation feature observed during the Asian summer monsoon. It is generally assumed that sensible heating over the Tibetan Plateau directly influences the location of the TEJ. However, other studies have suggested the importance of latent heating in determining the jet location. In this paper, the relative importance of latent heating on the maintenance of the TEJ is explored through simulations with a general circulation model. The simulation of the TEJ by the Community Atmosphere Model, version 3.1 is discussed in detail. These simulations showed that the location of the TEJ is well correlated with the location of the precipitation. Significant zonal shifts in the location of the precipitation resulted in similar shifts in the zonal location of the TEJ. These zonal shifts had minimal effect on the large-scale structure of the jet. Further, provided that precipitation patterns were relatively unchanged, orography did not directly impact the location of the TEJ. These changes were robust even with changes in the cumulus parameterization. This suggests the potential important role of latent heating in determining the location and structure of the TEJ. These results were used to explain the significant differences in the zonal location of the TEJ in the years 1988 and 2002. To understand the contribution of the latitudinal location of latent heating on the strength of the TEJ, aqua-planet simulations were carried out. It has been shown that for similar amounts of net latent heating, the jet is stronger when heating is in the higher tropical latitudes. This may partly explain the reason for the jet to be very strong during the JJA monsoon season.

  1. Simulating and Tracking a Heavily Rainy Wave over West Africa Using a Modeling Strategy with WRF Model

    NASA Astrophysics Data System (ADS)

    Sarr, A.

    2014-12-01

    The last decades, over Sahel, are characterized by a relative recovery in rainfall compared to the long drought, which affected this part of West Africa in the 70s, 80s and early 90s. It is also noted an increase of extreme events, mainly excess of rainfall causing damages to many parts of the Sahel area. In this study, we are focusing on an extreme case, which occurred during September 2009. A deep African Easterly Wave (AEW) crossed the region from Niger to Senegal giving heavy rains along its path with a maximum of more than 260mm in Ouagadougou, Burkina Faso. While continuing its trajectory other strong winds associated with the systems caused other kind of damages. A modeling strategy, based on a moving nest with the Weather Research and Forecast model (WRF-ARW), is used to simulate the system. The model is run at 27 and 9km respectively for the outer and inner domains. Key parameters are investigated in order to assess the ability of WRF model in simulating the even. The study has shown good performance of WRF in simulating tropical systems. Noted weaknesses are also highlighted in the study, which showed promising results in simulating extremes, hours to days head, in support to early warning systems (EWS) to mitigate the adverse effects of extremes. This is a key responsibility of National Meteorological Services lacking this capacity in developing countries of West Africa.

  2. Africans in America.

    ERIC Educational Resources Information Center

    Hart, Ayanna; Spangler, Earl

    This book introduces African-American history and culture to children. The first Africans in America came from many different regions and cultures, but became united in this country by being black, African, and slaves. Once in America, Africans began a long struggle for freedom which still continues. Slavery, the Civil War, emancipation, and the…

  3. African Outreach Workshop 1974.

    ERIC Educational Resources Information Center

    Schmidt, Nancy J.

    This report discusses the 1974 African Outreach Workshop planned and coordinated by the African Studies Program at the University of Illinois at Urbana-Champaign. Its major aim was to assist teachers in developing curriculum units on African using materials available in their local community. A second aim was for the African Studies Program to…

  4. Late Holocene vegetation dynamics and deforestation in Rano Aroi: Implications for Easter Island's ecological and cultural history

    NASA Astrophysics Data System (ADS)

    Rull, Valentí; Cañellas-Boltà, Núria; Margalef, Olga; Sáez, Alberto; Pla-Rabes, Sergi; Giralt, Santiago

    2015-10-01

    Easter Island (Rapa Nui) has been considered an example of how societies can cause their own destruction through the overexploitation of natural resources. The flagship of this ecocidal paradigm is the supposed abrupt, island-wide deforestation that occurred about one millennium ago, a few centuries after the arrival of Polynesian settlers to the island. Other hypotheses attribute the forest demise to different causes such as fruit consumption by rats or aridity but the occurrence of an abrupt, island-wide deforestation during the last millennium has become paradigmatic in Rapa Nui. We argue that such a view can be questioned, as it is based on the palynological study of incomplete records, owing to the existence of major sedimentary gaps. Here, we present a multiproxy (pollen, charcoal and geochemistry) study of the Aroi core, the first gap-free sedimentary sequence of the last millennia obtained to date in the island. Our results show changing vegetation patterns under the action of either climatic or anthropogenic drivers, or both, depending on the time interval considered. Palm forests were present in Aroi until the 16th century, when deforestation started, coinciding with fire exacerbation -likely of human origin- and a dry climate. This is the latest deforestation event recorded so far in the island and took place roughly a century before European contact. In comparison to other Easter Island records, this record shows that deforestation was neither simultaneous nor proceeded at the same pace over the whole island. These findings suggest that Easter Island's deforestation was a heterogeneous process in space and time, and highlights the relevance of local catchment traits in the island's environmental and land management history.

  5. Bioassay-guided fractionation of extracts from Easter lily (Lilium longiflorum) flowers reveals unprecedented structural variability of steroidal glycoalkaloids.

    PubMed

    Uhlig, Silvio; Hussain, Fozia; Wisløff, Helene

    2014-12-15

    Several Lilium species are nephrotoxic in cats (Felis silvestris catus), among them Easter lilies (Lilium longiflorum). Although clinical trials have been carried out, the causative toxic phytochemicals have not yet been identified. We thus aimed to determine the toxic constituents of Easter lily flowers applying a bioassay-guided approach based on a feline kidney cell line model. The bioassay-guided fractionation traced the observed cytotoxicity to a complex mixture of compounds that were tentatively identified as steroidal glycoalkaloids of the solasodine-type, based on multiple-fragmentation ion trap and high-resolution mass spectrometry. The glycoalkaloids in the active fraction possessed trisaccharide chains, and at least 16 different congeners could be separated using liquid chromatography-mass spectrometry. The two principal compounds were solasodine trisaccharides containing two hexose and one deoxy-hexose unit. In the remaining 14 analogues, one or two of the hydroxyl groups of the second hexose from the aglycone were acetylated. In addition, some of the analogues appeared to be carbonate esters. Esterification of steroidal glycoalkaloids in plants has only been reported once and was in accordance with higher antifungal activity of the acetylated versus the parent congener. Our pilot study shows that esterification of steroidal glycoalkaloids in Lilium species might be common resulting in an array of different analogues with largely unexplored structural variability and bioactivity. PMID:25269117

  6. Polynesian land use decisions in Hawai`i and Rapa Nui (Easter Island) (Invited)

    NASA Astrophysics Data System (ADS)

    Chadwick, O.; Ladefoged, T. N.; Haoa, S.; Stevenson, C.; Vitousek, P.

    2009-12-01

    Over the span of several centuries ancient Hawaiians and Rapanui (Easter Islanders) developed a range of intensive agricultural systems in their volcanic homelands. In leeward Kohala (Hawai`i) people targeted relatively young geologic substrates that were naturally enriched soil nutrient zones to construct a 60 km2 intensive rain-fed field system. A series of earthen and rock embankments and trails were built to facilitate sweet potato and dryland taro production and distribution. By comparing nutrient levels under embankments of different ages it has been possible to document significant nutrient depletion over approximately 150 years of pre-European gardening. On the wet windward side of Kohala leaching driven by high rainfall depleted soil nutrients in upland areas naturally, to levels unsuitable for intensive rain-fed agriculture. As an alternative, people exploited colluvial and alluvial zones for intensive rain-fed and irrigated agriculture, respectively. Analyses from Pololu in Kohala and Halawa on Moloka`i suggests that soil nutrient levels within colluvial zones were rejuvenated by erosion and deposition from fresh bedrock. In alluvial areas, soil nutrient levels were enhanced through the deposition of soluble elements via weathering of minerals along the flowpath between rainfall and delivery of irrigation water to Hawaiian crops. On Rapa Nui the lack of perennial streams meant that people were reliant on intensive rain-fed systems for their subsistence and surplus needs. In response to the matrix of geologic substrate ages and rainfall levels several innovative agricultural strategies were employed. Basalt outcrops were intentionally broken apart and large quantities of rock were distributed over the barren landscape. In places these “rock gardens” consisted of boulder concentrations and/or smaller rock veneers, whereas in other zones rocks were mulched into the soil to a depth of 30 cm to create growing medium. The advantages of these techniques

  7. Linkages of remote sea surface temperatures and Atlantic tropical cyclone activity mediated by the African monsoon

    NASA Astrophysics Data System (ADS)

    Taraphdar, Sourav; Leung, L. Ruby; Hagos, Samson

    2015-01-01

    sea surface temperatures (SSTs) in North Atlantic and Mediterranean (NAMED) can influence tropical cyclone (TC) activity in the tropical East Atlantic by modulating summer convection over western Africa. Analysis of 30 years of observations demonstrates that warm NAMED SST is linked to a strengthening of the Saharan heat low and enhancement of moisture and moist static energy in the lower troposphere over West Africa, which favors a northward displacement of the monsoonal front. These processes also lead to a northward shift of the African easterly jet that introduces an anomalous positive vorticity from western Africa to the main development region (50°W-20°E; 10°N-20°N) of Atlantic TCs. By modulating multiple African monsoon processes, NAMED SST explains comparable and approximately one third of the interannual variability of Atlantic TC frequency as that explained by local wind shear and local SST, respectively, which are known key factors that influence Atlantic TC development.

  8. Linkages of Remote Sea Surface Temperatures and Atlantic Tropical Cyclone Activity Mediated by the African Monsoon

    SciTech Connect

    Taraphdar, Sourav; Leung, Lai-Yung R.; Hagos, Samson M.

    2015-01-28

    Warm sea surface temperatures (SSTs) in North Atlantic and Mediterranean (NAMED) can influence tropical cyclone (TC) activity in the tropical East Atlantic by modulating summer convection over western Africa. Analysis of 30 years of observations show that the NAMED SST is linked to a strengthening of the Saharan heat low and enhancement of moisture and moist static energy in the lower atmosphere over West Africa, which favors a northward displacement of the monsoonal front. These processes also lead to a northward shift of the African easterly jet that introduces an anomalous positive vorticity from western Africa to the main development region (50W–20E; 10N–20N) of Atlantic TC. By modulating multiple processes associated with the African monsoon, this study demonstrates that warm NAMED SST explains 8% of interannual variability of Atlantic TC frequency. Thus NAME SST may provide useful predictability for Atlantic TC activity on seasonal-to-interannual time scale.

  9. Influence of 21st century atmospheric and sea surface temperature forcing on West African climate

    SciTech Connect

    Skinner, Chris B; Ashfaq, Moetasim; Diffenbaugh, Noah

    2011-01-01

    he persistence of extended drought events throughout West Africa during the 20th century has motivated a substantial effort to understand the mechanisms driving African climate variability, as well as the possible response to elevated greenhouse gas (GHG) forcing. We use an ensemble of global climate model experiments to examine the relative roles of future direct atmospheric radiative forcing and SST forcing in shaping potential future changes in boreal summer precipitation over West Africa. We find that projected increases in precipitation throughout the Western Sahel result primarily from direct atmospheric radiative forcing. The changes in atmospheric forcing generate a slight northward displacement and weakening of the African easterly jet (AEJ), a strengthening of westward monsoon flow onto West Africa and an intensification of the tropical easterly jet (TEJ). Alternatively, we find that the projected decreases in precipitation over much of the Guinea Coast region are caused by SST changes that are induced by the atmospheric radiative forcing. The changes in SSTs generate a weakening of the monsoon westerlies and the TEJ, as well as a decrease in low-level convergence and resultant rising air throughout the mid levels of the troposphere. Our experiments suggest a potential shift in the regional moisture balance of West Africa should global radiative forcing continue to increase, highlighting the importance of climate system feedbacks in shaping the response of regional-scale climate to global-scale changes in radiative forcing.

  10. Black African Traditional Mathematics

    ERIC Educational Resources Information Center

    Zaslavsky, Claudia

    1970-01-01

    Discusses the traditional number systems and the origin of the number names used by several African peoples living south of the Sahara. Also included are limitations in African mathematical development, and possible topics for research. (RP)

  11. Impacts of the ENSO Modoki and other Tropical Indo-Pacific Climate-Drivers on African Rainfall

    NASA Astrophysics Data System (ADS)

    Preethi, B.; Sabin, T. P.; Adedoyin, J. A.; Ashok, K.

    2015-11-01

    The study diagnoses the relative impacts of the four known tropical Indo-Pacific drivers, namely, El Niño Southern Oscillation (ENSO), ENSO Modoki, Indian Ocean Dipole (IOD), and Indian Ocean Basin-wide mode (IOBM) on African seasonal rainfall variability. The canonical El Niño and El Niño Modoki are in general associated with anomalous reduction (enhancement) of rainfall in southern (northern) hemispheric regions during March-May season. However, both the El Niño flavours anomalously reduce the northern hemispheric rainfall during June-September. Interestingly, during boreal spring and summer, in many regions, the Indian Ocean drivers have influences opposite to those from tropical Pacific drivers. On the other hand, during the October-December season, the canonical El Niño and/or positive IOD are associated with an anomalous enhancement of rainfall in the Eastern Africa, while the El Niño Modoki events are associated with an opposite impact. In addition to the Walker circulation changes, the Indo-Pacific drivers influence the African rainfall through modulating jet streams. During boreal summer, the El Niño Modoki and canonical El Niño (positive IOD) tend to weaken (strengthen) the tropical easterly jet, and result in strengthening (weakening) and southward shift of African easterly jet. This anomalously reduces (enhances) rainfall in the tropical north, including Sahelian Africa.

  12. Impacts of the ENSO Modoki and other Tropical Indo-Pacific Climate-Drivers on African Rainfall

    PubMed Central

    Preethi, B.; Sabin, T. P.; Adedoyin, J. A.; Ashok, K.

    2015-01-01

    The study diagnoses the relative impacts of the four known tropical Indo-Pacific drivers, namely, El Niño Southern Oscillation (ENSO), ENSO Modoki, Indian Ocean Dipole (IOD), and Indian Ocean Basin-wide mode (IOBM) on African seasonal rainfall variability. The canonical El Niño and El Niño Modoki are in general associated with anomalous reduction (enhancement) of rainfall in southern (northern) hemispheric regions during March-May season. However, both the El Niño flavours anomalously reduce the northern hemispheric rainfall during June-September. Interestingly, during boreal spring and summer, in many regions, the Indian Ocean drivers have influences opposite to those from tropical Pacific drivers. On the other hand, during the October-December season, the canonical El Niño and/or positive IOD are associated with an anomalous enhancement of rainfall in the Eastern Africa, while the El Niño Modoki events are associated with an opposite impact. In addition to the Walker circulation changes, the Indo-Pacific drivers influence the African rainfall through modulating jet streams. During boreal summer, the El Niño Modoki and canonical El Niño (positive IOD) tend to weaken (strengthen) the tropical easterly jet, and result in strengthening (weakening) and southward shift of African easterly jet. This anomalously reduces (enhances) rainfall in the tropical north, including Sahelian Africa. PMID:26567458

  13. Impacts of the ENSO Modoki and other Tropical Indo-Pacific Climate-Drivers on African Rainfall.

    PubMed

    Preethi, B; Sabin, T P; Adedoyin, J A; Ashok, K

    2015-01-01

    The study diagnoses the relative impacts of the four known tropical Indo-Pacific drivers, namely, El Niño Southern Oscillation (ENSO), ENSO Modoki, Indian Ocean Dipole (IOD), and Indian Ocean Basin-wide mode (IOBM) on African seasonal rainfall variability. The canonical El Niño and El Niño Modoki are in general associated with anomalous reduction (enhancement) of rainfall in southern (northern) hemispheric regions during March-May season. However, both the El Niño flavours anomalously reduce the northern hemispheric rainfall during June-September. Interestingly, during boreal spring and summer, in many regions, the Indian Ocean drivers have influences opposite to those from tropical Pacific drivers. On the other hand, during the October-December season, the canonical El Niño and/or positive IOD are associated with an anomalous enhancement of rainfall in the Eastern Africa, while the El Niño Modoki events are associated with an opposite impact. In addition to the Walker circulation changes, the Indo-Pacific drivers influence the African rainfall through modulating jet streams. During boreal summer, the El Niño Modoki and canonical El Niño (positive IOD) tend to weaken (strengthen) the tropical easterly jet, and result in strengthening (weakening) and southward shift of African easterly jet. This anomalously reduces (enhances) rainfall in the tropical north, including Sahelian Africa. PMID:26567458

  14. A 70,000 year multiproxy record of climatic and environmental change from Rano Aroi peatland (Easter Island)

    NASA Astrophysics Data System (ADS)

    Margalef, Olga; Cañellas-Boltà, Núria; Pla-Rabes, Sergi; Giralt, Santiago; Pueyo, Juan Jose; Joosten, Hans; Rull, Valentí; Buchaca, Teresa; Hernández, Armand; Valero-Garcés, Blas L.; Moreno, Ana; Sáez, Alberto

    2013-09-01

    The Rano Aroi mire on Easter Island (also known as Rapa Nui; 27°09‧S, 109°27‧W, 430 m above sea level) provides a unique non-marine record in the central South Pacific Ocean for reconstructing Late Pleistocene environmental changes. The results of a multiproxy study on two cores from the center and margin of the Rano Aroi mire, including peat stratigraphy, facies analysis, elemental and isotope geochemistry on bulk organic matter, X-ray fluorescence (XRF) core scanning and macrofossil analysis, were used to infer past water levels and vegetation changes. The chronology was based on 18 14C AMS dates for the upper 8.7 m. The extrapolated age for the base of the sequence is 70 kyr, which implies that this record is the oldest paleolimnological record on Easter Island. The recovered Rano Aroi sequence consists of a radicel peat formed primarily from the remains of sedges, grasses and Polygonaceae that have accumulated since Marine Isotopic Stage (MIS) 4 (70 kyr BP) to the present. From 60 to 40 kyr BP (MIS 3), high precipitation/runoff events were recorded as organic mud facies with lighter δ13C, low C/N values and high Ti content, indicating higher detritic input to the mire. A gradual shift in δ13C bulk organic matter from - 14% to - 26%, recorded between 50 and 45 cal kyr BP, suggests a progressive change in local peat-forming vegetation from C4 to C3 plant types. Post-depositional Ca and Fe enrichment during sub-aerial peat exposure and very low sedimentation rates indicate lower water tables during Late MIS 3 (39-31 cal kyr BP). During MIS 2 (27.8-19 cal kyr BP), peat production rates were very low, most likely due to cold temperatures, as reconstructed from other Easter Island records during the Last Glacial Maximum (LGM). Geochemical and macrofossil evidence shows that peat accumulation reactivates at approximately 17.5 cal kyr BP, reaching the highest accumulation rates at 14 cal kyr BP. Peat accretion decreased from 5.0 to 2.5 cal kyr BP, coinciding

  15. The African Connection

    ERIC Educational Resources Information Center

    Oguntoyinbo, Lekan

    2012-01-01

    From student and faculty exchanges to joint research projects, U.S. universities maintain a broad spectrum of collaborative relationships with African universities. It's unclear how many U.S. colleges and universities have partnerships with African universities. The African Studies Association, an organization of scholars, doesn't keep that kind…

  16. The West African Monsoon: variability and teleconnection with ENSO during the years 1948-57

    NASA Astrophysics Data System (ADS)

    Stickler, Alexander; Brönnimann, Stefan

    2010-05-01

    The intensity of the West African Monsoon (WAM) has been shown to be influenced by different factors. Most important for the existence of the monsoon system is the land-sea thermal contrast between the North African landmass and the Gulf of Guinea. ENSO plays an important role for its interannual variability via an atmospheric teleconnection bridging the Pacific and Atlantic oceanic basins and favouring either descent/weak low-level monsoon flow or ascent/strong low-level monsoon flow over tropical West Africa. Most published studies on the WAM variability are based on reanalysis datasets. However, while reproducing quite well the interannual variability, reanalysis products have been found to contain major biases in certain tropical regions before 1968. These lead to an unrealistic low frequency behaviour and might be explained by the lack of observations assimilated into the reanalyses, as is the case e.g. for tropical Africa where only the much sparser radiosonde data have been assimilated into the NCEP/NCAR Reanalysis (NNR). Here we present an analysis of the interannual WAM variability and its teleconnection with ENSO for the years 1948-57 which is not based on a reanalysis, but on early pilot balloon observational wind data from the Comprehensive Historical Upper Air Network (CHUAN). We have examined wind data from all 36 stations located in the domain (10°S-30°N, 20°W-20°E) on 5 levels up to the mid troposphere (corresponding roughly to the 925, 850, 700, 600 and 500 hPa pressure levels). This analysis shows that 7 subregions can be defined which are characterised by similar vertical wind profiles as well as seasonality: the NW (Mauritania, northern Senegal), the SW (southern Senegal to coastal Guinea), central sub-Saharan West Africa (SSWA, from interior Guinea in the W to coastal Cameroon and southern Niger in the E), central and eastern Niger, western Chad, the western Central African Republic, and the southern coastal regions east of the Gulf of

  17. Some Fantasy Characters of Young Children: An Examination of Children's Beliefs in Santa Claus, the Tooth Fairy, and the Easter Bunny.

    ERIC Educational Resources Information Center

    Manosevitz, Martin; Prentice, Norman M.

    This study examined children's beliefs in Santa Claus, the Easter Bunny, and the Tooth Fairy as well as the effects of parental encouragement or support of these fantasy characters upon the children's beliefs. Subjects were 60 children aged 4, 6 and 8 years and their parents. Measures included a parental questionnaire and child interviews. Partial…

  18. Analyzing the Multi-scale Interactions of Tropical Waves and Tropical Cyclone Formation with the NASA CMAVis System

    NASA Astrophysics Data System (ADS)

    Shen, B.; Nelson, B.; Tao, W.

    2011-12-01

    Among the scenarios in the Decadal Survey (DS) Missions, the advanced data processing group at the ESTO AIST PI workshop identified "Extreme Event Warning" and "Climate Projections" as two of the top priority scenarios. Recently, we (e.g., Shen et al., 2010a,b; 2011a,b) have made attempt of addressing the first by successfully developing the NASA Coupled Advanced global multiscale Modeling and concurrent Visualization systems (CAMVis) on NASA supercomputers, and demonstrating a great potential for extending the lead time (from 5~7 days up to 20 days) of tropical cyclone (TC) prediction with improved multi-scale interactions between a TC with large-scale environmental conditions such as African Easterly Waves (AEWs), and Madden Julian Oscillation (MJOs). In order to increase our confidence in long-term TC prediction and thus TC climate projection, the predictive relationships between large-scale tropical waves and TC formation need to be further examined and verified with massive model and satellite data sets. To achieve this goal, we have conducted multiscale analysis to study the TC genesis processes, accompanied downscaling (from large-scale events) and upscaling (from small-scale events) processes, and their subsequent non-linear interactions. In this study, we first illustrate the complicated multi-scale interactions during TC genesis with our newly-developed 3D streamline packages in the NASA CAMVis system. With selected cases that include twin TCs in 2002, TC Nargis (2008) and hurricane Helene (2006), we will show that the CAMVis can provide a detailed (zoomed-in) view on hurricane physical processes and an integrative (zoomed-out) view on its interactions with environmental conditions. In the end of talk, we will discuss our future work in multiscale analysis with the Hilbert Huang Transform and improved ensemble empiric mode decomposition.

  19. Three-dimensional inversion of the magnetic field over the Easter-Nazca propagating rift near 25°S, 112°25‧W

    NASA Astrophysics Data System (ADS)

    Sempere, Jean-Christophe; Gee, Jeff; Naar, David F.; Hey, Richard N.

    1989-12-01

    The Easter microplate boundary configuration is being reorganized by rift propagation. A Sea Beam survey of the Easter-Nazca spreading center, which forms the eastern boundary of the microplate, has revealed the presence of a young propagating rift growing northward (Naar and Hey, 1986). The tip of the propagating rift is associated with a high-amplitude positive magnetic anomaly. We have performed a three-dimensional inversion of the magnetic field over the propagating rift tip area. The magnetization solution suggests that the western and eastern pseudofaults strike 014° and 338°, respectively, and converge near the rift tip. These orientations yield a propagation to spreading rate ratio of 1.5, slightly higher than the estimate of Naar and Hey (1986). Using the revised estimate of the full spreading rate along the Easter-Nazca spreading center near 25°S (80 mm/yr) (D. F. Naar and R. N. Hey, unpublished manuscript, 1989), we obtain a propagation rate of 120 mm/yr. Within 27-30 km of the rift tip, the propagating rift curves by about 15° to the east toward the failing rift, probably as a result of the interaction between the two offset spreading centers. As at the Galapagos propagating rift, rift propagation appears to be a very orderly process along the Easter-Nazca spreading center. The magnetization distribution that we obtain exhibits a high at the propagating rift tip. At other large ridge axis discontinuities, similar magnetization highs have been interpreted as being the result of the eruption of highly differentiated basalts enriched in iron. The origin of the high magnetization zone in the case of the Easter-Nazca propagating rift near 25°S may be more complex. Preliminary rock magnetic measurements of basalts recovered in the vicinity of the propagating rift confirm the presence of highly magnetized basalts but suggest that the relationship between high magnetization intensities and high Fe content is not straightforward.

  20. Observed Oceanic and Terrestrial Drivers of North African Climate

    NASA Astrophysics Data System (ADS)

    Yu, Y.; Notaro, M.; Wang, F.; Mao, J.; Shi, X.; Wei, Y.

    2015-12-01

    Hydrologic variability can pose a serious threat to the poverty-stricken regions of North Africa. Yet, the current understanding of oceanic versus terrestrial drivers of North African droughts/pluvials is largely model-based, with vast disagreement among models. In order to identify the observed drivers of North African climate and develop a benchmark for model evaluations, the multivariate Generalized Equilibrium Feedback Assessment (GEFA) is applied to observations, remotely sensed data, and reanalysis products. The identified primary oceanic drivers of North African rainfall variability are the Atlantic, tropical Indian, and tropical Pacific Oceans and Mediterranean Sea. During the summer monsoon, positive tropical eastern Atlantic sea-surface temperature (SST) anomalies are associated with a southward shift of the Inter-Tropical Convergence Zone, enhanced ocean evaporation, and greater precipitable water across coastal West Africa, leading to increased West African monsoon (WAM) rainfall and decreased Sahel rainfall. During the short rains, positive SST anomalies in the western tropical Indian Ocean and negative anomalies in the eastern tropical Indian Ocean support greater easterly oceanic flow, evaporation over the western ocean, and moisture advection to East Africa, thereby enhancing rainfall. The sign, magnitude, and timing of observed vegetation forcing on rainfall vary across North Africa. The positive feedback of leaf area index (LAI) on rainfall is greatest during DJF for the Horn of Africa, while it peaks in autumn and is weakest during the summer monsoon for the Sahel. Across the WAM region, a positive LAI anomaly supports an earlier monsoon onset, increased rainfall during the pre-monsoon, and decreased rainfall during the wet season. Through unique mechanisms, positive LAI anomalies favor enhanced transpiration, precipitable water, and rainfall across the Sahel and Horn of Africa, and increased roughness, ascent, and rainfall across the WAM region

  1. African American legislators' perceptions of firearm violence prevention legislation.

    PubMed

    Payton, Erica; Thompson, Amy; Price, James H; Sheu, Jiunn-Jye; Dake, Joseph A

    2015-06-01

    Firearm mortality is the leading cause of death for young African American males, however, few studies have focused on racial/ethnic minority populations and firearm violence. The National Black Caucus of State Legislators advocates for legislation that promotes the health of African Americans. Thus, the purpose of this study was to collect baseline data on African American legislators' perceptions regarding firearm violence in the African American community. A cross-sectional study of African American legislators (n = 612) was conducted to investigate the research questions. Of the 612 questionnaires mailed, 12 were not deliverable, and 170 were returned (28%). Utilizing a three wave mailing process, African American legislators were invited to participate in the study. The majority (88%) of respondents perceived firearm violence to be very serious among African Americans. Few (10%) legislators perceived that addressing legislative issues would be an effective strategy in reducing firearm violence among African Americans. The majority (72%) of legislators perceived the most effective strategy to reducing firearm violence in the African American community should focus on addressing societal issues (e.g. crime and poverty). After adjusting for the number of perceived barriers, the number of perceived benefits was a significant predictor of legislators' perceived effectiveness of firearm violence prevention legislation for 8 of the 24 potential firearm violence prevention legislative bills. PMID:25301589

  2. Wave Forcing of Saturn's Equatorial Oscillation

    NASA Technical Reports Server (NTRS)

    Flasar, F. M.; Schlinder, P. J.; Guerlet, S.; Fouchet, T.

    2011-01-01

    Ground-based measurements and Cassini data from CIRS thermal-infrared spectra and radio-occultation soundings have characterized the spatial structure and temporal behavior of a 15-year equatorial oscillation in Saturn's stratosphere. The equatorial region displays a vertical pattern of alternating warm and cold anomalies and, concomitantly, easterly and westerly winds relative to the cloud-top winds, with a peak-to-peak amplitude of 200 m/s. Comparison of the Cassini data over a four-year period has established that the pattern of mean zonal winds and temperatures descends at a rate of roughly I scale height over 4 years. This behavior is reminiscent of the equatorial oscillations in Earth's middle atmosphere. Here the zonal-mean spatial structure and descending pattern are driven by the absorption of vertically propagating waves. The maximum excursions in the pattern of easterly and westerly winds is determined by the limits of the zonal phase velocities of the waves. Here we report on the characterization of the waves seen in the temperature profiles retrieved from the Cassini radio-occultation soundings. The equatorial profiles exhibit a complex pattern of wavelike structure with dimensions one pressure scale height and smaller. We combine a spectral decomposition with a WKBJ analysis, where the vertical wavelength is assumed to vary slowly with the ambient static stability and doppler-shifted phase velocity of the wave. Use of the temperature and zonal wind maps from CIRS makes this approach viable. On Earth, the wave forcing associated with the equatorial oscillations generates secondary meridional circulations that affect the mean flow and planetary wave ducting well away from the equator. This may relate to the triggering of the recently reported mid-latitude storms on Saturn.

  3. African and non-African admixture components in African Americans and an African Caribbean population.

    PubMed

    Murray, Tanda; Beaty, Terri H; Mathias, Rasika A; Rafaels, Nicholas; Grant, Audrey Virginia; Faruque, Mezbah U; Watson, Harold R; Ruczinski, Ingo; Dunston, Georgia M; Barnes, Kathleen C

    2010-09-01

    Admixture is a potential source of confounding in genetic association studies, so it becomes important to detect and estimate admixture in a sample of unrelated individuals. Populations of African descent in the US and the Caribbean share similar historical backgrounds but the distributions of African admixture may differ. We selected 416 ancestry informative markers (AIMs) to estimate and compare admixture proportions using STRUCTURE in 906 unrelated African Americans (AAs) and 294 Barbadians (ACs) from a study of asthma. This analysis showed AAs on average were 72.5% African, 19.6% European and 8% Asian, while ACs were 77.4% African, 15.9% European, and 6.7% Asian which were significantly different. A principal components analysis based on these AIMs yielded one primary eigenvector that explained 54.04% of the variation and captured a gradient from West African to European admixture. This principal component was highly correlated with African vs. European ancestry as estimated by STRUCTURE (r(2)=0.992, r(2)=0.912, respectively). To investigate other African contributions to African American and Barbadian admixture, we performed PCA on approximately 14,000 (14k) genome-wide SNPs in AAs, ACs, Yorubans, Luhya and Maasai African groups, and estimated genetic distances (F(ST)). We found AAs and ACs were closest genetically (F(ST)=0.008), and both were closer to the Yorubans than the other East African populations. In our sample of individuals of African descent, approximately 400 well-defined AIMs were just as good for detecting substructure as approximately 14,000 random SNPs drawn from a genome-wide panel of markers. PMID:20717976

  4. Glacial to Holocene climate changes in the SE Pacific. The Raraku Lake sedimentary record (Easter Island, 27°S)

    NASA Astrophysics Data System (ADS)

    Sáez, Alberto; Valero-Garcés, Blas L.; Giralt, Santiago; Moreno, Ana; Bao, Roberto; Pueyo, Juan J.; Hernández, Armand; Casas, David

    2009-12-01

    Easter Island (SE Pacific, 27°S) provides a unique opportunity to reconstruct past climate changes in the South Pacific region based on terrestrial archives. Although the general climate evolution of the south Pacific since the Last Glacial Maximum (LGM) is coherent with terrestrial records in southern South America and Polynesia, the details of the dynamics of the shifting Westerlies, the South Pacific Convergence Zone and the South Pacific Anticyclone during the glacial-interglacial transition and the Holocene, and the large scale controls on precipitation in tropical and extratropical regions remain elusive. Here we present a high-resolution reconstruction of lake dynamics, watershed processes and paleohydrology for the last 34 000 cal yrs BP based on a sedimentological and geochemical multiproxy study of 8 cores from the Raraku Lake sediments constrained by 22 AMS radiocarbon dates. This multicore strategy has reconstructed the sedimentary architecture of the lake infilling and provided a stratigraphic framework to integrate and correlate previous core and vegetation studies conducted in the lake. High lake levels and clastic input dominated sedimentation in Raraku Lake between 34 and 28 cal kyr BP. Sedimentological and geochemical evidences support previously reported pollen data showing a relatively open forest and a cold and relatively humid climate during the Glacial period. Between 28 and 17.3 cal kyr BP, including the LGM period, colder conditions contributed to a reduction of the tree coverage in the island. The coherent climate patterns in subtropical and mid latitudes of Chile and Eastern Island for the LGM (more humid conditions) suggest stronger influence of the Antarctic circumpolar current and an enhancement of the Westerlies. The end of Glacial Period occurred at 17.3 cal kyr BP and was characterized by a sharp decrease in lake level conducive to the development of major flood events and erosion of littoral sediments. Deglaciation (Termination

  5. The African superswell

    NASA Technical Reports Server (NTRS)

    Nyblade, Andrew A.; Robinson, Scott W.

    1994-01-01

    Maps of residual bathymetry in the ocean basins around the African continent reveal a broad bathymetric swell in the southeastern Atlantic Ocean with an amplitude of about 500 m. We propose that this region of anomalously shallow bathymetry, together with the contiguous eastern and southern African plateaus, form a superswell which we refer to as the African superswell. The origin of the African superswell is uncertain. However, rifting and volcanism in eastern Africa, as well as heat flow measurements in southern Africa and the southeastern Atlantic Ocean, suggest that the superswell may be attributed, at least in part, to heating of the lithosphere.

  6. Characteristics of easterly-induced snowfall in Yeongdong and its relationship to air-sea temperature difference

    NASA Astrophysics Data System (ADS)

    Nam, Hyoung-Gu; Kim, Byung-Gon; Han, Sang-Ok; Lee, Chulkyu; Lee, Seoung-Soo

    2014-08-01

    Characteristics of snowfall episodes have been investigated for the past ten years in order to study its association with lowlevel stability and air-sea temperature difference over the East Sea. In general, the selected snowfall episodes have similar synoptic setting such as the Siberian High extended to northern Japan along with the Low passing by the southern Korean Peninsula, eventually resulting in the easterly flow in the Yeongdong region. Especially in the heavy snowfall episodes, convective unstable layers have been identified over the East sea due to relatively warm sea surface temperature (SST) about 8˜10°C and specifically cold pool around 1˜2 km above the surface level (ASL), which can be derived from Regional Data Assimilation and Prediction System (RDAPS), but that have not been clearly exhibited in the weak snowfall episodes. The basic mechanism to initiate snowfall around Yeongdong seems to be similar to that of lake-effect snowstorms around Great Lakes in the United States (Kristovich et al., 2003). Difference of equivalent potential temperature ( θ e ) between 850 hPa and surface as well as difference between air and sea temperatures altogether gradually began to increase in the pre-snowfall period and reached their maximum values in the course of the period, whose air (850 hPa) — sea temperature difference and snowfall intensity in case of the heavy snowfall episodes are almost larger than 20°C and 6 tims greater than the weak snowfall episodes, respectively. Interestingly, snowfall appeared to begin in case of an air-sea temperature difference exceeding over 15°C. The current analysis is overall consistent with the previous finding (Lee et al., 2012) that an instabilityinduced moisture supply to the lower atmosphere from the East sea, being cooled and saturated in the lower layer, so to speak, East Sea-Effect Snowfall (SES), would make a low-level ice cloud which eventually moves inland by the easterly flow. In addition, a longlasting

  7. Vegetation changes and human settlement of Easter Island during the last millennia: a multiproxy study of the Lake Raraku sediments

    NASA Astrophysics Data System (ADS)

    Cañellas-Boltà, Núria; Rull, Valentí; Sáez, Alberto; Margalef, Olga; Bao, Roberto; Pla-Rabes, Sergi; Blaauw, Maarten; Valero-Garcés, Blas; Giralt, Santiago

    2013-07-01

    Earlier palynological studies of lake sediments from Easter Island suggest that the island underwent a recent and abrupt replacement of palm-dominated forests by grasslands, interpreted as a deforestation by indigenous people. However, the available evidence is inconclusive due to the existence of extended hiatuses and ambiguous chronological frameworks in most of the sedimentary sequences studied. This has given rise to an ongoing debate about the timing and causes of the assumed ecological degradation and cultural breakdown. Our multiproxy study of a core recovered from Lake Raraku highlights the vegetation dynamics and environmental shifts in the catchment and its surroundings during the late Holocene. The sequence contains shorter hiatuses than in previously recovered cores and provides a more continuous history of environmental changes. The results show a long, gradual and stepped landscape shift from palm-dominated forests to grasslands. This change started c. 450 BC and lasted about two thousand years. The presence of Verbena litoralis, a common weed, which is associated with human activities in the pollen record, the significant correlation between shifts in charcoal influx, and the dominant pollen types suggest human disturbance of the vegetation. Therefore, human settlement on the island occurred c. 450 BC, some 1500 years earlier than is assumed. Climate variability also exerted a major influence on environmental changes. Two sedimentary gaps in the record are interpreted as periods of droughts that could have prevented peat growth and favoured its erosion during the Medieval Climate Anomaly and the Little Ice Age, respectively. At c. AD 1200, the water table rose and the former Raraku mire turned into a shallow lake, suggesting higher precipitation/evaporation rates coeval with a cooler and wetter Pan-Pacific AD 1300 event. Pollen and diatom records show large vegetation changes due to human activities c. AD 1200. Other recent vegetation changes also

  8. Analysis of the Interactions of Planetary Waves with the Mean Flow of the Stratosphere

    NASA Technical Reports Server (NTRS)

    Newman, Paul A.

