Regional Climate Model Version Research Articles

Potential use of a regional climate model in seasonal tropical cyclone activity predictions in the western North Pacific

This study investigates the potential use of a regional climate model in forecasting seasonal tropical cyclone (TC) activity. A modified version of Regional Climate Model Version 3 (RegCM3) is used to examine the ability of the model to simulate TC genesis and landfalling TC tracks for the active TC season in the western North Pacific. In the model, a TC is identified as a vortex satisfying several conditions, including local maximum relative vorticity at 850 hPa with a value ≥450 × 10−6 s−1, and the temperature at 300 hPa being 1°C higher than the average temperature within 15° latitude radius from the TC center. Tracks are traced by following these found vortices. Six-month ensemble (8 members each) simulations are performed for each year from 1982 to 2001 so that the climatology of the model can be compared to the Joint Typhoon Warning Center (JTWC) observed best-track dataset. The 20-year ensemble experiments show that the RegCM3 can be used to simulate vortices with a wind structure and temperature profile similar to those of real TCs. The model also reproduces tracks very similar to those observed with features like genesis in the tropics, recurvature at higher latitudes and landfall/decay. The similarity of the 500-hPa geopotential height patterns between RegCM3 and the European Centre for Medium-Range Weather Forecasts 40 Year Re-analysis (ERA-40) shows that the model can simulate the subtropical high to a large extent. The simulated climatological monthly spatial distributions as well as the interannual variability of TC occurrence are also similar to the JTWC data. These results imply the possibility of producing seasonal forecasts of tropical cyclones using real-time global climate model predictions as boundary conditions for the RegCM3.

RegCM3 nested in HadAM3 scenarios A2 and B2: projected changes in extratropical cyclogenesis, temperature and precipitation over the South Atlantic Ocean

The RegCM3 (Regional Climate Model—version 3) was nested in HadAM3 model to simulate present (1975–1989, referred hereafter as RegHad) and two future climate scenarios (A2 and B2 from 2071 to 2085, referred as RegA2 and RegB2) over the South America (SA) and South Atlantic Ocean (SAO). Projected changes in the air temperature, precipitation, low level circulation and cyclogenesis climatology were investigated. The cyclogenesis were identified using an automatic scheme for tracking based on the minimum of relative vorticity (ζ) from 10-m height wind. During summer, a general decrease (increase) in the precipitation is projected by RegA2 and RegB2 over the northeastern SA (center-west and south Brazil, north Argentina and Uruguay). For winter, an anomalous low level anticyclonic circulation is associated with the reduction in the rainfall over the central part of southern Brazil in RegA2 and RegB2 scenarios. Similar to HadAM3, RegCM3 projects larger warming in A2 scenario. For the present climate, when compared to HadAM3, RegHad defines better both the location of the main cyclogenetic areas and its annual cycle near southwestern SAO. The projections indicate a reduction in the total number of cyclones of −7.2% and −4.7% for RegA2 and RegB2, respectively, while HadAM3 reduction is ~−4.5% for both scenarios. The decrease is larger for initially intense cyclones (ζ ≤ −2.5 × 10−5 s−1): −20.9% (RegA2) and −11.3% (RegB2). For the lifetime, distance traveled and mean velocity of the cyclones, the A2 and B2 scenarios present mean values close to the present climate (~3 days, ~1900 km, and ~9 m s−1, respectively). Regarding the initial mean vorticity of the systems, RegB2 simulates values similar to the present climate, but they are initially weaker in RegA2. In general, RegA2 and RegB2 show a large decrease in the number of cyclones over the southern SAO due to an anticyclonic anomaly covering SAO between 30–55°S. The reduction is larger in the scenario with higher concentrations of greenhouse gases (RegA2).

