scholarly journals Extreme Precipitation in the West African Cities of Dakar and Ouagadougou: Atmospheric Dynamics and Implications for Flood Risk Assessments

2017 ◽  
Vol 18 (11) ◽  
pp. 2937-2957 ◽  
Author(s):  
Thomas Engel ◽  
Andreas H. Fink ◽  
Peter Knippertz ◽  
Gregor Pante ◽  
Jan Bliefernicht
Keyword(s):  
Urban Areas ◽  
Generalized Pareto Distribution ◽  
Tropical Rainfall Measuring Mission ◽  
Extreme Rainfall ◽  
West African ◽  
Future Research ◽  
Climate Data ◽  
Easterly Waves ◽  
Convective Systems ◽  
Precipitation Estimation

Abstract Two extreme, high-impact events of heavy rainfall and severe floods in West African urban areas (Ouagadougou on 1 September 2009 and Dakar on 26 August 2012) are investigated with respect to their atmospheric causes and statistical return periods. In terms of the synoptic–convective dynamics, the Ouagadougou case is truly extraordinary. A succession of two slow-moving African easterly waves (AEWs) caused record-breaking values of tropospheric moisture. The second AEW, one of the strongest in recent decades, provided the synoptic forcing for the nighttime genesis of mesoscale convective systems (MCSs). Ouagadougou was hit by two MCSs within 6 h, as the strong convergence and rotation in the AEW-related vortex allowed a swift moisture refueling. An AEW was also instrumental in the overnight development of MCSs in the Dakar case, but neither the AEW vortex nor the tropospheric moisture content was as exceptional as in the Ouagadougou case. Tropical Rainfall Measuring Mission (TRMM) 3B42 precipitation data show some promise in estimating centennial return values (RVs) using the “peak over threshold” approach with a generalized Pareto distribution fit, although indications for errors in estimating extreme rainfall over the arid Sahel are found. In contrast, the Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks–Climate Data Record (PERSIANN-CDR) dataset seems less suitable for this purpose despite the longer record. Notably, the Ouagadougou event demonstrates that highly unusual dynamical developments can create extremes well outside of RV estimates from century-long rainfall observations. Future research will investigate whether such developments may become more frequent in a warmer climate.

scholarly journals Three MCS Cases Occurring in Different Synoptic Environments in the Sub-Sahelian Wet Zone during the 2002 West African Monsoon

2006 ◽  
Vol 63 (9) ◽  
pp. 2369-2382 ◽  
Author(s):  
Jon M. Schrage ◽  
Andreas H. Fink ◽  
Volker Ermert ◽  
Epiphane D. Ahlonsou
Keyword(s):  
West Africa ◽  
West African Monsoon ◽  
Lower Troposphere ◽  
Integrated Approach ◽  
West African ◽  
Easterly Waves ◽  
Convective Systems ◽  
Efficient Management ◽  
Mesoscale Convective ◽  
Wet Zone

Abstract Three mesoscale convective systems (MCSs) occurring in the sub-Sahelian wet zone of West Africa are examined using observations from the 2002 Integrated Approach to the Efficient Management of Scarce Water Resources in West Africa (IMPETUS) field campaign, the European Centre for Medium-Range Weather Forecasts (ECMWF) operational analyses, and Meteosat infrared imagery. These datasets enable the analysis of the synoptic-scale environment in which the MCSs were embedded, along with a high-resolution monitoring of surface parameters during the systems’ passages. The available data imply that cases I and II were of a squall-type nature. Case I propagated into a moderately sheared and rather moist lower and middle troposphere over the Upper Ouémé Valley (UOV). In contrast, case II was associated with a well-sheared and dry lower troposphere and a large, moist instability. In either case, behind the convective cluster a westward-propagating cyclonic vorticity maximum that was likely captured by the ECMWF analysis as a result of the special upper-air station at Parakou (Benin). In case I, the fast-moving vorticity signal slowed down over the Guinean Highlands where convection dissipated. Farther downstream, it might have played a role in the consolidation of an African easterly waves (AEW) trough over the West African coast and the eastern Atlantic. Case III proved to be a more stationary pattern of convection associated with a vortex in the monsoon flow. It also exhibited a moist and low shear environment.