    2007-01-01

    During the winter period, large scale waves (planetary waves) are observed to propagate from the troposphere into the stratosphere. Such wave events have been recognized since the 1 950s. The very largest wave events result in major stratospheric warmings. These large scale wave events have typical durations of a few days to 2 weeks. The wave events deposit easterly momentum in the stratosphere, decelerating the polar night jet and warming the polar region. In this presentation we show the typical characteristics of these events via a compositing analysis. We will show the typical periods and scales of motion and the associated decelerations and warmings. We will illustrate some of the differences between major and minor warming wave events. We will further illustrate the feedback by the mean flow on subsequent wave events.

  9. The relationship between the equatorial westerlies, upper-level zonal flow and interannual variability of the West African monsoon

    NASA Astrophysics Data System (ADS)

    Nicholson, S. E.

    2013-12-01

    Two of the most important circulation features governing the interannual variability of the West African monsoon are the low-level African westerly jet and the upper tropospheric Tropical Easterly Jet. Both jets are abnormally intense during wet years over the Sahel/Soudan region. This paper examines four new aspects of these systems and their role in interannual variability. One is the extent to which these systems explain recent variability in the region. A second is their role in western equatorial regions. A third is possible teleconnections of the low-level jet to rainfall in eastern equatorial Africa. A fourth is the mechanism by which intensification of the two jets appears to occur in tandem.

  10. 16 Extraordinary African Americans.

    ERIC Educational Resources Information Center

    Lobb, Nancy

    This collection for children tells the stories of 16 African Americans who helped make America what it is today. African Americans can take pride in the heritage of these contributors to society. Biographies are given for the following: (1) Sojourner Truth, preacher and abolitionist; (2) Frederick Douglass, abolitionist; (3) Harriet Tubman, leader…

  11. African Studies Computer Resources.

    ERIC Educational Resources Information Center

    Kuntz, Patricia S.

    African studies computer resources that are readily available in the United States with linkages to Africa are described, highlighting those most directly corresponding to African content. Africanists can use the following four fundamental computer systems: (1) Internet/Bitnet; (2) Fidonet; (3) Usenet; and (4) dial-up bulletin board services. The…

  12. African Literature as Celebration.

    ERIC Educational Resources Information Center

    Achebe, Chinua

    1989-01-01

    Describes the Igbo tradition of "Mbari," a communal creative enterprise that celebrates the world and the life lived in it through art. Contrasts the cooperative, social dimension of pre-colonial African culture with the exclusion and denial of European colonialism, and sees new African literature again celebrating human presence and dignity. (AF)

  13. Educating African American Males

    ERIC Educational Resources Information Center

    Bell, Edward E.

    2010-01-01

    Background: Schools across America spend money, invest in programs, and sponsor workshops, offer teacher incentives, raise accountability standards, and even evoke the name of Obama in efforts to raise the academic achievement of African American males. Incarceration and college retention rates point to a dismal plight for many African American…

  14. Africans Away from Home.

    ERIC Educational Resources Information Center

    Clarke, John Henrik

    Africans who were brought across the Atlantic as slaves never fully adjusted to slavery or accepted its inevitability. Resistance began on board the slave ships, where many jumped overboard or committed suicide. African slaves in South America led the first revolts against tyranny in the New World. The first slave revolt in the Caribbean occurred…

  15. Keeping African Masks Real

    ERIC Educational Resources Information Center

    Waddington, Susan

    2012-01-01

    Art is a good place to learn about our multicultural planet, and African masks are prized throughout the world as powerfully expressive artistic images. Unfortunately, multicultural education, especially for young children, can perpetuate stereotypes. Masks taken out of context lose their meaning and the term "African masks" suggests that there is…

  16. Diabetes in African Americans

    PubMed Central

    Marshall, M

    2005-01-01

    African Americans have a high risk for type 2 diabetes. Genetic traits, the prevalence of obesity, and insulin resistance all contribute to the risk of diabetes in the African American community. African Americans have a high rate of diabetic complications, because of poor glycaemic control and racial disparities in health care in the USA. African Americans with diabetes may have an atypical presentation that simulates type 1 diabetes, but then their subsequent clinical course is typical of type 2 diabetes. Culturally sensitive strategies, structured disease management protocols, and the assistance of nurses, diabetic educators, and other health care professionals are effective in improving the outcome of diabetes in the African American community. PMID:16344294

  17. African bees to control African elephants

    NASA Astrophysics Data System (ADS)

    Vollrath, Fritz; Douglas-Hamilton, Iain

    2002-11-01

    Numbers of elephants have declined in Africa and Asia over the past 30 years while numbers of humans have increased, both substantially. Friction between these two keystone species is reaching levels which are worryingly high from an ecological as well as a political viewpoint. Ways and means must be found to keep the two apart, at least in areas sensitive to each species' survival. The aggressive African bee might be one such method. Here we demonstrate that African bees deter elephants from damaging the vegetation and trees which house their hives. We argue that bees can be employed profitably to protect not only selected trees, but also selected areas, from elephant damage.

  18. African Genetic Ancestry is Associated with Sleep Depth in Older African Americans

    PubMed Central

    Halder, Indrani; Matthews, Karen A.; Buysse, Daniel J.; Strollo, Patrick J.; Causer, Victoria; Reis, Steven E.; Hall, Martica H.

    2015-01-01

    Study Objectives: The mechanisms that underlie differences in sleep characteristics between European Americans (EA) and African Americans (AA) are not fully known. Although social and psychological processes that differ by race are possible mediators, the substantial heritability of sleep characteristics also suggests genetic underpinnings of race differences. We hypothesized that racial differences in sleep phenotypes would show an association with objectively measured individual genetic ancestry in AAs. Design: Cross sectional. Setting: Community-based study. Participants: Seventy AA adults (mean age 59.5 ± 6.7 y; 62% female) and 101 EAs (mean age 60.5 ± 7 y, 39% female). Measurements and Results: Multivariate tests were used to compare the Pittsburgh Sleep Quality Index (PSQI) and in-home polysomnographic measures of sleep duration, sleep efficiency, apnea-hypopnea index (AHI), and indices of sleep depth including percent visually scored slow wave sleep (SWS) and delta EEG power of EAs and AAs. Sleep duration, efficiency, and sleep depth differed significantly by race. Individual % African ancestry (%AF) was measured in AA subjects using a panel of 1698 ancestry informative genetic markers and ranged from 10% to 88% (mean 67%). Hierarchical linear regression showed that higher %AF was associated with lower percent SWS in AAs (β (standard error) = −4.6 (1.5); P = 0.002), and explained 11% of the variation in SWS after covariate adjustment. A similar association was observed for delta power. No association was observed for sleep duration and efficiency. Conclusion: African genetic ancestry is associated with indices of sleep depth in African Americans. Such an association suggests that part of the racial differences in slow-wave sleep may have genetic underpinnings. Citation: Halder I, Matthews KA, Buysse DJ, Strollo PJ, Causer V, Reis SE, Hall MH. African genetic ancestry is associated with sleep depth in older African Americans. SLEEP 2015;38(8):1185–1193

  19. Tropical waves and the quasi-biennial oscillation in the lower stratosphere

    NASA Technical Reports Server (NTRS)

    Miller, A. J.; Angell, J. K.; Korshover, J.

    1976-01-01

    By means of spectrum analysis of 11 years of lower stratospheric daily winds and temperatures at Balboa, Ascension and Canton-Singapore, evidence is presented supporting the existence of two principal wave modes with periods of about 11-17 days (Kelvin waves) and about 4-5 days (mixed Rossby-gravity waves). The structure of the two wave modes, as well as the vertical eddy momentum flux by the waves, is shown to be related to the quasi-biennial cycle, although for the mixed Rossby-gravity waves this is obvious only at Ascension. In addition, the Coriolis term, suggested as a source of vertical easterly momentum flux for the mixed Rossby-gravity waves, is investigated and found to be of the same magnitude as the vertical eddy flux term. Finally, we have examined the mean meridional motion and the meridional eddy momentum flux for its possible association with the quasi- biennial variation.

  20. Quantitative analysis of steroidal glycosides in different organs of Easter lily (Lilium longiflorum Thunb.) by LC-MS/MS.

    PubMed

    Munafo, John P; Gianfagna, Thomas J

    2011-02-01

    The bulbs of the Easter lily ( Lilium longiflorum Thunb.) are regularly consumed in Asia as both food and medicine, and the beautiful white flowers are appreciated worldwide as an attractive ornamental. The Easter lily is a rich source of steroidal glycosides, a group of compounds that may be responsible for some of the traditional medicinal uses of lilies. Since the appearance of recent reports on the role steroidal glycosides in animal and human health, there is increasing interest in the concentration of these natural products in plant-derived foods. A LC-MS/MS method performed in multiple reaction monitoring (MRM) mode was used for the quantitative analysis of two steroidal glycoalkaloids and three furostanol saponins, in the different organs of L. longiflorum. The highest concentrations of the total five steroidal glycosides were 12.02 ± 0.36, 10.09 ± 0.23, and 9.36 ± 0.27 mg/g dry weight in flower buds, lower stems, and leaves, respectively. The highest concentrations of the two steroidal glycoalkaloids were 8.49 ± 0.3, 6.91 ± 0.22, and 5.83 ± 0.15 mg/g dry weight in flower buds, leaves, and bulbs, respectively. In contrast, the highest concentrations of the three furostanol saponins were 4.87 ± 0.13, 4.37 ± 0.07, and 3.53 ± 0.06 mg/g dry weight in lower stems, fleshy roots, and flower buds, respectively. The steroidal glycoalkaloids were detected in higher concentrations as compared to the furostanol saponins in all of the plant organs except the roots. The ratio of the steroidal glycoalkaloids to furostanol saponins was higher in the plant organs exposed to light and decreased in proportion from the aboveground organs to the underground organs. Additionally, histological staining of bulb scales revealed differential furostanol accumulation in the basal plate, bulb scale epidermal cells, and vascular bundles, with little or no staining in the mesophyll of the bulb scale. An understanding of the distribution of steroidal glycosides in the different

  1. Black versus Black: The Relationship among African, African American, and African Caribbean Persons.

    ERIC Educational Resources Information Center

    Jackson, Jennifer V.; Cothran, Mary E.

    2003-01-01

    Surveyed people of African descent regarding relationships among African, African-American, and African-Caribbean persons, focusing on contact and friendship, travel to countries of the diaspora, cross-cultural communication, thoughts and stereotypes, and education. Most respondents had contacts with the other groups, but groups had preconceived…

  2. CARIBIC measurements of methane and other trace gases in the easterly outflow of the Indian summer monsoon

    NASA Astrophysics Data System (ADS)

    Rhee, T.; Brenninkmeijer, C. A. M.; Schuck, T. J.; Slemr, F.; Zahn, A.

    2009-04-01

    Indian monsoon is one of the most important global meteorological phenomena in the tropics. In particular during Indian summer monsoon, deep convection occurring in Intertropical Convergence Zone located in the Indian subcontinent brings the polluted surface air to high altitude, perturbing clean free troposphere and/or the lowermost stratosphere. CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container, www.caribic-atmosphere.com) conducted atmospheric chemical composition measurements at 8-11 km using an automated instrumental package. Monthly regular flights between Germany and the Maldives or Sri Lanka from November 1997 until April 2001 provides an opportunity to investigate spatial and temporal variation of a variety of atmospheric chemical composition. In summer large enhancement of CH4 was observed in the easterly jet flowing from northern Indian subcontinent between 20°N and 30°N. At the same latitudes, other trace gases (CO, O3, NHMCs, CH3Cl) also show an increase, suggesting the influence of surface air masses driven by deep convection to the chemical composition at high altitude. Seasonal variation of CH4 reveals clear enhancement in summer which is opposite to background observations in the marine boundary layer. This reflects the impact of Indian summer monsoon to the chemical composition of free troposphere. Aided by temporal and spatial variation of other trace gases measured in CARIBIC, we will discuss the source regions of this CH4 plume and estimate the amount of trace gases delivered to the flight altitudes during Indian summer monsoon.

  3. Raindrop size distribution of easterly and westerly monsoon precipitation observed over Palau islands in the Western Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Krishna, U. V. Murali; Reddy, K. Krishna; Seela, Balaji Kumar; Shirooka, Ryuichi; Lin, Pay-Liam; Pan, Chen-Jeih

    2016-06-01

    This paper explores the characteristics of raindrop spectra in terms of raindrop size distribution (RSD) using 4 years of Joss-Waldvogel disdrometer data over Palau islands (7o 20‧ N, 134o 28‧ E) in Western Tropical Pacific ocean. The RSD characteristics are studied in two seasons (easterly monsoon-EM and westerly monsoon-WM) using three (stratiform, deep convection, and shallow convection) rain types identified from collocated 1290-MHz wind profiler radar (WPR). In addition to the ground-based sensors observations, TRMM and MODIS satellite-derived rain parameters and atmospheric parameters are utilized to study RSD characteristics. RSD characteristics stratified on the basis of rainrate show that the mean values of raindrop concentrations of small (medium and larger) drops are same (more) in WM compared to EM season. Normalized gamma distribution of RSD shows that the mean value of mass-weighted mean diameter, Dm (normalized intercept parameter, log10Nw), is higher (lower) in WM than the EM season. In addition, the mean value of Dm (log10Nw) is higher (lower) in deep convective precipitation as compared to the other two types of precipitation (stratiform and shallow convection) in both monsoon periods. In conjunction with the remote sensing data (MODIS & TRMM), RSD shows that the presences of cold clouds which extend to deeper altitudes are responsible for the higher Dm during WM season. The immediate significance of the present work is that (1) it contributes to our understanding of seasonal variations of RSD and distribution of different rain types, and (2) it provides information which is useful for quantitative estimation of rainfall from weather radar observations.

  4. Analytical pyrolysis and stable isotope analyses reveal past environmental changes in coralloid speleothems from Easter Island (Chile).

    PubMed

    Miller, Ana Z; De la Rosa, José M; Jiménez-Morillo, Nicasio T; Pereira, Manuel F C; González-Pérez, José A; Calaforra, José M; Saiz-Jimenez, Cesareo

    2016-08-26

    This study comprises an innovative approach based on the combination of chromatography (analytical pyrolysis and pyrolysis compound-specific isotope analysis (Py-CSIA)), light stable isotopes, microscopy and mineralogy analyses to characterize the internal layering of coralloid speleothems from the Ana Heva lava tube in Easter Island (Chile). This multidisciplinary proxy showed that the speleothems consist of banded siliceous materials of low crystallinity with different mineralogical compositions and a significant contribution of organic carbon. Opal-A constitutes the outermost grey layer of the coralloids, whereas calcite and amorphous Mg hydrate silicate are the major components of the inner whitish and honey-brown layers, respectively. The differences found in the mineralogical, elemental, molecular and isotopic composition of these distinct coloured layers are related to environmental changes during speleothem development. Stable isotopes and analytical pyrolysis suggested alterations in the water regime, pointing to wetter conditions during the formation of the Ca-rich layer and a possible increase in the amount of water dripping into the cave. The trend observed for δ(15)N values suggested an increase in the average temperature over time, which is consistent with the so-called climate warming during the Holocene. The pyrolysis compound-specific isotope analysis of each speleothem layer showed a similar trend with the bulk δ(13)C values pointing to the appropriateness of direct Py-CSIA in paleoenvironmental studies. The δ(13)C values for n-alkanes reinforced the occurrence of a drastic environmental change, indicating that the outermost Opal layer was developed under drier and more arid environmental conditions. PMID:27452992

  5. Directional wave climate and power variability along the Southeast Australian shelf

    NASA Astrophysics Data System (ADS)

    Mortlock, Thomas R.; Goodwin, Ian D.

    2015-04-01

    Variability in the modal wave climate is a key process driving large-scale coastal behaviour on moderate- to high-energy sandy coastlines, and is strongly related to variability in synoptic climate drivers. On sub-tropical coasts, shifts in the sub-tropical ridge (STR) modulate the seasonal occurrence of different wave types. However, in semi-enclosed seas, isolating directional wave climates and synoptic drivers is hindered by a complex mixed sea-swell environment. Here we present a directional wave climate typology for the Tasman Sea based on a combined statistical-synoptic approach using mid-shelf wave buoy observations along the Southeast Australian Shelf (SEAS). Five synoptic-scale wave climates exist during winter, and six during summer. These can be clustered into easterly (Tradewind), south-easterly (Tasman Sea) and southerly (Southern Ocean) wave types, each with distinct wave power signatures. We show that a southerly shift in the STR and trade-wind zone, consistent with an observed poleward expansion of the tropics, forces an increase in the total wave energy flux in winter for the central New South Wales shelf of 1.9 GJ m-1 wave-crest-length for 1° southerly shift in the STR, and a reduction of similar magnitude (approximately 1.8 GJ m-1) during summer. In both seasons there is an anti-clockwise rotation of wave power towards the east and south-east at the expense of southerly waves. Reduced obliquity of constructive wave power would promote a general disruption to northward alongshore sediment transport, with the cross-shore component becoming increasingly prevalent. Results are of global relevance to sub-tropical east coasts where the modal wave climate is influenced by the position of the zonal STR.

  6. Astronomy for African development

    NASA Astrophysics Data System (ADS)

    Govender, Kevindran

    2011-06-01

    In recent years there have been a number of efforts across Africa to develop the field of astronomy as well as to reap benefit from astronomy for African people. This presentation will discuss the case of the SALT (Southern African Large Telescope) Collateral Benefits Programme (SCBP) which was set up to ensure societal benefit from astronomy. With African society as the target, the SCBP has embarked on various projects from school level education to public understanding of science to socio-economic development, the latter mainly being felt in the rural communities surrounding the South African Astronomical Observatory (home to SALT). A development plan for ``Astronomy in Africa'' will also be discussed. This plan has been drawn up with input from all over Africa and themed ``Astronomy for Education''. The Africa case stands as a good example for the IYA cornerstone project ``Developing Astronomy Globally'' which focuses on developing regions.

  7. African American Suicide

    MedlinePlus

    ... accounted for 83.8% of Caucasian elderly suicides. • Firearms were the predominant method of suicide among African ... per 100,000 annually. Source: Centers for Disease Control and Prevention. National Vital Statistics System. Mortality Data. ...

  8. African-Americans and Alzheimer's

    MedlinePlus

    ... Share Plus on Google Plus African-Americans and Alzheimer's alz.org | IHaveAlz Introduction 10 Warning Signs Brain ... African-Americans are at a higher risk for Alzheimer's disease. Many Americans dismiss the warning signs of ...

  9. The Struggles over African Languages

    ERIC Educational Resources Information Center

    Maseko, Pam; Vale, Peter

    2016-01-01

    In this interview, African Language expert Pam Maseko speaks of her own background and her first encounter with culture outside of her mother tongue, isiXhosa. A statistical breakdown of South African languages is provided as background. She discusses Western (originally missionary) codification of African languages and suggests that this approach…

  10. Psychological Misdiagnosis of African Americans.

    ERIC Educational Resources Information Center

    Garretson, Deborah J.

    1993-01-01

    Reviews historical and current problems with making accurate psychological diagnoses of African Americans. Suggests that misdiagnosis is strongly related to pathologization of African-American culture itself. Explores diagnostic process, stereotypes of African-American psychopathology, cultural differences in values and life stressors, and…

  11. Narcolepsy in African Americans

    PubMed Central

    Kawai, Makoto; O'Hara, Ruth; Einen, Mali; Lin, Ling; Mignot, Emmanuel

    2015-01-01

    Study Objectives: Although narcolepsy affects 0.02–0.05% of individuals in various ethnic groups, clinical presentation in different ethnicities has never been fully characterized. Our goal was to study phenotypic expression across ethnicities in the United States. Design/Setting: Cases of narcolepsy from 1992 to 2013 were identified from searches of the Stanford Center for Narcolepsy Research database. International Classification of Sleep Disorders, Third Edition diagnosis criteria for type 1 and type 2 narcolepsy were used for inclusion, but subjects were separated as with and without cataplexy for the purpose of data presentation. Information extracted included demographics, ethnicity and clinical data, HLA-DQB1*06:02, polysomnography (PSG), multiple sleep latency test (MSLT) data, and cerebrospinal fluid (CSF) hypocretin-1 level. Patients: 182 African-Americans, 839 Caucasians, 35 Asians, and 41 Latinos with narcolepsy. Results: Sex ratio, PSG, and MSLT findings did not differ across ethnicities. Epworth Sleepiness Scale (ESS) score was higher and age of onset of sleepiness earlier in African Americans compared with other ethnicities. HLA-DQB1*06:02 positivity was higher in African Americans (91.0%) versus others (76.6% in Caucasians, 80.0% in Asians, and 65.0% in Latinos). CSF hypocretin-1 level, obtained in 222 patients, was more frequently low (≤ 110 pg/ml) in African Americans (93.9%) versus Caucasians (61.5%), Asians (85.7%) and Latinos (75.0%). In subjects with low CSF hypocretin-1, African Americans (28.3%) were 4.5 fold more likely to be without cataplexy when compared with Caucasians (8.1%). Conclusions: Narcolepsy in African Americans is characterized by earlier symptom onset, higher Epworth Sleepiness Scale score, higher HLA-DQB1*06:02 positivity, and low cerebrospinal fluid hypocretin-1 level in the absence of cataplexy. In African Americans, more subjects without cataplexy have type 1 narcolepsy. Citation: Kawai M, O'Hara R, Einen M, Lin L

  12. The Basic Reproduction Number ℛ0 and Effectiveness of Reactive Interventions during Dengue Epidemics: The 2002 Dengue Outbreak in Easter Island, Chile

    PubMed Central

    Chowell, G.; Fuentes, R.; Olea, A.; Aguilera, X.; Nesse, H.; Hyman, J. M.

    2015-01-01

    We use a stochastic simulation model to explore the effect of reactive intervention strategies during the 2002 dengue outbreak in the small population of Easter Island, Chile. We quantified the effect of interventions on the transmission dynamics and epidemic size as a function of the simulated control intensity levels and the timing of initiation of control interventions. Because no dengue outbreaks had been reported prior to 2002 in Easter Island, the 2002 epidemic provided a unique opportunity to estimate the basic reproduction number ℛ0 during the initial epidemic phase, prior to the start of control interventions. We estimated ℛ0 at 27.2 (95%CI: 14.8, 49.3). We found that the final epidemic size is highly sensitive to the timing of start of interventions. However, even when the control interventions start several weeks after the epidemic onset, reactive intervention efforts can have a significant impact on the final epidemic size. Our results indicate that the rapid implementation of control interventions can have a significant effect in reducing the epidemic size of dengue epidemics. PMID:24245625

  13. The Hetu'u Global Network: Using the rare June 5th/6th Transit of Venus to Bring Astronomy to the Remote Easter Island

    NASA Astrophysics Data System (ADS)

    Faherty, Jacqueline; Rodriguez, D.

    2013-01-01

    There are rare times in astronomy when a celestial event, visible in broad daylight, can be used to measure a fundamental parameter and inspire a globe full of school age students. The June 5th/6th transit of Venus was one such event. In celebration, nine astronomy postdocs from the Chilean mainland traveled to Easter Island to lead a series of astronomy outreach activities over three days, culminating in a transit-viewing event. Our team dubbed "Equipo Hetu'u" or "Team Star" in the Rapa Nui (Easter Island native) language spent two days giving astronomy talks and doing hands-on demonstrations at the Museo Antropologico P. Sebastian Englert. In the final day-and-a-half leading up to the transit, we visited the science classes in the majority of the schools on the island, in order to spread the message about the once-in-a-lifetime transit event, highlighting how we planned on using it to measure the distance to the Sun. We estimate over 25% 1500 people) of this remote island participated in one or more of our organized activities. Our experience with this project is an excellent lesson on how to organize, lead, and fully execute a major outreach endeavor that inspires hundreds with minimal resources (save the spectacular event provided by the cosmos).

  14. A New Barrier to Dispersal Trapped Old Genetic Clines That Escaped the Easter Microplate Tension Zone of the Pacific Vent Mussels

    PubMed Central

    Plouviez, Sophie; Faure, Baptiste; Le Guen, Dominique; Lallier, François H.; Bierne, Nicolas; Jollivet, Didier

    2013-01-01

    Comparative phylogeography of deep-sea hydrothermal vent species has uncovered several genetic breaks between populations inhabiting northern and southern latitudes of the East Pacific Rise. However, the geographic width and position of genetic clines are variable among species. In this report, we further characterize the position and strength of barriers to gene flow between populations of the deep-sea vent mussel Bathymodiolus thermophilus. Eight allozyme loci and DNA sequences of four nuclear genes were added to previously published sequences of the cytochrome c oxidase subunit I gene. Our data confirm the presence of two barriers to gene flow, one located at the Easter Microplate (between 21°33′S and 31°S) recently described as a hybrid zone, and the second positioned between 7°25′S and 14°S with each affecting different loci. Coalescence analysis indicates a single vicariant event at the origin of divergence between clades for all nuclear loci, although the clines are now spatially discordant. We thus hypothesize that the Easter Microplate barrier has recently been relaxed after a long period of isolation and that some genetic clines have escaped the barrier and moved northward where they have subsequently been trapped by a reinforcing barrier to gene flow between 7°25′S and 14°S. PMID:24312557

  15. A novel mating system analysis for modes of self-oriented mating applied to diploid and polyploid arctic Easter daisies (Townsendia hookeri).

    PubMed

    Thompson, S L; Ritland, K

    2006-08-01

    We have developed a new model for mating system analysis, which attempts to distinguish among alternative modes of self-oriented mating within populations. This model jointly estimates the rates of outcrossing, selfing, automixis and apomixis, through the use of information in the family structure given by dominant genetic marker data. The method is presented, its statistical properties evaluated, and is applied to three arctic Easter daisy populations, one consisting of diploids, the other two of tetraploids. The tetraploids are predominantly male sterile and reported to be apomictic while the diploids are male fertile. In each Easter daisy population, 10 maternal arrays of six progeny were assayed for amplified fragment length polymorphism markers. Estimates, confirmed with likelihood ratio tests of mating hypotheses, showed apomixis to be predominant in all populations (ca. 70%), but selfing or automixis was moderate (ca. 25%) in tetraploids. It was difficult to distinguish selfing from automixis, and simulations confirm that with even very large sample sizes, the estimates have a very strong negative statistical correlation, for example, they are not independent. No selfing or automixis was apparent in the diploid population, instead, moderate levels of outcrossing were detected (23%). Low but significant levels of outcrossing (2-4%) seemed to occur in the male-sterile tetraploid populations; this may be due to genotyping error of this level. Overall, this study shows apomixis can be partial, and provides evidence for higher levels of inbreeding in polyploids compared to diploids and for significant levels of apomixis in a diploid plant population. PMID:16721390

  16. Antibiotic resistance patterns in fecal bacteria isolated from Christmas shearwater (Puffinus nativitatis) and masked booby (Sula dactylatra) at remote Easter Island.

    PubMed

    Ardiles-Villegas, Karen; González-Acuña, Daniel; Waldenström, Jonas; Olsen, Björn; Hernández, Jorge

    2011-09-01

    Antibiotic use and its implications have been discussed extensively in the past decades. This situation has global consequences when antibiotic resistance becomes widespread in the intestinal bacterial flora of stationary and migratory birds. This study investigated the incidence of fecal bacteria and general antibiotic resistance, with special focus on extended spectrum beta-lactamase (ESBL) isolates, in two species of seabirds at remote Easter Island. We identified 11 species of bacteria from masked booby (Sula dactylatra) and Christmas shearwater (Puffinus nativitatis); five species of gram-negative bacilli, four species of Streptococcus (Enterococcus), and 2 species of Staphylococcus. In addition, 6 types of bacteria were determined barely to the genus level. General antibiotic susceptibility was measured in the 30 isolated Enterobacteriaceae to 11 antibiotics used in human and veterinary medicine. The 10 isolates that showed a phenotypic ESBL profile were verified by clavulanic acid inhibition in double mixture discs with cefpodoxime, and two ESBL strains were found, one strain in masked booby and one strain in Christmas shearwater. The two bacteria harboring the ESBL type were identified as Serratia odorifera biotype 1, which has zoonotic importance. Despite minimal human presence in the masked booby and Christmas shearwater habitats, and the extreme geographic isolation of Easter Island, we found several multiresistant bacteria and even two isolates with ESBL phenotypes. The finding of ESBLs has animal and public health significance and is of potential concern, especially because the investigation was limited in size and indicated that antibiotic-resistant bacteria now are distributed globally. PMID:22017052

  17. The Genetic Structure and History of Africans and African Americans

    PubMed Central

    Tishkoff, Sarah A.; Reed, Floyd A.; Friedlaender, Françoise R.; Ehret, Christopher; Ranciaro, Alessia; Froment, Alain; Hirbo, Jibril B.; Awomoyi, Agnes A.; Bodo, Jean-Marie; Doumbo, Ogobara; Ibrahim, Muntaser; Juma, Abdalla T.; Kotze, Maritha J.; Lema, Godfrey; Moore, Jason H.; Mortensen, Holly; Nyambo, Thomas B.; Omar, Sabah A.; Powell, Kweli; Pretorius, Gideon S.; Smith, Michael W.; Thera, Mahamadou A.; Wambebe, Charles; Weber, James L.; Williams, Scott M.

    2010-01-01

    Africa is the source of all modern humans, but characterization of genetic variation and of relationships among populations across the continent has been enigmatic. We studied 121 African populations, four African American populations, and 60 non-African populations for patterns of variation at 1327 nuclear microsatellite and insertion/deletion markers. We identified 14 ancestral population clusters in Africa that correlate with self-described ethnicity and shared cultural and/or linguistic properties. We observed high levels of mixed ancestry in most populations, reflecting historical migration events across the continent. Our data also provide evidence for shared ancestry among geographically diverse hunter-gatherer populations (Khoesan speakers and Pygmies). The ancestry of African Americans is predominantly from Niger-Kordofanian (~71%), European (~13%), and other African (~8%) populations, although admixture levels varied considerably among individuals. This study helps tease apart the complex evolutionary history of Africans and African Americans, aiding both anthropological and genetic epidemiologic studies. PMID:19407144

  18. Internal inertia-gravity waves in the tropical lower stratosphere observed by the Arecibo radar

    NASA Technical Reports Server (NTRS)

    Maekawa, Y.; Kato, S.; Fukao, S.; Sato, T.; Woodman, R. F.

    1984-01-01

    A quasi-periodic wind oscillation with an apparent 20-50 hour period was observed at between 16 and 20 km in every experiment conducted during three periods from 1979 to 1981 with the Arecibo UHF radar. The wave disappeared near 20 km, where the mean zonal flow had easterly shear with height. This phenomenon is discussed in terms of wave absorption at a critical level, and it is suggested that the wave had a westward horizontal phase speed of 10-20 m/sec. On the basis of a relationship from f-plane theory in which the Doppler-shifted wave frequency approaches the Coriolis frequency at the critical level, an intrinsic period and horizontal wavelength at the wave-generated height of 20-30 hours and about 2000 km, respectively, are inferred.

  19. The Other African Americans.

    ERIC Educational Resources Information Center

    Matory, J. Lorand

    Black North America is ethnically and culturally diverse. It contains many groups who do not call themselves or have not always called themselves "Negro,""Black,""African-American," and so forth, such as Louisiana Creoles of color and many of the Indian tribes east of the Mississippi. There are also numerous North American ethnic groups of African…

  20. African American rhinoplasty.

    PubMed

    Boyette, Jennings R; Stucker, Fred J

    2014-08-01

    Rhinoplasty in patients of African descent requires a patient-specific approach, because the goals and ideal proportions differ from the white nose. This article discusses approaches to surgical correction of common anatomic variations. In addition, common pitfalls are outlined. PMID:25049123

  1. Elective: African Literature.

    ERIC Educational Resources Information Center

    Jenkins, Kenneth V.

    The make-up of a course in African literature for high school students is discussed. It is pointed out that the course can be constructed on already familiar lines. High school students will be able to describe clearly, for example, the relationship between environment and character or the dilemma of characters caught between traditional values…

  2. African Ancestry Is Associated with Asthma Risk in African Americans

    PubMed Central

    Pino-Yanes, María; Wade, Michael S.; Pérez-Méndez, Lina; Kittles, Rick A.; Wang, Deli; Papaiahgari, Srinivas; Ford, Jean G.; Kumar, Rajesh; Garcia, Joe G. N.

    2012-01-01

    Background Asthma is a common complex condition with clear racial and ethnic differences in both prevalence and severity. Asthma consultation rates, mortality, and severe symptoms are greatly increased in African descent populations of developed countries. African ancestry has been associated with asthma, total serum IgE and lower pulmonary function in African-admixed populations. To replicate previous findings, here we aimed to examine whether African ancestry was associated with asthma susceptibility in African Americans. In addition, we examined for the first time whether African ancestry was associated with asthma exacerbations. Methodology/Principal Findings After filtering for self-reported ancestry and genotype data quality, samples from 1,117 self-reported African-American individuals from New York and Baltimore (394 cases, 481 controls), and Chicago (321 cases followed for asthma exacerbations) were analyzed. Genetic ancestry was estimated based on ancestry informative markers (AIMs) selected for being highly divergent among European and West African populations (95 AIMs for New York and Baltimore, and 66 independent AIMs for Chicago). Among case-control samples, the mean African ancestry was significantly higher in asthmatics than in non-asthmatics (82.0±14.0% vs. 77.8±18.1%, mean difference 4.2% [95% confidence interval (CI):2.0–6.4], p<0.0001). This association remained significant after adjusting for potential confounders (odds ratio: 4.55, 95% CI: 1.69–12.29, p = 0.003). African ancestry failed to show an association with asthma exacerbations (p = 0.965) using a model based on longitudinal data of the number of exacerbations followed over 1.5 years. Conclusions/Significance These data replicate previous findings indicating that African ancestry constitutes a risk factor for asthma and suggest that elevated asthma rates in African Americans can be partially attributed to African genetic ancestry. PMID:22235241

  3. Africans in the American Labor Market.

    PubMed

    Elo, Irma T; Frankenberg, Elizabeth; Gansey, Romeo; Thomas, Duncan

    2015-10-01

    The number of migrants to the United States from Africa has grown exponentially since the 1930s. For the first time in America's history, migrants born in Africa are growing at a faster rate than migrants from any other continent. The composition of African-origin migrants has also changed dramatically: in the mid-twentieth century, the majority were white and came from only three countries; but today, about one-fifth are white, and African-origin migrants hail from across the entire continent. Little is known about the implications of these changes for their labor market outcomes in the United States. Using the 2000-2011 waves of the American Community Survey, we present a picture of enormous heterogeneity in labor market participation, sectoral choice, and hourly earnings of male and female migrants by country of birth, race, age at arrival in the United States, and human capital. For example, controlling a rich set of human capital and demographic characteristics, some migrants-such as those from South Africa/Zimbabwe and Cape Verde, who typically enter on employment visas-earn substantial premiums relative to other African-origin migrants. These premiums are especially large among males who arrived after age 18. In contrast, other migrants-such as those from Sudan/Somalia, who arrived more recently, mostly as refugees-earn substantially less than migrants from other African countries. Understanding the mechanisms generating the heterogeneity in these outcomes-including levels of socioeconomic development, language, culture, and quality of education in countries of origin, as well as selectivity of those who migrate-figures prominently among important unresolved research questions. PMID:26304845

  4. Coarse, Intermediate and High Resolution Numerical Simulations of the Transition of a Tropical Wave Critical Layer to a Tropical Storm

    NASA Technical Reports Server (NTRS)

    Montgomery, M. T.; Dunkerton, T. J.; Wang, Z.