Regional Climate Model Simulations of the 1998 Summer China Flood: Dependence on Initial and Lateral Boundary Conditions

The dependence of the RegCM3 (Regional Climate Model version 3) downscaling skill on initial conditions (ICs) and lateral boundary conditions (LBCs) are investigated for the 1998 summer flood along the Yangtze River Basin in China. The effect of IC uncertainties is depicted by 15 realizations starting on each consecutive day from April 1 to 15 while all ending on September 1, 1998 with identical driving LBCs, analyses are based on June, July and August simulations. The result reveals certain IC effect on precipitation for daily evolution but little for summer mean geographical distribution. In contrast, the effect of LBCs uncertainties as represented by four different reanalyses are notably larger in both daily evolution and summer mean distribution. The ensemble average among either 15 IC realizations or 4 LBC runs does not show important skill improvement over the individuals. None of the RegCM3 simulations (including the ensemble means) captured the observed main rain band along the Yangtze River Basin. This general failure suggests the need for further model physics improvement.

Modeling the hydroclimatology of the midwestern United States. Part 1: current climate

An ensemble of six 22-year numerical experiments was conducted to evaluate the ability of Regional Climate Model version 3 (RegCM3) to simulate the energy and water budgets of the midwestern United States. RegCM3 was run using two surface physics schemes: Integrated Biosphere Simulator (IBIS) and Biosphere-Atmosphere Transfer Scheme 1e (BATS1e), and two convective closure assumptions: Fritsch & Chappell (FC80) and Arakawa & Schubert (AS74). Boundary conditions were provided by the National Centers for Environmental Prediction-Department of Energy Reanalysis 2 dataset and the ECHAM5 general circulation model. A companion paper examines the American Midwest under future climate scenarios. Overall, the model that reproduces the observed seasonal cycles of the midwestern United States climate system best is RegCM3 using IBIS and the AS74 convective closure assumption. IBIS simulates shortwave radiation more accurately, while BATS1e simulates longwave radiation more accurately. Summer two-meter air temperature is overestimated by the combination of IBIS and the FC80 convective closure assumption. All models contain a wet bias and overestimate evapotranspiration during the spring. Total runoff, surface runoff, groundwater runoff, and root zone soil moisture are best simulated by RegCM3 using IBIS and the AS74 convective closure assumption. While BATS1e does capture the seasonal cycle of total runoff, gross errors in the partitioning of total runoff between surface runoff and groundwater runoff exist. The seasonal cycle of root zone soil moisture simulated by RegCM3 using IBIS and the AS74 convective closure assumption is dry, but agrees with observations during the summer. The rest of the models underestimate root zone soil moisture.

The role of lateral boundary conditions in simulations of mineral aerosols by a regional climate model of Southwest Asia

The importance of specifying realistic lateral boundary conditions in the regional modeling of mineral aerosols has not been examined previously. This study examines the impact of assigning values for mineral aerosol (dust) concentrations at the lateral boundaries of Regional Climate Model version 3 (RegCM3) and its aerosol model over Southwest Asia. Currently, the dust emission module of RegCM3 operates over the interior of the domain, allowing dust to be transported to the boundaries, but neglecting any dust emitted at these points or from outside the domain. To account for possible dust occurring at, or entering from the boundaries, mixing ratios of dust concentrations from a larger domain RegCM3 simulation are specified at the boundaries of a smaller domain over Southwest Asia. The lateral boundary conditions are monthly averaged concentration values (μg of dust per kg of dry air) resolved in the vertical for all four dust bin sizes within RegCM3’s aerosol model. RegCM3 simulations with the aerosol/dust model including lateral boundary conditions for dust are performed for a five year period and compared to model simulations without prescribed dust concentrations at the boundaries. Results indicate that specifying boundary conditions has a significant impact on dust loading across the entire domain over Southwest Asia. More specifically, a nearly 30% increase in aerosol optical depth occurs during the summer months from specifying realistic dust boundary conditions, bringing model results closer to observations such as MISR. In addition, smaller dust particles at the boundaries have a more important impact than large particles in affecting the dust loading within the interior of this domain. Moreover, increases in aerosol optical depth and dust concentrations within the interior domain are not entirely caused by inflow from the boundaries; results indicate that an increase in the gradient of concentration at the boundaries causes an increase of diffusion from the boundaries. Lastly, experiments performed using a climatology of dust concentrations yield similar results to those using actual monthly values. Therefore, using a climatology of dust mixing ratios is sufficient in implementing lateral boundary conditions for mineral aerosols. In short, this work concludes that realistic specification of lateral boundary conditions for mineral aerosols can be important in modeling the dust loading over arid regional climates such as Southwest Asia.

