Jimy Dudhia | National Center for Atmospheric Research (NCAR) (original) (raw)
Papers by Jimy Dudhia
Bulletin of the American Meteorological Society
A unique, high-resolution, hydroclimate reanalysis, 40-plus-year (October 1979–September 2021), 4... more A unique, high-resolution, hydroclimate reanalysis, 40-plus-year (October 1979–September 2021), 4 km (named as CONUS404), has been created using the Weather Research and Forecasting Model by dynamically downscaling of the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis of the global climate dataset (ERA5) over the conterminous United States. The paper describes the approach for generating the dataset, provides an initial evaluation, including biases, and indicates how interested users can access the data. The motivation for creating this National Center for Atmospheric Research (NCAR)–U.S. Geological Survey (USGS) collaborative dataset is to provide research and end-user communities with a high-resolution, self-consistent, long-term, continental-scale hydroclimate dataset appropriate for forcing hydrological models and conducting hydroclimate scientific analyses over the conterminous United States. The data are archived and accessib...
... PERFORMANCE J. MICHALAKES, J. DUDHIA, D. GILL, T. HENDERSON, J. KLEMP, W. SKAMAROCK, W. WANG ... more ... PERFORMANCE J. MICHALAKES, J. DUDHIA, D. GILL, T. HENDERSON, J. KLEMP, W. SKAMAROCK, W. WANG Mesoscale ... 1999. WRF is coupled to a system composed of the ADCIRC ocean and SWAN wave models. ADCIRC ...
InTech eBooks, Mar 2, 2012
Journal Of Geophysical Research: Atmospheres, Feb 17, 2021
The land‐sea contrast in the Maritime Continent (MC) has been found to influence the Madden–Julia... more The land‐sea contrast in the Maritime Continent (MC) has been found to influence the Madden–Julian Oscillation (MJO). However, the specific contribution from individual islands to the precipitation over the surrounding islands during MJO propagation is not well known. We found that when an island is removed in the presence of lower‐tropospheric westerlies, precipitation increases over islands that are located to its east due to the strengthening of the westerlies. Frictional convergence of the stronger westerlies, aided by Coriolis, leads to an increase in vertical advection of moisture and precipitation over an island located to the east. On the other hand, the reduced heating over the removed island reduces the westerlies and precipitation to the west of the removed island and is consistent with the response of large‐scale circulation to tropical heating. During background easterlies prior to MJO arrival, a systematic decrease in precipitation was found in the surrounding islands to the west side of the removed island. But, on the eastern side of the removed island, no systematic change in precipitation was found. The results imply that changes in large‐scale circulation in response to convection (or a lack thereof) over a removed island may significantly influence precipitation in the neighboring islands. Therefore, biases in model precipitation over an island in the MC may arise from bias in precipitation over a neighboring island. Moreover, the presence of different island chains in the MC has led to a more conducive environment for more overall precipitation over the islands in the MC.
Theoretical and Applied Climatology, Jun 28, 2019
This paper presents an evaluation of the Weather Research and Forecasting (WRF) model in simulati... more This paper presents an evaluation of the Weather Research and Forecasting (WRF) model in simulating wet and dry West African monsoon (WAM) rainfall seasons. Three model experiments with varying selected microphysics (MP), cumulus convection (CU), and planetary boundary layer (PBL) schemes based on previous study were performed. Each of the model combinations is used to run four WAM seasons that consist of two wet (2008 and 2010) and two dry years (2001 and 2011). To investigate the behavior of WAM in the context of wet and dry years, the four seasons were used to compute composites of wet and dry WAM seasons in terms of rainfall amount. The analyses majorly focus on the rainfall composites relative to rainfall from Global Precipitation Climatology Project (GPCP) and Tropical Rainfall Measurement Mission (TRMM) as well as temperature, moisture, and atmospheric circulation fields with respect to NCEP reanalyses. This study documents significant sensitivity in simulation of the West African monsoon to the choices of the MP, CU, and PBL schemes. The simulation with the combination of WRF single moment 5 (WSM5) MP, Yonsei University (YSU) PBL, and new Simplified Arakawa-Schubert CU (WSM5-YSU-nSAS) shows good spatial distribution pattern of rainfall and the dynamics associated with the monsoon. Quantitatively, the combination shows less agreement in distinguishing the selected WAM seasons compared with the Goddard MP, Mellor-Yamada-Janjic PBL, and Betts-Miller-Janjić CU (GD-MYJ-BMJ) and the WSM5, Mellor-Yamada-Nakanishi-Niino 2.5 level and new Tiedtke CU (WSM5-MYNN-nTDK). Also, the dynamical structures of the wet and dry WAM circulation composites are reasonably reproduced in GD-MYJ-BMJ and WSM5-YSU-nSAS. The GD-MYJ-BMJ was able to distinguish between wet and dry years and thus underscores its potential to reproduce climate change signals in future work.