    2010-01-01

    Recent work has hypothesized that tropical cyclones in the deep Atlantic and eastern Pacific basins develop from within the cyclonic Kelvin cat's eye of a tropical easterly wave critical layer located equatorward of the easterly jet axis. The cyclonic critical layer is thought to be important to tropical cyclogenesis because its cat's eye provides (i) a region of cyclonic vorticity and weak deformation by the resolved flow, (ii) containment of moisture entrained by the developing flow and/or lofted by deep convection therein, (iii) confinement of mesoscale vortex aggregation, (iv) a predominantly convective type of heating profile, and (v) maintenance or enhancement of the parent wave until the developing proto-vortex becomes a self-sustaining entity and emerges from the wave as a tropical depression. This genesis sequence and the overarching framework for describing how such hybrid wave-vortex structures become tropical depressions/storms is likened to the development of a marsupial infant in its mother's pouch, and for this reason has been dubbed the "marsupial paradigm". Here we conduct the first multi-scale test of the marsupial paradigm in an idealized setting by revisiting the Kurihara and Tuleya problem examining the transformation of an easterly wave-like disturbance into a tropical storm vortex using the WRF model. An analysis of the evolving winds, equivalent potential temperature, and relative vertical vorticity is presented from coarse (28 km), intermediate (9 km) and high resolution (3.1 km) simulations. The results are found to support key elements of the marsupial paradigm by demonstrating the existence of rotationally dominant region with minimal strain/shear deformation near the center of the critical layer pouch that contains strong cyclonic vorticity and high saturation fraction. This localized region within the pouch serves as the "attractor" for an upscale "bottom up" development process while the wave pouch and proto-vortex move together.

  5. Uncertainties from above and below: West African monsoon patterns generated by a WRF multi-physics ensemble

    NASA Astrophysics Data System (ADS)

    Klein, Cornelia; Heinzeller, Dominikus; Bliefernicht, Jan; Kunstmann, Harald

    2015-04-01

    The credibility of regional climate simulations over West Africa stands and falls with the ability to reproduce the West African Monsoon (WAM) whose precipitation plays a pivotal role for people's livelihood. In this study, the ability of a 27-member mixed-physics ensemble of the Weather Research and Forecasting model to represent the WAM is investigated in a process-based manner in order to extract transferable information on parameterization influences. The uncertainties introduced by three cumulus (CU), microphysics (MP) and planetary boundary layer (PBL) parameterizations are analyzed to explore interdependencies of processes leading to a certain WAM regime during the wet year 1999. We identify the modification of the moist Hadley-type meridional circulation that connects the monsoon winds to the Tropical Easterly Jet as the main source for inter-member differences. It is predominantly altered by the PBL schemes because of their impact on the cloud fraction, that ranges from 8 to 20 % at 600 hPa during August. More low- and mid-level clouds result in less incoming radiation, weaker precipitation and a southward displaced African Easterly Jet and monsoon rainband. This identifies the representation of clouds as a critical "uncertainty from above" in simulating the WAM. The partitioning of sensible and latent heat fluxes is found to be another major source for the ensemble spread inducing "uncertainties from below" for the modeled monsoon regime. Finally, we show that regionally adapted simulations at convection-allowing scales with ingested dynamical land surface parameters improve the representation of convection, net radiation and surface flux partitioning.

  6. Understanding traditional African healing

    PubMed Central

    MOKGOBI, M.G.

    2015-01-01

    Traditional African healing has been in existence for many centuries yet many people still seem not to understand how it relates to God and religion/spirituality. Some people seem to believe that traditional healers worship the ancestors and not God. It is therefore the aim of this paper to clarify this relationship by discussing a chain of communication between the worshipers and the Almighty God. Other aspects of traditional healing namely types of traditional healers, training of traditional healers as well as the role of traditional healers in their communities are discussed. In conclusion, the services of traditional healers go far beyond the uses of herbs for physical illnesses. Traditional healers serve many roles which include but not limited to custodians of the traditional African religion and customs, educators about culture, counselors, social workers and psychologists. PMID:26594664

  7. North African vegetation-precipitation feedback in early and mid-Holocene climate simulations with CCSM3-DGVM

    NASA Astrophysics Data System (ADS)

    Rachmayani, R.; Prange, M.; Schulz, M.

    2015-02-01

    The present study analyses the sign, strength, and working mechanism of the vegetation-precipitation feedback over North Africa in middle (6 ka BP) and early Holocene (9 ka BP) simulations using the comprehensive coupled climate-vegetation model CCSM3-DGVM (Community Climate System Model version 3 and a dynamic global vegetation model). The coupled model simulates enhanced summer rainfall and a northward migration of the West African monsoon trough along with an expansion of the vegetation cover for the early and middle Holocene compared to the pre-industrial period. It is shown that dynamic vegetation enhances the orbitally triggered summer precipitation anomaly by approximately 20% in the Sahara-Sahel region (10-25° N, 20° W-30° E) in both the early and mid-Holocene experiments compared to their fixed-vegetation counterparts. The primary vegetation-rainfall feedback identified here operates through surface latent heat flux anomalies by canopy evaporation and transpiration and their effect on the mid-tropospheric African easterly jet, whereas the effects of vegetation changes on surface albedo and local water recycling play a negligible role. Even though CCSM3-DGVM simulates a positive vegetation-precipitation feedback in the North African region, this feedback is not strong enough to produce multiple equilibrium climate-ecosystem states on a regional scale.

  8. North African vegetation-precipitation feedback in early and mid-Holocene climate simulations with CCSM3-DGVM

    NASA Astrophysics Data System (ADS)

    Rachmayani, R.; Prange, M.; Schulz, M.

    2014-05-01

    The present study analyses the sign, strength and working mechanism of the vegetation-precipitation feedback over North Africa in middle (6 ka BP) and early Holocene (9 ka BP) simulations using the comprehensive coupled climate-vegetation model CCSM3-DGVM. The coupled model simulates enhanced summer rainfall and a northward migration of the West African monsoon trough along with an expansion of the vegetation cover for the early and middle Holocene compared to pre-industrial. It is shown that dynamic vegetation enhances the orbitally triggered summer precipitation anomaly by approximately 20% in the Sahara/Sahel region (10° N-25° N, 20° W-30° E) in both the early and mid-Holocene experiments compared to their fixed-vegetation counterparts. The primary vegetation-rainfall feedback identified here operates through surface latent heat flux anomalies by canopy evaporation and transpiration and their effect on the mid-tropospheric African Easterly Jet, whereas the effects of vegetation changes on surface albedo and local water recycling play a negligible role. Even though CCSM3-DGVM simulates a positive vegetation-precipitation feedback in the North African region, this feedback is not strong enough to produce multiple equilibrium climate-ecosystem states on a regional scale.

  9. African horse sickness.

    PubMed

    Zientara, S; Weyer, C T; Lecollinet, S

    2015-08-01

    African horse sickness (AHS) is a devastating disease of equids caused by an arthropod-borne virus belonging to the Reoviridae family, genus Orbivirus. It is considered a major health threat for horses in endemic areas in sub-Saharan Africa. African horse sickness virus (AHSV) repeatedly caused large epizootics in the Mediterranean region (North Africa and southern Europe in particular) as a result of trade in infected equids. The unexpected emergence of a closely related virus, the bluetongue virus, in northern Europe in 2006 has raised fears about AHSV introduction into Europe, and more specifically into AHSV-free regions that have reported the presence of AHSV vectors, e.g. Culicoides midges. North African and European countries should be prepared to face AHSV incursions in the future, especially since two AHSV serotypes (serotypes 2 and 7) have recently spread northwards to western (e.g. Senegal, Nigeria, Gambia) and eastern Africa (Ethiopia), where historically only serotype 9 had been isolated. The authors review key elements of AHS epidemiology, surveillance and prophylaxis. PMID:26601437

  10. Millennial-scale precipitation variability over Easter Island (South Pacific) during MIS 3: inter-hemispheric teleconnections with North Atlantic abrupt cold events

    NASA Astrophysics Data System (ADS)

    Margalef, O.; Cacho, I.; Pla-Rabes, S.; Cañellas-Boltà, N.; Pueyo, J. J.; Sáez, A.; Pena, L. D.; Valero-Garcés, B. L.; Rull, V.; Giralt, S.

    2015-04-01

    Marine Isotope Stage 3 (MIS 3, 59.4-27.8 kyr BP) is characterized by the occurrence of rapid millennial-scale climate oscillations known as Dansgaard-Oeschger cycles (DO) and by abrupt cooling events in the North Atlantic known as Heinrich events. Although both the timing and dynamics of these events have been broadly explored in North Atlantic records, the response of the tropical and subtropical latitudes to these rapid climatic excursions, particularly in the Southern Hemisphere, still remains unclear. The Rano Aroi peat record (Easter Island, 27° S) provides a unique opportunity to understand atmospheric and oceanic changes in the South Pacific during these DO cycles because of its singular location, which is influenced by the South Pacific Anticyclone (SPA), the Southern Westerlies (SW), and the Intertropical Convergence Zone (ITCZ) linked to the South Pacific Convergence Zone (SPCZ). The Rano Aroi sequence records 6 major events of enhanced precipitation between 38 and 65 kyr BP. These events are compared with other hydrological records from the tropical and subtropical band supporting a coherent regional picture, with the dominance of humid conditions in Southern Hemisphere tropical band during Heinrich Stadials (HS) 5, 5a and 6 and other Stadials while dry conditions prevailed in the Northern tropics. This antiphased hydrological pattern between hemispheres has been attributed to ITCZ migration, which in turn might be associated with an eastward expansion of the SPCZ storm track, leading to an increased intensity of cyclogenic storms reaching Easter Island. Low Pacific Sea Surface Temperature (SST) gradients across the Equator were coincident with the here-defined Rano Aroi humid events and consistent with a reorganization of Southern Pacific atmospheric and oceanic circulation also at higher latitudes during Heinrich and Dansgaard-Oeschger stadials.

  11. East African Rift Valley, Kenya

    NASA Technical Reports Server (NTRS)

    1990-01-01

    This rare, cloud free view of the East African Rift Valley, Kenya (1.5N, 35.5E) shows a clear view of the Turkwell River Valley, an offshoot of the African REift System. The East African Rift is part of a vast plate fracture which extends from southern Turkey, through the Red Sea, East Africa and into Mozambique. Dark green patches of forests are seen along the rift margin and tea plantations occupy the cooler higher ground.

  12. A Teacher's Guide to African Narratives. Studies in African Literature.

    ERIC Educational Resources Information Center

    O'Brien, Sara Talis

    This guide is designed to help secondary school teachers include African literature in their classes. It furnishes English and social studies teachers with a foundation for teaching African literature by offering critical commentary on the texts themselves. A synthesis of anthropological and historical material is presented to help both teachers…

  13. Upper Tropospheric Waves in the Tropics. Part I: Dynamical Analysis in the Wavenumber-Frequency Domain.

    NASA Astrophysics Data System (ADS)

    Zangvil, Abraham; Yanai, Michio

    1980-02-01

    Space and time spectra of large-scale wave disturbances at the 200 mb level in the latitude belt 20°S to 40°N are studied based on wind data for the period June-August 1967. The kinetic energy of the transient waves shows a minimum near 10°N where convective activity attains a maximum. The transient eddies in the zonal wind component have dominant scales of zonal wavenumbers s = 3-6 in most latitudes, while those in the meridional wind component have dominant scales of s = 6-8.By decomposing the wind data into symmetric and antisymmetric components with respect to the equator, three prototype equatorial wave modes are detected: 1) Kelvin waves of zonal wavenumber s = 1 and 2 and a period of 7 days, and s = 1 and periods longer than 20 days; 2) mixed Rossby-gravity waves of s = 4 and a period of 5 days; and 3) Rossby waves (of the lowest meridional nodal number) of s = 2 and a period near 12 days. Westward moving short waves (s = 7-15) gain kinetic energy from the mean easterly flow. Eastward moving waves in the middle latitudes do not propagate into the tropics because of the absorption at critical latitudes. Westward moving long waves of s 4 and periods near 5 days accompany a distinct peak in the equatorward wave energy flux, suggesting the origin of the observed mixed Rossby-gravity waves.

  14. African-American Sacred Music.

    ERIC Educational Resources Information Center

    Bailey, A. Peter

    1991-01-01

    The history of African-American sacred music is traced from the time of slavery to the present interest in gospel music. The religious music of African Americans is geared toward liberation themes. It is important that this music does not dilute its power through cross-over with other music forms. (SLD)

  15. Wave turbulence

    NASA Astrophysics Data System (ADS)

    Nazarenko, Sergey

    2015-07-01

    Wave turbulence is the statistical mechanics of random waves with a broadband spectrum interacting via non-linearity. To understand its difference from non-random well-tuned coherent waves, one could compare the sound of thunder to a piece of classical music. Wave turbulence is surprisingly common and important in a great variety of physical settings, starting with the most familiar ocean waves to waves at quantum scales or to much longer waves in astrophysics. We will provide a basic overview of the wave turbulence ideas, approaches and main results emphasising the physics of the phenomena and using qualitative descriptions avoiding, whenever possible, involved mathematical derivations. In particular, dimensional analysis will be used for obtaining the key scaling solutions in wave turbulence - Kolmogorov-Zakharov (KZ) spectra.

  16. KZai 02 pollen record, an insight into West African monsoon fluctuations during the Last Climatic Cycle

    NASA Astrophysics Data System (ADS)

    Dalibard, M.; Popescu, S.; Maley, J.; Suc, J.

    2012-12-01

    Climate of the circum-Atlantic intertropical zone is driven by the ocean/atmosphere dynamics in response to variations of yearly insolation. These latitudes correspond to the convergence of the Hadley cells expressed on earth surface by intense trade winds and in lower troposphere by the African easterly jet making the edges of the intertropical zone relatively dry, while humidity is concentrated near the Equator. This phenomenon generates a precipitation front, known as the InterTropical Convergence Zone (ITCZ), the oscillations of which regulate the latitudinal vegetation distribution. Pollen record of core KZai 02 (Guinea Gulf) allows high resolution reconstruction of variations of past ecosystems over Central Africa during the Last Climatic Cycle. Plant taxa recorded in pollen analyses have been clustered according to their ecological requirements and African phytogeography. Fluctuations of these groups inform on precipitation intensity and their distribution during the last 130 ka. During Glacials, an open vegetation made of Cyperaceae marshes developed in the central Zaire/Congo Basin, surrounded by savannah on borders and afromontane forests on reliefs. Composition and distribution of vegetation indicate a decrease in monsoon activity and the strengthening of the precipitation front in the center of the basin. Interglacial phases are characterized by rain forest expansion over Central Africa in response to a precipitation enhancement associated with a northward shift of the rainfall front. Replacement of afromontane forest and marsh ecosystems by savannah then lowland pioneering, warm-temperate and rain forests characterized glacial/interglacial transitions. This succession suggests the increasing influence of at least two climatic parameters: the water availability and temperature and/or CO2 fluctuation. Spectral analysis applied to vegetation groups evidences the forcing of insolation, mainly driven by precession, on the West African monsoon system. Sub

  17. African oil plays

    SciTech Connect

    Clifford, A.J. )

    1989-09-01

    The vast continent of Africa hosts over eight sedimentary basins, covering approximately half its total area. Of these basins, only 82% have entered a mature exploration phase, 9% have had little or no exploration at all. Since oil was first discovered in Africa during the mid-1950s, old play concepts continue to bear fruit, for example in Egypt and Nigeria, while new play concepts promise to become more important, such as in Algeria, Angola, Chad, Egypt, Gabon, and Sudan. The most exciting developments of recent years in African oil exploration are: (1) the Gamba/Dentale play, onshore Gabon; (2) the Pinda play, offshore Angola; (3) the Lucula/Toca play, offshore Cabinda; (4) the Metlaoui play, offshore Libya/Tunisia; (5) the mid-Cretaceous sand play, Chad/Sudan; and (6) the TAG-I/F6 play, onshore Algeria. Examples of these plays are illustrated along with some of the more traditional oil plays. Where are the future oil plays likely to develop No doubt, the Saharan basins of Algeria and Libya will feature strongly, also the presalt of Equatorial West Africa, the Central African Rift System and, more speculatively, offshore Ethiopia and Namibia, and onshore Madagascar, Mozambique, and Tanzania.

  18. Bioenergy and African transformation.

    PubMed

    Lynd, Lee R; Sow, Mariam; Chimphango, Annie Fa; Cortez, Luis Ab; Brito Cruz, Carlos H; Elmissiry, Mosad; Laser, Mark; Mayaki, Ibrahim A; Moraes, Marcia Afd; Nogueira, Luiz Ah; Wolfaardt, Gideon M; Woods, Jeremy; van Zyl, Willem H

    2015-01-01

    Among the world's continents, Africa has the highest incidence of food insecurity and poverty and the highest rates of population growth. Yet Africa also has the most arable land, the lowest crop yields, and by far the most plentiful land resources relative to energy demand. It is thus of interest to examine the potential of expanded modern bioenergy production in Africa. Here we consider bioenergy as an enabler for development, and provide an overview of modern bioenergy technologies with a comment on application in an Africa context. Experience with bioenergy in Africa offers evidence of social benefits and also some important lessons. In Brazil, social development, agricultural development and food security, and bioenergy development have been synergistic rather than antagonistic. Realizing similar success in African countries will require clear vision, good governance, and adaptation of technologies, knowledge, and business models to myriad local circumstances. Strategies for integrated production of food crops, livestock, and bioenergy are potentially attractive and offer an alternative to an agricultural model featuring specialized land use. If done thoughtfully, there is considerable evidence that food security and economic development in Africa can be addressed more effectively with modern bioenergy than without it. Modern bioenergy can be an agent of African transformation, with potential social benefits accruing to multiple sectors and extending well beyond energy supply per se. Potential negative impacts also cut across sectors. Thus, institutionally inclusive multi-sector legislative structures will be more effective at maximizing the social benefits of bioenergy compared to institutionally exclusive, single-sector structures. PMID:25709714

  19. Millennial scale precipitation changes over Easter Island (Southern Pacific) during MIS 3: Inter-hemispheric connections during North Atlantic abrupt cold events

    NASA Astrophysics Data System (ADS)

    Margalef, Olga; Cacho, Isabel; Pla-Rabes, Sergi; Cañellas-Boltà, Núria; Pueyo, Juan Jose; Sáez, Alberto; Valero-Garcés, Blas L.; Giralt, Santiago

    2013-04-01

    Marine Isotope Stage (MIS) 3 climate has been globally characterized by the occurrence of millennial-scale climate variations defined over North Atlantic as Dansgaard-Oeschger and Heinrich events. Despite climate variability has been broadly explored over North Atlantic records, the response of the tropical and subtropical latitudes, especially in the Southern Hemisphere, still remains as a matter of debate. Rano Aroi peat record (Easter Island, Chile, 27°S) provides a unique opportunity to understand Southern Pacific atmospheric and oceanic changes during these stadial-interstadial transitions because of its exceptional location on the interplay of the South Pacific Convergence Zone (SPCZ), the Intertropical Convergence Zone (ITCZ), the South Pacific Anticyclone (SPA) and the Southern Westerlies (SW). Rano Aroi record contains 8 main enhanced precipitation events between 70 and 40 kyr BP that can be correlated with the timing of Heinrich events 5, 5a and 6 as well as other cold stadials. These humid events are also present in other Southern Hemisphere continental sites and correspond to dry periods on Northern Hemisphere records. This opposite hydrologic trend has been explained by the latitudinal migration of ITCZ and has been supported by several climatic models. As Easter Island precipitation is mainly dependent on SPCZ storm track belt activity, we suggest that the southern migration of the ITCZ is associated to an expansion of SPCZ to the east. This process should be intimately related to a weakening of the Walker circulation, which is further supported by an estimation of d18Osw gradient along the equator for the same time period. Consequently, atmospheric and oceanic responses during these cold stadials and Heinrich events might lead to a configuration that resembles the warm ENSO state over Southern Pacific, as previously suggested by some global climatic models. Rano Aroi record clearly points out that shifts in hydrological cycle in tropical Southern

  20. Assimilation Differences among Africans in America.

    ERIC Educational Resources Information Center

    Dodoo, F. Nii-Amoo

    1997-01-01

    Census data (1990) indicate that male African immigrants earn more than their Caribbean-born counterparts or native-born African Americans, but controlling for relevant earnings-related endowments erases the African advantage and elevates Caribbean earnings above those of the other groups. Also, African (but not Caribbean) university degree…

  1. Successfully Educating Our African-American Students

    ERIC Educational Resources Information Center

    Moncree-Moffett, Kareem

    2013-01-01

    The purpose of this empirical study was to explore the lived experiences of African American retired female teachers who have prior experience with educating urban African American students in public schools. Also explored are the experiences of active African American female teachers of urban African American students and comparisons are…

  2. Chronotype of South African adults is affected by solar entrainment.

    PubMed

    Shawa, Nyambura; Roden, Laura Catherine

    2016-01-01

    Our daily lives are influenced by three different daily timers: the solar clock, our endogenous circadian clock and the societal clock. The way an individual's endogenous clock synchronises to the solar clock, through either advances or delays relative to sunrise and sunset, results in a phenomenon known as diurnal preference or chronotype. South Africa uses just one time zone, but in the most easterly regions of the country, the sun rises and sets up to an hour earlier than in the most westerly regions throughout the year. It was hypothesised first that South Africans living in the east of the country may have a greater preference for mornings (more morning chronotypes) than those living in the west; and second, that this difference would not be due to genetic differences in the populations, particularly a genetic polymorphism previously shown to influence chronotype. Here, we describe and compare the distribution of chorotype and PERIOD3 variable number tandem repeat (VNTR) polymorphism frequency in eastern (n = 129) and western (n = 175) sample populations. Using the Horne-Östberg Morningness, Eveningness Questionnaire we found that there was a significantly higher proportion of morning-types in the eastern population (56.6%) than in the western population (39.4%), and there were higher proportions of neither-types and evening-types in the western population (51.4% and 9.1%, respectively) than in the eastern population (37.2% and 6.2%, respectively) (p = 0.009). There were no significant differences in distribution of the PER3 genotype (p = 0.895) and allele (p = 0.636) frequencies. Although previous studies have shown associations between chronotype and PER3 VNTR genotypes, no significant associations were observed in either the eastern (p = 0.695) or the western (p = 0.630) populations. These findings indicate that, in South African populations, longitude influences chronotype independently of PER3 genotype. The impacts of the differences in chronotype whilst

  3. West African Monsoon dynamics in idealized simulations: the competitive roles of SST warming and CO2

    NASA Astrophysics Data System (ADS)

    Gaetani, Marco; Flamant, Cyrille; Hourdin, Frederic; Bastin, Sophie; Braconnot, Pascale; Bony, Sandrine

    2015-04-01

    The West African Monsoon (WAM) is affected by large climate variability at different timescales, from interannual to multidecadal, with strong environmental and socio-economic impacts associated to climate-related rainfall variability, especially in the Sahelian belt. State-of-the-art coupled climate models still show poor ability in correctly simulating the WAM past variability and also a large spread is observed in future climate projections. In this work, the July-to-September (JAS) WAM variability in the period 1979-2008 is studied in AMIP-like simulations (SST-forced) from CMIP5. The individual roles of global SST warming and CO2 concentration increasing are investigated through idealized experiments simulating a 4K warmer SST and a 4x CO2 concentration, respectively. Results show a dry response in Sahel to SST warming, with dryer conditions over western Sahel. On the contrary, wet conditions are observed when CO2 is increased, with the strongest response over central-eastern Sahel. The precipitation changes are associated to modifications in the regional atmospheric circulation: dry (wet) conditions are associated with reduced (increased) convergence in the lower troposphere, a southward (northward) shift of the African Easterly Jet, and a weaker (stronger) Tropical Easterly Jet. The co-variability between global SST and WAM precipitation is also investigated, highlighting a reorganization of the main co-variability modes. Namely, in the 4xCO2 simulation the influence of Tropical Pacific is dominant, while it is reduced in the 4K simulation, which also shows an increased coupling with the eastern Pacific and the Indian Ocean. The above results suggest a competitive action of SST warming and CO2 increasing on the WAM climate variability, with opposite effects on precipitation. The combination of the observed positive and negative response in precipitation, with wet conditions in central-eastern Sahel and dry conditions in western Sahel, is consistent with the

  4. Heat Waves

    MedlinePlus

    Heat Waves Dangers we face during periods of very high temperatures include: Heat cramps: These are muscular pains and spasms due ... that the body is having trouble with the heat. If a heat wave is predicted or happening… - ...

  5. Negro, Black, Black African, African Caribbean, African American or what? Labelling African origin populations in the health arena in the 21st century.

    PubMed

    Agyemang, Charles; Bhopal, Raj; Bruijnzeels, Marc

    2005-12-01

    Broad terms such as Black, African, or Black African are entrenched in scientific writings although there is considerable diversity within African descent populations and such terms may be both offensive and inaccurate. This paper outlines the heterogeneity within African populations, and discusses the strengths and limitations of the term Black and related labels from epidemiological and public health perspectives in Europe and the USA. This paper calls for debate on appropriate terminologies for African descent populations and concludes with the proposals that (1) describing the population under consideration is of paramount importance (2) the word African origin or simply African is an appropriate and necessary prefix for an ethnic label, for example, African Caribbean or African Kenyan or African Surinamese (3) documents should define the ethnic labels (4) the label Black should be phased out except when used in political contexts. PMID:16286485

  6. Gravity Waves

    Atmospheric Science Data Center

    2013-04-19

    article title:  Gravity Waves Ripple over Marine Stratocumulus Clouds ... Imaging SpectroRadiometer (MISR), a fingerprint-like gravity wave feature occurs over a deck of marine stratocumulus clouds. Similar ... that occur when a pebble is thrown into a still pond, such "gravity waves" sometimes appear when the relatively stable and stratified air ...

  7. Overly persistent circulation in climate models contributes to overestimated frequency and duration of heat waves and cold spells

    NASA Astrophysics Data System (ADS)

    Plavcová, Eva; Kyselý, Jan

    2016-05-01

    The study examines links of summer heat waves and winter cold spells in Central Europe to atmospheric circulation and specifically its persistence in an ensemble of regional climate models (RCMs). We analyse 13 RCMs driven by the ERA-40 reanalysis and compare them against observations over reference period 1971-2000. Using objective classification of circulation types and an efficiency coefficient with a block resampling test, we identify circulation types significantly conducive to heat waves and cold spells. We show that the RCMs have a stronger tendency to group together days with very high or low temperature and tend to simulate too many heat waves and cold spells, especially those lasting 5 days and more. Circulation types conducive to heat waves in summer are characterized by anticyclonic, southerly and easterly flow, with increasing importance of warm advection during heat waves. Winter cold spells are typically associated with easterly and anticyclonic flow, and the onset of cold spells tends to be linked to northerly and cyclonic flow with cold advection. The RCMs are generally able to reproduce the links between circulation and heat waves or cold spells, including the radiation-to-advection effect for heat waves and the opposite advection-to-radiation effect for cold spells. They capture relatively well also changes of mean temperature anomalies during sequences of given circulation types, namely the tendency towards temperature increase (decrease) during those types conducive to heat waves (cold spells). Since mean lengths of all circulation supertypes are overestimated in the RCMs, we conclude that the overly persistent circulation in climate models contributes to the overestimated frequency of long heat waves and cold spells. As these biases are rather general among the examined RCMs and similar drawbacks are likely to be manifested in climate model simulations for the twenty-first century, the results also suggest that climate change scenarios for

  8. African swine fever.

    PubMed

    Penrith, Mary-Louise

    2009-03-01

    African swine fever (ASF) is a devastating haemorrhagic fever of pigs that causes up to 100% mortality, for which there is no vaccine. It is caused by a unique DNA virus that is maintained in an ancient cycle between warthogs and argasid ticks, making it the only known DNA arbovirus. ASF has a high potential for transboundary spread, and has twice been transported from Africa to other continents--Europe and subsequently the Caribbean and Brazil (1957, 1959) and the Caucasus (2007). It is also a devastating constraint for pig production in Africa. Research at Onderstepoort Veterinary Institute has made and is making important contributions to knowledge of this disease, focusing on the cycle in warthogs and tampans and transmission from that cycle to domestic pigs, resistance to its effects in domestic pigs, and the molecular genetic characterisation and epidemiology of the virus. PMID:19967933

  9. The African Millennium Villages

    PubMed Central

    Sanchez, Pedro; Palm, Cheryl; Sachs, Jeffrey; Denning, Glenn; Flor, Rafael; Harawa, Rebbie; Jama, Bashir; Kiflemariam, Tsegazeab; Konecky, Bronwen; Kozar, Raffaela; Lelerai, Eliud; Malik, Alia; Modi, Vijay; Mutuo, Patrick; Niang, Amadou; Okoth, Herine; Place, Frank; Sachs, Sonia Ehrlich; Said, Amir; Siriri, David; Teklehaimanot, Awash; Wang, Karen; Wangila, Justine; Zamba, Colleen

    2007-01-01

    We describe the concept, strategy, and initial results of the Millennium Villages Project and implications regarding sustainability and scalability. Our underlying hypothesis is that the interacting crises of agriculture, health, and infrastructure in rural Africa can be overcome through targeted public-sector investments to raise rural productivity and, thereby, to increased private-sector saving and investments. This is carried out by empowering impoverished communities with science-based interventions. Seventy-eight Millennium Villages have been initiated in 12 sites in 10 African countries, each representing a major agroecological zone. In early results, the research villages in Kenya, Ethiopia, and Malawi have reduced malaria prevalence, met caloric requirements, generated crop surpluses, enabled school feeding programs, and provided cash earnings for farm families. PMID:17942701

  10. Tilted Rossby-wave critical layers in stratified atmospheres

    NASA Astrophysics Data System (ADS)

    Parham, Frederick Melvin, Jr.

    The quasigeostrophic potential vorticity equations linearized about a zonal mean flow, which describe Rossby waves, become singular at the critical level where the mean flow equals the wave's phase velocity. The Wentzel-Kramer-Brillouin solution describes a superposition of two eigenmodes, each of which has meridional structure corresponding to that of Dickenson's (1968) two-dimensional solutions. Rossby waves in a continuously stratified atmosphere are studied whose basic state zonal winds vary over large meridional scales. Again, WKB is used. The linearized potential vorticity equation is separable to lowest order. The WKB analysis applies to the outer solution. The inner solution, which provides a condition on the jump in the derivative of the outer solution across the critical line, depends on whether the critical line is desingularized by damping or by weak nonlinearity. Using the results on the matching across the critical line, the vertical structure eigenfunctions and eigenvalues are calculated for low critical layer heights with the basic state as given in the Charney model. Asymptotic values of the eigenvalues are also calculated as the critical height approaches zero or infinity. Finally, the eigenfunctions and eigenvalues are used to calculate the structure of waves on a basic state with a region of easterly winds surrounded by westerlies. The assumption of constant N makes it possible to compute the wave-forced change in the mean flow by means of modified Bessel functions.

  11. Larger genetic differences within africans than between Africans and Eurasians.

    PubMed Central

    Yu, Ning; Chen, Feng-Chi; Ota, Satoshi; Jorde, Lynn B; Pamilo, Pekka; Patthy, Laszlo; Ramsay, Michele; Jenkins, Trefor; Shyue, Song-Kun; Li, Wen-Hsiung

    2002-01-01

    The worldwide pattern of single nucleotide polymorphism (SNP) variation is of great interest to human geneticists, population geneticists, and evolutionists, but remains incompletely understood. We studied the pattern in noncoding regions, because they are less affected by natural selection than are coding regions. Thus, it can reflect better the history of human evolution and can serve as a baseline for understanding the maintenance of SNPs in human populations. We sequenced 50 noncoding DNA segments each approximately 500 bp long in 10 Africans, 10 Europeans, and 10 Asians. An analysis of the data suggests that the sampling scheme is adequate for our purpose. The average nucleotide diversity (pi) for the 50 segments is only 0.061% +/- 0.010% among Asians and 0.064% +/- 0.011% among Europeans but almost twice as high (0.115% +/- 0.016%) among Africans. The African diversity estimate is even higher than that between Africans and Eurasians (0.096% +/- 0.012%). From available data for noncoding autosomal regions (total length = 47,038 bp) and X-linked regions (47,421 bp), we estimated the pi-values for autosomal regions to be 0.105, 0.070, 0.069, and 0.097% for Africans, Asians, Europeans, and between Africans and Eurasians, and the corresponding values for X-linked regions to be 0.088, 0.042, 0.053, and 0.082%. Thus, Africans differ from one another slightly more than from Eurasians, and the genetic diversity in Eurasians is largely a subset of that in Africans, supporting the out of Africa model of human evolution. Clearly, one must specify the geographic origins of the individuals sampled when studying pi or SNP density. PMID:12019240

  12. [West African childbirth traditions].

    PubMed

    Hallgren, R

    1983-11-01

    Religious and medical practices are steeped in the traditions of West African culture vis-a-vis childbirth. It is customary for delivery to occur with the woman squatting on the ground surrounded by sisters and female relatives, some of whom function as midwives. Midwives get paid only if delivery is successful. A stool is also often used in childbirth. The name given to a child in the Yoruba tribe in Nigeria has to refer to the circumstances of the individual's birth. The contact with the earth (as in the squatting position) has religious overtones--it indicates the fecundity of the earth, and the mother's contact with it. Infertility is considered the greatest tragedy in traditional African society. In Senegal, a childless woman pays a fertile one a certain sum in return for bearing her a child who would be raised as her own (this tradition is not unlike surrogate motherhood in Western countries). Men are never present at birth; however, in urban settings this practice is changing. The burial of the placenta and umbilical cord is thought to restore the woman's fertility and help heal her womb. This practice was even recorded in 19th century Sweden harkening back to heathen times. In Ghana, an infertile woman urinates on the ground where the placenta is buried in the belief that her fertility will be restored. The birth of twins is regarded as a great blessing, and as a sign of fertility; however, the inability of the mother to breast-feed both twins may result in the death of the weaker child. The harmony of nature, animals, and human beings is paramount in traditional West Africa religion and life, and undoubtedly Western culture could learn from some of these beliefs. PMID:6558064

  13. Mantle support of the East African Rift System

    NASA Astrophysics Data System (ADS)

    Lin, S.; van Keken, P. E.; Brandenburg, J. P.; Furman, T.; Bryce, J.

    2007-12-01

    The African Superplume is a region of slow seismic wave velocities in the lower mantle under southern Africa. The uplift, volcanism and rifting that defines the much of eastern and southern Africa suggest a dynamic link between lower mantle dynamics and near-surface processes affecting the African plate. The dynamic link between the lower mantle and the surface, and the structure and dynamics of the upper mantle below the East African Rift System (EARS) remain unclear. As part of a comprehensive geochemical and numerical investigation of basaltic magmatism in the EARS we have modeled the interaction between putative upper mantle plumes and the rifting continental lithosphere. The modeling provides dynamically tested scenarios that explain the observed episodes of Cenozoic volcanism. Results from recent models that provided an explanation for the present day distribution of volcanism (Lin et al., EPSL, 237, 2005) suggest two plumes below Afar and Tanzania whose uplift is influenced by lithospheric topography. In new 3D modeling we provide improved quantification of the mantle involvement in generating EARS volcanism as constrained by the timing of uplift and regional volcanism. The time scales of episodicity of the volcanism observed at Turkana (related to the Tanzania-Kenya plume) since 45 Ma can be explained by deep- seated time-dependent plume activity. We suggest that this time-dependence is due to thermochemical interactions of dense recycled oceanic crust in the thermally hot regions in the African superplume region (Lin and Van Keken, Nature, 436, 2005).

  14. Predicting Relationship Stability Among Midlife African American Couples

    PubMed Central

    Cutrona, Carolyn E.; Russell, Daniel W.; Burzette, Rebecca G.; Wesner, Kristin A.; Bryant, Chalandra M.

    2012-01-01

    Objective This study examined predictors of relationship stability over 5 years among heterosexual cohabiting and married African American couples raising an elementary-school-age child. The vulnerability–stress–adaptation model of relationships (Karney & Bradbury, 1995) guided the investigation. Contextual variables were conceptualized as important determinants of education and income, which in turn influence family structure, stress, and relationship quality and stability. Religiosity was tested as a resource variable that enhances relationship stability. Method Couples (N = 207) were drawn from the Family and Community Health Study. Variables assessed at Wave 1 (education, income, religiosity, biological vs. stepfamily status, marital status, financial strain, and relationship quality) were used to predict relationship stability 5 years later. Results Higher levels of education were associated with higher income, lower financial strain, and family structures that research has shown to be more stable (marriage rather than cohabitation and biological-family rather than stepfamily status; Bumpass & Lu, 2000). These variables, in turn, influenced relationship quality and stability. Religiosity, an important resource in the lives of African Americans, promoted relationship stability through its association with marriage, biological-family status, and women’s relationship quality. Conclusions Enhancing the stability of African American couples’ relationships will require changes in societal conditions that limit opportunities for education and income and weaken relationship bonds. Programs to assist couples with blended families are needed, and incorporation of spirituality into culturally sensitive relationship interventions for African American couples may also prove beneficial. PMID:22004304

  15. Analysing the Floral Elements of the Lost Tree of Easter Island: A Morphometric Comparison between the Remaining Ex-Situ Lines of the Endemic Extinct Species Sophora toromiro

    PubMed Central

    Püschel, Thomas A.; Espejo, Jaime; Sanzana, María-José; Benítez, Hugo A.