Validation of a High-Resolution Version of the Regional Climate Model RegCM3 over the Carpathian Basin

Abstract This paper presents a validation study for a high-resolution version of the Regional Climate Model version 3 (RegCM3) over the Carpathian basin and its surroundings. The horizontal grid spacing of the model is 10 km—the highest reached by RegCM3. The ability of the model to capture temporal and spatial variability of temperature and precipitation over the region of interest is evaluated using metrics spanning a wide range of temporal (daily to climatology) and spatial (inner domain average to local) scales against different observational datasets. The simulated period is 1961–90. RegCM3 shows small temperature biases but a general overestimation of precipitation, especially in winter; although, this overestimate may be artificially enhanced by uncertainties in observations. The precipitation bias over the Hungarian territory, the authors’ main area of interest, is mostly less than 20%. The model captures well the observed late twentieth-century decadal-to-interannual and interseasonal variability. On short time scales, simulated daily temperature and precipitation show a high correlation with observations, with a correlation coefficient of 0.9 for temperature and 0.6 for precipitation. Comparison with two Hungarian station time series shows that the model performance does not degrade when going to the 10-km gridpoint scale. Finally, the model reproduces the spatial distribution of dry and wet spells over the region. Overall, it is assessed that this high-resolution version of RegCM3 is of sufficiently good quality to perform climate change experiments over the Carpathian region—and, in particular, the Hungarian territory—for application to impact and adaptation studies.

Interactions among ENSO, the Monsoon, and Diurnal Cycle in Rainfall Variability over Java, Indonesia

Abstract Using a high-resolution regional climate model—the Abdus Salam International Centre for Theoretical Physics Regional Climate Model version 3 (RegCM3)—and station and satellite observations, the authors have studied the spatial heterogeneity of climate variability over Java Island, Indonesia. Besides the well-known anomalous dry conditions that characterize the dry and transition seasons during an El Niño year, analysis of regional model output reveals a wet mountainous south versus dry northern plains in precipitation anomalies associated with El Niño over Java during the peak rainy season. Modeling experiments indicate that this mountains/plains contrast is caused by the interaction of the El Niño–induced monsoonal wind anomalies and the island/mountain-induced local diurnal cycle of winds and precipitation. During the wet season of El Niño years, anomalous southeasterly winds over the Indonesian region oppose the climatological northwesterly monsoon, thus reducing the strength of the monsoon winds over Java. This weakening is found to amplify the local diurnal cycle of land–sea breezes and mountain–valley winds, producing more rainfall over the mountains, which are located closer to the southern coast than to the northern coast. Therefore, the variability of the diurnal cycle associated with this local spatial asymmetry of topography is the underlying cause for the heterogeneous pattern of wet south/dry north rainfall anomalies during El Niño years. It is further shown that the mean southeasterly wind anomalies during December–February of El Niño years result from more frequent occurrence of a quiescent monsoon weather type, during which the strengthened sea-breeze and valley-breeze convergence leads to above normal rainfall over the mountains.

Climatic simulations of the eastern Andes low-level jet and its dependency on convective parameterizations