scholarly journals Regional Characteristics of Extreme Rainfall Extracted from TRMM PR Measurements

2014 ◽  
Vol 27 (21) ◽  
pp. 8151-8169 ◽  
Author(s):  
Atsushi Hamada ◽  
Yuki Murayama ◽  
Yukari N. Takayabu
Keyword(s):  
Regional Differences ◽  
Tropical Rainfall Measuring Mission ◽  
Extreme Rainfall ◽  
Horizontal Resolution ◽  
Mesoscale Convective Systems ◽  
Extreme Rainfall Events ◽  
Near Surface ◽  
Rainfall Events ◽  
Convective Systems ◽  
Mesoscale Convective

Abstract Characteristics and global distribution of regional extreme rainfall are presented using 12 yr of the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) measurements. By considering each rainfall event as a set of contiguous PR rainy pixels, characteristic values for each event are obtained. Regional extreme rainfall events are defined as those in which maximum near-surface rainfall rates are higher than the corresponding 99.9th percentile on a 2.5° × 2.5° horizontal-resolution grid. The geographical distribution of extreme rainfall rates shows clear regional differences. The size and volumetric rainfall of extreme events also show clear regional differences. Extreme rainfall rates show good correlations with the corresponding rain-top heights and event sizes over oceans but marginal or no correlation over land. The time of maximum occurrence of extreme rainfall events tends to be during 0000–1200 LT over oceans, whereas it has a distinct afternoon peak over land. There are also clear seasonal differences in which the occurrence over land is largely coincident with insolation. Regional extreme rainfall is classified by extreme rainfall rate (intensity) and the corresponding event size (extensity). Regions of “intense and extensive” extreme rainfall are found mainly over oceans near coastal areas and are likely associated with tropical cyclones and convective systems associated with the establishment of monsoons. Regions of “intense but less extensive” extreme rainfall are distributed widely over land and maritime continents, probably related to afternoon showers and mesoscale convective systems. Regions of “extensive but less intense” extreme rainfall are found almost exclusively over oceans, likely associated with well-organized mesoscale convective systems and extratropical cyclones.

Correction of Radar QPE Errors for Non-Uniform VPRs Using TRMM Observations

2013 ◽  
Vol 726-731 ◽  
pp. 3391-3396
Author(s):  
Man Zhang ◽  
You Cun Qi
Keyword(s):  
High Resolution ◽  
Large Scale ◽  
Tropical Rainfall Measuring Mission ◽  
Cool Season ◽  
Convective Systems ◽  
Freezing Level ◽  
Stratiform Region ◽  
Stratiform Precipitation ◽  
Precipitation Estimation ◽  
Mesoscale Convective

Mesoscale Convective Systems (MCSs) contain both regions of convective and stratiform precipitation, and a bright band (BB) or equivalent high-reflectivity region is often found in the stratiform precipitation. Inflated reflectivity intensities in the BB often cause positive biases in radar quantitative precipitation estimation (QPE), and a vertical profile of reflectivity (VPR) correction is necessary to reduce the error. VPR corrections of the radar QPE is more difficult for MCSs than for a widespread cool season stratiform precipitation because of the spatial non-homogeneity of MCSs. Further, microphysical processes in the MCS stratiform region are more complicated than in the large-scale cool season stratiform precipitation. A clearly defined BB bottom, which is critical for accurate VPR corrections, is often not found in ground radar VPRs from MCSs. This is a big challenge when the stratiform region of MCSs is far away from the radar where the radar beam is too high or too wide to resolve the BB bottom. Further, variations of reflectivity below the freezing level are much more significant in MCSs than in a large-scale cool season precipitation, requiring high-resolution radar observations near the ground for an effective VPR correction. The current study seeks to use the vertical precipitation structure observed from Tropical Rainfall Measuring Mission Precipitation Radar (TRMM PR) to aid VPR corrections of the ground radar QPE in MCSs. High-resolution VPRs are derived from TRMM data for MCSs and then applied for the correction of ground radar QPEs.