    2014-01-01

    Sophora toromiro (Phil) Skottsb. is a species that has been extinct in its natural habitat Easter Island (Rapa Nui) for over 50 years. However, seed collections carried out before its extinction have allowed its persistence ex-situ in different botanical gardens and private collections around the world. The progenies of these diverse collections have been classified in different lines, most of them exhibiting high similarity as corroborated by molecular markers. In spite of this resemblance observed between the different lines, one of them (Titze) has dissimilar floral elements, thus generating doubts regarding its species classification. The floral elements (wing, standard and keel) belonging to three different S. toromiro lines and two related species were analyzed using geometric morphometrics. This method was applied in order to quantify the floral shape variation of the standard, wing, and keel between the different lines and control species. Geometric morphometrics analyses were able to distinguish the floral elements at both intra (lines) and inter-specific levels. The present results are on line with the cumulative evidence that supports the Titze line as not being a proper member of the S. toromiro species, but probably a hybridization product or even another species of the Edwardsia section. The reintroduction programs of S. toromiro should consider this information when assessing the authenticity and origin of the lines that will be used to repopulate the island. PMID:25526512

  16. African hot spot volcanism: small-scale convection in the upper mantle beneath cratons.

    PubMed

    King, S D; Ritsema, J

    2000-11-10

    Numerical models demonstrate that small-scale convection develops in the upper mantle beneath the transition of thick cratonic lithosphere and thin oceanic lithosphere. These models explain the location and geochemical characteristics of intraplate volcanos on the African and South American plates. They also explain the presence of relatively high seismic shear wave velocities (cold downwellings) in the mantle transition zone beneath the western margin of African cratons and the eastern margin of South American cratons. Small-scale, edge-driven convection is an alternative to plumes for explaining intraplate African and South American hot spot volcanism, and small-scale convection is consistent with mantle downwellings beneath the African and South American lithosphere. PMID:11073447

  17. Gravity Wave Variance in LIMS Temperatures. Part II: Comparison with the Zonal-Mean Momentum Balance.

    NASA Astrophysics Data System (ADS)

    Fetzer, Eric J.; Gille, John C.

    1996-02-01

    Zonal-mean gravity wave variance in the Limb Infrared Monitor of the Stratosphere (LIMS) temperature data is seen to correlate strongly with the residual term in the LIMS zonal-mean momentum budget throughout much of the observed mesosphere. This momentum residual is attributed to gravity wave momentum transport at scales that cannot be directly sampled by the LIMS instrument Correlation is highest in the vicinity of the fall and winter mesospheric jets, where both gravity wave variance and momentum residual reach their largest values. Correlation is also high in the Southern Hemisphere subtropical mesophere, where gravity wave variance and the momentum residual have broad temporal maxima during the easterly acceleration of the stratopause semi-annual oscillation (SAO). This subtropical correlation has important implications for the SAO eastward acceleration, which several studies suggest is forced by gravity wave momentum flux divergence. Correlation between gravity wave variance and inferred gravity wave momentum flux divergence is unexpected because variance is dominated by large scales and long periods (inertio-gravity waves), while both theoretical arguments and ground-based observations indicate that momentum transport is dominated by periods under 1 h. The results of this study suggest a broadband gravity wave field experiencing forcing and loss processes, which are largely independent of frequency.

  18. Early African Hominids: Pedagogic Patterns.

    ERIC Educational Resources Information Center

    Newman, James L.

    1984-01-01

    By studying early African hominids, students can learn about the interactive testing and creative aspects of scientific thinking and sharpen their geographical skills. It is impossible to study this topic without giving prominence to space and time. (RM)

  19. The Female African American Presidents in Higher Education: Is There a Particular Journey toward Their Presidencies?

    ERIC Educational Resources Information Center

    Bennett, Vernell Anntoinette

    2013-01-01

    The rate of diversification in the academic president's office has been slow for decades. At least 25% of academic presidents are white males approaching retirement age. A potential wave of retirements means there is an opportunity to create greater diversity in the presidency. Although there are qualified, interested and capable African American…

  20. Working in High School and Adaptation in the Transition to Young Adulthood among African American Youth

    ERIC Educational Resources Information Center

    Bauermeister, Jose A.; Zimmerman, Marc A.; Barnett, Tracey E.; Caldwell, Cleopatra Howard

    2007-01-01

    Researchers have found mixed support for documenting whether work is protective or harmful during adolescence. This study examined the association between work and problem behaviors among African American youth (N = 592; 53% female; M = 14.8 years, SD = 0.60) followed from mid-adolescence to young adulthood over eight Waves (90% response rate over…

  1. Antecedents and Consequences of Psychiatric Disorders in African-American Adolescents

    ERIC Educational Resources Information Center

    Jin, Run; Ge, Xiaojia; Brody, Gene H.; Simons, Ronald L.; Cutrona, Carolyn E.; Gibbons, Frederick X.

    2008-01-01

    This study included three waves of data, collected from approximately 890 African-American children and their families. Antecedents and consequences of psychiatric disorders among this population were examined. Children's temperament, pubertal timing, and experience of stressful life events were tested as antecedents of psychiatric disorders.…

  2. Mechanisms of Family Impact on African American Adolescents' HIV-Related Behavior

    ERIC Educational Resources Information Center

    Kogan, Steven M.; Brody, Gene H.; Gibbons, Frederick X.; Chen, Yi-fu; Grange, Christina M.; Simons, Ronald L.; Gerrard, Meg; Cutrona, Carolyn E.

    2011-01-01

    A longitudinal model that tested mediating pathways between protective family processes and HIV-related behavior was evaluated with 195 African American youth. Three waves of data were collected when the youth were 13, 15, and 19 years old. Evidence of mediation and temporal priority were assessed for 3 constructs: academic engagement, evaluations…

  3. Quasi-biennial modulation of planetary-wave fluxes in the Northern Hemisphere winter

    NASA Technical Reports Server (NTRS)

    Dunkerton, Timothy J.; Baldwin, Mark P.

    1991-01-01

    Using 25 years of National Meteorological Center (NMC) data for 1964-88 the relation between tropical and extratropical quasi-biennial oscillations (QBOs) was examined for zonally averaged quantities and planetary-wave Eliassen-Palm fluxes in the Northern Hemisphere winter. The extratropical QBO discussed by Holton and Tan (1980) existed in both temporal halves of the dataset. Autocorrelation analysis demonstrated that it was an important mode of interannual variability in the extratropical winter stratosphere. Correlation with the tropics was strongest when 40-mb equatorial winds were used to define the tropical QBO. Easterly phase at 40 mb implied a weaker than normal polar night jet and warmer than normal polar temperature and vice versa. An opposite relationship was obtained using 10-mb equatorial winds. The association between tropical and extratropical QBOs was observed in about 90 percent of the winters and was statistically significant. It is shown that planetary-wave Eliassen-Palm fluxes were generally consistent with the extratropical QBO. These fluxes were more (less) convergent in the midlatitude (subtropical) upper stratosphere in the 40-mb east (= easterly) phase category relative to the west category.

  4. The African Pediatric Fellowship Program: Training in Africa for Africans.

    PubMed

    Wilmshurst, Jo M; Morrow, Brenda; du Preez, Avril; Githanga, David; Kennedy, Neil; Zar, Heather J

    2016-01-01

    Africa has a significant burden of childhood disease, with relatively few skilled health care professionals. The African Paediatric Fellowship Programme was developed by the Department of Pediatrics and Child Health at the University of Cape Town to provide relevant training for African child health professionals, by Africans, within Africa. Trainees identified by partner academic institutions spend 6 months to 2 years training in the Department of Pediatrics and allied disciplines. They then return to their home institution to build practice, training, research, and advocacy. From 2008 to 2015, 73 physicians have completed or are completing training in general pediatrics or a pediatric subspecialty. At 1 year posttraining, 98% to 100% are practicing back in their home institution. The impact of the returning fellows is evident from their practice interventions, research collaborations, and positions as stakeholders who can change health care policies. Thirty-three centers in 13 African countries are partners with the program, and the program template is now followed by other partner sites in Africa. Increasing and retaining the skills pool of African child health specialists is building a network of motivated, highly skilled clinicians who are equipped to advance child health in Africa. PMID:26659458

  5. Intermittency of gravity-wave momentum flux in the stratosphere

    NASA Astrophysics Data System (ADS)

    Hertzog, A.; Alexander, M. J.; Plougonven, R.

    2012-04-01

    Atmospheric gravity waves transfer energy and momentum from the troposphere to upper layers of the atmosphere. They significantly contribute to forcing the global-scale Brewer Dobson circulation in the middle atmosphere, and to driving the stratosphere out of radiative equilibrium. As most of the gravity waves are not explicitly resolved in current climate models, their effects on the general circulation must be parameterized. Strong assumptions are generally used in such parameterizations, like for instance constant and homogeneous non-orographic gravity-wave sources. In this study, we challenge this latter hypothesis, and use long-duration balloon- and space-borne observations as well as mesoscale numerical simulations to characterize the intermittency of gravity waves in the lower stratosphere above Antarctica. This is achieved through working on the gravity-wave momentum-flux probability density functions (pdfs) obtained with these three datasets. The pdfs consistently exhibit long tails associated with the occurrence of rare and large amplitude events. We provide a measure of the contribution of these events to the total gravity-wave momentum flux, and show that only a small fraction of the wavepackets are responsible for most of the momentum transport during the winter regime of the stratospheric circulation. On the other hand, the wave intermittency significantly decreases when stratospheric easterlies develop in late spring and summer. With the exception of mountainous areas in winter, the momentum-flux pdfs furthermore tend to behave like lognormal distributions. We find that this behaviour can result from the propagation of a wave spectrum into a varying background wind field that generates the occurrence of frequent critical levels.

  6. East African Rift

    NASA Technical Reports Server (NTRS)

    2008-01-01

    Places where the earth's crust has formed deep fissures and the plates have begun to move apart develop rift structures in which elongate blocks have subsided relative to the blocks on either side. The East African Rift is a world-famous example of such rifting. It is characterized by 1) topographic deep valleys in the rift zone, 2) sheer escarpments along the faulted walls of the rift zone, 3) a chain of lakes within the rift, most of the lakes highly saline due to evaporation in the hot temperatures characteristic of climates near the equator, 4) voluminous amounts of volcanic rocks that have flowed from faults along the sides of the rift, and 5) volcanic cones where magma flow was most intense. This example in Kenya displays most of these features near Lake Begoria.

    The image was acquired December 18, 2002, covers an area of 40.5 x 32 km, and is located at 0.1 degrees north latitude, 36.1 degrees east longitude.

    The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate.

  7. Kelvin wave variability in the upper stratosphere observed in SBUV ozone data. [SBUV (solar backscatter ultraviolet)

    SciTech Connect

    Randel, W.J.; Gille, J.C. )

    1991-11-01

    The signatures of equatorially trapped Kelvin waves in the upper stratosphere are analyzed in Solar Backscatter Ultraviolet (SBUV) ozone data over the years 1979-86. Comparisons are first made with contemporaneous Limb Infrared Monitor of the Stratosphere (LIMS) ozone data to validate the SBUV Kelvin wave signatures. SBUV and LIMS data both show coherent Kelvin wave oscillations in the upper stratosphere, where ozone is photochemically controlled, and mirrors the temperature fluctuations associated with Kelvin waves; however, SBUV data underestimate wave amplitudes by 20%-60%. Furthermore, transport-induced Kelvin wave patterns in the lower stratosphere are not observed in SBUV data. The eight years of SBUV data reveal the regular occurrence of eastward-propagating zonal wave 1-2 Kelvin waves with periods in the range of 5-15 days. These data show a strong semiannual modulation of Kelvin wave activity, as documented previously in rocketsonde observations. Eight-year-average ensemble spectra are compared to the semiannual oscillation (SAO) in stratospheric zonal winds; a seasonal asymmetry in the strength of Kelvin waves is found, which mimics that observed in the zonal winds. There is a near exact phasing of maxima in wave variance with the strongest easterly zonal winds, i.e., when the wind acceleration is near zero; this argues that Kelvin waves are not a determining factor in the westerly acceleration phase. An exception is found near the stratopause in January when Kelvin wave maxima coincide with strong westerly acceleration. Interannual variability of Kelvin waves is studied in relation to that of the stratospheric zonal winds. No consistent relationship with the quasi-biennial oscillation (QBO) in the lower stratosphere is observed, and correlations with upper stratospheric winds are weak or nonexistent. 35 refs., 11 figs., 1 tab.

  8. An African ethic for nursing?

    PubMed

    Haegert, S

    2000-11-01

    This article derives from a doctoral thesis in which a particular discourse was used as a 'paradigm case'. From this discourse an ethic set within a South African culture arose. Using many cultural 'voices' to aid the understanding of this narrative, the ethic shows that one can build on both a 'justice' and a 'care' ethic. With further development based on African culture one can take the ethic of care deeper and reveal 'layers of understanding'. Care, together with compassion, forms the foundation of morality. Nursing ethics has followed particular western moral philosophers. Often nursing ethics has been taught along the lines of Kohlberg's theory of morality, with its emphasis on rules, rights, duties and general obligations. These principles were universalistic, masculine and noncontextual. However, there is a new ethical movement among Thomist philosophers along the lines to be expounded in this article. Nurses such as Benner, Bevis, Dunlop, Fry and Gadow--to name but a few--have welcomed the concept of an 'ethic of care'. Gilligan's work gave a feminist view and situated ethics in the everyday aspects of responsiveness, responsibility, context and concern. Shutte's search for a 'philosophy for Africa' has resulted in finding similarities in Setiloane and in Senghor with those of Thomist philosophers. Using this African philosophy and a research participant's narrative, an African ethic evolves out of the African proverb: 'A person is a person through other persons', or its alternative rendering: 'I am because we are: we are because I am.' This hermeneutic narrative reveals 'the way affect imbues activity with ethical meaning' within the context of a black nursing sister in a rural South African hospital. It expands upon the above proverb and incorporates the South African constitutional idea of 'Ubuntu' (compassion and justice or humanness). PMID:11221391

  9. Rossby wave Green's functions in an azimuthal wind

    NASA Astrophysics Data System (ADS)

    Webb, G. M.; Duba, C. T.; Hu, Q.

    2016-05-01

    Green's functions for Rossby waves in an azimuthal wind are obtained, in which the stream-function $\\psi$ depends on $r$, $\\phi$ and $t$, where $r$ is cylindrical radius and $\\phi$ is the azimuthal angle in the $\\beta$-plane relative to the easterly direction, in which the $x$-axis points east and the $y$-axis points north. The Rossby wave Green's function with no wind is obtained using Fourier transform methods, and is related to the previously known Green's function obtained for this case, which has a different but equivalent form to the Green's function obtained in the present paper. We emphasize the role of the wave eikonal solution, which plays an important role in the form of the solution. The corresponding Green's function for a rotating wind with azimuthal wind velocity ${\\bf u}=\\Omega r{\\bf e}_\\phi$ ($\\Omega=$const.) is also obtained by Fourier methods, in which the advective rotation operator in position space is transformed to a rotation operator in ${\\bf k}$ transform space. The finite Rossby deformation radius is included in the analysis. The physical characteristics of the Green's functions are delineated and applications are discussed. In the limit as $\\Omega\\to 0$, the rotating wind Green's function reduces to the Rossby wave Green function with no wind.

  10. Ozone soundings on Easter Island (27ºS,109ºW,51 m.a.s.l): representativity and tendency analyses

    NASA Astrophysics Data System (ADS)

    Gallardo, L.; Quintana, J.; Valdés, R.

    2003-04-01

    About 70 ozone soundings have been collected on Easter Island (27ºS, 109ºW, 51 m.a.s.l.) since early 1996 . In this work we provide a representativity and tendency analysis of these soundings. Our aim is to characterize the station in terms of typical air masses and the influence of different processes affecting the tropospheric ozone balance. We are particularly interested in exploring the relative importance of photochemistry of biomass burning related species and stratosphere-troposphere exchange (STE). A spring maximum in ozone is a feature apparent on a hemispheric scale over the Southern Hemisphere as derived from satellite, in situ measurements and from model simulations. The visual inspection of climatological records from satellites strongly suggest that the spring maximum is due to secondary O3 formation in connection with the widely spread biomass burning in the tropics during spring, particularly over Africa and South America. However, the role of the quasi-stationary spring subtropical jet (STJ) over the Eastern Pacific cannot be ruled out. In fact, there is evidence that STE in connection with the STJ may be very important in the subtropics. We use potential vorticity (PV), water vapor and the like as STE proxies. The statistical analyses considers, on the one hand, the traditional climatological description of the data in terms of seasonal and annual cycles, and, on the other hand, a more process oriented analysis based on clustering techniques. When available, outputs of global models describing ozone are used. Altogether, we expect these data and the analyses provided hereby to improve our understanding of tropospheric ozone over this area of the Southern Hemisphere, and to promote and facilitate the use of these data for scientific purposes, for instance when improving satellite retrievals or when designing large-scale campaigns.

  11. Determination of green, blue and yellow artificial food colorants and their abuse in herb-coloured green Easter beers on tap.

    PubMed

    Stachová, Ivana; Lhotská, Ivona; Solich, Petr; Šatínský, Dalibor

    2016-07-01

    Beer is one of the most popular alcoholic beverages worldwide. For consumer acceptance, significant factors are its taste, flavour and colour. This study determines selected synthetic green, blue and yellow food colorants in popular Easter herb-coloured green beers on tap produced in breweries on Holy Thursday. The abuse of beer colouring with Tartrazine (E 102), Quinoline yellow (E 104), Sunset yellow (E 110), Patent blue (E 131), Indigo carmine (E 132), Brilliant blue FCF (E 133), Green S (E 142) and Fast green FCF (E 143) was assessed in 11 green beer samples purchased in local restaurants. HPLC was used for the separation and detection of artificial colorants with diode-array detection and a Chromolith Performance CN 100 × 4.6 mm column with guard pre-column Chromolith CN 5 × 4.6 mm. Separation was performed in gradient elution with mobile phase containing methanol-aqueous 2% ammonium acetate at pH 7.0. The study showed that eight beers (70%) marketed in the Czech Republic contained artificial colorants (Tartrazine and Brilliant blue FCF). The concentration of colorants found in analysed green herb-coloured beers ranged from 1.58 to 3.49 mg l(-)(1) for Tartrazine, 0.45-2.18 mg l(-)(1) for Brilliant blue, while Indigo carmine was detected only once at concentration 2.36 mg l(-)(1). Only three beers showed no addition of the synthetic colorants. However, the levels of artificial colorants found in beers marketed in the Czech region were very low and did not show a serious risk for consumers' health. PMID:27295128

  12. Macrofossils in Raraku Lake (Easter Island) integrated with sedimentary and geochemical records: towards a palaeoecological synthesis for the last 34,000 years

    NASA Astrophysics Data System (ADS)

    Cañellas-Boltà, N.; Rull, V.; Sáez, A.; Margalef, O.; Giralt, S.; Pueyo, J. J.; Birks, H. H.; Birks, H. J. B.; Pla-Rabes, S.

    2012-02-01

    Macrofossil analysis of a composite 19 m long sediment core from Rano Raraku Lake (Easter Island) was related to litho-sedimentary and geochemical features of the sediment. Strong stratigraphical patterns are shown by indirect gradient analyses of the data. The good correspondence between the stratigraphical patterns derived from macrofossil (Correspondence Analysis) and sedimentary and geochemical data (Principal Component Analysis) shows that macrofossil associations provide sound palaeolimnological information in conjunction with sedimentary data. The main taphonomic factors influencing the macrofossil assemblages are run-off from the catchment, the littoral plant belt, and the depositional environment within the basin. Five main stages during the last 34,000 calibrated years BP (cal yr BP) are characterised from the lithological, geochemical, and macrofossil data. From 34 to 14.6 cal kyr BP (last glacial period) the sediments were largely derived from the catchment, indicating a high energy lake environment with much erosion and run-off bringing abundant plant trichomes, lichens, and mosses into the centre of Raraku Lake. During the early Holocene the infilling of the lake basin and warmer conditions favoured the growth of a littoral plant belt that obstructed terrigenous input. Cladoceran remains and Solanaceae seeds are indicative of reduced run-off and higher values of N and organic C indicate increased aquatic and catchment productivity. From 8.7 to 4.5 cal kyr BP a swamp occupied the entire basin. The increase of Cyperaceae seeds reflects this swamp development and, with oribatid mites and coleopteran remains, indicates a peaty environment and more anoxic conditions in Raraku. At around 4.5 cal kyr BP dry conditions prevented peat growth and there is a sedimentary hiatus. About 800 cal yr BP, peat deposition resumed. Finally, in the last few centuries, a small lake formed within the surrounding swamp. Evidence of human activity is recorded in these

  13. Third Wave.

    ERIC Educational Resources Information Center

    Reed, Chris

    2000-01-01

    Third Wave is a Christian charity based in Derby (England) that offers training in vocational skills, preindustrial crafts, horticultural and agricultural skills, environmental education, and woodland survival skills to disadvantaged people at city and farm locations. Third Wave employs a holistic approach to personal development in a community…

  14. Microfluidic waves.

    PubMed

    Utz, Marcel; Begley, Matthew R; Haj-Hariri, Hossein

    2011-11-21

    The propagation of pressure waves in fluidic channels with elastic covers is discussed in view of applications to flow control in microfluidic devices. A theory is presented which describes pressure waves in the fluid that are coupled to bending waves in the elastic cover. At low frequencies, the lateral bending of the cover dominates over longitudinal bending, leading to propagating, non-dispersive longitudinal pressure waves in the channel. The theory addresses effects due to both the finite viscosity and compressibility of the fluid. The coupled waves propagate without dispersion, as long as the wave length is larger than the channel width. It is shown that in channels of typical microfluidic dimensions, wave velocities in the range of a few 10 m s(-1) result if the channels are covered by films of a compliant material such as PDMS. The application of this principle to design microfluidic band pass filters based on standing waves is discussed. Characteristic frequencies in the range of a few kHz are readily achieved with quality factors above 30. PMID:21966667

  15. African American Males. A Critical Link in the African American Family.

    ERIC Educational Resources Information Center

    Jones, Dionne J., Ed.

    African Americans are experiencing extreme stress in the United States, and African-American males appear to suffer the most. The chapters in this volume examine some of the issues confronting African-American men today. They include: (1) "Introduction" (Dionne J. Jones); (2) "Reaffirming Young African American Males: Mentoring and Community…

  16. African American Preschoolers' Language, Emergent Literacy Skills, and Use of African American English: A Complex Relation

    ERIC Educational Resources Information Center

    Connor, Carol McDonald; Craig, Holly K.

    2006-01-01

    Purpose: This study examined the relation between African American preschoolers' use of African American English (AAE) and their language and emergent literacy skills in an effort to better understand the perplexing and persistent difficulties many African American children experience learning to read proficiently. Method: African American…

  17. Technical Consulting: The African-American Perspective

    ERIC Educational Resources Information Center

    Whitfield, Tracy N.

    2010-01-01

    The qualitative research study explored the organizational characteristics necessary in addressing the low concentration of African American technical consultants employed in the information technology industry. Using research participants' professional experience, participants responded to a developed questionnaire. African American technical…

  18. Towards an African Philosophy of Education.

    ERIC Educational Resources Information Center

    Ocaya-Lakidi, Dent

    1980-01-01

    Compares and contrasts contemporary philosophies of education in Africa with two philosophical doctrines (naturalism and idealism). Topics discussed include value selectors, westernization, the role of missionaries in African education, critical consciousness, relevance, and African education today. (DB)

  19. African N Assessment

    NASA Astrophysics Data System (ADS)

    Bekunda, M.; Galford, G. L.; Hickman, J. E.; Palm, C.

    2011-12-01

    Africa's smallholder agricultural systems face unique challenges in planning for reducing poverty, concurrent with adaptation and mitigation to climate change. At continental level, policy seeks to promote a uniquely African Green Revolution to increase crop yields and food production, and improve local livelihoods. However, the consequences on the environment and climate are not clear; these pro-economic development measures should be linked to climate change adaptation and mitigation measures, and research is required to help achieve these policy proposals by identifying options, and testing impacts. In particular, increased nitrogen (N) inputs are essential for increasing food production in Africa, but are accompanied by inevitable increases in losses to the environment. These losses appear to be low at input levels promoted in agricultural development programs, while the increased N inputs both increase current food production and appear to reduce the vulnerability of food production to changes in climate. We present field and remote sensing evidence from Malawi that subsidizing improved seed and fertilizers increases resilience to drought without adding excess N to the environment. In Kenya, field research identified thresholds in N2O losses, where emissions are very low at fertilization rates of less than 200 kg ha-1. Village-scale models have identified potential inefficiencies in the food production process where the largest losses of reactive N occur, and which could be targeted to reduce the amount of N released to the environment. We further review some on-going research activities and progress in Africa that compare different methods of managing resources that target resilience in food production and adaptation to climate change, using nutrient N as an indicator, while evaluating the effects of these resource management practices on ecosystems and the environment.

  20. The African Cultural Astronomy Project

    NASA Astrophysics Data System (ADS)

    Urama, Johnson O.; Holbrook, Jarita C.

    2011-06-01

    Indigenous, endogenous, traditional, or cultural astronomy focuses on the many ways that people and cultures interact with celestial bodies. In most parts of Africa, there is very little or no awareness about modern astronomy. However, like ancient people everywhere, Africans wondered at the sky and struggled to make sense of it. The African Cultural Astronomy Project aims to unearth the body of traditional knowledge of astronomy possessed by peoples of the different ethnic groups in Africa and to consider scientific interpretations when appropriate for cosmogonies and ancient astronomical practices. Regardless of scientific validity, every scientist can relate to the process of making observations and creating theoretical mechanisms for explaining what is observed. Through linking the traditional and the scientific, it is believed that this would be used to create awareness and interest in astronomy in most parts of Africa. This paper discusses the vision, challenges and prospects of the African Cultural Astronomy Project in her quest to popularize astronomy in Africa.

  1. Plio-pleistocene African climate

    SciTech Connect

    deMenocal, P.B.

    1995-10-06

    Marine records of African climate variability document a shift toward more arid conditions after 2.8 million years ago (Ma), evidently resulting from remote forcing by cold North Atlantic sea-surface temperatures associated with the onset of Northern Hemisphere glacial cycles. African climate before 2.8 Ma was regulated by low-latitude insolation forcing of monsoonal climate due to Earth orbital precession. Major steps in the evolution of African hominids and other vertebrates are coincident with shifts to more arid, open conditions near 2.8 Ma, 1.7 Ma, and 1.0 Ma, suggesting that some Pliocene (Plio)-Pleistocene speciation events may have been climatically mediated. 65 refs., 6 figs.

  2. Plio-Pleistocene African Climate

    NASA Astrophysics Data System (ADS)

    Demenocal, Peter B.

    1995-10-01

    Marine records of African climate variability document a shift toward more arid conditions after 2.8 million years ago (Ma), evidently resulting from remote forcing by cold North Atlantic sea-surface temperatures associated with the onset of Northern Hemisphere glacial cycles. African climate before 2.8 Ma was regulated by low-latitude insolation forcing of monsoonal climate due to Earth orbital precession. Major steps in the evolution of African hominids and other vertebrates are coincident with shifts to more arid, open conditions near 2.8 Ma, 1.7 Ma, and 1.0 Ma, suggesting that some Pliocene (Plio)-Pleistocene speciation events may have been climatically mediated.

  3. Climate not to blame for African civil wars.

    PubMed

    Buhaug, Halvard

    2010-09-21

    Vocal actors within policy and practice contend that environmental variability and shocks, such as drought and prolonged heat waves, drive civil wars in Africa. Recently, a widely publicized scientific article appears to substantiate this claim. This paper investigates the empirical foundation for the claimed relationship in detail. Using a host of different model specifications and alternative measures of drought, heat, and civil war, the paper concludes that climate variability is a poor predictor of armed conflict. Instead, African civil wars can be explained by generic structural and contextual conditions: prevalent ethno-political exclusion, poor national economy, and the collapse of the Cold War system. PMID:20823241

  4. The Education of African-Americans.

    ERIC Educational Resources Information Center

    Willie, Charles V., Ed.; And Others

    The 17 papers in this volume are products of a study group on the education of African Americans that was part of a national project, "The Assessment of the Status of African-Americans." The volume takes a comprehensive look at the education of African Americans, specifically early childhood through postsecondary education, and relevant public…

  5. An Introduction to West African Literature.

    ERIC Educational Resources Information Center

    Taiwo, Oladele

    Intended to provide help for those interested in studying West African literature, this book is divided into three parts. Part One provides background information: the various African oral traditions are discussed, related to the way of life of the people, and examined for the extent to which they form the basis of present West African literary…

  6. Engaging African Americans in Smoking Cessation Programs

    ERIC Educational Resources Information Center

    Wallen, Jacqueline; Randolph, Suzanne; Carter-Pokras, Olivia; Feldman, Robert; Kanamori-Nishimura, Mariano

    2014-01-01

    Background: African Americans are disproportionately exposed to and targeted by prosmoking advertisements, particularly menthol cigarette ads. Though African Americans begin smoking later than whites, they are less likely to quit smoking than whites. Purpose: This study was designed to explore African American smoking cessation attitudes,…

  7. Freedom Road: Adult Education of African Americans.

    ERIC Educational Resources Information Center

    Peterson, Elizabeth A., Ed.

    This book contains six chapters by various authors about the history of African Americans' contributions and participation in adult education. The book reports on how some African American leaders saw the connection between education and the eventual freedom or uplift of the African American people. Following a foreword (Phyllis M. Cunningham) and…

  8. A Scale To Assess African American Acculturation.

    ERIC Educational Resources Information Center

    Snowden, Lonnie R.; Hines, Alice M.

    1999-01-01

    Investigated an acculturation scale designed for use in the African-American population. Responses from more than 900 African Americans generally indicate an African-American orientation within the sample, although there are notable variations on all 10 scale items. Discusses evidence for scale reliability and validity. (SLD)

  9. Towards a Norm in South African Englishes.

    ERIC Educational Resources Information Center

    van der Walt, Johann L.; van Rooy, Bertus

    2002-01-01

    Investigates the perception and application of the norm in South African English with specific reference to Black South African English. Hypothesizes that South African English is in the hibernation and expansion phase. Three sets of data are presented and analyzed. (Author/VWL)

  10. African Heritage Curriculum Materials. Teacher's Manual.

    ERIC Educational Resources Information Center

    Museum of African Art, Washington, DC.

    This guide for secondary teachers focuses on sub-Saharan (Black) African history and culture. Although the guide is intended to be used in conjunction with the audiovisual materials on African heritage produced by the Museum of African Art, it can also be used as a source of background reading for teachers and as a guide to additional…

  11. Atmospheric Waves

    NASA Technical Reports Server (NTRS)

    2007-01-01

    With its Multispectral Visible Imaging Camera (MVIC), half of the Ralph instrument, New Horizons captured several pictures of mesoscale gravity waves in Jupiter's equatorial atmosphere. Buoyancy waves of this type are seen frequently on Earth - for example, they can be caused when air flows over a mountain and a regular cloud pattern forms downstream. In Jupiter's case there are no mountains, but if conditions in the atmosphere are just right, it is possible to form long trains of these small waves. The source of the wave excitation seems to lie deep in Jupiter's atmosphere, below the visible cloud layers at depths corresponding to pressures 10 times that at Earth's surface. The New Horizons measurements showed that the waves move about 100 meters per second faster than surrounding clouds; this is about 25% of the speed of sound on Earth and is much greater than current models of these waves predict. Scientists can 'read' the speed and patterns these waves to learn more about activity and stability in the atmospheric layers below.

  12. Quasitravelling waves

    SciTech Connect

    Beklaryan, Leva A

    2011-02-11

    A finite difference analogue of the wave equation with potential perturbation is investigated, which simulates the behaviour of an infinite rod under the action of an external longitudinal force field. For a homogeneous rod, describing solutions of travelling wave type is equivalent to describing the full space of classical solutions to an induced one-parameter family of functional differential equations of point type, with the characteristic of the travelling wave as parameter. For an inhomogeneous rod, the space of solutions of travelling wave type is trivial, and their 'proper' extension is defined as solutions of 'quasitravelling' wave type. By contrast to the case of a homogeneous rod, describing the solutions of quasitravelling wave type is equivalent to describing the quotient of the full space of impulsive solutions to an induced one-parameter family of point-type functional differential equations by an equivalence relation connected with the definition of solutions of quasitravelling wave type. Stability of stationary solutions is analyzed. Bibliography: 9 titles.

  13. Moreton Waves

    NASA Technical Reports Server (NTRS)

    Thompson, B. J.

    1999-01-01

    "Moreton waves," named for the observer who popularized them, are a solar phenomenon also known in scientific literature as "Moreton-Ramsey wave," "flare waves," "flare-associated waves," "MHD blast waves," "chromospheric shock fronts" and various other combinations of terms which connote violently propagating impulsive disturbances. It is unclear whether all of the observations to which these terms have been applied pertain to a single physical phenomenon: there has perhaps been some overlap between the observations and the assumed physical properties of the observed occurrence. Moreton waves are ideally observed in the wings of H alpha, and appear as semi-circular fronts propagating at speeds ranging from several hundred to over a thousand km/sec. They form an arc, or "brow shape" which can span up to 180 degrees. Extrapolating the speed and locations of the arc indicates that the phenomenon's origin intersects well with the impulsive phase of the associated H alpha flare (if the flare exhibits an impulsive phase). However, the arc may not form or may not be observable until it is tens of megameters from the flaring region, and subsequently can propagate to distances exceeding 100 megameters. The high speeds and distances of propagation, plus the associated radio and energetic particle observations, provided strong evidence of a coronal, rather than a chromospheric origin. The H alpha manifestation of the wave is assumed to be the "ground track" or "skirt" of a three-dimensional disturbance.

  14. Ship waves and lee waves

    NASA Technical Reports Server (NTRS)

    Sharman, R. D.; Wurtele, M. G.

    1983-01-01

    Dynamics analogous to those of surface ship waves on water of finite depth are noted for the three-dimensional trapped lee wave modes produced by an isolated obstacle in a stratified fluid. This vertical trapping of wave energy is modeled by uniform upstream flow and stratification, bounded above by a rigid lid, and by a semiinfinite fluid of uniform stability whose wind velocity increases exponentially with height, representing the atmosphere. While formal asymptotic solutions are produced, limited quantitative usefulness is obtained through them because of the limitations of the approximations and the infinity of modes in the solution. Time-dependent numerical models are accordingly developed for both surface ship waves and internal and atmospheric ship waves, yielding a variety of results.

  15. Studies of quasi horizontally propagating gravity waves in the troposphere using the Piura ST wind profiler

    NASA Astrophysics Data System (ADS)

    Liziola, Luis E.; Balsley, Ben B.

    1998-04-01

    VHF profiler observations of the troposphere obtained over a flat desert in northern Perú show the presence of strong, quasi-sinusoidal oscillations in the vertical wind velocity with periods of around 8-18 min. These oscillations are a very typical feature of the vertical velocities over Piura. This paper presents an overview of the wave characteristics obtained at Piura until this point, including results obtained using two additional antennas built a few hundred meters to the west and south of the main antenna to measure horizontal wavelengths and phase velocities. Briefly, the Piura waves appear to have horizontal wavelengths of 1-3 km, with either westward or eastward phase velocities (in a ground-based reference frame) of 0.5-4 m s-1. Their occurrence appears to be causally related to the magnitude of the easterly wind, which blows over the Andean Cordillera some 60 km to the east of the site.

  16. African-American Children's Stories.

    ERIC Educational Resources Information Center

    Nichols, Patricia C.

    Examination of representative stories told by black American children of West African descent in South Carolina shows that specific cultural motifs have been preserved in the oral tradition of black communities. Typical stories are tales of the supernatural, such as the Hag story about mortals who shed their skin at night to do evil deeds.…

  17. African American Men in College

    ERIC Educational Resources Information Center

    Cuyjet, Michael J., Ed.

    2006-01-01

    This book is a much-needed resource that includes examples of real-world programs and activities to enhance academic success in the college environment for African American men. The examples are collected from a variety of institutions across the country. With contributions from leading practitioners and scholars in the field, this book explores…

  18. Vitamin D and African Americans

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Vitamin D insufficiency is more prevalent among African Americans than other Americans and, in North America, most young, healthy blacks do not achieve optimal 25-hydroxyvitamin D [25(OH)D] concentrations at any time of the year. This is primarily due to the fact that pigmentation reduces vitamin D...

  19. Classic African American Children's Literature

    ERIC Educational Resources Information Center

    McNair, Jonda C.