The South American low level jet (SALLJ) of the Eastern Andes is investigated with Regional Climate Model version 3 (RegCM3) simulations during the 2002–2003 austral summer using two convective parameterizations (Grell and Emanuel). The simulated SALLJ is compared with the special observations of SALLJEX (SALLJ Experiment). Both the Grell and Emanuel schemes adequately simulate the low level flow over South America. However, there are some intensity differences. Due to the larger (smaller) convective activity, the Emanuel (Grell) scheme simulates more intense (weaker) low level wind than analysis in the tropics and subtropics. The objectives criteria of Sugahara (SJ) and Bonner (BJ) were used for LLJ identification. When applied to the observations, both criteria suggest a larger frequency of the SALLJ in Santa Cruz, followed by Mariscal, Trinidad and Asuncion. In Mariscal and Asuncion, the diurnal cycle indicates that SJ occurs mainly at 12 UTCs (morning), while the BJ criterion presents the SALLJ as more homogenously distributed. The concentration into two of the four-times-a-day observations does not allow conclusions about the diurnal cycle in Santa Cruz and Trinidad. The simulated wind profiles result in a lower than observed frequency of SALLJ using both the SJ and BJ criteria, with fewer events obtained with the BJ. Due to the stronger simulated winds, the Emanuel scheme produces an equal or greater relative frequency of SALLJ than the Grell scheme. However, the Grell scheme using the SJ criterion simulates the SALLJ diurnal cycle closer to the observed one. Although some discrepancies between observed and simulated mean vertical profiles of the horizontal wind are noted, there is large agreement between the composites of the vertical structure of the SALLJ, especially when the SJ criterion is used with the Grell scheme. On an intraseasonal scale, a larger southward displacement of SALLJ in February and December when compared with January has been noted. The Grell and Emanuel schemes simulated this observed oscillation in the low-level flow. However, the spatial pattern and intensity of rainfall and circulation anomalies simulated by the Grell scheme are closer to the analyses than those obtained with the Emanuel scheme.

The Sensitivity of Latent Heat Flux to Changes in the Radiative Forcing: A Framework for Comparing Models and Observations

Abstract A climate model must include an accurate surface physics scheme in order to examine the interactions between the land and atmosphere. Given an increase in the surface radiative forcing, the sensitivity of latent heat flux to available energy plays an important role in determining the energy budget and has a significant impact on the response of surface temperature. The Penman–Monteith equation is used to construct a theoretical framework for evaluating the climatology of evapotranspiration and the sensitivity of latent heat flux to available energy. Regional Climate Model version 3 coupled to Integrated Biosphere Simulator (RegCM3–IBIS); RegCM3 with its native land surface model, Biosphere–Atmosphere Transfer Scheme 1e (RegCM3–BATS1e); and Flux Network (FLUXNET) micrometeorological tower observations are compared and contrasted using the developed methodology. RegCM3–IBIS and RegCM3–BATS1e simulate the observed sensitivity of latent heat flux to available energy reasonably well during the summer on average; however, there are significant variations in the monthly values. Additional information provided by the physically based Penman–Monteith framework is employed for identifying deficiencies and guiding improvements in models, allowing calibration of both the climatology of evapotranspiration and the sensitivity of latent heat flux to available energy.

Seasonal and interannual variations of surface climate elements over Vietnam

The 1991-2000 climate over Vietnam and the Indochina Peninsula is simulated using the Regional Climate Model version 3.0 (RegCM3). The domain of interest extends from 80° E to 130° E and 5° S to 40° N. The model is driven by the ERA-40 reanalysis data as initial and lateral boundary conditions, and is forced by the Optimum Interpolation Sea Surface Temperature (OISST) data over the oceans. Validations were carried out by comparing the simulated circulation fields, 2 m air temperatures, and precipitation to globally available observation data, and data from 50 meteoro- logical stations over 7 sub-regions of Vietnam. In general, the simulated patterns of the interested fields are in good agreement with observed data. Although being somewhat wetter or dryer and cooler, RegCM3 reproduces relatively well the observed annual cycle and the inter-annual variabil- ity of surface air temperature and precipitation. A large proportion of the negative biases in temper- ature over Vietnam is explained by the lapse rate correction process. After correction for elevation differences, the model still underestimates air temperature over most of the sub-regions. In rainy and dry seasons, RegCM3 generally underestimates and overestimates precipitation, respectively.