Journal of Geophysical Research: Atmospheres, 2016
The November event of the Madden‐Julian oscillation (MJO) during the Dynamics of North Atlantic M... more The November event of the Madden‐Julian oscillation (MJO) during the Dynamics of North Atlantic Models (DYNAMO) field campaign was simulated using the global compressible nonhydrostatic Model for Prediction Across Scales with global coarse (60 and 15 km) and regional (the Indian Ocean) cloud‐permitting (3 km) meshes. The purpose of this study is to compare roles of parameterized deep and shallow cumulus and microphysics in MJO simulations. Two cumulus schemes were used: Tiedtke and Grell‐Freitas. The deep and shallow components of Tiedtke scheme can be turned on and off individually. The results reveal that microphysics alone (without cumulus parameterization) is able to produce strong signals of the MJO in precipitation with 3 km mesh and weak MJO signals with 15 km mesh. A shallow scheme (Tiedtke) along with microphysics strengthens the MJO signals but makes them less well organized on large scales. A deep cumulus scheme can either improve the large‐scale organization of MJO preci...
Advances in Meteorology, Aug 7, 2020
Simulations with four land surface models (LSMs) (i.e., Noah, Noah-MP, Noah-MP with ground water ... more Simulations with four land surface models (LSMs) (i.e., Noah, Noah-MP, Noah-MP with ground water GW option, and CLM4) using the Weather Research and Forecasting (WRF) model at 12 km horizontal grid resolution were carried out as two sets for 3 months (December-February 2011/2012 and July-September 2012) over West Africa. e objective is to assess the performance of WRF LSMs in simulating meteorological parameters over West Africa. e model precipitation was assessed against TRMM while surface temperature was compared with the ERA-Interim reanalysis dataset. Results show that the LSMs performed differently for different variables in different land-surface conditions. Based on precipitation and temperature, Noah-MP GW is overall the best for all the variables and seasons in combination, while Noah came last. Specifically, Noah-MP GW performed best for JAS temperature and precipitation; CLM4 was the best in simulating DJF precipitation, while Noah was the best in simulating DJF temperature. Noah-MP GW has the wettest Sahel while Noah has the driest one. e strength of the Tropical Easterly Jet (TEJ) is strongest in Noah-MP GW and Noah-MP compared with that in CLM4 and Noah. e core of the African Easterly Jet (AEJ) lies around 12°N in Noah and 15°N for Noah-MP GW. Noah-MP GW and Noah-MP simulations have stronger influx of moisture advection from the southwesterly monsoonal wind than the CLM4 and Noah with Noah showing the least influx. Also, analysis of the evaporative fraction shows sharp gradient for Noah-MP GW and Noah-MP with wetter Sahel further to the north and further to the south for Noah. Noah-MP-GW has the highest amount of soil moisture, while the CLM4 has the least for both the JAS and DJF seasons. e CLM4 has the highest LH for both DJF and JAS seasons but however has the least SH for both DJF and JAS seasons. e principal difference between the LSMs is in the vegetation representation, description, and parameterization of the soil water column; hence, improvement is recommended in this regard.