    2010-01-01

    The purpose of this article is to assert that there are classic African American children's books and to identify a sampling of them. The author presents multiple definitions of the term classic based on the responses of children's literature experts and relevant scholarship. Next, the manner in which data were collected and analyzed in regard to…

  20. Simulation of the West African monsoon onset using the HadGEM3-RA regional climate model

    NASA Astrophysics Data System (ADS)

    Diallo, Ismaïla; Bain, Caroline L.; Gaye, Amadou T.; Moufouma-Okia, Wilfran; Niang, Coumba; Dieng, Mame D. B.; Graham, Richard

    2014-08-01

    the African Easterly Jet and Tropical Easterly Jet that intensifies around the time of onset. This region of ascent is weaker and located further south near 5°N in the driving ERA-Interim reanalysis, for reasons that may be related to the coarser resolution or the physics of the underlying model, and this is consistent with a less realistic latitudinal rainfall profile than found in the HadGEM3-RA simulations.

  1. Developing anatomical terms in an African language.

    PubMed

    Madzimbamuto, Farai Daniel

    2012-03-01

    Clinical and technical information imparted in most African languages involves inexact terminology and code switching, so it lacks the explanatory power characterised by the English language. African languages are absent in the tertiary science education environment and forums where African scientists could present scientific material in the medium of African languages. This limits the development of African languages in the scientific domain. There has recently been a trend in several African languages to develop and intellectualise them, especially in the field of medical sciences. The ChiShona language is used to explore the ability of an African language to develop new terminology, to name the vertebral skeleton and describe it scientifically. It uses word compounding to demonstrate terminology development. ChiShona has similarities with several hundred other Bantu languages in East, Central and Southern Africa. Advancing this language can promote similar developments in others, making them more explanatory for the lay public and health professionals. PMID:22380900

  2. Intermediate and high resolution numerical simulations of the transition of a tropical wave critical layer to a tropical storm

    NASA Astrophysics Data System (ADS)

    Montgomery, M. T.; Wang, Z.; Dunkerton, T. J.

    2009-12-01

    Recent work has hypothesized that tropical cyclones in the deep Atlantic and eastern Pacific basins develop from the cyclonic Kelvin cat's eye of a tropical easterly wave critical layer located equatorward of the easterly jet axis that typifies the trade wind belt. The cyclonic critical layer is thought to be important to tropical cyclogenesis because its cat's eye provides (i) a region of cyclonic vorticity and weak deformation by the resolved flow, (ii) containment of moisture entrained by the developing flow and/or lofted by deep convection therein, (iii) confinement of mesoscale vortex aggregation, (iv) a predominantly convective type of heating profile, and (v) maintenance or enhancement of the parent wave until the developing proto-vortex becomes a self-sustaining entity and emerges from the wave as a tropical depression. This genesis sequence and the overarching framework for describing how such hybrid wave-vortex structures become tropical depressions/storms is likened to the development of a marsupial infant in its mother's pouch, and for this reason has been dubbed the "marsupial paradigm". Here we conduct the first multi-scale test of the marsupial paradigm in an idealized setting by revisiting the problem of the transformation of an easterly wave-like disturbance into a tropical storm vortex using the WRF model. An analysis of the evolving winds, equivalent potential temperature, and relative vertical vorticity is presented from coarse (28 km) and high resolution (3.1 km) simulations. The results are found to support key elements of the marsupial paradigm by demonstrating the existence of a vorticity dominant region with minimal strain/shear deformation within the critical layer pouch that contains strong cyclonic vorticity and high saturation fraction. This localized region within the pouch serves as the "attractor" for an upscale "bottom up" development process while the wave pouch and proto-vortex move together. Implications of these findings are

  3. Coarse, intermediate and high resolution numerical simulations of the transition of a tropical wave critical layer to a tropical storm

    NASA Astrophysics Data System (ADS)

    Montgomery, M. T.; Wang, Z.; Dunkerton, T. J.

    2010-11-01

    Recent work has hypothesized that tropical cyclones in the deep Atlantic and eastern Pacific basins develop from within the cyclonic Kelvin cat's eye of a tropical easterly wave critical layer located equatorward of the easterly jet axis. The cyclonic critical layer is thought to be important to tropical cyclogenesis because its cat's eye provides (i) a region of cyclonic vorticity and weak deformation by the resolved flow, (ii) containment of moisture entrained by the developing flow and/or lofted by deep convection therein, (iii) confinement of mesoscale vortex aggregation, (iv) a predominantly convective type of heating profile, and (v) maintenance or enhancement of the parent wave until the developing proto-vortex becomes a self-sustaining entity and emerges from the wave as a tropical depression. This genesis sequence and the overarching framework for describing how such hybrid wave-vortex structures become tropical depressions/storms is likened to the development of a marsupial infant in its mother's pouch, and for this reason has been dubbed the "marsupial paradigm". Here we conduct the first multi-scale test of the marsupial paradigm in an idealized setting by revisiting the Kurihara and Tuleya problem examining the transformation of an easterly wave-like disturbance into a tropical storm vortex using the WRF model. An analysis of the evolving winds, equivalent potential temperature, and relative vertical vorticity is presented from coarse (28 km), intermediate (9 km) and high resolution (3.1 km) simulations. The results are found to support key elements of the marsupial paradigm by demonstrating the existence of a rotationally dominant region with minimal strain/shear deformation near the center of the critical layer pouch that contains strong cyclonic vorticity and high saturation fraction. This localized region within the pouch serves as the "attractor" for an upscale "bottom up" development process while the wave pouch and proto-vortex move together

  4. Gravity wave characteristics in the mesopause region revealed from OH airglow imager observations over Northern Colorado

    NASA Astrophysics Data System (ADS)

    Tang, Yihuan; Dou, Xiankang; Li, Tao; Nakamura, Takuji; Xue, Xianghui; Huang, Can; Manson, Alan; Meek, Chris; Thorsen, Denise; Avery, Susan

    2014-01-01

    Using 5 years of all-sky OH airglow imager data over Yucca Ridge Field Station, CO (40.7°N, 104.9°W), from September 2003 to September 2008, we extract and deduce quasi-monochromatic gravity wave (GW) characteristics in the mesopause region. The intrinsic periods are clustered between approximately 4 and 10 min, and many of them are unstable and evanescent. GW occurrence frequency exhibits a clear semiannual variation with equinoctial minima, which is likely related to the seasonal variation of background wind. The anomalous propagation direction in January 2006, with strong southward before major warming starting in 21 January and weak southward propagation afterward, was most likely affected by stratospheric sudden warming. The momentum fluxes show strongly anticorrelated with the tides, with ~180° out of phase in the zonal component. While in the meridional component, the easterly maximum occurred approximately 2-6 h after maximum easterly tidal wind. However, the anticorrelations are both weakest during the summer. The dissipating and breaking of small-scale and high-frequency GW's components could have a potential impact on the general circulation in the mesopause region.

  5. Projections of 21st Century African Climate: Implications for African Savanna Fire Dynamics, Human Health and Food Security

    NASA Astrophysics Data System (ADS)

    Adegoke, J. O.

    2015-12-01

    Fire is a key agent of change in the African savannas, which are shaped through the complex interactions between trees, C4 grasses, rainfall, temperature, CO2 and fire. These fires and their emitted smoke can have numerous direct and indirect effects on the environment, water resources, air quality, and climate. For instance, veld fires in southern Africa cause large financial losses to agriculture, livestock production and forestry on an annual basis. This study contributes to our understanding of the implications of projected surface temperature evolution in Africa for fire risk, human health and agriculture over the coming decades. We use an ensemble of high-resolution regional climate model simulations of African climate for the 21st century. Regional dowscalings and recent global circulation model projections obtained for Africa indicate that African temperatures are likely to rise at 1.5 times the global rate of temperature increase in the tropics, and at almost twice the global rate of increase in the subtropics. Warming is projected to occur during the 21st century, with increases of 4-6 °C over the subtropics and 3-5 °C over the tropics plausible by the end of the century relative to present-day climate under the A2 (low mitigation) scenario. We explore the significance of the projected warming by documenting increases in projected high fire danger days and heat-wave days. General drying is projected across the continent, even for areas (e.g. tropical Africa) where an increase in rainfall is plausible. This is due to the drastic increases in temperature that are projected, which leads to drier soils (through enhanced evaporation) despite the rainfall increases. This will likely impact negatively on crop yield, particularly on the maize crop that is of crucial importance in terms of African food security.

  6. Significant impacts of radiation physics in the Weather Research and Forecasting model on the precipitation and dynamics of the West African Monsoon

    NASA Astrophysics Data System (ADS)

    Li, R.; Jin, J.; Wang, S.-Y.; Gillies, R. R.

    2015-03-01

    Precipitation from the West African Monsoon (WAM) provides food security and supports the economy in the region. As a consequence of the intrinsic complexities of the WAM's evolution, accurate simulations of the WAM and its precipitation regime, through the application of regional climate models, are challenging. We used the coupled Weather Research and Forecasting (WRF) and Community Land Model (CLM) to explore impacts of radiation physics on the precipitation and dynamics of the WAM. Our results indicate that the radiation physics schemes not only produce biases in radiation fluxes impacting radiative forcing, but more importantly, result in large bias in precipitation of the WAM. Furthermore, the different radiation schemes led to variations in the meridional gradient of surface temperature between the north that is the Sahara desert and the south Guinean coastline. Climate diagnostics indicated that the changes in the meridional gradient of surface temperature affect the position and strength of the African Easterly Jet as well as the low-level monsoonal inflow from the Gulf of Guinea. The net result was that each radiation scheme produced differences in the WAM precipitation regime both spatially and in intensity. Such considerable variances in the WAM precipitation regime and dynamics, resulting from radiation representations, likely have strong feedbacks within the climate system and so have inferences when it comes to aspects of predicted climate change both for the region and globally.

  7. The UCAR Africa Initiative: Enabling African Solutions to African Needs

    NASA Astrophysics Data System (ADS)

    Pandya, R.; Bruintjes, R.; Foote, B.; Heck, S.; Hermann, S.; Hoswell, L.; Konate, M.; Kucera, P.; Laing, A.; Lamptey, B.; Moncrieff, M.; Ramamurthy, M.; Roberts, R.; Spangler, T.; Traoré, A.; Yoksas, T.; Warner, T.

    2007-12-01

    The University Corporation for Atmospheric Research (UCAR) Africa Initiative (AI) is a coordinated effort aimed at building sustainable partnerships between UCAR and African institutions in order to pursue research and applications for the benefit of the African people. The initiative is based on four fundamental operating principles, concisely summarized by the overall philosophy of enabling African solutions to African needs. The four principles are: • Collaborate with African institutions • Focus on institutional capacity building and research support • Explore science research themes critical to Africa and important for the world • Leverage the research infrastructure in UCAR to add value These principles are realized in a set of pilot activities, chosen for their high probability of short-term results and ability to set the stage for longer-term collaboration. The three pilot activities are listed below. 1. A modest radar network and data-distribution system in Mali and Burkina Faso, including a data-sharing MOU between the Mail and Burkina Faso Weather Services. 2. A partnership among UCAR, the Ghana Meteorological Agency, and the Ghana university community to develop an operational Weather Research and Forecasting (WRF) model for West Africa. The output is used by researchers and operational forecasters in Africa. Model output is also part of a demonstration project that aims to allow humanitarian agencies to share geo-referenced information in Africa via a web portal. 3. A workshop in Ouagadougou, Burkina Faso from April 2-6, 2007, with the theme Improving Lives by Understanding Weather. The workshop, co-organized with Programme SAAGA and the Commité Permanent Inter-Etats de Lutte Contre la Sécheresse dans le Sahel (CILSS), included over 80 participants from 18 countries, and produced a set of recommendations for continued collaboration. Our presentation will provide an update of these pilot activities and point to future directions. Recognizing

  8. Religious Participation is Associated with Increases in Religious Social Support in a National Longitudinal Study of African Americans.

    PubMed

    Le, Daisy; Holt, Cheryl L; Hosack, Dominic P; Huang, Jin; Clark, Eddie M

    2016-08-01

    This study reports on the association between religious beliefs and behaviors and the change in both general and religious social support using two waves of data from a national sample of African Americans. The Religion and Health in African Americans (RHIAA) study is a longitudinal telephone survey designed to examine relationships between various aspects of religious involvement and psychosocial factors over time. RHIAA participants were 3173 African American men (1281) and women (1892). A total of 1251 men (456) and women (795) participated in wave 2 of data collection. Baseline religious behaviors were associated with increased overall religious social support from baseline to wave 2 (p < .001) and with increased religious social support from baseline to wave 2 in each of the following religious social support subscales: emotional support received (p < .001), emotional support provided (p < .001), negative interaction (p < .001), and anticipated support (p < .001). Religious beliefs did not predict change in any type of support, and neither beliefs nor behaviors predicted change in general social support. African Americans who are active in faith communities showed increases in all types of religious social support, even the negative aspects, over a relatively modest longitudinal study period. This illustrates the strength of the church as a social network and the role that it plays in people's lives. PMID:26493343

  9. Genome-wide patterns of population structure and admixture in West Africans and African Americans.

    PubMed

    Bryc, Katarzyna; Auton, Adam; Nelson, Matthew R; Oksenberg, Jorge R; Hauser, Stephen L; Williams, Scott; Froment, Alain; Bodo, Jean-Marie; Wambebe, Charles; Tishkoff, Sarah A; Bustamante, Carlos D

    2010-01-12

    Quantifying patterns of population structure in Africans and African Americans illuminates the history of human populations and is critical for undertaking medical genomic studies on a global scale. To obtain a fine-scale genome-wide perspective of ancestry, we analyze Affymetrix GeneChip 500K genotype data from African Americans (n = 365) and individuals with ancestry from West Africa (n = 203 from 12 populations) and Europe (n = 400 from 42 countries). We find that population structure within the West African sample reflects primarily language and secondarily geographical distance, echoing the Bantu expansion. Among African Americans, analysis of genomic admixture by a principal component-based approach indicates that the median proportion of European ancestry is 18.5% (25th-75th percentiles: 11.6-27.7%), with very large variation among individuals. In the African-American sample as a whole, few autosomal regions showed exceptionally high or low mean African ancestry, but the X chromosome showed elevated levels of African ancestry, consistent with a sex-biased pattern of gene flow with an excess of European male and African female ancestry. We also find that genomic profiles of individual African Americans afford personalized ancestry reconstructions differentiating ancient vs. recent European and African ancestry. Finally, patterns of genetic similarity among inferred African segments of African-American genomes and genomes of contemporary African populations included in this study suggest African ancestry is most similar to non-Bantu Niger-Kordofanian-speaking populations, consistent with historical documents of the African Diaspora and trans-Atlantic slave trade. PMID:20080753

  10. African American Therapists Working with African American Families: An Exploration of the Strengths Perspective in Treatment

    ERIC Educational Resources Information Center

    Bell-Tolliver, Laverne; Burgess, Ruby; Brock, Linda J.

    2009-01-01

    With the exception of Hill's (1971, 1999) work, historically much of the literature on African American families has focused more on pathology than strengths. This study used interviews with 30 African American psychotherapists, self-identified as employing a strengths perspective with African American families, to investigate which strengths they…

  11. Karla Holloway to Lead African and African-American Studies at Duke University.

    ERIC Educational Resources Information Center

    Hawkins, B. Denise

    1996-01-01

    The appointment of Karla F. C. Holloway, an African American woman, as director of the Duke University (North Carolina) African American Studies program is representative of an institutional effort to stabilize the program and to recruit African American scholars to the institution, across disciplines. During Holloway's interim directorship,…

  12. 75 FR 2844 - African Development Foundation, Board of Directors Meeting

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-01-19

    ...; ] AFRICAN DEVELOPMENT FOUNDATION African Development Foundation, Board of Directors Meeting Time: Tuesday, January 26, 2010, 8:30 a.m. to 1 p.m. Place: African Development Foundation, Conference Room, 1400...

  13. 75 FR 14418 - African Development Foundation, Board of Directors Meeting

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-03-25

    ...; ] AFRICAN DEVELOPMENT FOUNDATION African Development Foundation, Board of Directors Meeting Time: Tuesday, April 13, 2010, 9:30 a.m. to 1 p.m. Place: African Development Foundation, Conference Room, 1400...

  14. 75 FR 45600 - African Development Foundation, Board of Directors Meeting

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-03

    ...; ] AFRICAN DEVELOPMENT FOUNDATION African Development Foundation, Board of Directors Meeting Time: Tuesday, August 17, 2010, 8:30 a.m. to 1 p.m. Place: African Development Foundation, Conference Room, 1400...

  15. Cultural aspects of African American eating patterns.

    PubMed

    Airhihenbuwa, C O; Kumanyika, S; Agurs, T D; Lowe, A; Saunders, D; Morssink, C B

    1996-09-01

    The high mortality from diet-related diseases among African Americans strongly suggests a need to adopt diets lower in total fat, saturated fat and salt and higher in fiber. However, such changes would be contrary to some traditional African American cultural practices. Focus group interviews were used to explore cultural aspects of eating patterns among low- and middle-income African Americans recruited from an urban community in Pennsylvania. In total, 21 males and 32 females, aged 13-65+ years were recruited using a networking technique. Participants identified eating practices commonly attributed to African Americans and felt that these were largely independent of socioeconomic status. They were uncertain about links between African American eating patterns and African origins but clear about influences of slavery and economic disadvantage. The perception that African American food patterns were characteristically adaptive to external conditions, suggest that, for effective dietary change in African American communities, changes in the food availability will need to precede or take place in parallel with changes recommended to individuals. Cultural attitudes about where and with whom food is eaten emerged as being equivalent in importance to attitudes about specific foods. These findings emphasize the importance of continued efforts to identify ways to increase the relevance of cultural context and meanings in dietary counseling so that health and nutrition interventions are anchored in values as perceived, in this case, by African Americans. PMID:9395569

  16. Race, health, and the African Diaspora.

    PubMed

    Spigner, Clarence

    Health inequalities exist throughout the African Diaspora and are viewed in this article as largely color-coded. In developed, developing, and undeveloped nations today, "racial" stratification is consistently reflected in an inability to provide adequate health regardless of national policy or ideology. For instance, African Americans experience less than adequate health care very similar to Blacks in Britain, in spite of each nations differing health systems. Latin America's Africana Negra communities experience poorer health similar to Blacks throughout the Caribbean. The African continent itself is arguably the poorest on earth. A common history of racism correlates with health disparities across the African Diaspora. PMID:18364304

  17. Gentle Africanized bees on an oceanic island

    PubMed Central

    Rivera-Marchand, Bert; Oskay, Devrim; Giray, Tugrul

    2012-01-01

    Oceanic islands have reduced resources and natural enemies and potentially affect life history traits of arriving organisms. Among the most spectacular invasions in the Western hemisphere is that of the Africanized honeybee. We hypothesized that in the oceanic island Puerto Rico, Africanized bees will exhibit differences from the mainland population such as for defensiveness and other linked traits. We evaluated the extent of Africanization through three typical Africanized traits: wing size, defensive behavior, and resistance to Varroa destructor mites. All sampled colonies were Africanized by maternal descent, with over 65% presence of European alleles at the S-3 nuclear locus. In two assays evaluating defense, Puerto Rican bees showed low defensiveness similar to European bees. In morphology and resistance to mites, Africanized bees from Puerto Rico are similar to other Africanized bees. In behavioral assays on mechanisms of resistance to Varroa, we directly observed that Puerto Rican Africanized bees groomed-off and bit the mites as been observed in other studies. In no other location, Africanized bees have reduced defensiveness while retaining typical traits such as wing size and mite resistance. This mosaic of traits that has resulted during the invasion of an oceanic island has implications for behavior, evolution, and agriculture. PMID:23144660

  18. Forced Planetary Waves in the Northern Hemisphere Winter: Wave-Coupled Orographic and Thermal Forcings.

    NASA Astrophysics Data System (ADS)

    Chen, Shyh-Chin; Trenberth, Kevin E.

    1988-02-01

    A more complete and new formulation of the orographic forcing and new thermal forcings are included in a steady state model of the Northern Hemisphere planetary waves. When both forcings are included, the simulation produces excellent results which are compared in detail with observations. In particular, the Siberian high, the tropospheric East Asian trough and subtropical tropospheric East Asian jet stream maxima are well reproduced even though the forcing is primarily extratropical in origin.The modes uses a lower boundary condition in which the orographic forcing is determined by the effects of the total flow, not just the zonal mean basic state. Consequently, the net orographic forcing changes when thermal forcing is added and the tow solution is not equal to the linear sum of the solutions with orographic and thermal forcings separately. The thermally induced orographic forcing is found to be very significant and, in the troposphere, there is strong interaction between the two forcings with both of roughly equal importance. However, the Iowa-latitude vertically propagating waves am deflected by the subtropical jet and absorbed in the low-latitude easterlies. Thus only the mid-high latitude planetary waves are important in the stratosphere which seems to be dominated by the thermally forced component.The model is forced with new estimates of diabetic heating from several FGGE analyses. The sensitivity of the results to different heatings and their assumed vertical profile is examined. The amplitude of the lower-troposphere response is very sensitive to the vertical profile but there are much smaller changes at upper levels which are dominated by the remote response. Large differences in the response to the different diabatic heatings are found at high latitudes and over the Pacific Ocean. However, when orographic forcing is also included, these differences diminish indicating a smaller sensitivity to uncertainties in heating, and thus the orographic forcing is

  19. Intraseasonal and Interannual Variability of the Quasi-Two Day Wave in the Northern Hemisphere Summer Mesosphere

    NASA Technical Reports Server (NTRS)

    McCormack, J. P.; Coy, L.; Singer, W.

    2013-01-01

    This study uses global synoptic meteorological fields from a high-altitude data assimilation system to investigate the spatial and temporal characteristics of the quasi-2 day wave (Q2DW) and migrating diurnal tide during the Northern Hemisphere summers of 2007, 2008, and 2009. By applying a 2-dimensional fast Fourier transform to meridional wind and temperature fields, we are able to identify Q2DW source regions and to diagnose propagation of Q2DW activity into the upper mesosphere and lower thermosphere. We find that Q2DW is comprised primarily of westward propagating zonal wavenumber 3 and wavenumber 4 components that originate from within baroclinically unstable regions along the equatorward flank of the summer midlatitude easterly jet. Amplitude variations of wavenumbers 3 and 4 tend to be anti-correlated throughout the summer, with wavenumber 3 maximizing in July and wavenumber 4 maximizing in late June and early August. Monthly mean Q2DW amplitudes between 30 50N latitude are largest when diurnal tidal amplitudes are smallest and vice versa. However, there is no evidence of any rapid amplification of the Q2DW via nonlinear interaction with the diurnal tide. Instead, variations of Q2DW amplitudes during July are closely linked to variations in the strength and location of the easterly jet core from one summer to the next, with a stronger jet producing larger Q2DW amplitudes. Linear instability model calculations based on the assimilated wind fields find fast growing zonal wavenumber 3 and 4 modes with periods near 2 days in the vicinity of the easterly jet.

  20. Studies of quasi-horizontally propagating gravity waves in the troposphere using the Piura ST wind profiler

    NASA Astrophysics Data System (ADS)

    Liziola, Luis Enrique

    The purpose of this thesis is to report a series of investigations of an unusual atmospheric phenomenon observed over the desert-like terrain along the northern Peruvian coast. This phenomenon is manifested by quasi- sinusoidal oscillations observed in the vertical wind velocity throughout the troposphere using a conventional VHF Profiler. We will present the results of a five-year study using the Piura profiler, in addition to two other small closely-spaced VHF radar designed to measure the horizontal characteristics of the wave-like oscillations. We will show that the most likely source of these waves lies in orographic effects of the Andean Cordillera combined with the consistent easterly flow of the tropospheric winds.

  1. Influence of the sudden stratospheric warming on quasi-2-day waves

    NASA Astrophysics Data System (ADS)

    Gu, Sheng-Yang; Liu, Han-Li; Dou, Xiankang; Li, Tao

    2016-04-01

    The influence of the sudden stratospheric warming (SSW) on a quasi-2-day wave (QTDW) with westward zonal wave number 3 (W3) is investigated using the Thermosphere-Ionosphere-Mesosphere Electrodynamics General Circulation Model (TIME-GCM). The summer easterly jet below 90 km is strengthened during an SSW, which results in a larger refractive index and thus more favorable conditions for the propagation of W3. In the winter hemisphere, the Eliassen-Palm (EP) flux diagnostics indicate that the strong instabilities at middle and high latitudes in the mesopause region are important for the amplification of W3, which is weakened during SSW periods due to the deceleration or even reversal of the winter westerly winds. Nonlinear interactions between the W3 and the wave number 1 stationary planetary wave produce QTDW with westward zonal wave number 2 (W2). The meridional wind perturbations of the W2 peak in the equatorial region, while the zonal wind and temperature components maximize at middle latitudes. The EP flux diagnostics indicate that the W2 is capable of propagating upward in both winter and summer hemispheres, whereas the propagation of W3 is mostly confined to the summer hemisphere. This characteristic is likely due to the fact that the phase speed of W2 is larger, and therefore its waveguide has a broader latitudinal extension. The larger phase speed also makes W2 less vulnerable to dissipation and critical layer filtering by the background wind when propagating upward.

  2. Gravity Waves and Mesospheric Clouds in the Summer Middle Atmosphere: A Comparison of Lidar Measurements and Ray Modeling of Gravity Waves Over Sondrestrom, Greenland

    NASA Technical Reports Server (NTRS)

    Gerrard, Andrew J.; Kane, Timothy J.; Eckermann, Stephen D.; Thayer, Jeffrey P.

    2004-01-01

    We conducted gravity wave ray-tracing experiments within an atmospheric region centered near the ARCLITE lidar system at Sondrestrom, Greenland (67N, 310 deg E), in efforts to understand lidar observations of both upper stratospheric gravity wave activity and mesospheric clouds during August 1996 and the summer of 2001. The ray model was used to trace gravity waves through realistic three-dimensional daily-varying background atmospheres in the region, based on forecasts and analyses in the troposphere and stratosphere and climatologies higher up. Reverse ray tracing based on upper stratospheric lidar observations at Sondrestrom was also used to try to objectively identify wave source regions in the troposphere. A source spectrum specified by reverse ray tracing experiments in early August 1996 (when atmospheric flow patterns produced enhanced transmission of waves into the upper stratosphere) yielded model results throughout the remainder of August 1996 that agreed best with the lidar observations. The model also simulated increased vertical group propagation of waves between 40 km and 80 km due to intensifying mean easterlies, which allowed many of the gravity waves observed at 40 km over Sondrestrom to propagate quasi-vertically from 40-80 km and then interact with any mesospheric clouds at 80 km near Sondrestrom, supporting earlier experimentally-inferred correlations between upper stratospheric gravity wave activity and mesospheric cloud backscatter from Sondrestrom lidar observations. A pilot experiment of real-time runs with the model in 2001 using weather forecast data as a low-level background produced less agreement with lidar observations. We believe this is due to limitations in our specified tropospheric source spectrum, the use of climatological winds and temperatures in the upper stratosphere and mesosphere, and missing lidar data from important time periods.

  3. On neutron surface waves

    SciTech Connect

    Ignatovich, V. K.

    2009-01-15

    It is shown that neutron surface waves do not exist. The difference between the neutron wave mechanics and the wave physics of electromagnetic and acoustic processes, which allows the existence of surface waves, is analyzed.

  4. Gravity Waves

    NASA Technical Reports Server (NTRS)

    Vanzandt, T. E.

    1985-01-01

    Atmospheric parameters fluctuate on all scales. In the mesoscale these fluctuations are occasionally sinusoidal so that they can be interpreted as gravity waves. Usually, however, the fluctuations are noise like, so that their cause is not immediately evident. Results of mesoscale observations in the 20 to 120 m altitude range that are suitable for incorporation into a model atmosphere are very limited. In the stratosphere and lower mesosphere observations are sparse and very little data has been summarized into appropriate form. There is much more data in the upper mesosphere and lower thermosphere, but again very little of it has been summarized. The available mesoscale spectra of horizontal wind u versus vertical wave number m in the 20 to 120 km altitude range are shown together with a spectrum from the lower atmosphere for comparison. Further information about these spectra is given. In spite of the large range of altitudes and latitudes, the spectra from the lower atmosphere (NASA, 1971 and DEWAN, 1984) are remarkably similar in both shape and amplitude. The mean slopes of -2.38 for the NASA spectrum and -2.7 for the Dewan spectra are supported by the mean slope of -2.75 found by ROSENBERG et al. (1974). The mesospheric spectrum is too short to establish a shape. Its amplitude is about an order of magnitude larger than the NASA spectrum in the same wave number range. The NASA and Dewan spectra suggest that the mesoscale spectra in the lower atmosphere are insensitive to meteorological conditions.

  5. Assessment of Uncertainties in the Response of the African Monsoon Precipitation to Land Use Change in Regional Model Simulations

    NASA Astrophysics Data System (ADS)

    Hagos, S. M.; Leung, L.; Xue, Y.; Boone, A. A.; Huang, M.; Yoon, J.

    2013-12-01

    Land use and land cover over Africa have changed substantially over the last sixty years and this change has been proposed to affect monsoon circulation and precipitation. This study examines the uncertainties on the effect of these changes on the African Monsoon system and Sahel precipitation using an ensemble of regional model simulations with different combinations of land surface and cumulus parameterization schemes. Although the magnitude of the response covers a broad range of values, most of the simulations show a decline in Sahel precipitation due to the expansion of pasture and croplands at the expense of trees and shrubs and an increase in surface air temperature. The relationship between the model responses to land use change and the climatologies of the control simulations is also examined. Simulations that are climatologically too dry or too wet compared to observations and reanalyses have weak response to land use change because they are in moisture or energy limited regimes respectively. The ones that lie in between and therefore land-atmosphere interactions play a more significant role have stronger response to the land use and land cover changes. Much of the change in precipitation is related to changes in circulation, particularly to the response of the intensity and latitudinal position of the African Easterly Jet, which varies with the changes in meridional surface temperature gradients. The study highlights the need for measurements of the surface fluxes across the meridional cross-section of the Sahel to evaluate models and thereby allowing human impacts such as land use change on the monsoon to be projected more realistically.

  6. Assessment of uncertainties in the response of the African monsoon precipitation to land use change simulated by a regional model

    NASA Astrophysics Data System (ADS)

    Hagos, Samson; Leung, L. Ruby; Xue, Yongkang; Boone, Aaron; de Sales, Fernando; Neupane, Naresh; Huang, Maoyi; Yoon, Jin-Ho

    2014-11-01

    Land use and land cover (LULC) over Africa have changed substantially over the last 60 years and this change has been proposed to affect monsoon circulation and precipitation. This study examines the uncertainties of model simulated response in the African monsoon system and Sahel precipitation due to LULC change using a set of regional model simulations with different combinations of land surface and cumulus parameterization schemes. Although the magnitude of the response covers a broad range of values, most of the simulations show a decline in Sahel precipitation due to the expansion of pasture and croplands at the expense of trees and shrubs and an increase in surface air temperature. The relationship between the model responses to LULC change and the climatologists of the control simulations is also examined. Simulations that are climatologically too dry or too wet compared to observations and reanalyses have weak response to land use change because they are in moisture or energy limited regimes respectively. The ones that lie in between have stronger response to the LULC changes, showing a more significant role in land-atmosphere interactions. Much of the change in precipitation is related to changes in circulation, particularly to the response of the intensity and latitudinal position of the African Easterly Jet, which varies with the changes in meridional surface temperature gradients. The study highlights the need for measurements of the surface fluxes across the meridional cross-section of the Sahel to evaluate models and thereby allowing human impacts such as land use change on the monsoon to be projected more realistically.

  7. Overly persistent circulation in climate models contributes to overestimated frequency and duration of heat waves and cold spells

    NASA Astrophysics Data System (ADS)

    Plavcova, Eva; Kysely, Jan

    2016-04-01

    The study examines links of summer heat waves and winter cold spells in Central Europe to atmospheric circulation and specifically its persistence in an ensemble of regional climate models (RCMs). We analyse 13 RCMs driven by the ERA-40 reanalysis and compare them against observations over 1971-2000. Using objective classification of circulation types and an efficiency coefficient with a block resampling test, we identify circulation types significantly conducive to heat waves and cold spells. We show that the RCMs have a stronger tendency to group together days with very high or low temperature and tend to simulate too many heat waves and cold spells, especially those lasting 5 days and more. Circulation types conducive to heat waves in summer are characterized by anticyclonic, southerly and easterly flow, with increasing importance of warm advection during heat waves. Winter cold spells are typically associated with easterly and anticyclonic flow, and the onset of cold spells tends to be linked to northerly and cyclonic flow with cold advection. The RCMs are generally able to reproduce the links between circulation and heat waves or cold spells, including the radiation-to-advection effect for heat waves and the opposite advection-to-radiation effect for cold spells. They capture relatively well also changes of mean temperature anomalies during sequences of given circulation types, namely the tendency towards an increase (decrease) of temperature during the types conducive to heat waves (cold spells). Since mean lengths of all circulation supertypes are overestimated in the RCMs, we conclude that the overly persistent circulation in climate models contributes to the overestimated frequency of long heat waves and cold spells. As these biases are rather general among the examined RCMs and similar drawbacks are likely to be manifested in climate model simulations for the 21st century, the results also suggest that climate change scenarios for spells of days with high

  8. Environmental health and African Americans.

    PubMed Central

    Walker, B

    1991-01-01

    As environmental health has taken on immensely increased significance in the prevention of disease, dysfunction, and premature death, its boundaries have been anything but stable. This instability, along with a multitude of demographic, social, and economic currents, have brought into stark relief the increasing demand for scientists who have the skills and knowledge to perform environmental risk assessment and implement effective risk management policies and services. Despite this demand far too few African Americans want, or are prepared, to pursue careers in sciences. This paper describes efforts to address this problem and suggests why such initiatives may not yield the desired results. PMID:1951793

  9. Environmental sensing by African trypanosomes.

    PubMed

    Roditi, Isabel; Schumann, Gabriela; Naguleswaran, Arunasalam

    2016-08-01

    African trypanosomes, which divide their life cycle between mammals and tsetse flies, are confronted with environments that differ widely in temperature, nutrient availability and host responses to infection. In particular, since trypanosomes cannot predict when they will be transmitted between hosts, it is vital for them to be able to sense and adapt to their milieu. Thanks to technical advances, significant progress has been made in understanding how the parasites perceive external stimuli and react to them. There is also a growing awareness that trypanosomes use a variety of mechanisms to exchange information with each other, thereby enhancing their chances of survival. PMID:27131101

  10. Improving African American Achievement in Geometry Honors

    ERIC Educational Resources Information Center

    Mims, Adrian B.

    2010-01-01

    This case study evaluated the significance of implementing an enrichment mathematics course during the summer to rising African American ninth graders entitled, "Geometry Honors Preview." In the past, 60 to 70 percent of African American students in this school district had withdrawn from Geometry Honors by the second academic quarter. This study…

  11. Heart Truth for African American Women

    MedlinePlus

    THE HEART TRUTH ® FOR AFRICAN AMERICAN WOMEN: AN ACTION PLAN When you hear the term “heart disease,” what’s your first reaction? Like many women, you may ... in four women dies of heart disease. For African American women, the risk of heart disease is especially ...

  12. A Mirror Image African American Student Reflections

    ERIC Educational Resources Information Center

    Cannon Dawson, Candice

    2012-01-01

    This dissertation is a narrative inquiry research project that focuses on the collegiate experiences of African American students at both historically black colleges and universities (HBCUs) and predominantly white institutions (PWIs). I look at how African American college students who engage in race or culturally specific activities, the degree…

  13. The African Student in the American University.

    ERIC Educational Resources Information Center

    Riley, Doris

    This paper gathers information on the values, cognition, and educational background of African students studying at universities in the United States. The section on values notes that Americans are task-oriented individualists, while Africans are primarily relationship-oriented collectivists. These values of sharing and relationship orientation…

  14. African (Black) Psychology: Issues and Synthesis.

    ERIC Educational Resources Information Center

    Baldwin, Joseph A.

    1986-01-01

    Reviews the recent attempts of Black psychologists and social scientists to formulate a conceptual-operational framework for the study of psychological phenomena as they bear on the cultural-survival conditions of Black-African people. Outlines issues and problems in the attempt to define African (Black) psychology and discusses its relation to…

  15. African American Women in Higher Education

    ERIC Educational Resources Information Center

    Zamani, Eboni M.

    2003-01-01

    African American women hold a unique position as members of two groups that have been treated in a peripheral manner by postsecondary education (Moses, 1989). Membership in both marginalized groups often makes African American women invisible in colleges and universities. Given the complex intersection of race and gender, more attention should be…

  16. African-American Student Achievement Research Project.

    ERIC Educational Resources Information Center

    Wagstaff, Mark; Melton, Jerry; Lawless, Brenda; Combs, Linda

    Data from the Texas Assessment of Academic Skills (TAAS) reveal that gains in performance for the African American student population of Region VII of the state's educational system were not keeping pace with the performance of African Americans in the rest of Texas. This study investigated practices in school districts in the region in which…

  17. Cancer and the African American Experience

    Cancer.gov

    The first plenary of the EPEC-O (Education in Palliative and End-of-Life Care for Oncology) Self-Study: Cultural Considerations When Caring for African Americans explores the many factors that lead to inequalities in cancer care outcomes for African Americans.