scholarly journals Observations of Coastally Transitioning West African Mesoscale Convective Systems during NAMMA

2012 ◽  
Vol 2012 ◽  
pp. 1-25
Author(s):  
Bradley W. Klotz ◽  
Paul Kucera
Keyword(s):  
West African ◽  
Radar Reflectivity ◽  
Mesoscale Convective Systems ◽  
Environmental Stability ◽  
Tropical Cyclogenesis ◽  
Easterly Waves ◽  
Convective Systems ◽  
Maximum Reflectivity ◽  
Multidisciplinary Analysis ◽  
Mesoscale Convective

Observations from the NASA 10 cm polarimetric Doppler weather radar (NPOL) were used to examine structure, development, and oceanic transition of West African Mesoscale Convective Systems (MCSs) during the NASA African Monsoon Multidisciplinary Analysis (NAMMA) to determine possible indicators leading to downstream tropical cyclogenesis. Characteristics examined from the NPOL data include echo-top heights, maximum radar reflectivity, height of maximum radar reflectivity, and convective and stratiform coverage areas. Atmospheric radiosondes launched during NAMMA were used to investigate environmental stability characteristics that the MCSs encountered while over land and ocean, respectively. Strengths of African Easterly Waves (AEWs) were examined along with the MCSs in order to improve the analysis of MCS characteristics. Mean structural and environmental characteristics were calculated for systems that produced TCs and for those that did not in order to determine differences between the two types. Echo-top heights were similar between the two types, but maximum reflectivity and height and coverage of intense convection (>50 dBZ) are all larger than for the TC producing cases. Striking differences in environmental conditions related to future TC formation include stronger African Easterly Jet, increased moisture especially at middle and upper levels, and increased stability as the MCSs coastally transition.

scholarly journals Tropical Atlantic Hurricanes, Easterly Waves, and West African Mesoscale Convective Systems

2010 ◽  
Vol 2010 ◽  
pp. 1-13 ◽  
Author(s):  
Yves K. Kouadio ◽  
Luiz A. T. Machado ◽  
Jacques Servain
Keyword(s):  
West Africa ◽  
West African ◽  
Mesoscale Convective Systems ◽  
Tropical Atlantic ◽  
Atmospheric Conditions ◽  
Easterly Waves ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Sst Anomaly ◽  
Atlantic Hurricanes

The relationship between tropical Atlantic hurricanes (Hs), atmospheric easterly waves (AEWs), and West African mesoscale convective systems (MCSs) is investigated. It points out atmospheric conditions over West Africa before hurricane formation. The analysis was performed for two periods, June–November in 2004 and 2005, during which 12 hurricanes (seven in 2004, five in 2005) were selected. Using the AEW signature in the 700 hPa vorticity, a backward trajectory was performed to the African coast, starting from the date and position of each hurricane, when and where it was catalogued as a tropical depression. At this step, using the Meteosat-7 satellite dataset, we selected all the MCSs around this time and region, and tracked them from their initiation until their dissipation. This procedure allowed us to relate each of the selected Hs with AEWs and a succession of MCSs that occurred a few times over West Africa before initiation of the hurricane. Finally, a dipole in sea surface temperature (SST) was observed with a positive SST anomaly within the region of H generation and a negative SST anomaly within the Gulf of Guinea. This SST anomaly dipole could contribute to enhance the continental convergence associated with the monsoon that impacts on the West African MCSs formation.

scholarly journals Uncertainty Assessments of Satellite Derived Rainfall Products