Meteorology
At multi-kilometer grid scales, numerical weather prediction models represent surface-based conve... more At multi-kilometer grid scales, numerical weather prediction models represent surface-based convective eddies as a completely sub-grid one-dimensional vertical mixing and transport process. At tens of meters grid scales, large-eddy simulation models, explicitly resolve all the primary three-dimensional eddies associated with boundary-layer transport from the surface and entrainment at the top. Between these scales, at hundreds of meters grid size, is a so-called grey zone in which the primary transport is neither entirely sub-grid nor resolved, where explicit large-eddy models and sub-grid boundary-layer parameterization models fail in different ways that are outlined in this review article. This article also reviews various approaches that have been taken to span this gap in the proper representation of eddy transports in the sub-kilometer grid range using scale-aware approaches. Introduction of moisture with condensation in the eddies expands this problem to that of handling shall...
Atmosphere
Climate variability and change greatly affect agricultural and water resource management over Wes... more Climate variability and change greatly affect agricultural and water resource management over West Africa. This paper presents the current characteristics and projected change in regional crop water demand (CWD), irrigation requirement (IR), and water availability (WA) over West Africa. Observed and simulated daily rainfall, minimum temperature, maximum temperature, and evapotranspiration are used to derive the above agro-meteorological and hydrological variables. For future periods, high-resolution climate data from three regional climate models under two different scenarios, i.e., representative concentration pathway (RCP) 4.5 and 8.5, are considered. Evaluation of the characteristics of present-day CWD, IR, and WA indicated that the ensemble mean of the model-derived outputs reproduced the prevailing spatial patterns of CWD and IR. Moreover, the wetter part of the domain, especially along the southern coast, was correctly delineated from the drier northern regions, despite having...
Historically, time-split schemes for numerically integrating the nonhydrostatic compressible equa... more Historically, time-split schemes for numerically integrating the nonhydrostatic compressible equations of motion have not formally conserved mass and other first-order flux quantities. In this paper, split-explicit integration techniques are developed that numerically conserve these properties by integrating prognostic equations for conserved quantities represented in flux form. These procedures are presented for both terrain-following height and hydrostatic pressure (mass) vertical coordinates, two potentially attractive frameworks for which the equation sets and integration techniques differ significantly. For each set of equations, the linear dispersion equation for acoustic/gravity waves is derived and analyzed to determine which terms must be solved in the small (acoustic) time steps and how these terms are represented in the time integration to achieve stability. Efficient techniques for including numerical filters for acoustic and external modes are also presented. Simulation...
Modeling Earth Systems and Environment, 2021
The Advanced Hurricane WRF (AHW) is a relatively new derivative of the Advanced Research WRF (ARW... more The Advanced Hurricane WRF (AHW) is a relatively new derivative of the Advanced Research WRF (ARW) model that was initially developed from the community release of the WRF model after the 2005 season (Davis et al. 2008). The use of a moving, 2-way nested grid system allows local resolution of roughly 1 km, making it ideal for the prediction of the multiple length scales present in hurricanes ranging from the scale of outflow (1000 km or more) to the sharp gradients inside the eye wall (5-10 km). During the past four Atlantic hurricane seasons, the nested model was run in real time and in retrospective mode to produce forecasts of hurricane track, intensity and structure out to several days lead time. During the 2004 and 2005 hurricane seasons, the model performed comparably to operational models using an innermost nest of 4 km grid spacing, with evidence of improved intensity forecasts beyond 1.5 days during the 2005 season as shown by Davis et al.. During 2006, a second nest of 1.3...
P redicting a hurricane’s intensity remains a daunting challenge even after four decades of resea... more P redicting a hurricane’s intensity remains a daunting challenge even after four decades of research. The intrinsic difficulties lie in the vast range of spatial and temporal scales of atmospheric motions that affect tropical cyclone intensity. The range of spatial scales is literally millimeters to 1,000 kilometers or more. Atmospheric dynamical models must account for all these scales simultaneously. Being a nonlinear system, these scales can interact. Although forecasters must make approximations to keep computations finite, there’s a continued push for finer resolution to capture as many of these scales as possible.