  18. Computer Networks and African Studies Centers.

    ERIC Educational Resources Information Center

    Kuntz, Patricia S.

    The use of electronic communication in the 12 Title VI African Studies Centers is discussed, and the networks available for their use are reviewed. It is argued that the African Studies Centers should be on the cutting edge of contemporary electronic communication and that computer networks should be a fundamental aspect of their programs. An…

  19. Reading Comprehension among African American Graduate Students

    ERIC Educational Resources Information Center

    Onwuegbuzie, Anthony J.; Mayes, Eric; Arthur, Leslie; Johnson, Joseph; Robinson, Veronica; Ashe, Shante; Elbedour, Salman; Collins, Kathleen M. T.

    2004-01-01

    A study was conducted to examine the reading comprehension performance of African American graduate students. The result showed that though the African American sample attained statistically significantly higher levels of reading comprehension than a normative sample of undergraduate students, they achieved lower levels of reading comprehension…

  20. Technology Builds Global Acceptance among African Students.

    ERIC Educational Resources Information Center

    John, Martha Tyler; John, Floyd Idwal

    This paper describes how a new university, African Nazarene University (ANU) in Kenya, used various means, including computer technology, for implementing learning goals for students from a wide variety of African countries and tribes. The paper stresses that the school, which opened in 1994 with 65 students, emphasized tolerance of differences…

  1. Genetics Home Reference: African iron overload

    MedlinePlus

    ... of a genetic condition? Genetic and Rare Diseases Information Center Frequency African iron overload is common in rural areas of central and ... more about the gene associated with African iron overload SLC40A1 Related Information What is a gene? What is a gene ...

  2. African Higher Education: An International Reference Handbook.

    ERIC Educational Resources Information Center

    Teferra, Damtew, Ed.; Altbach, Philip G., Ed.

    This book is a comprehensive survey of all aspects and dimensions of higher education in Africa. It includes a historical overview of higher education, descriptions of the higher education systems in each African country, and analyses of current and timely topics in higher education. Part 1, "Themes," contains 13 essays on trends in African higher…

  3. African American Art: A Los Angeles Legacy.

    ERIC Educational Resources Information Center

    Walker, Harriet

    This curriculum unit focuses on the importance of Los Angeles (California) as a center for African American art and shows how African American artists have developed their own styles and how critics and collectors have encouraged them. The unit consists of four lessons, each of which can stand alone or be used in conjunction with the others. It…

  4. New data on African health professionals abroad

    PubMed Central

    Clemens, Michael A; Pettersson, Gunilla

    2008-01-01

    Background The migration of doctors and nurses from Africa to developed countries has raised fears of an African medical brain drain. But empirical research on the causes and effects of the phenomenon has been hampered by a lack of systematic data on the extent of African health workers' international movements. Methods We use destination-country census data to estimate the number of African-born doctors and professional nurses working abroad in a developed country circa 2000, and compare this to the stocks of these workers in each country of origin. Results Approximately 65,000 African-born physicians and 70,000 African-born professional nurses were working overseas in a developed country in the year 2000. This represents about one fifth of African-born physicians in the world, and about one tenth of African-born professional nurses. The fraction of health professionals abroad varies enormously across African countries, from 1% to over 70% according to the occupation and country. Conclusion These numbers are the first standardized, systematic, occupation-specific measure of skilled professionals working in developed countries and born in a large number of developing countries. PMID:18186916

  5. Beyond Afrocentricism: Alternatives for African American Studies.

    ERIC Educational Resources Information Center

    Hall, Perry A.

    1991-01-01

    Discusses new directions for African-American studies curricula. Argues that the Afrocentrist perspective presents a static model that does not adequately address the dynamic interaction of Afrocentric sensibility with Western-dominated economic, cultural, and political structures. The African-American studies discipline should be conceptualized…

  6. Traditional African Religion: A Resource Unit.

    ERIC Educational Resources Information Center

    Garland, William E.

    This resource unit is based on research conducted by Lynn Mitchell and Ernest Valenzuela, experienced classroom teachers of African history and culture. The unit consists of an introduction by Mr. Garland and two major parts. Part I is an annotated bibliography of selected sources on various aspects of traditional African Religion useful in…

  7. The African American Woman. Runta (Truth).

    ERIC Educational Resources Information Center

    Jackson, Monica L.; Watson, Betty Collier, Ed.

    1989-01-01

    The African American woman has commanded widespread public attention, but popular misconceptions of her socioeconomic role and status differ sharply from her actual situation. The following basic characteristics of the contemporary African American woman, drawn from census figures, are outlined: (1) demographically, females comprise a majority of…

  8. Kunta Kinte's Struggle to be African

    ERIC Educational Resources Information Center

    Courlander, Harold

    1986-01-01

    This article reveals the differences between the character Kunta Kinte and the historical record concerning African males in the preslavery period. Kunta's non-African behaviors include displays of blind anger and rage, prudishness, and actions unknown in his Mandinka culture. These represent the many misrepresentations and ambiguities in Alex…

  9. France: Africans and the French Revolution.

    ERIC Educational Resources Information Center

    Fatunde, Tunde

    1989-01-01

    The French Revolution had profound and long-term effects for Africans, both in Africa and throughout the Western hemisphere. Revolutionary leaders not only opposed the emancipation of slaves in French territories but supported an intensified slave trade, sparking numerous rebellions. French exploitation of Africans extended well into the twentieth…

  10. African American Undergraduates and the Academic Library

    ERIC Educational Resources Information Center

    Whitmire, Ethelene

    2006-01-01

    This study examines the academic library experiences of African American undergraduates attending a research university in the Midwest. Data collection techniques included questionnaires and ethnographic observations. The results indicated that African American undergraduates are using the academic library primarily to read and to study with their…

  11. Hidden Education among African Americans during Slavery

    ERIC Educational Resources Information Center

    Gundaker, Grey

    2007-01-01

    Background/Context: Historical studies examine aspects of African American education in and out of school in detail (Woodson 1915, 1933, Bullock 1970, Anderson 1988, Morris 1982, Rachal 1986, Rose 1964, Webber 1978, Williams 2005). Scholars of African American literacy have noted ways that education intersects other arenas such as religion and…

  12. British African Caribbean Women and Depression

    ERIC Educational Resources Information Center

    Adkison-Bradley, Carla; Maynard, Donna; Johnson, Phillip; Carter, Stephaney

    2009-01-01

    Depression is a common condition among women in the United Kingdom. However, little is known about the context of depression among British African Caribbean women. This article offers a preliminary discussion regarding issues and information pertaining to depression among British African Caribbean women. Characteristics and symptoms of depression…

  13. Depression, Sociocultural Factors, and African American Women

    ERIC Educational Resources Information Center

    Hunn, Vanessa Lynn; Craig, Carlton David

    2009-01-01

    The authors discuss depression in African American women from a sociocultural perspective, including aspects of oppression and racism that affect symptom manifestation. The authors highlight John Henryism as a coping mechanism, the history and continuing role of the African American church as a safe haven, and strategies for culturally competent…

  14. Variability of West African monsoon patterns generated by a WRF multi-physics ensemble

    NASA Astrophysics Data System (ADS)

    Klein, Cornelia; Heinzeller, Dominikus; Bliefernicht, Jan; Kunstmann, Harald

    2015-11-01

    The credibility of regional climate simulations over West Africa stands and falls with the ability to reproduce the West African monsoon (WAM) whose precipitation plays a pivotal role for people's livelihood. In this study, we simulate the WAM for the wet year 1999 with a 27-member multi-physics ensemble of the Weather Research and Forecasting (WRF) model. We investigate the inter-member differences in a process-based manner in order to extract generalizable information on the behavior of the tested cumulus (CU), microphysics (MP), and planetary boundary layer (PBL) schemes. Precipitation, temperature and atmospheric dynamics are analyzed in comparison to the Tropical Rainfall Measuring Mission (TRMM) rainfall estimates, the Global Precipitation Climatology Centre (GPCC) gridded gauge-analysis, the Global Historical Climatology Network (GHCN) gridded temperature product and the forcing data (ERA-Interim) to explore interdependencies of processes leading to a certain WAM regime. We find that MP and PBL schemes contribute most to the ensemble spread (147 mm month-1) for monsoon precipitation over the study region. Furthermore, PBL schemes have a strong influence on the movement of the WAM rainband because of their impact on the cloud fraction, that ranges from 8 to 20 % at 600 hPa during August. More low- and mid-level clouds result in less incoming radiation and a weaker monsoon. Ultimately, we identify the differing intensities of the moist Hadley-type meridional circulation that connects the monsoon winds to the Tropical Easterly Jet as the main source for inter-member differences. The ensemble spread of Sahel precipitation and associated dynamics for August 1999 is comparable to the observed inter-annual spread (1979-2010) between dry and wet years, emphasizing the strong potential impact of regional processes and the need for a careful selection of model parameterizations.

  15. Interannual to interdecadal variability of winter and summer southern African rainfall, and their teleconnections

    NASA Astrophysics Data System (ADS)

    Dieppois, Bastien; Pohl, Benjamin; Rouault, Mathieu; New, Mark; Lawler, Damian; Keenlyside, Noel

    2016-06-01

    This study examines for the first time the changing characteristics of summer and winter southern African rainfall and their teleconnections with large-scale climate through the dominant time scales of variability. As determined by wavelet analysis, the austral summer and winter rainfall indices exhibit three significant time scales of variability over the twentieth century: interdecadal (15-28 years), quasi-decadal (8-13 years), and interannual (2-8 years). Teleconnections with global sea surface temperature and atmospheric circulation anomalies are established here but are different for each time scale. Tropical/subtropical teleconnections emerge as the main driver of austral summer rainfall variability. Thus, shifts in the Walker circulation are linked to the El Niño-Southern Oscillation (ENSO) and, at decadal time scales, to decadal ENSO-like patterns related to the Pacific Decadal Oscillation and the Interdecadal Pacific Oscillation. These global changes in the upper zonal circulation interact with asymmetric ocean-atmospheric conditions between the South Atlantic and South Indian Oceans; together, these lead to a shift in the South Indian Convergence Zone and a modulation of the development of convective rain-bearing systems over southern Africa in summer. Such regional changes, embedded in quasi-annular geopotential patterns, consist of easterly moisture fluxes from the South Indian High, which dominate southerly moisture fluxes from the South Atlantic High. Austral winter rainfall variability is more influenced by midlatitude atmospheric variability, in particular the Southern Annular Mode. The rainfall changes in the southwestern regions of southern Africa are determined by asymmetrical changes in the midlatitude westerlies between the Atlantic and Indian Oceans.

  16. Observed decadal variability of southern African rainfall, their teleconnections, and uncertainties

    NASA Astrophysics Data System (ADS)

    Dieppois, Bastien; Pohl, Benjamin; Rouault, Mathieu; New, Mark; Lawler, Damian; Keenlyside, Noel

    2016-04-01

    This study examines for the first time the changing characteristics of summer and winter southern African rainfall, and their teleconnections with large-scale climate through the dominant timescales of variability. The summer and winter rainfall indices exhibit three significant timescales of variability over the 20th century: interdecadal (15-28 year), quasi-decadal (8-13 year) and interannual (2-8 year). Teleconnections with global sea-surface temperature and atmospheric circulation anomalies, which have been established here using different data sets, are different for each timescale. Uncertainty related to the choice of observed-based SST and reanalysis data sets appears stronger over the winter rainfall region and at the interdecadal timescale. However, only SST and atmospheric anomalies which show an agreement greater than 90% between data sets, or between the members of the reanalysis, have been described. Tropical/subtropical teleconnections emerge as the main driver of summer rainfall variability. Thus, shifts in the Walker circulation are linked to the El Niño Southern Oscillation (ENSO) and, at decadal timescales, to decadal ENSO-like patterns related to the Pacific Decadal Oscillation and the Interdecadal Pacific Oscillation. These global changes in the upper-zonal circulation interact with asymmetric ocean-atmospheric modifications between the South Atlantic and South Indian Oceans; together these lead to shift in the South Indian Convergence Zone, and a modulation of the development of convective rain bearing systems over southern Africa in summer. Such regional changes, embedded in quasi-annular geopotential patterns, consist of easterly moisture fluxes from the Mascarene High, which dominate southerly moisture fluxes from the St Helena High. Winter rainfall variability is more influenced by mid-latitude atmospheric variability, in particular the Southern Annular Mode, but interactions with ENSO remain, especially in the subtropics. Asymmetrical

  17. Skill, reproducibility and potential predictability of the West African monsoon in coupled GCMs

    NASA Astrophysics Data System (ADS)

    Philippon, N.; Doblas-Reyes, F. J.; Ruti, P. M.

    2010-07-01

    In the framework of the ENSEMBLES FP6 project, an ensemble prediction system based on five different state-of-the-art European coupled models has been developed. This study evaluates the performance of these models for forecasting the West African monsoon (WAM) at the monthly time scale. From simulations started the 1 May of each year and covering the period 1991-2001, the reproducibility and potential predictability (PP) of key parameters of the WAM—rainfall, zonal and meridional wind at four levels from the surface to 200 hPa, and specific humidity, from July to September—are assessed. The Sahelian rainfall mode of variability is not accurately reproduced contrary to the Guinean rainfall one: the correlation between observations (from CMAP) and the multi-model ensemble mean is 0.17 and 0.55, respectively. For the Sahelian mode, the correlation is consistent with a low PP of about ~6%. The PP of the Guinean mode is higher, ~44% suggesting a stronger forcing of the sea surface temperature on rainfall variability over this region. Parameters relative to the atmospheric dynamics are on average much more skillful and reproducible than rainfall. Among them, the first mode of variability of the zonal wind at 200 hPa that depicts the Tropical Easterly Jet, is correlated at 0.79 with its “observed” counterpart (from the NCEP/DOE2 reanalyses) and has a PP of 39%. Moreover, models reproduce the correlations between all the atmospheric dynamics parameters and the Sahelian rainfall in a satisfactory way. In that context, a statistical adaptation of the atmospheric dynamic forecasts, using a linear regression model with the leading principal components of the atmospheric dynamical parameters studied, leads to moderate receiver operating characteristic area under the curve and correlation skill scores for the Sahelian rainfall. These scores are however much higher than those obtained using the modelled rainfall.

  18. Intimate partner violence in African American women.

    PubMed

    Campbell, Doris Williams; Sharps, Phyllis W; Gary, Faye A; Campbell, Jacquelyn C; Lopez, Loretta M

    2002-01-01

    Violence against African American women, specifically intimate partner abuse, has a significant impact on their health and well being. Intimate partner femicide and near fatal intimate partner femicide are the major causes of premature death and disabling injuries for African American women. Yet, despite this, there is a paucity of research and interventions specific and culturally relevant for these women. This article focuses on issues relevant to intimate partner violence and abuse against African American women by examining existing empirical studies of prevalence and health outcomes of intimate partner violence against women in general, plus what limited research there is about African American women, specifically. It includes a discussion of specific recommendations for research, practice, education, and policy to reduce and prevent intimate partner violence against African American women. PMID:12044219

  19. Suicidal behavior in black South Africans.

    PubMed

    Schlebusch, Lourens; Vawda, Naseema B M; Bosch, Brenda A

    2003-01-01

    In the past suicidal behavior among Black South Africans has been largely underresearched. Earlier studies among the other main ethnic groups in the country showed suicidal behavior in those groups to be a serious problem. This article briefly reviews some of the more recent research on suicidal behavior in Black South Africans. The results indicate an apparent increase in suicidal behavior in this group. Several explanations are offered for the change in suicidal behavior in the reported clinical populations. This includes past difficulties for all South Africans to access health care facilities in the Apartheid (legal racial separation) era, and present difficulties of post-Apartheid transformation the South African society is undergoing, as the people struggle to come to terms with the deleterious effects of the former South African racial policies, related socio-cultural, socio-economic, and other pressures. PMID:12809149

  20. African electricity infrastructure, interconnections and exchanges

    SciTech Connect

    Hammons, T.J.; Taher, F.; Gulstone, A.B.; Blyden, B.K.; Johnston, R.; Isekemanga, E.; Paluku, K.; Calitz, A.C.; Simanga, N.N.

    1997-01-01

    A 1996 IEEE PES Summer Meeting panel session focused on African Electricity Infrastructure, Interconnections, and Electricity Exchanges. The session was sponsored by the PES Energy Development and Power Generation Committee and organized/moderated by T.J. Hammons, chair of the International Practices Subcommittee. Panelists discussed energy resources, feasibility studies to interconnect power systems, the present state of the electric power sector, future expansion of African power systems, interconnections and power exchanges, and the impact of the private sector on electricity supply. The presentations were as follows: Prospects of the Evolution of a Unified Interconnection Power System in Africa, Fouad Taher; The World Bank`s Involvement with African Electricity Infrastructure, Alfred Gulstone; Towards the implementation of an Integrated African Grid, Bai K. Blyden, Raymond Johnston; Grand Inga Interconnection Projects, Elese Isekemanga, K. Paluku; The Innovative Southern African Kilowatt Hour, Andries C. Calitz; Report on Burundi, Rwanda, and Zaire, Ngove-Ngulu Simanga.

  1. Proposed geomagnetic control of semiannual waves in the mesospheric zonal wind

    NASA Technical Reports Server (NTRS)

    Belmont, A. D.; Nastrom, G. D.; Mayr, H. G.

    1974-01-01

    The polar semiannual oscillation in zonal wind can explain midwinter weakening of the polar vortex and the relatively short stratospheric and mesospheric summar easterlies. The phase of the wind oscillation is equinoctial, as is the phase of the semiannual component in magnetic storm activity. For a given altitude, the contours of amplitude of the semiannual wind oscillation have less variability in geomagnetic than in geographic coordinates. It is suggested that polar wind oscillations are caused by the semiannual maxima in magnetic storm activity which lead to electron dissociation of O2 into O, in turn increasing ozone more rapidly than the dissociation of N2 destroys ozone, and thereby inducing a semiannual variation in the thermal and wind fields. This implies that geomagnetic processes may cause or affect the development of sudden warmings. As the tropical semiannual wind oscillation is symmetric about the geomagnetic equator, the same processes may also influence the location of the tropical wind wave.

  2. Proposed geomagnetic control of semiannual waves in the mesospheric zonal wind

    NASA Technical Reports Server (NTRS)

    Belmont, A. D.; Nastrom, G. D.; Mayr, H. G.

    1975-01-01

    The polar semiannual oscillation in zonal wind explains midwinter weakening of the polar vortex and the relatively short stratospheric and mesospheric summer easterlies. The phase of the wind oscillation is equinoctial, as is the phase of the semiannual component in magnetic storm activity. For a given altitude, the contours of amplitude of the semiannual wind oscillation have less variability in geomagnetic than in geographic coordinates. It is suggested that the polar wind oscillations are caused by the semiannual maxima in magnetic storm activity, which lead to electron dissociation of O2 into O, in turn increasing ozone more rapidly than the dissociation of N2 destroys ozone, and inducing a semiannual variation in the thermal and wind fields. This implies that geomagnetic processes may cause or affect the development of sudden warmings. As the tropical semiannual wind oscillation is symmetric about the geomagnetic equator, the same processes may also influence the location of the tropical wind wave.

  3. South African AIDS plan criticised.

    PubMed

    Sidley, P

    1998-10-17

    In a television broadcast, Deputy President Mbeki of South Africa announced a campaign against HIV/AIDS that would involve coordination between various government departments and nongovernmental organizations. Mbeki, who is associated with Virodene (a drug treatment for AIDS that is considered a scam), replaced President Mandela at the last minute in the broadcast. Two days after the broadcast, the government refused to support treatment of pregnant women infected with HIV with zidovudine to prevent transmission of the virus to the baby. The treatment is considered cost-effective by AIDS workers and public health officials. According to Mark Heywood of the AIDS law project at Witwatersrand University, 16% of pregnant women attending antenatal clinics were HIV-positive in 1997; this means that about 3 million South Africans (8% of the population) were living with HIV. Heywood said that the government believes there are 1500 new cases daily. By the end of 1998, 3.5 million South Africans will be living with HIV. Although the government is asking other sectors to join in the campaign, what the government is doing is unclear. Mother-to-child transmission of HIV is second only to transmission of the virus through heterosexual sex in South Africa. PMID:9841037

  4. West Indian Ocean variability and East African fish catch.

    PubMed

    Jury, M; McClanahan, T; Maina, J

    2010-08-01

    We describe marine climate variability off the east coast of Africa in the context of fish catch statistics for Tanzania and Kenya. The time series exhibits quasi-decadal cycles over the period 1964-2007. Fish catch is up when sea surface temperature (SST) and atmospheric humidity are below normal in the tropical West Indian Ocean. This pattern relates to an ocean Rossby wave in one phase of its east-west oscillation. Coastal-scale analyses indicate that northward currents and uplift on the shelf edge enhance productivity of East African shelf waters. Some of the changes are regulated by the south equatorial current that swings northward from Madagascar. The weather is drier and a salty layer develops in high catch years. While the large-scale West Indian Ocean has some impact on East African fish catch, coastal dynamics play a more significant role. Climatic changes are reviewed using 200 years of past and projected data. The observed warming trend continues to increase such that predicted SST may reach 30 degrees C by 2100 while SW monsoon winds gradually increase, according to a coupled general circulation model simulation with a gradual doubling of CO(2). PMID:20471674

  5. Sensitivity of the African and Asian Monsoons to Mid-Holocene Insolation and Data-Inferred Surface Changes.

    NASA Astrophysics Data System (ADS)

    Texier, Delphine; de Noblet, Nathalie; Braconnot, Pascale

    2000-01-01

    tropical easterly jet at 200 hPa is increased in all 6-kyr-BP simulations, but only over Africa in the case of a prescribed green Sahara. The African easterly jet has been pushed at higher altitude in response to all prescribed forcings; wind speed is then reduced at 700 hPa but increased at higher altitude.

  6. Examining Tropical Cyclone - Kelvin Wave Interactions using Adjoint Diagnostics

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Adjoint-based tools can provide valuable insight into the mechanisms that influence the evolution and predictability of atmospheric phenomena, as they allow for the efficient and rigorous computation of forecast sensitivity to changes in the initial state. We apply adjoint-based tools from the non-hydrostatic Coupled Atmosphere/Ocean Mesoscale Prediction System (COAMPS) to explore the initial-state sensitivity and interactions between a tropical cyclone and atmospheric equatorial waves associated with the Madden Julian Oscillation (MJO) in the Indian Ocean during the DYNAMO field campaign. The development of Tropical Cyclone 5 (TC05) coincided with the passage of an equatorial Kelvin wave and westerly wind burst associated with an MJO that developed in the Indian Ocean in late November 2011, but it was unclear if and how one affected the other. COAMPS 24-h and 36-h adjoint sensitivities are analyzed for both TC05 and the equatorial waves to understand how the evolution of each system is sensitive to the other. The sensitivity of equatorial westerlies in the western Indian Ocean on 23 November shares characteristics with the classic Gill (1980) Rossby and Kelvin wave response to symmetric heating about the equator, including symmetric cyclonic circulations to the north and south of the westerlies, and enhanced heating in the area of convergence between the equatorial westerlies and easterlies. In addition, there is sensitivity in the Bay of Bengal associated with the cyclonic circulation that eventually develops into TC05. At the same time, the developing TC05 system shows strongest sensitivity to local wind and heating perturbations, but sensitivity to the equatorial westerlies is also clear. On 24 November, when the Kelvin wave is immediately south of the developing tropical cyclone, both phenomena are sensitive to each other. On 25 November TC05 no longer shows sensitivity to the Kelvin wave, while the Kelvin Wave still exhibits some weak sensitivity to TC05. In

  7. The quasi 2 day wave activities during 2007 austral summer period as revealed by Whole Atmosphere Community Climate Model

    NASA Astrophysics Data System (ADS)

    Gu, Sheng-Yang; Liu, Han-Li; Pedatella, N. M.; Dou, Xiankang; Li, Tao; Chen, Tingdi

    2016-03-01

    The quasi 2 day wave (QTDW) observed during 2007 austral summer period is well reproduced in an reanalysis produced by the data assimilation version of the Whole Atmosphere Community Climate Model (WACCM + Data Assimilation Research Testbed) developed at National Center for Atmospheric Research (NCAR). It is found that the QTDW peaked 3 times from January to February but with different zonal wave numbers. Diagnostic analysis shows that the mean flow instabilities, refractive index, and critical layers of QTDWs are fundamental for their propagation and amplification, and thus, the temporal variations of the background wind are responsible for the different wave number structures at different times. The westward propagating wave number 2 mode (W2) grew and maximized in the first half of January, when the mean flow instabilities related to the summer easterly jet were enclosed by the critical layers of the westward propagating wave number 3 (W3) and wave number 4 (W4) modes. This prevented W3 and W4 from approaching and extracting energy from the unstable region. The W2 decayed rapidly thereafter due to the recession of critical layer and thus the lack of additional amplification by the mean flow instability. The W3 peaked in late January, when the instabilities were still encircled by the critical layer of W4. The attenuation of W3 afterward was also due to the disappearance of critical layer and thus the lack of overreflection. Finally, the W4 peaked in late February when both the instability and critical layer were appropriate.

  8. Long Wave Resonance in Tropical Oceans and Implications on Climate: The Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Pinault, Jean-Louis

    2016-06-01

    The dynamics of the tropical Pacific can be understood satisfactorily by invoking the coupling between the basin modes of 1-, 4- and 8-year average periods. The annual quasi-stationary wave (QSW) is a first baroclinic-mode, fourth meridional-mode Rossby wave resonantly forced by easterlies. The quadrennial QSW is built up from a first baroclinic-mode Kelvin wave and a first baroclinic-mode, first meridional-mode Rossby wave equatorially trapped and two off-equatorial Rossby waves, their dovetailing forming a resonantly forced wave (RFW). The 8-year period QSW is a replica of the quadrennial QSW for the second-baroclinic mode. The coupling between basin modes results from the merging of modulated currents both in the western part of the North Equatorial Counter Current and along the South Equatorial Current. Consequently, a sub-harmonic mode locking occurs, which means that the average period of QSWs is 1-, 4- and 8-year exactly. The quadrennial sub-harmonic is subject to two modes of forcing. One results from coupling with the annual QSW that produces a Kelvin wave at the origin of transfer of the warm waters from the western part of the basin to the central-eastern Pacific. The other is induced by El Niño and La Niña that self-sustain the sub-harmonic by stimulating the Rossby wave accompanying the westward recession of the QSW at a critical stage of its evolution. The interpretation of ENSO from the coupling of different basin modes allows predicting and estimating the amplitude of El Niño events a few months before they become mature from the accelerations of the geostrophic component of the North Equatorial Counter Current.

  9. Long Wave Resonance in Tropical Oceans and Implications on Climate: The Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Pinault, Jean-Louis

    2015-12-01

    The dynamics of the tropical Pacific can be understood satisfactorily by invoking the coupling between the basin modes of 1-, 4- and 8-year average periods. The annual quasi-stationary wave (QSW) is a first baroclinic-mode, fourth meridional-mode Rossby wave resonantly forced by easterlies. The quadrennial QSW is built up from a first baroclinic-mode Kelvin wave and a first baroclinic-mode, first meridional-mode Rossby wave equatorially trapped and two off-equatorial Rossby waves, their dovetailing forming a resonantly forced wave (RFW). The 8-year period QSW is a replica of the quadrennial QSW for the second-baroclinic mode. The coupling between basin modes results from the merging of modulated currents both in the western part of the North Equatorial Counter Current and along the South Equatorial Current. Consequently, a sub-harmonic mode locking occurs, which means that the average period of QSWs is 1-, 4- and 8-year exactly. The quadrennial sub-harmonic is subject to two modes of forcing. One results from coupling with the annual QSW that produces a Kelvin wave at the origin of transfer of the warm waters from the western part of the basin to the central-eastern Pacific. The other is induced by El Niño and La Niña that self-sustain the sub-harmonic by stimulating the Rossby wave accompanying the westward recession of the QSW at a critical stage of its evolution. The interpretation of ENSO from the coupling of different basin modes allows predicting and estimating the amplitude of El Niño events a few months before they become mature from the accelerations of the geostrophic component of the North Equatorial Counter Current.

  10. Fatigue Severity among African Americans: Gender and Age Interactions.

    ERIC Educational Resources Information Center

    Song, Sharon; Jason, Leonard A.; Taylor, Renee R.; Torres-Harding, Susan R.; Helgerson, Jena; Witter, Elizabeth

    2002-01-01

    Investigated the relationship between fatigue, age, and gender among African Americans, Caucasians, and Latinos. Survey results found significant age and gender interactions among African Americans and Caucasians. African American women and older African American men had the highest fatigue rates. There was no significant difference in levels of…

  11. The Notion of Ubuntu and Communalism in African Educational Discourse

    ERIC Educational Resources Information Center

    Venter, Elza

    2004-01-01

    The notion of "ubuntu" and "communalism" is of great importance in an African educational discourse, as well as in African Philosophy of Education and in African philosophical discourse. "Ubuntu" is a philosophy that promotes the common good of society and includes humanness as an essential element of human growth. In African culture the community…

  12. The African-American History of Martha's Vineyard.

    ERIC Educational Resources Information Center

    Weintraub, Elaine

    1993-01-01

    Reports on research into African American history and experiences in Martha's Vineyard (Massachusetts). Examines primary sources and oral traditions of African American cultural and social history from 1703 to the present. Discusses African American sailors, race relations, and contributions by African American individuals to the community. (CFR)

  13. Educational Adaptation and Pan-Africanism: Trends in Africa.

    ERIC Educational Resources Information Center

    Marah, John Karefah

    1987-01-01

    European colonialists believed that Africans should be educated in African traditional values, and that Africans should be made into dedicated workers, not holders of power. The African nationalists of the 1960s, in contrast, rejected most of the arduous aspects of European education as instruments of domination, and lay the foundation for the…

  14. The Call for an African University: A Critical Reflection

    ERIC Educational Resources Information Center

    van Wyk, Berte; Higgs, Philip

    2007-01-01

    In this paper, we draw on philosophy (particularly African philosophy) to analyse the call for an African university. The call for an African university may be viewed as a call that insists that all critical and transformative educators in Africa embrace an indigenous African worldview and root their nation's educational paradigms in an indigenous…

  15. ASTER Waves

    NASA Technical Reports Server (NTRS)

    2000-01-01

    The pattern on the right half of this image of the Bay of Bengal is the result of two opposing wave trains colliding. This ASTER sub-scene, acquired on March 29, 2000, covers an area 18 kilometers (13 miles) wide and 15 kilometers (9 miles) long in three bands of the reflected visible and infrared wavelength region. The visible and near-infrared bands highlight surface waves due to specular reflection of sunlight off of the wave faces.

    Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is one of five Earth-observing instruments launched December 18, 1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of International Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products. Dr. Anne Kahle at NASA's Jet Propulsion Laboratory, Pasadena, California, is the U.S. science team leader; Moshe Pniel of JPL is the project manager. ASTER is the only high-resolution imaging sensor on Terra. The primary goal of the ASTER mission is to obtain high-resolution image data in 14 channels over the entire land surface, as well as black and white stereo images. With revisit time of between 4 and 16 days, ASTER will provide the capability for repeat coverage of changing areas on Earth's surface. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is one of five Earth-observing instruments launched December 18, 1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of International Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products. Dr. Anne Kahle at NASA's Jet Propulsion Laboratory, Pasadena, California, is the U.S. science team leader; Moshe Pniel of JPL is the project manager. ASTER is the only high-resolution imaging sensor on Terra. The primary goal of the ASTER mission is to obtain high-resolution image data in 14 channels

  16. MHD simple waves and the divergence wave

    SciTech Connect

    Webb, G. M.; Pogorelov, N. V.; Zank, G. P.

    2010-03-25

    In this paper we investigate magnetohydrodynamic (MHD) simple divergence waves in MHD, for models in which nablacentre dotBnot =0. These models are related to the eight wave Riemann solvers in numerical MHD, in which the eighth wave is the divergence wave associated with nablacentre dotBnot =0. For simple wave solutions, all physical variables (the gas density, pressure, fluid velocity, entropy, and magnetic field induction in the MHD case) depend on a single phase function phi. We consider the form of the MHD equations used by both Powell et al. and Janhunen. It is shown that the Janhunen version of the equations possesses fully nonlinear, exact simple wave solutions for the divergence wave, but no physically meaningful simple divergence wave solution exists for the Powell et al. system. We suggest that the 1D simple, divergence wave solution for the Janhunen system, may be useful for the testing and validation of numerical MHD codes.

  17. Misconceptions of Depression in African Americans

    PubMed Central

    Sohail, Zohaib; Bailey, Rahn Kennedy; Richie, William D.

    2014-01-01

    Major depression is a very common disabling disorder. Although the relationship between race and depression is complex, depression affects all races, all ethnic and geographic locations as well as all age groups. The prevalence of depression in African Americans is controversial, due to the paucity of research. The deficit in the knowledge and skills in treating depression in African Americans have not been adequately addressed so far. Inadequate and insufficient data on African Americans contributes to the problems of under diagnoses, misdiagnosis, and under treatment of depression. This article will highlight the existing problem of depression in Afro American with a focus on diagnostic and treatment issues. PMID:24999332

  18. Discussing Cancer: Communication with African Americans

    PubMed Central

    Caito, Nikki; Hood, Sula; Thompson, Vetta L. Sanders

    2015-01-01

    Regular screening for colorectal cancer (CRC) facilitates earlier detection, lowers mortality, and may reduce incidence through detection and removal of pre-cancerous polyps. Optimizing health professional delivery of CRC screening information and recommendations can assist in reducing CRC disparity in the African American community. This paper presents qualitative data on African Americans’ attitudes about health professional CRC communications based on the analysis of focus groups (N=79). Using a social-ecological framework, colorectal cancer and professional communication themes are examined to offer four general and nine cancer specific theoretically based and culturally appropriate strategies for improving health professional cancer communication with African Americans. PMID:25050658

  19. Assessing spirituality in mentally ill African Americans.

    PubMed

    Perdue, Bobbie; Johnson, Deanna; Singley, Doretha; Jackson, Cheylon

    2006-01-01

    The case scenario illustrates the advantage of using spirituality as a tool for recovery when working with mentally ill African American clients. Often spiritual and clinical perspectives are seen as contradictory. But for African Americans, these perspectives can be mutually reinforcing. Spirituality can serve as a resource of strength. It can provide emotional consolation, inspiration, guidance, and security. It can foster personal responsibility, identity, respect for ethical codes and community building. Mental Health professionals who use spirituality as a tool for recovery can expect to have better client outcomes when working with African Americans than those who do not. PMID:18402348

  20. Waves and Tsunami Project

    ERIC Educational Resources Information Center

    Frashure, K. M.; Chen, R. F.; Stephen, R. A.; Bolmer, T.; Lavin, M.; Strohschneider, D.; Maichle, R.; Micozzi, N.; Cramer, C.

    2007-01-01

    Demonstrating wave processes quantitatively in the classroom using standard classroom tools (such as Slinkys and wave tanks) can be difficult. For example, waves often travel too fast for students to actually measure amplitude or wavelength. Also, when teaching propagating waves, reflections from the ends set up standing waves, which can confuse…

  1. African diatom palaeoecology and biostratigraphy

    NASA Astrophysics Data System (ADS)

    Gasse, F.; Fourtanier, E.

    This paper illustrates the different types of information which can be deduced from African diatoms studies. The first section is devoted to the reconstruction of palaeoenvironments. The accuracy of ecological data (estimates of ecological variables e.g. types of habitats, water chemistry…) depends on the times scale and on the spatial scale considered: short-term environments in a given waterbody, environmental evolution during individual humid episodes considered locally or regionally, long-term changes in diatom flora induced by major climatic tendencies at a regional or continental scale. One then summarizes our present state of knowledge in diatom biostratigraphy in Africa. Several centric taxa, belonging to the genera Aulacoseira, Mesodictyon, Cyclotella, Stephanodiscus and Cyclostephanos appear to have limited stratigraphical ranges and to be good chronological markers.