2016 ◽  
Author(s):  
Margaret Kimani ◽  
Joost Hoedjes ◽  
Zhongbo Su
Keyword(s):  
Large Scale ◽  
Rainfall Variability ◽  
Tropical Rainfall Measuring Mission ◽  
Global Precipitation Climatology Project ◽  
Rain Gauge ◽  
Climate Data ◽  
Error Distributions ◽  
Precipitation Estimation ◽  
Scatter Plots ◽  
Global Precipitation

Accurate and consistent rainfall observations are vital for climatological studies in support of better planning and decision making. However, estimation of accurate spatial rainfall is limited by sparse rain gauge distributions. Satellite rainfall products can thus potentially play a role in spatial rainfall estimation but their skill and uncertainties need to be under-stood across spatial-time scales. This study aimed at assessing the temporal and spatial performance of seven satellite products (TARCAT (Tropical Applications of Meteorology using SATellite and ground-based observations (TAMSAT) African Rainfall Climatology And Time series), Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS), Tropical Rainfall Measuring Mission (TRMM-3B43), Climate Prediction Center (CPC) Morphing (CMORPH), the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks- Climate Data Record (PERSIANN-CDR), CPC Merged Analysis of Precipitation (CMAP) and Global Precipitation Climatology Project (GPCP) using gridded (0.05o) rainfall data over East Africa for 15 years(1998-2012). The products’ error distributions were qualitatively compared with large scale horizontal winds (850 mb) and elevation patterns with respect to corresponding rain gauge data for each month during the ‘long’ (March-May) and ‘short’ (October-December) rainfall seasons. For validation only rainfall means extracted from 284 rain gauge stations were used, from which qualitative analysis using continuous statistics of Root Mean Squared Difference, Standard deviations, Correlations, coefficient of determinations (from scatter plots) were used to evaluate the products’ performance. Results revealed rainfall variability dependence on wind flows and modulated by topographic influences. The products’ errors showed seasonality and dependent on rainfall intensity and topography. Single sensor and coarse resolution products showed lowest performance on high ground areas. All the products showed low skills in retrieving rainfall during ‘short’ rainfall season when orographic processes were dominant. CHIRPS, CMORPH and TRMM performed well, with TRMM showing the best performance in both seasons. There is need to reduce products’ errors before applications.

scholarly journals Comparison between Two Case Studies of Developing and Nondeveloping African Easterly Waves during NAMMA and AMMA/SOP-3: Absolute Vertical Vorticity Budget

2010 ◽  
Vol 138 (4) ◽  
pp. 1420-1445 ◽  
Author(s):  
Joël Arnault ◽  
Frank Roux
Keyword(s):  
Large Scale ◽  
West African ◽  
Convective Activity ◽  
Cyclonic Vorticity ◽  
Easterly Waves ◽  
Horizontal Advection ◽  
Convective Systems ◽  
Multidisciplinary Analysis ◽  
Outward Transport ◽  
Vorticity Production

Abstract Two West African disturbances observed in August and September 2006 during the National Aeronautics and Space Administration African Monsoon Multidisciplinary Analysis (NAMMA) and the Special Observing Period 3 (AMMA/SOP-3) have been simulated using the Méso-NH numerical model with explicit convection. The first disturbance spawned Hurricane Helene (2006) off the West African coast, and the second one, referred to as perturbation D, though relatively intense, failed to develop. Over the continent, each case was associated with a well-defined African easterly wave (AEW) trough with embedded growing and decaying convective activity of various size, duration, and intensity. The aim of this work is to investigate the contribution of these convective systems in the generation and maintenance of cyclonic vorticity associated with the AEW trough, with respect to the synoptic-scale processes. The absolute vorticity budgets are analyzed during the “continental” and “oceanic transition” stages of these AEW troughs in order to highlight the similarities and differences between the developing pre-Helene disturbance and the nondeveloping perturbation D. For the developing case, low- to midlevel cyclonic vorticity was produced by convective processes through tilting and stretching. Cyclonic vorticity was then transported upward through vertical advection associated with convection and outward through horizontal advection mostly induced by the large-scale midlevel diverging circulation related to the downstream AEW ridge. For the nondeveloping case, low- to midlevel cyclonic vorticity production through stretching and tilting, and its vertical transport were relatively similar over the continent but smaller over the oceanic transition because of weaker convective activity. The outward transport through horizontal advection was also weaker as there was little midlevel divergence induced by the downstream AEW ridge in this case.