Sensitivity of the simulated African monsoon of summers 1993 and 1999 to convective parameterization schemes in RegCM3

In this study, the International Center for Theoretical Physics Regional Climate Model version 3 (RegCM3) was used to investigate the sensitivity of the simulation of the West African monsoon using four different cumulus and closures parameterization schemes of Anthes Kuo (AK), Grell and Fristish Chappell (GFC), Grell and Arakawa Schubert (GAS), and MIT-Emmanuel (EM) while maintaining other physical packages unchanged. The contrasting monsoon years of 1993 and 1999, which were dry and wet years, respectively, were simulated. The model was integrated from a period of 5 months, starting from May 1 to September 30 of each year using the European Centre for Medium-Range-Weather Forecast (ECMWF) Reanalysis data (ERA40) as input boundary conditions. The 6-hourly reanalysis data were used to provide the lateral boundary conditions, and the observed weekly Reynolds Sea Surface Temperature interpolated to 6 h was used as the lower boundary forcing. The results show that in West Africa, monsoon precipitations are sensitive to the choice of cumulus parameterization and closure schemes. None of the schemes is able to simulate the monsoon rainfall accurately, and furthermore, there is little difference in behavior among schemes between dry and wet years. The spatial features of precipitation are not identical among schemes, although they all show a northward shift of the rain bands, giving a very wet Sahel and dry Guinean Coast. The GFC and EM schemes are able to capture the diurnal cycle of precipitation and the zonal averages of stratiform rain fractions as observed in the Tropical Rainfall Measuring Mission (TRMM), although they overestimated rainfall amounts. The most important deficiencies, however, cannot be attributed to the schemes. In particular, the northward shift of both the rain band and the AEJ in RegCM3 is the result of unrealistic soil moisture resulting from the way albedo is parameterized, leading to an excessive northward penetration of monsoon flow. A sensitivity study showed that an adjustment of initial albedo values over the Sahel improved the simulation, and in particular the position of rain bands and of the AEJ.

Numerical model simulation of the Saharan dust event of 6–11 March 2006 using the Regional Climate Model version 3 (RegCM3)

The Sahara desert is the world's primary source of mineral dust aerosols and is known to be an important but poorly understood component of the climate system. Climate models which incorporate dust modules have the potential to improve our understanding of the climate impacts of dust. In this study, the performance of the Regional Climate Model version 3 (RegCM3) with an active dust scheme is evaluated, using a major dust event of 6–11 March 2006 as a test case. To account for the distribution of preferential dust source regions, soil texture characteristics were modified in dust source regions identified from long‐term SEVIRI satellite data. The dust event was associated with a pronounced cold outbreak of midlatitude air over the northern Sahara which produced anomalously strong northerly winds, which propagated from west to east over the Sahara during the study period. This resulted in dust mobilization from multiple dust sources across the domain. RegCM3 represents the space/time structure of near‐surface meteorology well, although surface winds are underestimated in absolute terms. The experiment in which soils are modified provides a better representation of local dust sources and emission and resulting atmospheric optical thickness (AOT). In this experiment, model simulated dust flux exported from the Sahara to the Sahel and the tropical east Atlantic is estimated as 1.9 Tg d−1. The dust event had a profound impact on the surface solar radiation budget of ∼−140 W m−2 per unit AOT (domain average). The shortwave radiative effect at the top of the atmosphere is ∼−10 W m−2 per unit AOT over the study domain. However, this is strongly dependent on surface albedo. The results also highlight how errors in model simulated circulation lead to errors in the position of the dust plume.

Precipitation diurnal cycle and summer climatology assessment over South America: An evaluation of Regional Climate Model version 3 simulations