Monthly Weather Review, 2013
An Intel R © Fortran compiler ag that relaxes IEEE arithmetic rules for divisions and square root... more An Intel R © Fortran compiler ag that relaxes IEEE arithmetic rules for divisions and square roots has been a part of the arch/configure.defaults le for the Intel R © Itanium R ©-based SGI Altix since WRF version 2.0.2. At the time of its introduction, use of the ag resulted in substantial performance gains at apparently little loss in precision. Since then, several dozen upgrades and four major revisions of the compiler have been released. Recent tests with WRF version 2.2 and the latest upgrades of the three most recent major revisions show that continued use of the compiler ag can result in substantial numerical di erences, especially with the later compilers, but its removal incurs only a modest loss of performance. An account of the testing and the results is given.
Atmospheric Research, 2021
Abstract A set of numerical experiments was conducted in order to investigate the impacts of glob... more Abstract A set of numerical experiments was conducted in order to investigate the impacts of global warming on West African monsoon rainfall for selected five years. The experiments varied different cumulus, microphysics and planetary boundary layer parameterization schemes. Rainfall characteristics over three climatic zones, Guinea Coast, Savannah and Sahel, was analyzed. The potential change associated with global warming is assessed by the pseudo global warming (PGW) downscaling method. Multiple PGW runs were conducted using climate perturbation from the 40-member ensemble of the Community Earth System Model version 1 (CESM1) coupled with Community Atmospheric Model version 5.2 (CAM5.2) component large ensemble project. The model output was compared with TRMM and GPCP rainfall and atmospheric parameters from ECMWF reanalysis datasets. Results show that the rainfall amount in the 2070s estimated from the PGW runs substantially increases, especially in the eastern Sahel due to enhanced moisture convergence, compared to the current climate. The percentage change in simulated total rainfall amount can increase or decrease by 50% in the PGW runs and the theoretical rainfall computed based on Clausius-Clapeyron relation. Also, found is an increase (decrease) in heavy (both light and moderate) rainfall amount. These results, however, depend on the GCM used as the boundary conditions of the RCM. This suggests that the 4 o C change in average surface temperature derived from the 40-member ensemble model strongly influenced the increased rainfall simulated by the PGW experiments. Thus, highlighting the advantage of using the PGW technique to estimate the likely difference between present and future climate with reduced large-scale model biases and computational resources.
Heavy rainfall occurred over the western side of Taiwan's complex terrain from August 10 to 1... more Heavy rainfall occurred over the western side of Taiwan's complex terrain from August 10 to 13, 1994 after Typhoon Doug moved northward from the East China Sea into Taiwan and on towards the Yellow Sea. On August 10, most of the rainfall fell over sloped areas. The heaviest daily rainfall totals were in excess of 200 mm over southwestern as well as central Taiwan. However, not much rainfall occurred over northern Taiwan. The lack of rainfall over northern Taiwan also occurred on August 11, 12 and 13. The larger rainfall amounts shifted westward from the sloped areas on August 10 toward lower terrain on August 11. On August 12 and 13, most of the higher rainfall amounts were found over the coastal area in southwestern Taiwan. Notably, about 300 to 400 mm per day fell over the coastal area in southwest Taiwan on August 12 and 13. The distribution of rainfall amount was different on August 10 and 11 (termed as Case 1) compared to August 12 and 13 (termed as Case 2). The environmental situation and precipitation characteristics are analyzed using EC/TOGA data, ground-based radar data, surface rainfall patterns, surface wind data, and upper air soundings. Chen at al. (2001) also categorized the precipitation pattern into two types, propagating and quasi-stationary. For the propagating type of precipitation, rainrates increased or remained the same as systems went from the plains to mountainous regions. With the quasi-stationary type of precipitation, however, rainrates decreased as precipitation propagated across the plains and into the mountains. The focus of this study is to understand what causes the h1aher amounts of rainfall over Taiwan, and what factors influence where the higher amounts of rainfall will occur, over sloped areas or over coastal areas.