scholarly journals Evaluation of PERSIANN-CDR Constructed Using GPCP V2.2 and V2.3 and A Comparison with TRMM 3B42 V7 and CPC Unified Gauge-Based Analysis in Global Scale

2019 ◽  
Vol 11 (23) ◽  
pp. 2755 ◽  
Author(s):  
Mojtaba Sadeghi ◽  
Ata Akbari Asanjan ◽  
Mohammad Faridzad ◽  
Vesta Afzali Gorooh ◽  
Phu Nguyen ◽  
...  
Keyword(s):  
Tropical Rainfall Measuring Mission ◽  
Global Precipitation Climatology Project ◽  
Global Scale ◽  
Climate Data ◽  
Promising Alternative ◽  
Rain Gauges ◽  
Precipitation Estimation ◽  
Precipitation Records ◽  
Global Precipitation ◽  
Trmm 3B42

Providing reliable long-term global precipitation records at high spatial and temporal resolutions is crucial for climatological studies. Satellite-based precipitation estimations are a promising alternative to rain gauges for providing homogeneous precipitation information. Most satellite-based precipitation products suffer from short-term data records, which make them unsuitable for various climatological and hydrological applications. However, Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Climate Data Record (PERSIANN-CDR) provides more than 35 years of precipitation records at 0.25° × 0.25° spatial and daily temporal resolutions. The PERSIANN-CDR algorithm uses monthly Global Precipitation Climatology Project (GPCP) data, which has been recently updated to version 2.3, for reducing the biases in the output of the PERSIANN model. In this study, we constructed PERSIANN-CDR using the newest version of GPCP (V2.3). We compared the PERSIANN-CDR dataset that is constructed using GPCP V2.3 (from here on referred to as PERSIANN-CDR V2.3) with the PERSIANN-CDR constructed using GPCP V2.2 (from here on PERSIANN-CDR V2.2), at monthly and daily scales for the period from 2009 to 2013. First, we discuss the changes between PERSIANN-CDR V2.3 and V2.2 over the land and ocean. Second, we evaluate the improvements in PERSIANN-CDR V2.3 with respect to the Climate Prediction Center (CPC) unified gauge-based analysis, a gauged-based reference, and Tropical Rainfall Measuring Mission (TRMM 3B42 V7), a commonly used satellite reference, at monthly and daily scales. The results show noticeable differences between PERSIANN-CDR V2.3 and V2.2 over oceans between 40° and 60° latitude in both the northern and southern hemispheres. Monthly and daily scale comparisons of the two bias-adjusted versions of PERSIANN-CDR with the above-mentioned references emphasize that PERSIANN-CDR V2.3 has improved mostly over the global land area, especially over the CONUS and Australia. The updated PERSIANN-CDR V2.3 data has replaced V2.2 data for the 2009–2013 period on CHRS data portal and NOAA National Centers for Environmental Information (NCEI) Program.

scholarly journals Evaluation of Multi-Satellite Precipitation Datasets and Their Error Propagation in Hydrological Modeling in a Monsoon-Prone Region

2020 ◽  
Vol 12 (21) ◽  
pp. 3550
Author(s):  
Jie Chen ◽  
Ziyi Li ◽  
Lu Li ◽  
Jialing Wang ◽  
Wenyan Qi ◽  
...  
Keyword(s):  
Hydrological Modeling ◽  
Tropical Rainfall Measuring Mission ◽  
Transformation Process ◽  
Hydrologic Model ◽  
Hydrological Models ◽  
Random Errors ◽  
Climate Data ◽  
Precipitation Estimation ◽  
Real Performance ◽  
Climate Data Record

