scholarly journals The effect of topography on east African rainfall based on regional climate model

MAUSAM ◽  
2021 ◽  
Vol 67 (2) ◽  
pp. 431-440
Author(s):  
BOB ALEX OGWANG ◽  
HAISHAN CHEN ◽  
L. I. XING
Keyword(s):  
Regional Climate Model ◽  
East Africa ◽  
Climate Model ◽  
Regional Climate ◽  
Research Unit ◽  
Theoretical Physics ◽  
East African ◽  
Maximum Rainfall ◽  
Low Level ◽  
The Mean

The effect of topography on June to August (JJA) rainfall over east Africa is investigated using the International Centre for Theoretical Physics (ICTP) Regional Climate Model (RegCM4.0). Grell convection scheme with Fritsch-Chappell closure assumption is used. The control simulation is done with actual topography and sensitivity experiments are carried out with topography reduced to 75%, 25% and to zero. The model output was evaluated against Climate Research Unit (CRU) dataset, gridded at 0.5 degree resolution and ERA-interim datasets, gridded at 0.75 degree resolution. Results show that the mean JJA rainfall significantly reduces over the region when topography elevation is reduced. Based on the model, when the topography over the selected region (KTU) is reduced to 25%, the mean JJA rainfall over east Africa is reduced by roughly half. The maximum rainfall reduction is however observed around the region over which topography is reduced. The reduction in topography resulted into an anomalous moisture divergence over the region at low level (850 hPa). Divergence at low level results in vertical shrinking which suppresses convection due to subsidence. The strength of moisture transport and the zonal wind speed at 850hpa increased with decrease in topography, which may be responsible for the observed shift in moisture convergence zone from western Kenya to northern Uganda. The findings from this study would provide insight into the effect of topography on the east African climate and call for more detailed investigative research, particularly in the region. The results may motivate researchers and modeling centers to further improve on the performance of the model over the region.

scholarly journals The Influence of Topography on East African October to December Climate: Sensitivity Experiments with RegCM4

2014 ◽  
Vol 2014 ◽  
pp. 1-14 ◽  
Author(s):  
Bob Alex Ogwang ◽  
Haishan Chen ◽  
Xing Li ◽  
Chujie Gao
Keyword(s):  
High Frequency ◽  
Climate Model ◽  
Regional Climate ◽  
Theoretical Physics ◽  
East African ◽  
African Region ◽  
Maximum Rainfall ◽  
Remote Areas ◽  
East African Region ◽  
The Mean

The influence of topography on east African climate is investigated using the International Centre for Theoretical Physics Regional Climate Model, with focus on October to December season. Results show that the mean rainfall (temperature) significantly reduces (increases) over the region when topography elevation is reduced. Based on the model, when topography over the selected region (KTU) is reduced to 25%, the mean rainfall (temperature) over east Africa is reduced (increased) by about 19% (1.4°C). The maximum rainfall (temperature) reduction (increase) is however observed around the region over which topography is reduced. The reduction in topography elevation resulted in an anomalous moisture divergence at low level and descending motion over the region. KTU topography enhances the surface heat flux over KTU region and tends to enhance convection over both KTU and the east African region. The topography also helps in the generation of the high frequency mesoscale and subsynoptic disturbances over the region. These disturbances produce precipitation over the region and may also enhance precipitation systems over remote areas due to propagation of the disturbances. The magnitude of the zonal wind speed at 850 hpa increases with the decrease in topography elevation.