Bulletin of the American Meteorological Society
A unique, high-resolution, hydroclimate reanalysis, 40-plus-year (October 1979–September 2021), 4... more A unique, high-resolution, hydroclimate reanalysis, 40-plus-year (October 1979–September 2021), 4 km (named as CONUS404), has been created using the Weather Research and Forecasting Model by dynamically downscaling of the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis of the global climate dataset (ERA5) over the conterminous United States. The paper describes the approach for generating the dataset, provides an initial evaluation, including biases, and indicates how interested users can access the data. The motivation for creating this National Center for Atmospheric Research (NCAR)–U.S. Geological Survey (USGS) collaborative dataset is to provide research and end-user communities with a high-resolution, self-consistent, long-term, continental-scale hydroclimate dataset appropriate for forcing hydrological models and conducting hydroclimate scientific analyses over the conterminous United States. The data are archived and accessib...
... PERFORMANCE J. MICHALAKES, J. DUDHIA, D. GILL, T. HENDERSON, J. KLEMP, W. SKAMAROCK, W. WANG ... more ... PERFORMANCE J. MICHALAKES, J. DUDHIA, D. GILL, T. HENDERSON, J. KLEMP, W. SKAMAROCK, W. WANG Mesoscale ... 1999. WRF is coupled to a system composed of the ADCIRC ocean and SWAN wave models. ADCIRC ...
InTech eBooks, Mar 2, 2012
Journal Of Geophysical Research: Atmospheres, Feb 17, 2021
The land‐sea contrast in the Maritime Continent (MC) has been found to influence the Madden–Julia... more The land‐sea contrast in the Maritime Continent (MC) has been found to influence the Madden–Julian Oscillation (MJO). However, the specific contribution from individual islands to the precipitation over the surrounding islands during MJO propagation is not well known. We found that when an island is removed in the presence of lower‐tropospheric westerlies, precipitation increases over islands that are located to its east due to the strengthening of the westerlies. Frictional convergence of the stronger westerlies, aided by Coriolis, leads to an increase in vertical advection of moisture and precipitation over an island located to the east. On the other hand, the reduced heating over the removed island reduces the westerlies and precipitation to the west of the removed island and is consistent with the response of large‐scale circulation to tropical heating. During background easterlies prior to MJO arrival, a systematic decrease in precipitation was found in the surrounding islands to the west side of the removed island. But, on the eastern side of the removed island, no systematic change in precipitation was found. The results imply that changes in large‐scale circulation in response to convection (or a lack thereof) over a removed island may significantly influence precipitation in the neighboring islands. Therefore, biases in model precipitation over an island in the MC may arise from bias in precipitation over a neighboring island. Moreover, the presence of different island chains in the MC has led to a more conducive environment for more overall precipitation over the islands in the MC.
Theoretical and Applied Climatology, Jun 28, 2019
This paper presents an evaluation of the Weather Research and Forecasting (WRF) model in simulati... more This paper presents an evaluation of the Weather Research and Forecasting (WRF) model in simulating wet and dry West African monsoon (WAM) rainfall seasons. Three model experiments with varying selected microphysics (MP), cumulus convection (CU), and planetary boundary layer (PBL) schemes based on previous study were performed. Each of the model combinations is used to run four WAM seasons that consist of two wet (2008 and 2010) and two dry years (2001 and 2011). To investigate the behavior of WAM in the context of wet and dry years, the four seasons were used to compute composites of wet and dry WAM seasons in terms of rainfall amount. The analyses majorly focus on the rainfall composites relative to rainfall from Global Precipitation Climatology Project (GPCP) and Tropical Rainfall Measurement Mission (TRMM) as well as temperature, moisture, and atmospheric circulation fields with respect to NCEP reanalyses. This study documents significant sensitivity in simulation of the West African monsoon to the choices of the MP, CU, and PBL schemes. The simulation with the combination of WRF single moment 5 (WSM5) MP, Yonsei University (YSU) PBL, and new Simplified Arakawa-Schubert CU (WSM5-YSU-nSAS) shows good spatial distribution pattern of rainfall and the dynamics associated with the monsoon. Quantitatively, the combination shows less agreement in distinguishing the selected WAM seasons compared with the Goddard MP, Mellor-Yamada-Janjic PBL, and Betts-Miller-Janjić CU (GD-MYJ-BMJ) and the WSM5, Mellor-Yamada-Nakanishi-Niino 2.5 level and new Tiedtke CU (WSM5-MYNN-nTDK). Also, the dynamical structures of the wet and dry WAM circulation composites are reasonably reproduced in GD-MYJ-BMJ and WSM5-YSU-nSAS. The GD-MYJ-BMJ was able to distinguish between wet and dry years and thus underscores its potential to reproduce climate change signals in future work.