This study comprehensively evaluates eight satellite-based precipitation datasets in streamflow simulations on a monsoon-climate watershed in China. Two mutually independent datasets—one dense-gauge and one gauge-interpolated dataset—are used as references because commonly used gauge-interpolated datasets may be biased and unable to reflect the real performance of satellite-based precipitation due to sparse networks. The dense-gauge dataset includes a substantial number of gauges, which can better represent the spatial variability of precipitation. Eight satellite-based precipitation datasets include two raw satellite datasets, Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN) and Climate Prediction Center MORPHing raw satellite dataset (CMORPH RAW); four satellite-gauge datasets, Tropical Rainfall Measuring Mission 3B42 (TRMM), PERSIANN Climate Data Record (PERSIANN CDR), CMORPH bias-corrected (CMORPH CRT), and gauge blended datasets (CMORPH BLD); and two satellite-reanalysis-gauge datasets, Multi-Source Weighted-Ensemble Precipitation (MSWEP) and Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS). The uncertainty related to hydrologic model physics is investigated using two different hydrological models. A set of statistical indices is utilized to comprehensively evaluate the precipitation datasets from different perspectives, including detection, systematic, random errors, and precision for simulating extreme precipitation. Results show that CMORPH BLD and MSWEP generally perform better than other datasets. In terms of hydrological simulations, all satellite-based datasets show significant dampening effects for the random error during the transformation process from precipitation to runoff; however, these effects cannot hold for the systematic error. Even though different hydrological models indeed introduce uncertainties to the simulated hydrological processes, the relative hydrological performance of the satellite-based datasets is consistent in both models. Namely, CMORPH BLD performs the best, which is followed by MSWEP, CMORPH CRT, and TRMM. PERSIANN CDR and CHIRPS perform moderately well, and two raw satellite datasets are not recommended as proxies of gauged observations for their worse performances.

scholarly journals Correction of Radar QPE Errors for Nonuniform VPRs in Mesoscale Convective Systems Using TRMM Observations

2013 ◽  
Vol 14 (5) ◽  
pp. 1672-1682 ◽  
Author(s):  
Youcun Qi ◽  
Jian Zhang ◽  
Qing Cao ◽  
Yang Hong ◽  
Xiao-Ming Hu
Keyword(s):  
High Resolution ◽  
Vertical Direction ◽  
Tropical Rainfall Measuring Mission ◽  
The United States ◽  
Mesoscale Convective Systems ◽  
Convective Systems ◽  
Quantitative Precipitation Estimation ◽  
Stratiform Region ◽  
Precipitation Estimation ◽  
Mesoscale Convective

Abstract Mesoscale convective systems (MCSs) contain both regions of convective and stratiform precipitation, and a bright band (BB) is often found in the stratiform region. Inflated reflectivity intensities in the BB often cause positive biases in radar quantitative precipitation estimation (QPE). A vertical profile of reflectivity (VPR) correction is necessary to reduce such biases. However, existing VPR correction methods for ground-based radars often perform poorly for MCSs owing to their coarse resolution and poor coverage in the vertical direction, especially at far ranges. Spaceborne radars such as the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR), on the other hand, can provide high resolution VPRs. The current study explores a new approach of incorporating the TRMM VPRs into the VPR correction for the Weather Surveillance Radar-1988 Doppler (WSR-88D) radar QPE. High-resolution VPRs derived from the Ku-band TRMM PR data are converted into equivalent S-band VPRs using an empirical technique. The equivalent S-band TRMM VPRs are resampled according to the WSR-88D beam resolution, and the resampled (apparent) VPRs are then used to correct for BB effects in the WSR-88D QPE when the ground radar VPR cannot accurately capture the BB bottom. The new scheme was tested on six MCSs from different regions in the United States and it was shown to provide effective mitigation of the radar QPE errors due to BB contamination.

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