A Regional Climate Model Laboratory for Understanding Coastal Climate

2021 ◽  
Author(s):  
Travis O'Brien ◽  
Thomas Burkle ◽  
Michael Krauter ◽  
Thomas Trapp
Keyword(s):  
Steady State ◽  
Regional Climate Model ◽  
Climate Model ◽  
Regional Climate ◽  
Cloud Fraction ◽  
Theoretical Physics ◽  
Coastal Regions ◽  
Local Climate ◽  
Coastal Climate ◽  
Mean Climate

<p>Midlatitude western coastal regions are recognized as being important for the global energy cycle, marine and terrestrial biodiversity, and regional economies.  These coastal regions exhibit a rich range of weather and climate phenomena, including persistent stratocumulus clouds, sea-breeze circulations, coastally-trapped Kelvin waves, and wind-driven upwelling. During the summer season, when impacts from transient synoptic systems are relatively reduced, the local climate is governed by a complex set of interactions among the atmosphere, land, and ocean.  This complexity has so far inhibited basic understanding of the drivers of western coastal climate, climate variability, and climate change.</p><p>As a way of simplifying the system, we have developed a hierarchical regional climate model experimental framework focused on the western United States. We modify the International Centre for Theoretical Physics RegCM4 to use steady-state initial, lateral, and top-of-model boundary conditions: average July insolation (no diurnal cycle) and average meteorological state (winds, temperature, humidity, surface pressure).  This July <em>Base State</em> simulation rapidly reaches a steady state solution that closely resembles the observed mean climate and the mean climate achieved using RegCM4 in a standard reanalysis-driven configuration.  It is particularly notable that the near-coastal stratocumulus field is spatially similar to the satellite-observed stratocumulus field during arbitrary July days: including gaps in stratocumulus coverage downwind of capes. We run similar <em>Base State</em> simulations for the other calendar months and find that these simulations mimic the annual cycle.  This suggests that the summer coastal stratocumulus field results from the steady-state response of the marine boundary layer to summertime climatological forcing; if true for the real world, this would imply that stratocumulus cloud fraction, within a given month, is temporally modulated by deviations from the summer base state (e.g., transient synoptic disturbances that interrupt the cloud field).  We describe modifications to this simplified experimental framework aimed at understanding the factors that govern stratocumulus cloud fraction and its variability.</p>

scholarly journals Simulation of Rainfall over Bangladesh Using Regional Climate Model (RegCM4.7)

Jalawaayu ◽  
2021 ◽  
Vol 1 (2) ◽  
pp. 1-19
Author(s):  
Muhammad Tanjilur Rahman ◽  
Md. Nazmul Ahasan ◽  
Md. Abdul Mannan ◽  
Madan Sigdel ◽  
Dibas Shrestha ◽  
...  
Keyword(s):  
Regional Climate Model ◽  
Bias Correction ◽  
Climate Model ◽  
Regional Climate ◽  
Rainfall Simulation ◽  
Theoretical Physics ◽  
Convective Precipitation ◽  
Annual Rainfall ◽  
Linear Scaling ◽  
Simulated Rainfall

Regional climate model is a scientific tool to monitor present climate change and to provide reliable estimation of future climate projection. In this study, the Regional Climate Model version 4.7 (RegCM4.7) developed by International Centre for Theoretical Physics (ICTP) has been adopted to simulate rainfall scenario of Bangladesh. The study examines model performance of rainfall simulation through the period of 1991-2018 with ERA-Interim75 data of 75 km horizontal resolution as lateral boundaries, downscaled at 25km resolution using the mixed convective precipitation scheme; MIT-Emanuel scheme over land and Grell scheme with Fritsch-Chappell closure over ocean. The simulated rainfall has been compared both at spatial and temporal scales (monthly, seasonal and annual) with observed data collected from Bangladesh Meteorological Department (BMD) and Climate Research Unit (CRU). Simulated annual rainfall showed that the model overestimated in most of the years. Overestimation has been observed in the monsoon and underestimation in pre-monsoon and post-monsoon seasons. Spatial distribution of simulated rainfall depicts overestimation in the southeast coastal region and underestimation in the northwest and northeast border regions of Bangladesh. Better estimation of rainfall has been found in the central and eastern parts of the country. The simulated annual rainfall has been validated through the Linear Scaling bias correction method for the years of 2016, 2017, and 2018 considering the rainfall of 1991-2015 as reference. The bias correction with linear scaling method gives fairly satisfactory results and it can be considered in the future projection of rainfall over Bangladesh.