Journal of Geophysical Research: Atmospheres, 2016
The November event of the Madden‐Julian oscillation (MJO) during the Dynamics of North Atlantic M... more The November event of the Madden‐Julian oscillation (MJO) during the Dynamics of North Atlantic Models (DYNAMO) field campaign was simulated using the global compressible nonhydrostatic Model for Prediction Across Scales with global coarse (60 and 15 km) and regional (the Indian Ocean) cloud‐permitting (3 km) meshes. The purpose of this study is to compare roles of parameterized deep and shallow cumulus and microphysics in MJO simulations. Two cumulus schemes were used: Tiedtke and Grell‐Freitas. The deep and shallow components of Tiedtke scheme can be turned on and off individually. The results reveal that microphysics alone (without cumulus parameterization) is able to produce strong signals of the MJO in precipitation with 3 km mesh and weak MJO signals with 15 km mesh. A shallow scheme (Tiedtke) along with microphysics strengthens the MJO signals but makes them less well organized on large scales. A deep cumulus scheme can either improve the large‐scale organization of MJO preci...
Advances in Meteorology, Aug 7, 2020
Simulations with four land surface models (LSMs) (i.e., Noah, Noah-MP, Noah-MP with ground water ... more Simulations with four land surface models (LSMs) (i.e., Noah, Noah-MP, Noah-MP with ground water GW option, and CLM4) using the Weather Research and Forecasting (WRF) model at 12 km horizontal grid resolution were carried out as two sets for 3 months (December-February 2011/2012 and July-September 2012) over West Africa. e objective is to assess the performance of WRF LSMs in simulating meteorological parameters over West Africa. e model precipitation was assessed against TRMM while surface temperature was compared with the ERA-Interim reanalysis dataset. Results show that the LSMs performed differently for different variables in different land-surface conditions. Based on precipitation and temperature, Noah-MP GW is overall the best for all the variables and seasons in combination, while Noah came last. Specifically, Noah-MP GW performed best for JAS temperature and precipitation; CLM4 was the best in simulating DJF precipitation, while Noah was the best in simulating DJF temperature. Noah-MP GW has the wettest Sahel while Noah has the driest one. e strength of the Tropical Easterly Jet (TEJ) is strongest in Noah-MP GW and Noah-MP compared with that in CLM4 and Noah. e core of the African Easterly Jet (AEJ) lies around 12°N in Noah and 15°N for Noah-MP GW. Noah-MP GW and Noah-MP simulations have stronger influx of moisture advection from the southwesterly monsoonal wind than the CLM4 and Noah with Noah showing the least influx. Also, analysis of the evaporative fraction shows sharp gradient for Noah-MP GW and Noah-MP with wetter Sahel further to the north and further to the south for Noah. Noah-MP-GW has the highest amount of soil moisture, while the CLM4 has the least for both the JAS and DJF seasons. e CLM4 has the highest LH for both DJF and JAS seasons but however has the least SH for both DJF and JAS seasons. e principal difference between the LSMs is in the vegetation representation, description, and parameterization of the soil water column; hence, improvement is recommended in this regard.