Regional Climate Model version 3 (RegCM3) simulations of 17 summers (1988–2004) over part of South America south of 5°S were evaluated to identify model systematic errors. Model results were compared to different rainfall data sets (Climate Research Unit (CRU), Climate Prediction Center (CPC), Global Precipitation Climatology Project (GPCP), and National Centers for Environmental Prediction (NCEP) reanalysis), including the five summers mean (1998–2002) precipitation diurnal cycle observed by the Tropical Rainfall Measuring Mission (TRMM)‐Precipitation Radar (PR). In spite of regional differences, the RegCM3 simulates the main observed aspects of summer climatology associated with the precipitation (northwest‐southeast band of South Atlantic Convergence Zone (SACZ)) and air temperature (warmer air in the central part of the continent and colder in eastern Brazil and the Andes Mountains). At a regional scale, the main RegCM3 failures are the underestimation of the precipitation in the northern branch of the SACZ and some unrealistic intense precipitation around the Andes Mountains. However, the RegCM3 seasonal precipitation is closer to the fine‐scale analyses (CPC, CRU, and TRMM‐PR) than is the NCEP reanalysis, which presents an incorrect north‐south orientation of SACZ and an overestimation of its intensity. The precipitation diurnal cycle observed by TRMM‐PR shows pronounced contrasts between Tropics and Extratropics and land and ocean, where most of these features are simulated by RegCM3. The major similarities between the simulation and observation, especially the diurnal cycle phase, are found over the continental tropical and subtropical SACZ regions, which present afternoon maximum (1500–1800 UTC) and morning minimum (0900–1200 UTC). More specifically, over the core of SACZ, the phase and amplitude of the simulated precipitation diurnal cycle are very close to the TRMM‐PR observations. Although there are amplitude differences, the RegCM3 simulates the observed nighttime rainfall in the eastern Andes Mountains, over the Atlantic Ocean, and also over northern Argentina. The main simulation deficiencies are found in the Atlantic Ocean and near the Andes Mountains. Over the Atlantic Ocean the convective scheme is not triggered; thus the rainfall arises from the grid‐scale scheme and therefore differs from the TRMM‐PR. Near the Andes, intense (nighttime and daytime) simulated precipitation could be a response of an incorrect circulation and topographic uplift. Finally, it is important to note that unlike most reported bias of global models, RegCM3 does not trigger the moist convection just after sunrise over the southern part of the Amazon.

Coupling of Integrated Biosphere Simulator to Regional Climate Model Version 3

Abstract A description of the coupling of Integrated Biosphere Simulator (IBIS) to Regional Climate Model version 3 (RegCM3) is presented. IBIS introduces several key advantages to RegCM3, most notably vegetation dynamics, the coexistence of multiple plant functional types in the same grid cell, more sophisticated plant phenology, plant competition, explicit modeling of soil/plant biogeochemistry, and additional soil and snow layers. A single subroutine was created that allows RegCM3 to use IBIS for surface physics calculations. A revised initialization scheme was implemented for RegCM3–IBIS, including an IBIS-specific prescription of vegetation and soil properties. To illustrate the relative strengths and weaknesses of RegCM3–IBIS, one 4-yr numerical experiment was completed to assess ability of both RegCM3–IBIS (with static vegetation) and RegCM3 with its native land surface model, Biosphere–Atmosphere Transfer Scheme 1e (RegCM3–BATS1e), to simulate the energy and water budgets. Each model was evaluated using the NASA Surface Radiation Budget, FLUXNET micrometeorological tower observations, and Climate Research Unit Time Series 2.0. RegCM3–IBIS and RegCM3–BATS1e simulate excess shortwave radiation incident and absorbed at the surface, especially during the summer months. RegCM3–IBIS limits evapotranspiration, which allows for the correct estimation of latent heat flux, but increases surface temperature, sensible heat flux, and net longwave radiation. RegCM3–BATS1e better simulates temperature, net longwave radiation, and sensible heat flux, but systematically overestimates latent heat flux. This objective comparison of two different land surface models will help guide future adjustments to surface physics schemes within RegCM3.

Regionalization of Climate Change Simulations over the Eastern Mediterranean

Abstract In this study, the potential role of global warming in modulating the future climate over the eastern Mediterranean (EM) region has been investigated. The primary vehicle of this investigation is the Abdus Salam International Centre for Theoretical Physics Regional Climate Model version 3 (ICTP-RegCM3), which was used to downscale the present and future climate scenario simulations generated by the NASA’s finite-volume GCM (fvGCM). The present-day (1961–90; RF) simulations and the future climate change projections (2071–2100; A2) are based on the Intergovernmental Panel on Climate Change (IPCC) greenhouse gas (GHG) emissions. During the Northern Hemispheric winter season, the general increase in precipitation over the northern sector of the EM region is present both in the fvGCM and RegCM3 model simulations. The regional model simulations reveal a significant increase (10%–50%) in winter precipitation over the Carpathian Mountains and along the east coast of the Black Sea, over the Kackar Mountains, and over the Caucasus Mountains. The large decrease in precipitation over the southeastern Turkey region that recharges the Euphrates and Tigris River basins could become a major source of concern for the countries downstream of this region. The model results also indicate that the autumn rains, which are primarily confined over Turkey for the current climate, will expand into Syria and Iraq in the future, which is consistent with the corresponding changes in the circulation pattern. The climate change over EM tends to manifest itself in terms of the modulation of North Atlantic Oscillation. During summer, temperature increase is as large as 7°C over the Balkan countries while changes for the rest of the region are in the range of 3°–4°C. Overall the temperature increase in summer is much greater than the corresponding changes during winter. Presentation of the climate change projections in terms of individual country averages is highly advantageous for the practical interpretation of the results. The consistence of the country averages for the RF RegCM3 projections with the corresponding averaged station data is compelling evidence of the added value of regional climate model downscaling.