scholarly journals Evidence and analysis of 2012 Greenland records from spaceborne observations, a regional climate model and reanalysis data

2012 ◽  
Vol 6 (6) ◽  
pp. 4939-4976 ◽  
Author(s):  
M. Tedesco ◽  
X. Fettweis ◽  
T. Mote ◽  
J. Wahr ◽  
P. Alexander ◽  
...  
Keyword(s):  
Regional Climate Model ◽  
Mass Balance ◽  
Climate Model ◽  
Regional Climate ◽  
Ice Sheet ◽  
Reanalysis Data ◽  
Surface Mass Balance ◽  
Near Surface ◽  
Surface Mass ◽  
The Mean

Abstract. A combined analysis of remote sensing observations, regional climate model (RCM) outputs and reanalysis data over the Greenland ice sheet provides evidence that multiple records were set during summer 2012. Melt extent was the largest in the satellite era (extending up to ~ 97% of the ice sheet) and melting lasted up to ~ two months longer than the 1979–2011 mean. Model results indicate that near surface temperature was ~ 3 standard deviations (σ) above the 1958–2011 mean, while surface mass balance was ~ 3σ below the mean and runoff was 3.9σ above the mean over the same period. Albedo, exposure of bare ice and surface mass balance also set new records, as did the total mass balance with summer and annual mass changes of, respectively, −627 Gt and −574 Gt, 2σ below the 2003–2012 mean. We identify persistent anticyclonic conditions over Greenland associated with anomalies in the North Atlantic Oscillation (NAO), changes in surface conditions (e.g. albedo) and pre-conditioning of surface properties from recent extreme melting as major driving mechanisms for the 2012 records. Because of self-amplifying positive feedbacks, less positive if not increasingly negative SMB will likely occur should large-scale atmospheric circulation and induced surface characteristics observed over the past decade persist. Since the general circulation models of the Coupled Model Intercomparison Project Phase 5 (CMIP5) do not simulate the abnormal anticyclonic circulation resulting from extremely negative NAO conditions as observed over recent years, contribution to sea level rise projected under different warming scenarios will be underestimated should the trend in NAO summer values continue.

scholarly journals Evidence and analysis of 2012 Greenland records from spaceborne observations, a regional climate model and reanalysis data

2013 ◽  
Vol 7 (2) ◽  
pp. 615-630 ◽  
Author(s):  
M. Tedesco ◽  
X. Fettweis ◽  
T. Mote ◽  
J. Wahr ◽  
P. Alexander ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Regional Climate Model ◽  
Mass Balance ◽  
Climate Model ◽  
Regional Climate ◽  
Ice Sheet ◽  
Reanalysis Data ◽  
Surface Mass Balance ◽  
Surface Mass ◽  
The Mean

Abstract. A combined analysis of remote sensing observations, regional climate model (RCM) outputs and reanalysis data over the Greenland ice sheet provides evidence that multiple records were set during summer 2012. Melt extent was the largest in the satellite era (extending up to ∼97% of the ice sheet) and melting lasted up to ∼2 months longer than the 1979–2011 mean. Model results indicate that near surface temperature was ∼3 standard deviations (σ) above the 1958–2011 mean, while surface mass balance (SMB) was ∼3σ below the mean and runoff was 3.9σ above the mean over the same period. Albedo, exposure of bare ice and surface mass balance also set new records, as did the total mass balance with summer and annual mass changes of, respectively, −627 Gt and −574 Gt, 2σ below the 2003–2012 mean. We identify persistent anticyclonic conditions over Greenland associated with anomalies in the North Atlantic Oscillation (NAO), changes in surface conditions (e.g., albedo, surface temperature) and preconditioning of surface properties from recent extreme melting as major driving mechanisms for the 2012 records. Less positive if not increasingly negative SMB will likely occur should these characteristics persist.

scholarly journals Discharge simulations performed with a hydrological model using bias corrected regional climate model input