  2. Enhancing the African bioethics initiative

    PubMed Central

    Ogundiran, Temidayo O

    2004-01-01

    Background Medical ethics has existed since the time of Hippocrates. However, formal training in bioethics did not become established until a few decades ago. Bioethics has gained a strong foothold in health sciences in the developed world, especially in Europe and North America. The situation is quite different in many developing countries. In most African countries, bioethics – as established and practiced today in the west- is either non-existent or is rudimentary. Discussion Though bioethics has come of age in the developed and some developing countries, it is still largely "foreign" to most African countries. In some parts of Africa, some bioethics conferences have been held in the past decade to create research ethics awareness and ensure conformity to international guidelines for research with human participants. This idea has arisen in recognition of the genuine need to develop capacity for reviewing the ethics of research in Africa. It is also a condition required by external sponsors of collaborative research in Africa. The awareness and interest that these conferences have aroused need to be further strengthened and extended beyond research ethics to clinical practice. By and large, bioethics education in schools that train doctors and other health care providers is the hook that anchors both research ethics and clinical ethics. Summary This communication reviews the current situation of bioethics in Africa as it applies to research ethics workshops and proposes that in spite of the present efforts to integrate ethics into biomedical research in Africa, much still needs to be done to accomplish this. A more comprehensive approach to bioethics with an all-inclusive benefit is to incorporate formal ethics education into health training institutions in Africa. PMID:15488145

  3. Cultural Rationales Guiding Medication Adherence Among African American with HIV/AIDS

    PubMed Central

    Neufeld, Stewart; Berry, Rico; Luborsky, Mark

    2011-01-01

    Abstract To date, only modest gains have been achieved in explaining adherence to medical regimens, limiting effective interventions. This is a particularly important issue for African Americans who are disproportionately affected by the HIV epidemic. Few studies have focused on intragroup variation among African Americans in adherence to ART. The aim of this study was to identify and describe the cultural rationales guiding African American patients' formulation and evaluation of adherence. Rationales are key features of purposeful human action. In-depth interviews with 80 seropositive African Americans were tape recorded, transcribed, and analyzed. Participant CD4, viral load and medical histories were collected at each data point. Analysis of four waves of panel data identified three types of adherence rationales: Authoritative Knowledge Rationale (AKR; n=29, 36.3%), Following Doctors' Orders Rationale (DOR; n=24, 30.0%) and Individualized Adherence Rationale (IAR; n=27, 33.8%). Differences in mean reported adherence between the rationale groups did not achieve statistical significance. However, the fraction reporting low adherence (<70%), although not different by rationale group at the first interview (T1), was significantly higher for the IAR group by the fourth interview (T4). Objective clinical markers (CD4 and viral load) improved over time (from T1 to T4) for AKR and DOR groups, but remained unchanged for the IAR group, yet self-reported adherence declined for all groups over the course of the four interviews. PMID:21777141

  4. Cenozoic extension, volcanism and plateau uplift in eastern Africa and the African Superplume

    NASA Astrophysics Data System (ADS)

    Nyblade, A.; O'Donnell, J.; Mulibo, G. D.; Adams, A. N.

    2013-12-01

    Recent body and surface wave studies combine to image mantle velocity structure to a depth of 1200 km beneath eastern Africa using teleseismic earthquake data recorded by the AfricaArray East African Seismic Experiment in conjunction with permanent stations and previously deployed temporary stations. The combined network spans Kenya, Uganda, Tanzania, Zambia and Malawi. The 3-D shear wave velocity structure of the uppermost mantle was imaged using fundamental-mode Rayleigh wave phase velocities measured at periods ranging from 20 to 182 s, subsequently inverted for shear velocity structure. When considered in conjunction with mapped seismicity, the shear velocity model supports a secondary western rift branch striking southwestwards from Lake Tanganyika, likely exploiting the relatively weak lithosphere of the southern Kibaran Belt between the Bangweulu Block and the Congo Craton. In eastern Tanzania a low-velocity region suggests that the eastern rift branch trends southeastwards offshore eastern Tanzania coincident with the purported location of the northern margin of the proposed Ruvuma microplate. The results suggest that existing lithospheric structures exert a significant governing influence on rift development. Sub-lithospheric mantle wave speed variations extending to a depth of 1200 km were tomographically imaged from the inversion of P and S wave relative arrival time residuals. The images shows a low wave speed anomaly (LWA) well developed at shallow depths (100-200 km) beneath the Eastern and Western branches of the rift system and northwestern Zambia, and a fast wave speed anomaly at depths greater than 350 km beneath the central and northern parts of the East African Plateau and the eastern and central parts of Zambia. At depths below 350 km the LWA is most prominent under the central and southern parts of the East African Plateau and dips to the southwest beneath northern Zambia, extending to a depth of at least 900 km. The amplitude of the LWA is

  5. Longitudinal links among parenting, self-presentations to peers, and the development of externalizing and internalizing symptoms in African American siblings.

    PubMed

    Brody, Gene H; Kim, Sooyeon; Murry, Velma McBride; Brown, Anita C

    2005-01-01

    A longitudinal model that linked involved-supportive parenting and siblings' ability-camouflaging self-presentations to peers with the development of externalizing and internalizing symptoms was tested with 152 pairs of first- and second-born African American siblings (mean ages 12.7 years and 10.2 years at the first wave of data collection). Three waves of data were collected at 1-year intervals. Teachers assessed siblings' externalizing symptoms, internalizing symptoms, and academic competence; siblings reported their own self-presentations and desire for peer acceptance; and mothers and siblings provided multiinformant assessments of involved-supportive parenting. Involved-supportive parenting at Wave 1 was linked with peer-directed self-presentations at Wave 2. Wave 2 self-presentations were linked indirectly with changes from Wave 1 to Wave 3 in externalizing and internalizing symptoms through their association with academic competence. PMID:15971766

  6. Cardiac assessment of African hedgehogs (Atelerix albiventris).

    PubMed

    Black, Peter A; Marshall, Cecilia; Seyfried, Alice W; Bartin, Anne M

    2011-03-01

    Cardiomyopathy is a common finding in captive African hedgehogs (Atelerix albiventris) at postmortem exam. To date, treatment attempts have been mostly empirical and unrewarding. The objective of this study was to determine reference cardiac values for captive African hedgehogs based on echocardiogram, electrocardiogram (ECG), and radiographs. Adult African hedgehogs with no clinical signs of cardiac disease (n = 13) were selected. Each animal was anesthetized with isoflurane via facemask and an echocardiogram, ECG, and radiographs were performed. Standard measurements were taken and the descriptive statistics performed. Values were comparable to limited data available in other hedgehog species and other similar-sized exotic species. Two animals were removed from consideration of reference values due to valvular defects that were considered significant. These data are the first establishing cardiac parameters in normal African hedgehogs using radiographic cardiac measurement, echocardiogram, and ECG. Evaluating animals with possible cardiomyopathy may allow for earlier diagnosis and more successful treatment. PMID:22946370

  7. Secretarial Improvement Program for African Office Employees

    ERIC Educational Resources Information Center

    Kurtz, Margaret A.

    1970-01-01

    For the past two years, Colby Junior College, in New London, New Hampshire, in cooperation with Operation Crossroads Africa of New York City, has successfully operated an eight-week secretarial improvement course for African office employees. (Author)

  8. [African research in odontostomatology and international cooperation].

    PubMed

    Berard, A; Page, T; Brouste, Ph; Ndobo-Epoy, Ph

    2004-09-01

    In this study, the authors measure the efficacy of the African odonto-stomatologic research in the International Assocation for Dental Research (I.A.D.R.) and value the impact of the international cooperation upon that research. This evaluation is realized from the number of publications presented by the African countries at the congressess of I.A.D.R. The obtained results show: 1. The African odonto-stomatologic is the less successful in the world and produced, in 1997, 0.4% of the studies published on the world, 2. Some of the African countries are able to produce scientific results of International valour (South Africa, Egypt and Nigeria in a less degree). Generally, these countries work jointly with anglo-saxon universities. 3. During these last two years, Cameroon obtained very encouraging results thanks to his collaboration with the University of Bordeaux 2 (France), represented by the regretted Professeur Ph. NDOBO-EPOY. PMID:15900824

  9. Mellonee Burnim on African American Music.

    ERIC Educational Resources Information Center

    Campbell, Patricia Shehan

    1995-01-01

    Describes the role and influence of Mellonee Burnim on U.S. music education. Discusses the origins and impact of African American gospel music. Includes a list of selected resources and two lesson plans featuring gospel music. (CFR)

  10. African-Americans and Heart Disease, Stroke

    MedlinePlus

    ... more about African-Americans and stroke at our Power To End Stroke website This content was last reviewed July 2015. ... Attack • Heart Failure (HF) • Heart Valve Problems and Disease • High Blood ...

  11. Health Conditions Common in African American Women

    MedlinePlus

    ... health. Return to top Health conditions common in African-American women Asthma Breast cancer Cancer Cervical cancer Diabetes Glaucoma and cataracts Heart disease High blood pressure High cholesterol HIV/AIDS Infant death Kidney disease Lupus Mental health ...

  12. African Americans: Diverse People, Diverse Career Needs.

    ERIC Educational Resources Information Center

    Kimbrough, Verna D.; Salomone, Paul R.

    1993-01-01

    Identifies the many subgroups within the African-American population and suggests guidelines for career counseling with different subcultures: rural and urban lower class, middle class, and underclass. (SK)

  13. Surface wave tomography

    NASA Technical Reports Server (NTRS)

    Anderson, D. L.

    1984-01-01

    Vertically polarized shear wave velocity (VSV), determined primarily from fundamental mode Rayleigh waves, and the difference between the velocity of horizontally polarized shear waves (VSH) and VSV, therefore a measure of anisotropy, are shown.

  14. Corynebacterial pneumonia in an African hedgehog.

    PubMed

    Raymond, J T; Williams, C; Wu, C C

    1998-04-01

    A 3-mo-old, male African hedgehog (Atelerix albiventris) was anorectic and lethargic for a period of 3 days prior to death. Necropys revealed lungs that were diffusely firm, dark red, and dorsally adhered by fibrinous tags to the pericardial sac. Histopathology revealed necrosuppurative bronchopneumonia with pulmonary abscesses and suppurative pericarditis and myocarditis. A Corynebacterium sp. was isolated from the lungs. We believe this is the first reported case of corynebacterial pneumonia in an African hedgehog. PMID:9577794

  15. Intestinal lymphosarcoma in captive African hedgehogs.

    PubMed

    Raymond, J T; Clarke, K A; Schafer, K A

    1998-10-01

    Two captive adult female African hedgehogs (Atelerix albiventris) had inappetance and bloody diarrhea for several days prior to death. Both hedgehogs had ulceration of the small intestine and hepatic lipidosis. Histopathology revealed small intestinal lymphosarcoma with metastasis to the liver. Extracellular particles that had characteristics of retroviruses were observed associated with the surface of some neoplastic lymphoid cells by transmission electron microscopy. These are the first reported cases of intestinal lymphosarcoma in African hedgehogs. PMID:9813852

  16. Interannual Variability of South-Eastern African Summer Rainfall. Part 1: Relationships with Air-Sea Interaction Processes

    NASA Astrophysics Data System (ADS)

    Rocha, Alfredo; Simmonds, Ian

    1997-03-01

    This paper investigates the role that air-sea interaction processes may play in interannual variability of south-eastern African summer rainfall. The principal spatial modes of south-eastern African summer rainfall are first identified using principal component analysis. Four modes are retained. The most important mode of variability is found to represent rainfall variability over most of the domain, particularly in the regions to the south.The influence of ENSO (as measured by the SOI) on summer rainfall is investigated in detail for different SOI leads. The relationship is such that during the summer following the onset of an ENSO event, south-eastern Africa tends to experience dry conditions. Strongest relationships are found with the SOI leading rainfall by about 3 to 6 months.A second index, the Brandon-Marion Index (BMI) which is indicative of changes in the pressure field over the Indian Ocean correlates with rainfall better than the SOI. Strongest correlations are found when this index leads rainfall by about 1 to 3 months. More importantly, a partial correlation analysis reveals that the BMI influences rainfall independently of ENSO. Both the SOI and the BMI are potential predictors of summer rainfall.An investigation of rainfall associations with global SST anomalies reveals areas in the tropical Indian and Pacific Oceans that are linked with rainfall changes over the subcontinent. The relationship is such that warm anomalies tend to be followed by dry conditions over much of south-eastern Africa. Strongest relationships are found when SSTs lead the rainfall season by about 1 to 3 months. Well-defined atmospheric anomalies are identified during dry south-eastern African summers. These include, amongst others, anomalously warm tropospheric temperatures and marked low-level cyclonic circulation anomalies over the central Indian Ocean, which generate abnormally weak easterly winds along much of the south-eastern coast of Africa. These perturbations to the

  17. Seismic waves from elephant vocalizations: A possible communication mode?

    NASA Astrophysics Data System (ADS)

    Günther, Roland H.; O'Connell-Rodwell, Caitlin E.; Klemperer, Simon L.

    2004-06-01

    We conducted experiments with trained African elephants that show that low-frequency elephant vocalizations produce Rayleigh waves. We model a potential range for these seismic waves, under ideal conditions, of c. 2 km. In appropriate conditions, surface waves from an elephant's infrasonic vocalizations might propagate further than airborne sound and provide advantages over acoustic communication. However, if we use the detection capabilities of the human ear as a benchmark for the signal-detection thresholds of elephants, our estimates of attenuation and ambient seismic noise suggest that the seismic detection range is unlikely to exceed the acoustic detection range under normal atmospheric conditions. We conclude that elephants may benefit from seismic detection in circumstances where the range of acoustic communication is limited, or in cases where multimodal communication is advantageous. Given our current understanding, elephants are unlikely to rely on seismic waves as their primary mode for long-range communication.

  18. What physicians should know about Africanized honeybees.

    PubMed

    Sherman, R A

    1995-12-01

    The Africanized honeybee, popularly known as the "killer bee," is already well established in Texas and has recently entered California and Arizona. As the Africanized honeybee spreads in North America, the medical community must become aware of the problems associated with this insect and ensure that sting emergencies can be handled quickly and appropriately. The major differences between Africanized and European honeybees are that the former are more irritable, they swarm more readily and frequently, they defend their hives more vehemently, and they sting more collectively. It is not the composition nor the volume of an individual bee's venom, but rather the cumulative dose of multiple stings that accounts for the morbidity and mortality associated with Africanized honeybee-sting incidents. Even nonallergic persons are susceptible to the toxic effects of these large combined venom loads. Africanized honeybee-sting victims are treated the same as victims of European honeybee stings. Authorities will prepare for the bees' arrival by expanding public awareness, teaching risk-avoidance behavior, providing for the removal of troublesome hives, and developing sting treatment protocols that can be initiated rapidly in the field or emergency departments. Health care professionals should participate in the educational efforts and in the development of needed emergency response protocols so that the effects of the Africanized honeybee will be merely a nuisance rather than a plague. PMID:8553637

  19. What physicians should know about Africanized honeybees.

    PubMed Central

    Sherman, R A

    1995-01-01

    The Africanized honeybee, popularly known as the "killer bee," is already well established in Texas and has recently entered California and Arizona. As the Africanized honeybee spreads in North America, the medical community must become aware of the problems associated with this insect and ensure that sting emergencies can be handled quickly and appropriately. The major differences between Africanized and European honeybees are that the former are more irritable, they swarm more readily and frequently, they defend their hives more vehemently, and they sting more collectively. It is not the composition nor the volume of an individual bee's venom, but rather the cumulative dose of multiple stings that accounts for the morbidity and mortality associated with Africanized honeybee-sting incidents. Even nonallergic persons are susceptible to the toxic effects of these large combined venom loads. Africanized honeybee-sting victims are treated the same as victims of European honeybee stings. Authorities will prepare for the bees' arrival by expanding public awareness, teaching risk-avoidance behavior, providing for the removal of troublesome hives, and developing sting treatment protocols that can be initiated rapidly in the field or emergency departments. Health care professionals should participate in the educational efforts and in the development of needed emergency response protocols so that the effects of the Africanized honeybee will be merely a nuisance rather than a plague. PMID:8553637

  20. Geometrical versus wave optics under gravitational waves

    NASA Astrophysics Data System (ADS)

    Angélil, Raymond; Saha, Prasenjit

    2015-06-01

    We present some new derivations of the effect of a plane gravitational wave on a light ray. A simple interpretation of the results is that a gravitational wave causes a phase modulation of electromagnetic waves. We arrive at this picture from two contrasting directions, namely, null geodesics and Maxwell's equations, or geometric and wave optics. Under geometric optics, we express the geodesic equations in Hamiltonian form and solve perturbatively for the effect of gravitational waves. We find that the well-known time-delay formula for light generalizes trivially to massive particles. We also recover, by way of a Hamilton-Jacobi equation, the phase modulation obtained under wave optics. Turning then to wave optics—rather than solving Maxwell's equations directly for the fields, as in most previous approaches—we derive a perturbed wave equation (perturbed by the gravitational wave) for the electromagnetic four-potential. From this wave equation it follows that the four-potential and the electric and magnetic fields all experience the same phase modulation. Applying such a phase modulation to a superposition of plane waves corresponding to a Gaussian wave packet leads to time delays.

  1. The Impact of Stress on the Life History Strategies of African American Adolescents: Cognitions, Genetic Moderation, and the Role of Discrimination

    ERIC Educational Resources Information Center

    Gibbons, Frederick X.; Roberts, Megan E.; Gerrard, Meg; Li, Zhigang; Beach, Steven R. H.; Simons, Ronald L.; Weng, Chih-Yuan; Philibert, Robert A.

    2012-01-01

    The impact of 3 different sources of stress--environmental, familial (e.g., low parental investment), and interpersonal (i.e., racial discrimination)--on the life history strategies (LHS) and associated cognitions of African American adolescents were examined over an 11-year period (5 waves, from age 10.5 to 21.5). Analyses indicated that each one…

  2. The East African rift system

    NASA Astrophysics Data System (ADS)

    Chorowicz, Jean

    2005-10-01

    This overview paper considers the East African rift system (EARS) as an intra-continental ridge system, comprising an axial rift. It describes the structural organization in three branches, the overall morphology, lithospheric cross-sections, the morphotectonics, the main tectonic features—with emphasis on the tension fractures—and volcanism in its relationships with the tectonics. The most characteristic features in the EARS are narrow elongate zones of thinned continental lithosphere related to asthenospheric intrusions in the upper mantle. This hidden part of the rift structure is expressed on the surface by thermal uplift of the rift shoulders. The graben valleys and basins are organized over a major failure in the lithospheric mantle, and in the crust comprise a major border fault, linked in depth to a low angle detachment fault, inducing asymmetric roll-over pattern, eventually accompanied by smaller normal faulting and tilted blocks. Considering the kinematics, divergent movements caused the continent to split along lines of preexisting lithospheric weaknesses marked by ancient tectonic patterns that focus the extensional strain. The hypothesis favored here is SE-ward relative divergent drifting of a not yet well individualized Somalian plate, a model in agreement with the existence of NW-striking transform and transfer zones. The East African rift system comprises a unique succession of graben basins linked and segmented by intracontinental transform, transfer and accommodation zones. In an attempt to make a point on the rift system evolution through time and space, it is clear that the role of plume impacts is determinant. The main phenomenon is formation of domes related to plume effect, weakening the lithosphere and, long after, failure inducing focused upper mantle thinning, asthenospheric intrusion and related thermal uplift of shoulders. The plume that had formed first at around 30 Ma was not in the Afar but likely in Lake Tana region (Ethiopia

  3. A cascade model connecting life stress to risk behavior among rural African American emerging adults.

    PubMed

    Brody, Gene H; Chen, Yi-Fu; Kogan, Steven M

    2010-08-01

    A three-wave cascade model linking life stress to increases in risk behavior was tested with 347 African American emerging adults living in the rural South. Data analyses using structural equation modeling and latent growth curve modeling demonstrated that life stress was linked to increases in risk behavior as African Americans transitioned out of secondary school. The cascade model indicated that life stress fostered increases in negative emotions. Negative emotions, in turn, were linked to increases in affiliations with deviant peers and romantic partners; this forecast increases in risk behavior. The findings supported a stress proliferation framework, in which primary stressors affect increases in secondary stressors that carry forward to influence changes in risk behaviors that can potentially compromise mental health. PMID:20576186

  4. Gender Dynamics Predict Changes in Marital Love Among African American Couples

    PubMed Central

    Stanik, Christine E.; McHale, Susan M.; Crouter, Ann C.

    2013-01-01

    This study examined the implications of gender attitudes and spouses’ divisions of household labor, time with children, and parental knowledge for their trajectories of love in a sample of 146 African American couples. Multilevel modeling in the context of an accelerated longitudinal design accommodated 3 annual waves of data. The results revealed that traditionality in husbands’ gender attitudes was linked to lower levels of love. Furthermore, divisions of household labor and parental knowledge moderated changes in love such that couples with more egalitarian divisions exhibited higher and more stable patterns of love, whereas more traditional couples exhibited significant declines in love over time. Finally, greater similarity between spouses’ time with their children was linked to higher levels of marital love. The authors highlight the implications of gender dynamics for marital harmony among African American couples and discuss ways that this work may be applied and extended in practice and future research. PMID:23956462

  5. Life stress, maternal optimism, and adolescent competence in single mother, African American families.

    PubMed

    Taylor, Zoe E; Larsen-Rife, Dannelle; Conger, Rand D; Widaman, Keith F; Cutrona, Carolyn E

    2010-08-01

    Although research demonstrates many negative family outcomes associated with single-parent households, little is known about processes that lead to positive outcomes for these families. Using 3 waves of longitudinal data, we examined how maternal dispositional optimism and life stressors are associated with parenting and child outcomes in 394 single mother African American families. Confirming prior research, we found that mothers' childhood adversities, current economic pressure, and internalizing problems were associated with lower levels of maternal warmth and child management and with lower child school competence. Extending previous studies, we found that maternal optimism was a positive resource, predicting lower levels of maternal internalizing symptoms and higher levels of effective child management and moderating the impact of economic stress on maternal internalizing problems. These findings highlight the need for further investigation of processes and resources that promote positive outcomes for African American mother-headed families and single mother families in general. PMID:20731493

  6. Trade in Educational Services: Reflections on the African and South African Higher Education System

    ERIC Educational Resources Information Center

    Sehoole, Chika Trevor

    2004-01-01

    This article discusses and analyses the emergence of globalisation and its impact on developments within the African continent. Africa's response at a regional level through the New Partnership for Africa's Development and at a subregional level through the Southern African Development Community's "Protocol on Education" come under scrutiny. These…

  7. African Self-Consciousness and Health-Promoting Behaviors among African American College Students.

    ERIC Educational Resources Information Center

    Thompson, Shawn N.; Chambers, John W., Jr.

    2000-01-01

    Investigated three models of relationships between African self-consciousness, health consciousness, and health-promoting behaviors among African American college students. The models included the mediator model, moderator model, and independent model. Surveys of 80 students supported the independent model, suggesting that African…

  8. Research with African Americans: Lessons Learned about Recruiting African American Women

    ERIC Educational Resources Information Center

    Coker, Angela D.; Huang, Hsin-Hsin; Kashubeck-West, Susan

    2009-01-01

    The authors briefly explore literature related to recruiting African American research participants, reflect on their experiences conducting body image research with a sample of African American college women in an earlier study (S. Kashubeck-West et al., 2008), and discuss some methodological and cultural challenges that they encountered during…

  9. Crossing Cultures in Marriage: Implications for Counseling African American/African Couples

    ERIC Educational Resources Information Center

    Durodoye, Beth A.; Coker, Angela D.

    2008-01-01

    A wealth of literature exists regarding intermarriage between White and ethnic minority couples. Noticeably lacking, however, is information considering within-group diversity amongst Black couples. This paper will focus on cultural dynamics that may operate with African American and African couples residing in the United States. Through an…

  10. African swine fever virus serotype-specific proteins are significant protective antigens for African swine fever

    Technology Transfer Automated Retrieval System (TEKTRAN)

    African swine fever (ASF) is an emerging disease threat for the swine industry worldwide. No ASF vaccine is available and progress is hindered by lack of knowledge concerning the extent of African swine fever virus (ASFV) strain diversity and the viral antigens conferring type specific protective im...

  11. African American Pastors' Beliefs and Actions Regarding Childhood Incest in the African American Community

    ERIC Educational Resources Information Center

    Wells, Tesia Denis

    2012-01-01

    This quantitative study sought to explore African American pastors' beliefs and actions regarding childhood incest in the African American community and their decisions to inform the proper authorities. This exploratory study was developed in order to draw both public and academic attention to the understudied phenomenon of childhood incest…

  12. African Sojourn: Two Narratives of African American Women Educators' Educational Philosophy.

    ERIC Educational Resources Information Center

    Pollard, Mignonne Y.

    This paper examines how the educational philosophies of two representative African American women university professors were influenced by multiple sojourns between Africa and North America. Two African American women born in the 1940s were interviewed about their early educational experiences, racial identity, and experiences in Africa. Each…

  13. Changing Fatherhood: An Exploratory Qualitative Study with African and African Caribbean Men in England

    ERIC Educational Resources Information Center

    Williams, Robert; Hewison, Alistair; Wildman, Stuart; Roskell, Carolyn

    2013-01-01

    This paper presents findings from a qualitative study undertaken with 46 African and African Caribbean men exploring their experiences of fatherhood. Data analysis was informed by Connell's theoretical work on changing gender relations. Findings indicate that fathers' lives were mediated by masculinities, racism, gender, migration and…

  14. Perceptions of African American and European American Teachers on the Education of African American Boys

    ERIC Educational Resources Information Center

    Bacon, Ellen; Banks, Joy; Young, Kathryn; Jackson, Francesina R.

    2007-01-01

    The authors interviewed 27 teachers (16 African American and 11 European American) on instructional factors contributing to overidentification of behavior problems in African American boys. Interviews focused on teachers' perspectives of effective teachers, teacher-student relationships, and communication styles. Analysis of the interviews showed…

  15. FXIIIA subtypes in Indonesians, Bangladeshis, Tibetans, South African blacks and South African whites.

    PubMed

    Kido, A; Susukida, R; Oya, M; Fujitani, N; Kimura, H; Hara, M

    2001-03-01

    The polymorphism of FXIIIA was investigated in 105 Indonesians, 141 Bangladeshis, 186 Tibetans, 101 South African Blacks and 100 South African Whites using isoelectric focusing followed by immunoblotting. These population data conformed to the Hardy-Weinberg equilibrium. A circum-pan-Pacific cline in the FXIII*1A (or FXIII*1B) allele frequency appeared to exist among the Mongoloids. PMID:11360808

  16. Teaching African American Youth: Learning from the Lives of Three African American Social Studies Teachers

    ERIC Educational Resources Information Center

    McBride, Chantee Earl

    2010-01-01

    This study examines the life histories of three African American social studies teachers, focusing on the evolution and changes in their identities, perspectives, and attitudes related to their profession and instructional practice. In addition, the study addresses the significance of the teachers' racialized experiences as African Americans and…

  17. "Women ... Mourn and Men Carry on": African Women Storying Mourning Practices--A South African Example

    ERIC Educational Resources Information Center

    Kotze, Elmarie; Els, Lishje; Rajuili-Masilo, Ntsiki

    2012-01-01

    African mourning of loss of lives in South Africa has been shaped by discursive practices of both traditional African cultures and the sociopolitical developments under apartheid and in post-apartheid South Africa. This article reports on changes in mourning practices on the basis of a literature review and uses a collection of examples to…

  18. A SNP test to identify Africanized honeybees via proportion of 'African' ancestry.

    PubMed

    Chapman, Nadine C; Harpur, Brock A; Lim, Julianne; Rinderer, Thomas E; Allsopp, Michael H; Zayed, Amro; Oldroyd, Benjamin P

    2015-11-01

    The honeybee, Apis mellifera, is the world's most important pollinator and is ubiquitous in most agricultural ecosystems. Four major evolutionary lineages and at least 24 subspecies are recognized. Commercial populations are mainly derived from subspecies originating in Europe (75-95%). The Africanized honeybee is a New World hybrid of A. m. scutellata from Africa and European subspecies, with the African component making up 50-90% of the genome. Africanized honeybees are considered undesirable for bee-keeping in most countries, due to their extreme defensiveness and poor honey production. The international trade in honeybees is restricted, due in part to bans on the importation of queens (and semen) from countries where Africanized honeybees are extant. Some desirable strains from the United States of America that have been bred for traits such as resistance to the mite Varroa destructor are unfortunately excluded from export to countries such as Australia due to the presence of Africanized honeybees in the USA. This study shows that a panel of 95 single nucleotide polymorphisms, chosen to differentiate between the African, Eastern European and Western European lineages, can detect Africanized honeybees with a high degree of confidence via ancestry assignment. Our panel therefore offers a valuable tool to mitigate the risks of spreading Africanized honeybees across the globe and may enable the resumption of queen and bee semen imports from the Americas. PMID:25846634

  19. A comparison study between two long-lasting synoptic-scale wave trains and associated tropical cyclogeneses

    NASA Astrophysics Data System (ADS)

    Feng, Tao; Huang, Ronghui; Yang, Xiuqun; Wu, Liang; Zhou, Wen

    2016-04-01

    Tropical cyclogenesis is closely related to the activity of convectively coupled equatorial waves over the western North Pacific. Previous studies usually focused on the role of single cyclonic disturbance on tropical cyclogenesis. From a view of continuously propagating wave train, this study compared two long-lasting synoptic-scale wave trains with distinct tropical cyclone activities in 2004 and 2006 for investigating the essential factors affecting low-level perturbations and tropical cyclone activities. By employing CFSR reanalysis data, JTWC best track, TRMM precipitation rate and ERSST sea surface temperature, analyses show that the long-lasting wave train during 2004 mainly occurs over the region from 130°E to 160°E, featuring enhanced synoptic perturbations in association with enhanced tropical cyclone activity. In contrast, during 2006, the wave train maintains over the region from 120°E to 150°E with more poleward propagation, and the tropical cyclone activity is relatively inactive. Furthermore, the substantial differences between these two wave trains are that the primary propagation occurring at mid-lower-troposphere with a nearly equivalent barotropic structure during 2004, but at upper- and lower- troposphere with significant westward tilt during 2006. This is essentially attributed to effects of different vertical wind shears. In 2004, affected by weak easterly shear, the synoptic-scale waves are confined at mid-low-level. However, in 2006, waves are usually trapped at upper-troposphere by weak westerly shear. Thus, different patterns of vertical wind shears fundamentally affect the structures of synoptic-scale waves and associated tropical cyclogeneses.

  20. Equatorial atmospheric Kelvin waves during El Niño episodes and their effect on stratospheric QBO.

    PubMed

    Das, Uma; Pan, C J

    2016-02-15

    Equatorial atmospheric Kelvin waves are investigated during a positive El Niño Southern Oscillation (ENSO) episode using temperature data retrieved from GPS Radio Occultation (RO) observations of FORMOSAT-3/COSMIC during the period from August 2006 to December 2013. Enhanced Kelvin wave amplitudes are observed during the El Niño episode of 2009-2010 and it is also observed that these amplitudes correlate with the Niño 3.4 index and also with outgoing longwave radiation and trade wind index. This study indicates that the enhanced equatorial atmospheric Kelvin wave amplitudes might be produced by geophysical processes that were involved in the onset and development of the El Niño episode. Further, easterly winds above the tropopause during this period favored the vertically upward propagation of these waves that induced a fast descending westerly regime by the end of 2010, where the zero-wind line is observed to take only 5 months to descend from 10 to 50 hPa. The current study presents observational evidence of enhanced Kelvin wave amplitudes during El Niño that has affected the stratospheric quasi-biennial oscillation (QBO) through wave-mean flow interactions. Earlier El Niño episodes of 1987 and 1998 are also qualitatively investigated, using reanalysis data. It is found that there might have been an enhancement in the equatorial Kelvin wave amplitudes during almost all El Niño episodes, however, an effect of a fast descending westerly is observed in the QBO only when the ambient zonal winds in the lower stratosphere favor the upward propagation of the Kelvin waves and consequently they interact with the mean flow. This study indicates that the El Niño and QBO are not linearly related and wave mean flow interactions play a very important role in connecting these two geophysical phenomena. PMID:26771207

  1. An intensely sympathetic awareness: Experiential similarity and cultural norms as means for gaining older African Americans’ trust of scientific research

    PubMed Central

    Sabir, Myra G.; Pillemer, Karl A.

    2014-01-01

    Well-known trust-building methods are routinely used to recruit and retain older African Americans into scientific research studies, yet the quandary over how to overcome this group’s hesitance to participate in research remains. We present two innovative and testable methods for resolving the dilemma around increasing older African Americans’ participation in scientific research studies. Certain specific and meaningful experiential similarities between the primary researcher and the participants, as well as clear recognition of the elders’ worth and dignity, improved older African Americans’ willingness to adhere to a rigorous research design. Steps taken in an intervention study produced a potentially replicable strategy for achieving strong results in recruitment, retention and engagement of this population over three waves of assessment. Sixty-two (n = 62) older African Americans were randomized to treatment and control conditions of a reminiscence intervention. Sensitivity to an African-American cultural form of respect for elders (recognition of worth and dignity), and intersections between the lived experience of the researcher and participants helped dispel this population’s well-documented distrust of scientific research. Results suggest that intentional efforts to honor the worth and dignity of elders through high level hospitality and highlighting meaningful experiential similarities between the researcher and the participants can improve recruitment and retention results. Experiential similarities, in particular, may prove more useful to recruitment and retention than structural similarities such as age, race, or gender, which may not in themselves result in the trust experiential similarities elicit. PMID:24655682

  2. Southern African AIDS Training Programme.

    PubMed

    Dafoe, G H

    1994-01-01

    The Canadian Public Health Association (CPHA) with the Canadian International Development Agency (CIDA), in a little over 2 years, have established a Southern African AIDS Training Programme (SAT) that is effective in developing community-based responses to acquired immunodeficiency syndrome (AIDS). Based in Harare, Zimbabwe, the program provides financial assistance, training, monitoring, and advice and information to 120 project partners. The average grant size is $40,000. In a second phase of the project, SAT will attempt to meet the requests of its partners for more services. Currently, to meet needs for rapid, responsive training, and novel approaches to skill building, SAT has developed a collaborative nongovernmental organization (NGO) initiative, "The School Without Walls". This program identifies and amplifies what has worked effectively for organizations and programs. Other similar organizations and programs learn from these experiences. Site visits, apprenticeships, mentor organizations, and skills-building based on shared problem-diagnosis and resolution are some of the techniques employed. A draft report of the CIDA midterm external evaluation of SAT recommends renewal of the program, resourcing of the program to meet its regional responsibilities, and adoption of "The School Without Walls" as a central strategy for southern Africa. PMID:8180923

  3. Antigenic variation in African trypanosomes

    PubMed Central

    Horn, David

    2014-01-01

    Studies on Variant Surface Glycoproteins (VSGs) and antigenic variation in the African trypanosome, Trypanosoma brucei, have yielded a remarkable range of novel and important insights. The features first identified in T. brucei extend from unique to conserved-among-trypanosomatids to conserved-among-eukaryotes. Consequently, much of what we now know about trypanosomatid biology and much of the technology available has its origin in studies related to VSGs. T. brucei is now probably the most advanced early branched eukaryote in terms of experimental tractability and can be approached as a pathogen, as a model for studies on fundamental processes, as a model for studies on eukaryotic evolution or often all of the above. In terms of antigenic variation itself, substantial progress has been made in understanding the expression and switching of the VSG coat, while outstanding questions continue to stimulate innovative new approaches. There are large numbers of VSG genes in the genome but only one is expressed at a time, always immediately adjacent to a telomere. DNA repair processes allow a new VSG to be copied into the single transcribed locus. A coordinated transcriptional switch can also allow a new VSG gene to be activated without any detectable change in the DNA sequence, thereby maintaining singular expression, also known as allelic exclusion. I review the story behind VSGs; the genes, their expression and switching, their central role in T. brucei virulence, the discoveries that emerged along the way and the persistent questions relating to allelic exclusion in particular. PMID:24859277

  4. Climate Change Projections for African Urban Areas

    NASA Astrophysics Data System (ADS)

    Simonis, Ingo; Engelbrecht, Francois; Bucchignani, Edoardo; Mercogliano, Paola; Naidoo, Mogesh

    2013-04-01

    Mainly driven by changes in the orbital characteristics of Earth around the sun, the planet's climate has been continuously changing over periods of tens of thousands of years. However, the warming that has been detected in the Earth's atmosphere over the last century is occurring at a rate that cannot be explained by any known natural cycle. Main-stream science has indeed reached consensus that the 'enhanced green house effect', caused by the interplay of incoming short-wave irradiation, outgoing long-wave radiation and the absorption of energy by enhanced levels of CO2 and water vapour in the troposphere, is the main forcing mechanism responsible for the phenomena of global warming. The enhanced greenhouse effect strengthens the 'natural green house effect' that results from the CO2 and water vapour occurring naturally in the atmosphere. The continuous burning of fossil fuels since the industrial revolution and the simultaneous degradation of large forests, are the main reasons for the increase in CO2 concentrations in the atmosphere. The availability of climate change projection data varies considerably for different areas on Earth. Whereas the data centres storing climate change projections for Europe and North America now store petabytes of data, regionally downscaled projections for Africa are rarely available. In the context of the research project CLUVA, (Assessing vulnerability of urban systems, populations and goods in relation to natural and man-made disasters in Africa, co-funded by the European Commission under grant agreement no: 265137), the Council for Industrial and Scientific Research (CSIR) in South Africa and the Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC) in Italy have produced a large set of projections of climate change over Africa, covering the time period 1950 to 2100. Through the collaboration between CMCC and CSIR, a multi-model ensemble of eight high-resolution simulations of climate change over parts of West and East

  5. Long-term observations of the quasi two-day wave by Hawaii MF radar

    NASA Astrophysics Data System (ADS)

    Gu, Sheng-Yang; Li, Tao; Dou, Xiankang; Wang, Ning-Ning; Riggin, Dennis; Fritts, David

    2013-12-01

    mesospheric horizontal wind data set measured during 1991-2006 by the medium frequency (MF) radar at Kauai, Hawaii (22°N, 160°W) is analyzed to examine the long-term variability of the quasi two-day wave (QTDW). The QTDW over Hawaii is amplified twice a year, with the January and July events most likely being the representation of zonal wave numbers 3 and 4 modes, respectively. The amplitudes of the January monthly mean QTDW in both meridional and zonal winds and the July monthly mean QTDW in meridional component are nearly in phase with the solar cycle but with the solar maxima leading the QTDW maxima by 1 or 2 years. However, the July monthly mean QTDW in zonal wind is more antiphase with the solar cycle. Enhanced QTDW oscillations are evident in both wind components in January 1998, which is likely related to the strong El Niño event during the winter of 1997/1998. The enhanced gravity wave activity and the increased barotropic/baroclinic/inertial instability related to the strengthened stratosphere summer easterly jet might provide additional forcing to amplify the QTDW. Moreover, the enhanced migrating diurnal tide during warm El Niño-Southern Oscillation events could also contribute to the abnormally strong QTDW by increasing the refractive index and thus the growth rate of the QTDW. Additional enhancement of the QTDW with a short period of ~43 h is observed during the major sudden stratospheric warming in January 2006.