Characteristics of an East–Asian summer monsoon climatology simulated by the RegCM3

We investigated the characteristics of a 22-year-long regional climatology of the East Asian summer monsoon (EASM) simulated by the Regional Climate Model version 3 (RegCM3). The RegCM3 was forced by the perfect boundary conditions, i.e., the National Centers for Environmental Prediction (NCEP)/Department of Energy (DOE) reanalysis (R-2), for summer (June–July–August, JJA) during the period of 1982–2003 with a 60 km horizontal resolution. This study stresses the evaluation of the seasonal mean climatology and interannual variations against the R-2 as well as a shorter time-scale variation, such as intraseasonal and diurnal variations over the Korean Peninsula, against the station-observed datasets. The RegCM3 is able to reproduce overall features of the seasonal mean climatology with a wet bias of 0.54 mm day−1 and a certain cold (warm) bias in the lower (upper) troposphere. Interannual variability during the 22 years also shows good agreement with the R-2 reanalysis, both in precipitation and temperature. The capability of the RegCM3 in reproducing intraseasonal variability is reasonable in terms of a 22-year-long climatology. The daily variations of the simulated climatology in surface temperature and in precipitation over Korea are also reasonably reproduced during June and July but are relatively poorly resolved for August. The skill degradation is clearer in the last eight years of 1996–2003 than the first period of 1982–1989, which raises an issue of the RegCM3’s ability to capture the observed decadal change in the mid-1990s. Diurnal variations of surface climate simulated by the model exhibit overestimated (underestimated) amplitudes in precipitation (temperature).

Modeling the Hydroclimatology of Kuwait: The Role of Subcloud Evaporation in Semiarid Climates

Abstract A new subcloud layer evaporation scheme is incorporated into Regional Climate Model, version 3 (RegCM3), to better simulate the rainfall distribution over a semiarid region around Kuwait. The new scheme represents subcloud layer evaporation of convective as well as large-scale rainfall. Model results are compared to observations from rain gauge data networks and satellites. The simulations show significant response to the incorporation of subcloud layer evaporation as a reduction by as much as 20% in annual rainfall occurs over the region. As a result, the new model simulations of annual rainfall are within 15% of observations. In addition, results indicate that the interannual variability of rainfall simulated by RegCM3 is sensitive to the specification of boundary conditions. For example, forcing RegCM3’s lateral boundary conditions with the 40-yr ECMWF Re-Analysis (ERA-40) data, instead of NCEP–NCAR’s Reanalysis Project 2 (NNRP2), reduces interannual variability by over 25%. Moreover, with subcloud layer evaporation incorporated and ERA-40 boundary conditions implemented, the model’s bias and root-mean-square error are significantly reduced. Therefore, the model’s ability to reproduce observed annual rainfall and the year-to-year variation of rainfall is greatly improved. Thus, these results elucidate the critical role of this natural process in simulating the hydroclimatology of semiarid climates. Last, a large discrepancy between observation datasets over the region is observed. It is believed that the inherent characteristics that are used to construct these datasets explain the differences observed in the annual and interannual variability of Kuwait’s rainfall.