Meteorology
At multi-kilometer grid scales, numerical weather prediction models represent surface-based conve... more At multi-kilometer grid scales, numerical weather prediction models represent surface-based convective eddies as a completely sub-grid one-dimensional vertical mixing and transport process. At tens of meters grid scales, large-eddy simulation models, explicitly resolve all the primary three-dimensional eddies associated with boundary-layer transport from the surface and entrainment at the top. Between these scales, at hundreds of meters grid size, is a so-called grey zone in which the primary transport is neither entirely sub-grid nor resolved, where explicit large-eddy models and sub-grid boundary-layer parameterization models fail in different ways that are outlined in this review article. This article also reviews various approaches that have been taken to span this gap in the proper representation of eddy transports in the sub-kilometer grid range using scale-aware approaches. Introduction of moisture with condensation in the eddies expands this problem to that of handling shall...
Atmosphere
Climate variability and change greatly affect agricultural and water resource management over Wes... more Climate variability and change greatly affect agricultural and water resource management over West Africa. This paper presents the current characteristics and projected change in regional crop water demand (CWD), irrigation requirement (IR), and water availability (WA) over West Africa. Observed and simulated daily rainfall, minimum temperature, maximum temperature, and evapotranspiration are used to derive the above agro-meteorological and hydrological variables. For future periods, high-resolution climate data from three regional climate models under two different scenarios, i.e., representative concentration pathway (RCP) 4.5 and 8.5, are considered. Evaluation of the characteristics of present-day CWD, IR, and WA indicated that the ensemble mean of the model-derived outputs reproduced the prevailing spatial patterns of CWD and IR. Moreover, the wetter part of the domain, especially along the southern coast, was correctly delineated from the drier northern regions, despite having...
Historically, time-split schemes for numerically integrating the nonhydrostatic compressible equa... more Historically, time-split schemes for numerically integrating the nonhydrostatic compressible equations of motion have not formally conserved mass and other first-order flux quantities. In this paper, split-explicit integration techniques are developed that numerically conserve these properties by integrating prognostic equations for conserved quantities represented in flux form. These procedures are presented for both terrain-following height and hydrostatic pressure (mass) vertical coordinates, two potentially attractive frameworks for which the equation sets and integration techniques differ significantly. For each set of equations, the linear dispersion equation for acoustic/gravity waves is derived and analyzed to determine which terms must be solved in the small (acoustic) time steps and how these terms are represented in the time integration to achieve stability. Efficient techniques for including numerical filters for acoustic and external modes are also presented. Simulation...
Modeling Earth Systems and Environment, 2021
The Advanced Hurricane WRF (AHW) is a relatively new derivative of the Advanced Research WRF (ARW... more The Advanced Hurricane WRF (AHW) is a relatively new derivative of the Advanced Research WRF (ARW) model that was initially developed from the community release of the WRF model after the 2005 season (Davis et al. 2008). The use of a moving, 2-way nested grid system allows local resolution of roughly 1 km, making it ideal for the prediction of the multiple length scales present in hurricanes ranging from the scale of outflow (1000 km or more) to the sharp gradients inside the eye wall (5-10 km). During the past four Atlantic hurricane seasons, the nested model was run in real time and in retrospective mode to produce forecasts of hurricane track, intensity and structure out to several days lead time. During the 2004 and 2005 hurricane seasons, the model performed comparably to operational models using an innermost nest of 4 km grid spacing, with evidence of improved intensity forecasts beyond 1.5 days during the 2005 season as shown by Davis et al.. During 2006, a second nest of 1.3...
P redicting a hurricane’s intensity remains a daunting challenge even after four decades of resea... more P redicting a hurricane’s intensity remains a daunting challenge even after four decades of research. The intrinsic difficulties lie in the vast range of spatial and temporal scales of atmospheric motions that affect tropical cyclone intensity. The range of spatial scales is literally millimeters to 1,000 kilometers or more. Atmospheric dynamical models must account for all these scales simultaneously. Being a nonlinear system, these scales can interact. Although forecasters must make approximations to keep computations finite, there’s a continued push for finer resolution to capture as many of these scales as possible.