  6. Stratospheric gravity waves generated by typhoon--A numerical simulation study SIMULATION STUDY

    NASA Astrophysics Data System (ADS)

    Chen, Zeyu; Preusse, P.; Jarisch, M.; Ern, M.; Offermann, D.

    In this presentation the results of a numerical simulation study focusing on investigating the typhoon effect of generating stratospheric GWs will be presented. With applying the PSU/NCAR mm5 model for a northwestern Pacific typhoon (Winnie, 05-23 August 1997), the critical features of the typhoon (comparing with the brightness temperature observations from GMS-5 satellite) and the mean state of the background circulations (comparing with the temperatures observations of the stratosphere from the CRISTA II mission) were captured by the simulation. Detailed investigations revealed that significant stratospheric GWs were triggered by the typhoon. A Typhoon related Gravity Waves Active Area (hereafter referred to as TGWAA) was defined. Momentum flux spectrum with respect to the zonal wave number and frequency in the TGWAA was calculated. Results indicated that the GWs dominant modes were those propagating in the upstream of the background flow (Easterly wind) with a spatial scale ranging from 500 km to 1000 km in the horizontal, and from 7 km to 10 km in the vertical. The temporal scale was rather monotonic with the periods concentrated at 15 hr. The averaged momentum flux in the TGWAA was ˜ 0.001 Pascal at 19 km altitude, 0.0008 Pascal at 25 km altitude, indicating that the waves effect on the mean flow should be paid much attention.

  7. A Simple Wave Driver

    ERIC Educational Resources Information Center

    Temiz, Burak Kagan; Yavuz, Ahmet

    2015-01-01

    This study was done to develop a simple and inexpensive wave driver that can be used in experiments on string waves. The wave driver was made using a battery-operated toy car, and the apparatus can be used to produce string waves at a fixed frequency. The working principle of the apparatus is as follows: shortly after the car is turned on, the…

  8. Financial Rogue Waves

    NASA Astrophysics Data System (ADS)

    Yan, Zhen-Ya

    2010-11-01

    We analytically give the financial rogue waves in the nonlinear option pricing model due to Ivancevic, which is nonlinear wave alternative of the Black—Scholes model. These rogue wave solutions may he used to describe the possible physical mechanisms for rogue wave phenomenon in financial markets and related fields.

  9. Ozone and stratospheric height waves for opposite phases of the QBO

    NASA Technical Reports Server (NTRS)

    Mo, Kingtse C.; Nogues-Paegle, Julia

    1994-01-01

    The stratospheric quasi-biennial oscillation (QBO) provides an important source of interannual variations in the Northern Hemisphere. O'sullivan and Salby (1990) related extra-tropical eddy transport with the phase of the tropical QBO. When the tropical wind is easterly, the zero wind line is shifted into the winter hemisphere. Enhanced wave activity in middle latitudes acts to weaken the polar vortex. When the tropical wind is in the westerly phase the situation reverses. Heights at 30 mb and ozone configurations are contrasted in this paper for these two QBO phases. When the winter vortex deforms due to the amplification of planetary waves 1 and 2, extends westward and equatorward, the complementary band of low vorticity air spirals in toward the pole from lower latitudes. Sometimes, these planetary waves break (Juckes and McIntyre, 1987) and an irreversible mixing of air takes place between high and mid-latitudes. Global ozone patterns, as obtained form satellite observations, appear to be affected by planetary wave breaking (Leovy et al. 1985). This mixing results on regions with uniform ozone and potential vorticity. In the Southern Hemisphere (SH), Newman and Randel (1988) using Total Ozone Mapping Spectrometer (TOMS) data and the NMC analyses have found strong spatial correlation between the October mean temperature in the lower stratosphere and total ozone for the 1979 through 1986 years. Recently Nogues-Paegle et al.(1992) analyzed SH ozone and height data from 1986 to 1989. They found that leading empirical orthogonal functions (EOFs) for both ozone and 50 mb heights exhibit zonal wave 1 and 2 and that the correlations between ozone and 50 mb principal components (PCs) are high. The results were found to be consistent with a linear planetary wave advecting a passive tracer. In this paper, the dominant patterns of variability for 30 mb NMC heights and TOMS total ozone are obtained for the winter to summer transition (January to May) in the Northern

  10. Gravity wave transmission diagram

    NASA Astrophysics Data System (ADS)

    Tomikawa, Yoshihiro

    2016-07-01

    A possibility of gravity wave propagation from a source region to the airglow layer around the mesopause has been discussed based on the gravity wave blocking diagram taking into account the critical level filtering alone. This paper proposes a new gravity wave transmission diagram in which both the critical level filtering and turning level reflection of gravity waves are considered. It shows a significantly different distribution of gravity wave transmissivity from the blocking diagram.

  11. Africans and Black Americans in the United States: Social Distance and Differential Acculturation.

    ERIC Educational Resources Information Center

    Emoungu, Paul-Albert

    1992-01-01

    Presents an exploratory examination of the causes of social distance characterizing the association between Africans and African Americans. African American's perceptions about Africa and Africans are assessed through anecdotes and impressions, and thoughts and criticisms of Africans about African Americans are considered. A social science…

  12. Hyperinsulinemia and acanthosis nigricans in African Americans.

    PubMed Central

    Stuart, C. A.; Gilkison, C. R.; Keenan, B. S.; Nagamani, M.

    1997-01-01

    Compared with the US white, non-Hispanic population, the African-American population has a nearly two-fold higher prevalence of noninsulin-dependent diabetes mellitus (NIDDM). Obesity, which usually precedes NIDDM, is associated with the skin lesion acanthosis nigricans in African Americans. This study was undertaken to determine what the relationship of acanthosis nigricans was to hyperinsulinemia, a major risk factor for NIDDM. Eighty-nine African-American subjects with acanthosis nigricans and 25 others without the skin lesion were evaluated using oral glucose tolerance testing and responsiveness to insulin. Noninsulin-dependent diabetes mellitus was present in 19 of the subjects with acanthosis nigricans. The prevalence of NIDDM in this group increased with increasing age, reaching 50% among those in their 40s. Fasting plasma insulin concentration was in direct proportion to the severity of the acanthosis nigricans involvement of the neck. These data suggest that among African Americans, this skin lesion is a marker for hyperinsulinemia and insulin resistance. Furthermore, the presence of acanthosis nigricans identifies a subset with a much higher prevalence of NIDDM than is present in African Americans in the general population. PMID:9264219

  13. An African VLBI Network of radio telescopes

    NASA Astrophysics Data System (ADS)

    Gaylard, M. J.; Bietenholz, M. F.; Combrinck, L.; Booth, R. S.; Buchner, S. J.; Fanaroff, B. L.; MacLeod, G. C.; Nicolson, G. D.; Quick, J. F. H.; Stronkhorst, P.; Venkatasubramani, T. L.

    The advent of international wideband communication by optical fibre has produced a revolution in communications and the use of the internet. Many African countries are now connected to undersea fibre linking them to other African countries and to other continents. Previously international communication was by microwave links through geostationary satellites. These are becoming redundant in some countries as optical fibre takes over, as this provides 1000 times the bandwidth of the satellite links. In the 1970's and 1980's some two dozen large (30m diameter class) antennas were built in various African countries to provide the satellite links. Twenty six are currently known in 19 countries. As these antennas become redundant, the possibility exists to convert them for radio astronomy at a cost of roughly one tenth that of a new antenna of similar size. HartRAO, SKA South Africa and the South African Department of Science and Technology (DST) have started exploring this possibility with some of the African countries.

  14. Photoelectron wave function in photoionization: plane wave or Coulomb wave?

    PubMed

    Gozem, Samer; Gunina, Anastasia O; Ichino, Takatoshi; Osborn, David L; Stanton, John F; Krylov, Anna I

    2015-11-19

    The calculation of absolute total cross sections requires accurate wave functions of the photoelectron and of the initial and final states of the system. The essential information contained in the latter two can be condensed into a Dyson orbital. We employ correlated Dyson orbitals and test approximate treatments of the photoelectron wave function, that is, plane and Coulomb waves, by comparing computed and experimental photoionization and photodetachment spectra. We find that in anions, a plane wave treatment of the photoelectron provides a good description of photodetachment spectra. For photoionization of neutral atoms or molecules with one heavy atom, the photoelectron wave function must be treated as a Coulomb wave to account for the interaction of the photoelectron with the +1 charge of the ionized core. For larger molecules, the best agreement with experiment is often achieved by using a Coulomb wave with a partial (effective) charge smaller than unity. This likely derives from the fact that the effective charge at the centroid of the Dyson orbital, which serves as the origin of the spherical wave expansion, is smaller than the total charge of a polyatomic cation. The results suggest that accurate molecular photoionization cross sections can be computed with a modified central potential model that accounts for the nonspherical charge distribution of the core by adjusting the charge in the center of the expansion. PMID:26509428

  15. Men of African Descent and Carcinoma of the Prostate Consortium

    Cancer.gov

    The Men of African Descent and Carcinoma of the Prostate Consortium collaborates on epidemiologic studies to address the high burden of prostate cancer and to understand the causes of etiology and outcomes among men of African ancestry.

  16. What about African Americans and High Blood Pressure?

    MedlinePlus

    ANSWERS by heart Lifestyle + Risk Reduction High Blood Pressure What About African Americans and High Blood Pressure? The prevalence of high blood pressure in African Americans is among the highest in ...

  17. Afro-Americans and Early Pan-Africanism

    ERIC Educational Resources Information Center

    Contee, Clarence G.

    1970-01-01

    History of the Pan-African movement, the roles of W.E.B.Du Bois and Marcus Garvey in the movement activities, and the shift to African based leadership of the movement in the 1940's are discussed. (KG)

  18. Doctoral training of African scientists.

    PubMed

    Doumbo, O K; Krogstad, D J

    1998-02-01

    There are two principal rationales for doctoral training of African scientists in health: 1) these scientists are essential for the nations of sub-Saharan Africa to define and implement their own health priorities, and 2) the research they perform is essential for development. However, this training is difficult because of its expense (> $20,000 per year), because many developed country mentors are unaware of the realities of research in sub-Saharan Africa, and because major differences in salary provide a financial disincentive to return. We describe a training strategy that reduces attrition because it is linked to the investigators' responsibilities before and after training, and to home country priorities. This strategy requires a close relationship between the developing country (on-site) and developed country (off-site) mentors, with joint participation in the selection and funding process, followed by course work and short-term, independent projects off-site that lead to a thesis project in the developing country, and subsequently to a defined professional position in the developing country after completion of the doctoral degree. For this strategy to succeed, the developed country mentor must have both field experience and investigative expertise; the developing country mentor must have an understanding of modern biology, as well as clinical and epidemiologic experience. In addition, we would like to emphasize that the long-term retention of these talented, highly-trained individuals requires a similar long-term commitment by their developed country mentors, well beyond the short term of most research funding. PMID:9502592

  19. Role of gravity waves in the spatial and temporal variability of stratospheric temperature measured by COSMIC/FORMOSAT-3 and Rayleigh lidar observations

    NASA Astrophysics Data System (ADS)

    McDonald, Adrian J.; Tan, Bo; Chu, Xinzhao

    2010-10-01

    This study utilizes COSMIC satellite and lidar observations to examine the spatial and temporal variability of stratospheric temperature at a number of scales. The geographic variation of the RMS temperature difference between pairs of COSMIC profiles shows a strong correspondence to previous climatologies of gravity wave activity. In addition, the second-order structure functions we form can be directly related to the horizontal wave number power spectrum. These structure functions for different seasons and altitudes display a close correspondence to previous studies which examined the form of the horizontal wave number power spectra. Our analysis suggests that the wavefield may be particularly affected by changes in the zonal wind between 15 and 25 km and that the wind reversal between tropospheric westerlies and stratospheric easterlies in summer strongly contributes to critical-level filtering. Inspection also shows that longer horizontal wavelength waves are preferentially removed in this region. At low altitudes, the variability related to gravity waves shows a remarkably similar pattern as a function of horizontal separation in both hemispheres but is quite different at higher altitudes. Such contrast implies that seasonal variability at higher altitudes may be dominated by changes in propagation conditions in the lower stratosphere. Examination of temperature variability as a function of spatial and temporal separation indicates that gravity wave activity dominates stratospheric temperature variability, and this has impacts on validation study site selection. For example, validation exercises in the summer hemisphere stratosphere are likely to be less affected by geophysical variability than those in the winter hemisphere.

  20. KSC kicks off African-American History Month

    NASA Technical Reports Server (NTRS)

    2000-01-01

    Clothed in her traditional African garb, Michelle Amos, mistress of ceremonies, welcomes the audience on Feb. 3 at the kick-off of African-American History Month. The theme for this year's observation is 'Heritage and Horizons: The African-American Legacy and the Challenges of the 21st Century.' February is designated each year as a time to celebrate the achievements and contributions of African Americans to Kennedy Space Center, NASA and the nation.

  1. Shear wave logging using guided waves

    SciTech Connect

    Winbow, G.A.; Chen, S.T.; Rice, J.A.

    1988-09-27

    This patent describes a method for acoustically logging an earth formation surrounding a borehole which contains a liquid where the approximate shear wave velocity v of the formation is known. The method consists of: vibrating a dipole source in the liquid to generate in the liquid a guided wave the frequencies of which include a critical frequency f given by zeta = ..nu..12a where a is the borehole radius, so that the fastest component of the guided wave has velocity substantially equal to ..nu..; and detecting the arrival of the fastest component of the guided wave at least one location in the liquid spaced longitudinally along the borehole from the dipole source.

  2. IDEAL Symposium on the East African Lakes

    NASA Astrophysics Data System (ADS)

    Johnson, T. C.; Kelts, K.; Lehman, J. T.; Wuest, A.

    A vast array of interdisciplinary problems presented by the African Great Lakes were highlighted at the International Symposium on the Limnology, Climatology and Paleoclimatology of the East African Lakes, organized by the International Decade for the East African Lakes (IDEAL) February 17-21 in Jinja, Uganda. Approximately 125 scientists attended from North America, Europe, Africa, and New Zealand. Jinja is located on the northern shore of Lake Victoria at the head-waters of the Nile and is the site of the host institution for the symposium, the Uganda Freshwater Fisheries Research Organization (UFFRO). The conveners of the symposium were Tom Johnson of Duke University, George Kitaka of UNESCO-ROSTA, and Eric Odada of the University of Nairobi.

  3. Novel African Trypanocidal Agents: Membrane Rigidifying Peptides

    PubMed Central

    Harrington, John M.; Scelsi, Chris; Hartel, Andreas; Jones, Nicola G.; Engstler, Markus; Capewell, Paul; MacLeod, Annette; Hajduk, Stephen

    2012-01-01

    The bloodstream developmental forms of pathogenic African trypanosomes are uniquely susceptible to killing by small hydrophobic peptides. Trypanocidal activity is conferred by peptide hydrophobicity and charge distribution and results from increased rigidity of the plasma membrane. Structural analysis of lipid-associated peptide suggests a mechanism of phospholipid clamping in which an internal hydrophobic bulge anchors the peptide in the membrane and positively charged moieties at the termini coordinate phosphates of the polar lipid headgroups. This mechanism reveals a necessary phenotype in bloodstream form African trypanosomes, high membrane fluidity, and we suggest that targeting the plasma membrane lipid bilayer as a whole may be a novel strategy for the development of new pharmaceutical agents. Additionally, the peptides we have described may be valuable tools for probing the biosynthetic machinery responsible for the unique composition and characteristics of African trypanosome plasma membranes. PMID:22970207

  4. Antineoplastic constituents of some Southern African plants.

    PubMed

    Charlson, A J

    1980-12-01

    Extracts of several Southern African plants which have been used in folk remedies have been prepared, and the extracts were tested in a variety of experimental tumour test-systems. Raphionacme hirsuta and Cheilanthes contracta have been used in African anticancer medicines. Extracts of these plants showed antitumor activity in some rodent test-systems, but the results were not confirmed. In the folk-lore, Haemanthus natalensis has been used in emetics and Urginea capitata preparations have been used to vaccinate African chiefs. Extracts of these plants showed significant cytotoxicity in the KB cell culture test-system. Infusions of Brunsvigia radulosa have been used as folk remedies for abdominal troubles. An extract of this Amaryllis plant increased the life span of P-388 leukaemic mice. Amaryllis bellandonna has also been investigated. Extracts of Amaryllis belladonna had to be fractionated in order to produce significant antitumour activity in the P-388 lymphocytic leukaemia test-system. PMID:7421280

  5. Intimate Partner Violence among West African Immigrants

    PubMed Central

    AKINSULURE-SMITH, ADEYINKA M.; CHU, TRACY; KEATLEY, EVA; RASMUSSEN, ANDREW

    2013-01-01

    Although the number of African immigrants arriving to the United States has increased significantly, there has been little investigation regarding their experiences of intimate partner violence or coping strategies. This study used focus groups and individual interviews to explore intimate partner violence among 32 heterosexual West African immigrants. Results suggest that although cultural expectations influence their coping strategies, West African–born men and women face different realities, with women reporting multiple instances of abuse and a sense of frustration with the existing options for assistance. Although participants discussed multilevel support structures within the immediate West African community to address intimate partner violence, all of these options maintained a gender hierarchy, leaving women dissatisfied. Challenges and barriers to partner violence resolution and coping strategies are identified. Results are examined in terms of their implications for addressing the needs of this underserved population. Implications for future research and services are discussed and highlighted. PMID:23730146

  6. Trichomonas vaginalis, HIV, and African-Americans.

    PubMed Central

    Sorvillo, F.; Smith, L.; Kerndt, P.; Ash, L.

    2001-01-01

    Trichomonas vaginalis may be emerging as one of the most important cofactors in amplifying HIV transmission, particularly in African-American communities of the United States. In a person co-infected with HIV, the pathology induced by T. vaginalis infection can increase HIV shedding. Trichomonas infection may also act to expand the portal of entry for HIV in an HIV-negative person. Studies from Africa have suggested that T. vaginalis infection may increase the rate of HIV transmission by approximately twofold. Available data indicate that T. vaginalis is highly prevalent among African-Americans in major urban centers of the United States and is often the most common sexually transmitted infection in black women. Even if T. vaginalis increases the risk of HIV transmission by a small amount, this could translate into an important amplifying effect since Trichomonas is so common. Substantial HIV transmission may be attributable to T. vaginalis in African-American communities of the United States. PMID:11747718

  7. Simulation of West African monsoon circulation in four atmospheric general circulation models forced by prescribed sea surface temperature

    NASA Astrophysics Data System (ADS)

    Moron, Vincent; Philippon, Nathalie; Fontaine, Bernard

    2004-12-01

    The mean evolution of the West African monsoon (WAM) circulation and its interannual variability have been studied using an ensemble of 21 simulations (common period 1961-1994) performed with four different atmospheric general circulation models (AGCMs) (European Center/Hamburg (ECHAM) 3, ECHAM 4, Action de Recherche Petite Echelle Grande Echelle (ARPEGE), and Goddard Institute for Space Studies (GISS)) and forced by the same observed sea surface temperature (SST) data set. The results have been compared with European Centre for Medium-Range Weather Forecasts reanalyses (ERA-40). The climatological means of WAM winds for the AGCMs are similar to the ERA-40 ones. However, the AGCMs tend to underestimate the southern wind component at low levels around 10°N compared to the ERA-40. The simulated Tropical Easterly Jet (TEJ) is usually shifted northward and also too weak for ECHAM 3 and ECHAM 4 compared to ERA-40. The interannual variability of an atmospheric WAM index (WAMI) is quite successfully reproduced (the correlations between the mean ensemble of each AGCM and ERA-40 time series over 1961-1994 range between 0.51 and 0.64). In particular, the four AGCMs reproduce quite well the mean teleconnection structure with El Niño-Southern Oscillation, i.e., a strong (weak) monsoon during La Niña (El Niño) events, even if the largest absolute correlations between WAMI and SST in the eastern and central equatorial Pacific are weaker than in ERA-40. On a yearly basis, WAMI is more predictable and skillful during the cold ENSO years than during the warm ENSO ones. The unskillful warm ENSO events are associated with a significant cooling over the equatorial Atlantic and Western Pacific Ocean and a significant warming in the tropical Indian Ocean.

  8. Magneto-atmospheric waves

    NASA Technical Reports Server (NTRS)

    Thomas, J. H.

    1983-01-01

    A theoretical treatment of magneto-atmospheric waves is presented and applied to the modelling of waves in the solar atmosphere. The waves arise in compressible, stratified, electrically conductive atmospheres within gravitational fields when permeated by a magnetic field. Compression, buoyancy, and distortion of the magnetic field all contribute to the existence of the waves. Basic linearized equations are introduced to describe the waves and attention is given to plane-stratified atmospheres and their stability. A dispersion relation is defined for wave propagation in a plane-stratified atmosphere when there are no plane-wave solutions. Solutions are found for the full wave equation in the presence of either a vertical or a horizontal magnetic field. The theory is applied to describing waves in sunspots, in penumbrae, and flare-induced coronal disturbances.

  9. ULF Waves at Mercury

    NASA Astrophysics Data System (ADS)

    Kim, E.-H.; Boardsen, S. A.; Johnson, J. R.; Slavin, J. A.

    2016-02-01

    This chapter provides a brief overview of the observed characteristics of ultra-low-frequency (ULF) waves at Mercury. It shows how field-aligned propagating ULF waves at Mercury can be generated by externally driven fast compressional waves (FWs) via mode conversion at the ion-ion hybrid resonance. Then, the chapter reviews the interpretation that the strong magnetic compressional waves near and its harmonics observed with 20 of Mercury's magnetic equator could be the ion Bernstein wave (IBW) mode. A recent statistical study of ULF waves at Mercury based on MESSENGER data reported the occurrence and polarization of the detected waves. The chapter further introduces the field line resonance and the electromagnetic ion Bernstein waves to explain such waves, and shows that both theories can partially explain the observations.

  10. Fracture channel waves

    SciTech Connect

    Nihei, K.T.; Yi, W.; Myer, L.R.; Cook, N.G.; Schoenberg, M.

    1999-03-01

    The properties of guided waves which propagate between two parallel fractures are examined. Plane wave analysis is used to obtain a dispersion equation for the velocities of fracture channel waves. Analysis of this equation demonstrates that parallel fractures form an elastic waveguide that supports two symmetric and two antisymmetric dispersive Rayleigh channel waves, each with particle motions and velocities that are sensitive to the normal and tangential stiffnesses of the fractures. These fracture channel waves degenerate to shear waves when the fracture stiffnesses are large, to Rayleigh waves and Rayleigh-Lamb plate waves when the fracture stiffnesses are low, and to fracture interface waves when the fractures are either very closely spaced or widely separated. For intermediate fracture stiffnesses typical of fractured rock masses, fracture channel waves are dispersive and exhibit moderate to strong localization of guided wave energy between the fractures. The existence of these waves is examined using laboratory acoustic measurements on a fractured marble plate. This experiment confirms the distinct particle motion of the fundamental antisymmetric fracture channel wave (A{sub 0} mode) and demonstrates the ease with which a fracture channel wave can be generated and detected. {copyright} 1999 American Geophysical Union

  11. Assessing the contributions of East African and West Pacific warming to the 2014 boreal spring East African drought

    USGS Publications Warehouse

    Funk, Christopher C.; Shukla, Shraddhanand; Hoell, Andrew; Livneh, Ben

    2015-01-01

    Anthropogenic warming contributed to the 2014 East African drought by increasing East African and west Pacific temperatures, and increasing the gradient between standardized western and central Pacific SST causing reduced rainfall, evapotranspiration, and soil moisture.

  12. South African-ness Among Adolescents: The Emergence of a Collective Identity within the Birth to Twenty Cohort Study

    PubMed Central

    Norris, Shane A; Roeser, Robert W.; Richter, Linda M; Lewin, Nina; Ginsburg, Carren; Fleetwood, Stella A; Taole, Elizabeth; van der Wolf, Kees

    2009-01-01

    We assessed the emergence of a South African identity among Black, Colored (mixed ancestral origin), White (predominantly English speaking), and Indian adolescents participating in a birth cohort study called “Birth to Twenty” in Johannesburg, South Africa. We examined young people's certainty of their self-categorization as South African, the centrality of their personal, racial and linguistic, and South African identities in their self-definition, and their perceptions of South African life and society today. These results reflect a historical opportunity for full citizenship and national enfranchisement that the end of Apartheid heralded for Black and Colored individuals. Black and Colored youth tend to be more certain about their South African-ness, have a more collective identity, and have a more positive perception around South Africa. In contrast, White and Indian youth are less certain about their South African-ness, have a more individualistic identity, and have a less positive perception about South Africa today. PMID:19461896

  13. African American Single Mothers Raising Sons: Implications for Family Therapy

    ERIC Educational Resources Information Center

    Gantt, Ann L.; Greif, Geoffrey L.

    2009-01-01

    Being raised by a single mother is one factor that has been suggested as contributing to the plight of African American males. Yet few studies have focused specifically on African American single mothers' experiences with raising sons. This qualitative study explored the following questions: (1) What are the experiences of African American single…

  14. Barriers to Hospice Use among African Americans: A Systematic Review

    ERIC Educational Resources Information Center

    Washington, Karla T.; Bickel-Swenson, Denise; Stephens, Nathan

    2008-01-01

    The present review was undertaken to explore recent evidence in the professional literature pertaining to use of hospice services by African Americans. The article addresses the research methods that have been used to study African American hospice use, obstacles to African American participation in hospice that have been identified, and…

  15. Student-Centered Designs of Pan-African Literature Courses

    ERIC Educational Resources Information Center

    M'Baye, Babacar

    2010-01-01

    A student-centered teaching methodology is an essential ingredient of a successful Pan-African literary course. In this article, the author defines Pan-Africanism and how to go about designing a Pan-African literature course. The author combines reading assignments with journals, film presentations, and lectures in a productive learning…

  16. Achievement and Underachievement: The Experiences of African Caribbeans

    ERIC Educational Resources Information Center

    Rhamie, Jasmine

    2012-01-01

    The disproportionate representation of African Caribbeans in all the negative educational statistics has been well documented. Despite this, there are African Caribbeans who achieve academically but relatively few studies have explored this area. This study aimed to investigate the factors that contribute to African Caribbean academic success,…

  17. Against the Wind: Five South Africans Follow Their Dreams.

    ERIC Educational Resources Information Center

    Lewis, Lesley

    This book for beginning readers tells the story of five South Africans who, though not very famous, all did things that no black South African had ever done before. They include: Simon Mkhize who, year after year, ran the Comrades Marathon unofficially, ignoring its racial bans; Magema M. Fuze, who was the first black South African to publish a…

  18. Beating the Odds: Raising Academically Successful African American Males.

    ERIC Educational Resources Information Center

    Hrabowski, Freemen A., III; Maton, Kenneth I.; Greif, Geoffrey L.

    This book on African American males presents the first step in an ongoing exploration of the relationship between parenting and academic achievement among African American children. Subjects of the study were high-achieving members of the Meyerhoff Scholars, young African Americans distinguished for their achievement. The Meyerhoff Scholar program…

  19. Exposure of African-American Youth to Alcohol Advertising.

    ERIC Educational Resources Information Center

    2003

    The marketing of alcohol products in African-American communities has, on occasion, stirred national controversy and met with fierce resistance from African Americans and others. Despite occasional media and community spotlights on the marketing of alcohol products in the African-American community, there has been no systematic review of the…

  20. African American Educational Leadership in the School Superintendency

    ERIC Educational Resources Information Center

    Smith, Eva C.

    2013-01-01

    African American educational leadership has long been part of American education and African American activism to resist oppression. However, the field of educational leadership has rarely included the contributions of African American leaders, particularly women leaders, into mainstream leadership theory and practices. This omission is difficult…

  1. Oral Cancer in African Americans: Addressing Health Disparities

    ERIC Educational Resources Information Center

    Dodd, Virginia J.; Watson, Jennifer M.; Choi, Youjin; Tomar, Scott L.; Logan, Henrietta L.

    2008-01-01

    Objectives: To explore factors underlying African Americans' perceptions of oral cancer and the oral cancer exam. Study findings were used to guide development of oral cancer messages designed to increase oral cancer exams among African Americans. Methods: Focus groups were conducted to understand African Americans' attitudes and expectations…

  2. Some Growth Points in African Child Development Research

    ERIC Educational Resources Information Center

    Serpell, Robert; Marfo, Kofi

    2014-01-01

    We reflect on ways in which research presented in earlier chapters responds to challenges of generating an African child development field and identify additional issues calling for the field's attention. The chapters collectively display a variety of African contexts and reflexive evidence of the authors' African cultural roots.…

  3. African American Males in Counseling: Who's Pulling the Trigger Now?

    ERIC Educational Resources Information Center

    Bethea-Whitfield, Patricia

    African American males face numerous challenges to their physical and psychological well-being. This project is a survey of the literature and trends relative to African American males from 1987 to the present. In reviewing the fifteen years since Parham and McDavis published their now famous article on African American men as an endangered…

  4. Neo-African Literature: A History of Black Writing.

    ERIC Educational Resources Information Center

    Jahn, Janheinz

    Chapters in this book classify the literature reflecting the overlap of African and Western cultures according to its content, stylistic features, and patterns of literary expression. Areas covered are (1) early writers of African descent; (2) the African scene--oral, Afro-Arabic, "apprentice" and "protest," and Southern Bantu literatures; (3) the…

  5. Seeing African Americans as Competent Parents: Implications for Family Counselors

    ERIC Educational Resources Information Center

    Adkison-Bradley, Carla

    2011-01-01

    One of the primary roles of parents is to guide and socialize children to make meaningful life choices. African American parents, in particular, have the additional tasks of preparing their children to thrive in an environment that has historically been hostile toward African Americans. Yet, many African American parents are often depicted as…

  6. Help-Seeking Attitudes among African American College Students

    ERIC Educational Resources Information Center

    So, Dominicus W.; Gilbert, Stefanie; Romero, Sergio

    2005-01-01

    Traditionally, African American students display a low-rate of seeking mental health treatment. Issues such as mistrust of White therapists, attitudes toward mental health problems, and African American spirituality affect their help-seeking behavior. The present study examined a sample of 134 African American students at a Historically Black…

  7. Persistence among African American Males in the Honors College

    ERIC Educational Resources Information Center

    Anderson Goins, Johnell Roxann

    2014-01-01

    Retaining African American students, specifically African American males, is an issue that plagues the American higher education system. Research shows that African American male students are the lowest represented group in the gifted studies programs (Ford, 2010). Lockie and Burke (1999); Chen and DeJardins (2010) and Bell (2010a) found that…

  8. Teaching African Politics at American Colleges and Universities: A Survey.

    ERIC Educational Resources Information Center

    Kenski, Henry C.; Kenski, Margaret C.

    Political scientists who teach African politics courses at U.S. colleges and universities were surveyed in 1973 to (1) discover successful teaching techniques, approaches, and texts; (2) determine the popularity of courses in African politics; and (3) collect data on the status of African politics as a research area. A questionnaire was mailed to…

  9. Perceptions of Domestic Violence: A Dialogue with African American Women

    ERIC Educational Resources Information Center

    Bent-Goodley, Tricia B.

    2004-01-01

    Although empirical research has accumulated over the past 20 years regarding African Americans and domestic violence, many questions remain about African American perceptions of domestic violence. This article explores African American women's perceptions about domestic violence through three focus groups held at a New York social services agency.…

  10. Requests in a South African Variety of English

    ERIC Educational Resources Information Center

    Kasanga, Luanga A.

    2006-01-01

    The main assumption in this article is that the pragmatics of the variety of South African English commonly referred to as black South African English (BSAE) have been shaped, over time, by educated bilinguals, through a transfer of features from African languages. Transfer of syntactic forms, now firmly established in the variety, is evidenced…

  11. African American Acculturation and Black Racial Identity: A Preliminary Investigation.

    ERIC Educational Resources Information Center

    Pope-Davis, Donald B.; Liu, William M.; Ledesma-Jones, Shannon; Nevitt, Jonathan

    2000-01-01

    Examines the relationship between acculturation and racial identity among African Americans. One hundred eighty-seven African American students completed the Black Racial Identity Attitude Scale and the African American Acculturation Scale (AAAS). Acculturation was associated with three of the five AAAS subscales: Dissonance, Immersion, and…

  12. An Exploration of African American Students' Attitudes toward Online Learning

    ERIC Educational Resources Information Center

    Okwumabua, Theresa M.; Walker, Kristin M.; Hu, Xiangen; Watson, Andrea

    2011-01-01

    The current work presents exploratory research findings concerning African American students' attitudes toward online learning. The Online Tutoring Attitudes Scale (OTAS; Graff, 2003) was administered to 124 African American students in a positive youth development program. Findings suggest that African American students' attitudes toward…

  13. Perceived Attractiveness, Facial Features, and African Self-Consciousness.

    ERIC Educational Resources Information Center

    Chambers, John W., Jr.; And Others

    1994-01-01

    Investigated relationships between perceived attractiveness, facial features, and African self-consciousness (ASC) among 149 African American college students. As predicted, high ASC subjects used more positive adjectives in descriptions of strong African facial features than did medium or low ASC subjects. Results are discussed in the context of…

  14. Engaging Youth through African-Derived Dance and Culture

    ERIC Educational Resources Information Center

    Franklin, Kikora

    2013-01-01

    This article provides a brief history of African and African-derived dance and culture and highlights the physical health, dance education, historical, and cultural benefits of a school-based program that incorporates African dance as its core component. The article also includes the phases of the programming and brings attention to potential…

  15. Empowerment Groups for Urban African American Girls: A Response

    ERIC Educational Resources Information Center

    Holcomb-McCoy, Cheryl C.

    2005-01-01

    Although the author wanted to read Bemak, Chung, and Siroskey-Sabdo's article in an objective sense, her response to their article is most likely influenced by her own experiences as an African American female and mother of an African American daughter. To her, the paramount issue facing African American females is the double and sometimes triple…

  16. Perceptions of Discrimination and Achievement in African American Students.

    ERIC Educational Resources Information Center

    Rowley, Stephanie Johnson

    This study explored the processes that lead to relatively lower academic performance among African American students. It has been suggested that African American students perceive that, because of discrimination, education is less useful as a tool for upward mobility for African Americans than it is for members of other ethnic groups. The nature…

  17. Gender Differences in African American Attitudes toward Gay Males.

    ERIC Educational Resources Information Center

    Battle, Juan; Lemelle, Anthony J., Jr.

    2002-01-01

    Used data from the 1993 National Black Politics Study to examine the way gender worked in explaining African American attitudes toward gay men. Results indicated that African American females expressed more positive attitudes toward homosexual men than did African American males, and of the variables examined (including age, church attendance,…

  18. Contrastive Studies - African Languages and English. Specialised Bibliography C9.

    ERIC Educational Resources Information Center

    British Council, London (England). English-Teaching Information Centre.

    This selective bibliography lists 8 books and 19 journal articles dealing with contrastive studies of African languages and English. The entries range in date from 1953 to 1972 with the majority published since 1965. The books cited are African and British publications and the articles appeared in well-known African, European or American…

  19. From Crisis to Empowerment: African American Women in Community Colleges

    ERIC Educational Resources Information Center

    Bates, Marcie Ann

    2012-01-01

    Social challenges tear at the fabric of the African American family, revealing complexities that identify a de facto leader, the African American woman. She exists in a chasm of overt circumstances which heavily influences her successes. The purpose of this study is to identify factors that motivated seven female African American community college…

  20. Effective Coping Strategies Employed in African-American Relationships.

    ERIC Educational Resources Information Center

    Washington, Novella Channell

    Living in a society that is quick to label and condemn, has been, and continues to be a source of pain for African-Americans. However, society's microscope has for sometime had a one dimensional lens, particularly when examining the coping styles of African-American male-female relationships within the African-American family. There exists a great…