2009 ◽  
Vol 6 (3) ◽  
pp. 4589-4618 ◽  
Author(s):  
S. C. van Pelt ◽  
P. Kabat ◽  
H. W. ter Maat ◽  
B. J. J. M. van den Hurk ◽  
A. H. Weerts
Keyword(s):  
Regional Climate Model ◽  
Bias Correction ◽  
Hydrological Model ◽  
Climate Model ◽  
Regional Climate ◽  
Horizontal Resolution ◽  
Precipitation Pattern ◽  
River Meuse ◽  
The Mean ◽  
Regional Atmospheric Climate Model

Abstract. Studies have demonstrated that precipitation on Northern Hemisphere mid-latitudes has increased in the last decades and that it is likely that this trend will continue. This will have an influence on discharge of the river Meuse. The use of bias correction methods is important when the effect of precipitation change on river discharge is studied. The objective of this paper is to investigate the effect of using two different bias correction methods on output from a Regional Climate Model (RCM) simulation. In this study a Regional Atmospheric Climate Model (RACMO2) run is used, forced by ECHAM-5 under the condition of the SRES-A1B emission scenario, with a 25 km horizontal resolution. The RACMO2 runs contain a systematic precipitation bias on which two bias correction methods are applied. The first method corrects for the wet day fraction and wet day average (WD bias correction) and the second method corrects for the mean and coefficient of variance (MV bias correction). The WD bias correction initially corrects well for the average, but it appears that too many successive precipitation days were removed with this correction. The second method performed less well on average bias correction, but the temporal precipitation pattern was better. Subsequently, the discharge was calculated by using RACMO2 output as forcing to the HBV-96 hydrological model. A large difference was found between the simulated discharge of the uncorrected RACMO2 run, the WD bias corrected run and the MV bias corrected run. These results show the importance of an appropriate bias correction.

scholarly journals Sensitivity of western north Pacific summertime tropical synoptic- scale disturbances to extratropical forcing – A regional climate model study

2021 ◽  
Author(s):  
Ying Lung Liu ◽  
Chi-Yung Tam ◽  
Andie Yee Man Au-Yeung
Keyword(s):  
Regional Climate Model ◽  
North Pacific ◽  
Western North Pacific ◽  
Climate Model ◽  
Regional Climate ◽  
Wave Activity ◽  
Synoptic Scale ◽  
Low Level ◽  
Zonal Wavenumber ◽  
Extratropical Forcing

Abstract The role of extratropical forcing on the summertime tropical synoptic-scale disturbances (TSDs) in the western north Pacific has been investigated, by conducting parallel integrations of the Regional Climate Model (RegCM). The suite of experiments consists of a control run (CTRL) with European Centre for Medium Range Forecasts (ECMWF) Reanalysis data as boundary conditions, and an experimental run (EXPT) with the same setting, except that signals with zonal wavenumber > 6 were suppressed at the northern boundary (located at 42°N) of the model domain. Comparison between CTRL and EXPT showed that, without extratropical forcing, there is weaker TSD activity in the June-to-August season, with reduced precipitation over the TSD pathway. Associated with suppressed TSD, southeastward-directed wave activity is also reduced, leading to less active mixed Rossby gravity (MRG) waves in the equatorial western Pacific area. Further analysis revealed that extratropical forcing and associated circulation changes can modulate the TSD wavetrain and its coherence structure, in relation to low-level vorticity in far western north Pacific. In CTRL, west of about 140°E, TSD-related circulation tends to be stronger; in EXPT, vorticity signals and vertical motions are found to be slightly more coherent in the more eastern portion of the TSD wavetrain. The latter enhanced coherency of TSD east of 140°E, from the EXPT simulations, might be due to changes in wave activity transport channelled by modulated upper-level mid-latitude westerlies in EXPT. Energetics indicate that changes in low-level background circulation itself can also influence TSD characteristics. Our results serve to quantify how extratropical forcing and related general circulation features influence western north Pacific summertime TSD activities. Implications on understanding the initiation of TSD, as well as their variability on longer time scales, are discussed.

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