Monthly Weather Review, 2013
An Intel R © Fortran compiler ag that relaxes IEEE arithmetic rules for divisions and square root... more An Intel R © Fortran compiler ag that relaxes IEEE arithmetic rules for divisions and square roots has been a part of the arch/configure.defaults le for the Intel R © Itanium R ©-based SGI Altix since WRF version 2.0.2. At the time of its introduction, use of the ag resulted in substantial performance gains at apparently little loss in precision. Since then, several dozen upgrades and four major revisions of the compiler have been released. Recent tests with WRF version 2.2 and the latest upgrades of the three most recent major revisions show that continued use of the compiler ag can result in substantial numerical di erences, especially with the later compilers, but its removal incurs only a modest loss of performance. An account of the testing and the results is given.
Atmospheric Research, 2021
Abstract A set of numerical experiments was conducted in order to investigate the impacts of glob... more Abstract A set of numerical experiments was conducted in order to investigate the impacts of global warming on West African monsoon rainfall for selected five years. The experiments varied different cumulus, microphysics and planetary boundary layer parameterization schemes. Rainfall characteristics over three climatic zones, Guinea Coast, Savannah and Sahel, was analyzed. The potential change associated with global warming is assessed by the pseudo global warming (PGW) downscaling method. Multiple PGW runs were conducted using climate perturbation from the 40-member ensemble of the Community Earth System Model version 1 (CESM1) coupled with Community Atmospheric Model version 5.2 (CAM5.2) component large ensemble project. The model output was compared with TRMM and GPCP rainfall and atmospheric parameters from ECMWF reanalysis datasets. Results show that the rainfall amount in the 2070s estimated from the PGW runs substantially increases, especially in the eastern Sahel due to enhanced moisture convergence, compared to the current climate. The percentage change in simulated total rainfall amount can increase or decrease by 50% in the PGW runs and the theoretical rainfall computed based on Clausius-Clapeyron relation. Also, found is an increase (decrease) in heavy (both light and moderate) rainfall amount. These results, however, depend on the GCM used as the boundary conditions of the RCM. This suggests that the 4 o C change in average surface temperature derived from the 40-member ensemble model strongly influenced the increased rainfall simulated by the PGW experiments. Thus, highlighting the advantage of using the PGW technique to estimate the likely difference between present and future climate with reduced large-scale model biases and computational resources.
Heavy rainfall occurred over the western side of Taiwan's complex terrain from August 10 to 1... more Heavy rainfall occurred over the western side of Taiwan's complex terrain from August 10 to 13, 1994 after Typhoon Doug moved northward from the East China Sea into Taiwan and on towards the Yellow Sea. On August 10, most of the rainfall fell over sloped areas. The heaviest daily rainfall totals were in excess of 200 mm over southwestern as well as central Taiwan. However, not much rainfall occurred over northern Taiwan. The lack of rainfall over northern Taiwan also occurred on August 11, 12 and 13. The larger rainfall amounts shifted westward from the sloped areas on August 10 toward lower terrain on August 11. On August 12 and 13, most of the higher rainfall amounts were found over the coastal area in southwestern Taiwan. Notably, about 300 to 400 mm per day fell over the coastal area in southwest Taiwan on August 12 and 13. The distribution of rainfall amount was different on August 10 and 11 (termed as Case 1) compared to August 12 and 13 (termed as Case 2). The environmental situation and precipitation characteristics are analyzed using EC/TOGA data, ground-based radar data, surface rainfall patterns, surface wind data, and upper air soundings. Chen at al. (2001) also categorized the precipitation pattern into two types, propagating and quasi-stationary. For the propagating type of precipitation, rainrates increased or remained the same as systems went from the plains to mountainous regions. With the quasi-stationary type of precipitation, however, rainrates decreased as precipitation propagated across the plains and into the mountains. The focus of this study is to understand what causes the h1aher amounts of rainfall over Taiwan, and what factors influence where the higher amounts of rainfall will occur, over sloped areas or over coastal areas.