Connection between Spring Conditions and Peak Summer Monsoon Rainfall in South America: Role of Soil Moisture, Surface Temperature, and Topography in Eastern Brazil

Abstract A link between peak summer monsoon rainfall in central-east Brazil, composing part of the South American monsoon core region, and antecedent conditions in spring is disclosed. Rainfall in this region during part of spring holds a significant inverse correlation with rainfall in peak summer, especially during ENSO years. A surface–atmosphere feedback hypothesis is proposed to explain this relationship: low spring precipitation leads to low spring soil moisture and high late spring surface temperature; this induces a topographically enhanced low-level anomalous convergence and cyclonic circulation over southeast Brazil that enhances the moisture flux from northern and central South America into central-east Brazil, setting up favorable conditions for excess rainfall. Antecedent wet conditions in spring lead to opposite anomalies. The main links in this hypothesis are confirmed through correlation analysis of observed data: spring precipitation is negatively correlated to late spring surface temperature in central-east Brazil, and surface temperature in southeast Brazil is positively correlated with peak summer monsoon precipitation in central-east Brazil. The intermediary links of the surface–atmosphere feedback are tested in sensitivity experiments with the regional climate model version 3 (RegCM3). These experiments confirm that the proposed links are possible: the reduced soil moisture in central-east Brazil is shown to increase the surface temperature and produce a cyclonic anomaly over southeast Brazil, as well as increased precipitation in central-east Brazil. A crucial role of the mountains of southeast Brazil in anchoring the patterns of intraseasonal variability, and sustaining the “dipolelike” precipitation mode observed over South America, is suggested. The low predictability of monsoon rainfall anomalies in central-east Brazil during the austral summer might be partially ascribed to the fact that the models do not well reproduce the topographical features and the land–atmosphere interactions that are important for the variability in that region.

Regional Climate Modeling for the Developing World: The ICTP RegCM3 and RegCNET

Regional climate models are important research tools available to scientists around the world, including in economically developing nations (EDNs). The Earth Systems Physics (ESP) group of the Abdus Salam International Centre for Theoretical Physics (ICTP) maintains and distributes a state-of-the-science regional climate model called the ICTP Regional Climate Model version 3 (RegCM3), which is currently being used by a large research community for a diverse range of climate-related studies. The RegCM3 is the central, but not only, tool of the ICTP-maintained Regional Climate Research Network (RegCNET) aimed at creating south–south and north–south scientific interactions on the topic of climate and associated impacts research and modeling. In this paper, RegCNET, RegCM3, and illustrative results from RegCM3 benchmark simulations applied over south Asia, Africa, and South America are presented. It is shown that RegCM3 performs reasonably well over these regions and is therefore useful for climate studies in EDNs.

Regional Climate Model–Simulated Timing and Character of Seasonal Rains in South America

Abstract The potential of an experimental nested prediction system to improve the simulation of subseasonal rainfall statistics including daily precipitation intensity, rainy season onset and withdrawal, and the frequency and duration of dry spells is evaluated by examining a four-member ensemble of regional climate model simulations performed for the period 1982–2002 over South America. The study employs the International Centre for Theoretical Physics (ICTP) regional climate model, version 3 (RegCM3), driven with the NCEP–NCAR reanalysis and the European Centre–Hamburg GCM, version 4.5. Statistics were examined for five regions: the northern Amazon, southern Amazon, the monsoon region, Northeast Brazil, and southeastern South America. RegCM3 and the GCM are able to replicate the distribution of daily rainfall intensity in most regions. The analysis of the rainy season timing shows the observed onset occurring first over the monsoon region and then spreading northward into the southern Amazon, in contrast to some previous studies. Correlations between the onset and withdrawal date and SSTs reveal a strong relationship between the withdrawal date in the monsoon region and SSTs in the equatorial Pacific, with above-average SSTs associated with late withdrawal. Over Northeast Brazil, the regional model errors are smaller than those shown by the GCM, and the strong interannual variability in the timing of the rainy season is better simulated by RegCM3. However, the regional model displays an early bias in onset and withdrawal over the southern Amazon and the monsoon regions. Both RegCM3 and the GCM tend to underestimate (overestimate) the frequency of shorter (longer) dry spells, although the differences in dry spell frequency during warm and cold ENSO events are well simulated. The results presented here show that there is potential for added value from the regional model in simulating subseasonal statistics; however, improvements in the physical parameterizations are needed for this tropical region.