Regional Climate Model Version Research Articles

Variability of East African rainfall based on multiyear Regcm3 simulations

AbstractThe International Center for Theoretical Physics (ICTP) regional climate model version 3 (ICTP‐RegCM3) multiyear simulations of East Africa rainfall during the October–December, short rains season are evaluated. Two parallel runs; based on NCEP reanalysis and NASA FvGCM lateral boundary conditions are performed. The simulated monthly and seasonal rainfall climatology as well as the interannual variability are found to be fairly consistent with the observations. The model climatology over specific homogeneous climate subregions, except central Kenya (CKE) highlands, also reasonably agrees with the observed. The latitude‐time evolution (intraseasonal variability) of the simulated seasonal rainfall exhibits two distinct modes of behavior. The first is a quasistationary mode associated with high rainfall throughout the season within the equatorial belt between 1°S and 2°N. The second mode is associated with the intertropical convergence zone (ITCZ)‐driven southward migration of regions of rainfall maxima as the season progresses, which is also consistent with the observed. Furthermore, observed rainfall variability over distinct homogeneous climate subregions is also fairly reproduced by the model, except over central Kenya highlands and northeastern parts of Kenya. The spatial correlation between the simulated seasonal rainfall and some of the global teleconnections (DMI and Nino3.4 indices) shows that the regional model conserves some of the observed regional ‘hot spots’ where rainfall‐ENSO/DMI associations are strong. At the same time, unlike observations, the model reveals that along the East Africa Rift Valley and over western parts of the Lake Victoria Basin, the association is weak, perhaps an indication that nonlinear interactions between local forcing (captured by the model) and large‐scale systems either suppress or obscur the dominant influence of the teleconnections on rainfall over certain parts. Copyright © 2006 Royal Meteorological Society.

Simulation of West African monsoon using the RegCM3. Part I: Model validation and interannual variability

The West African monsoon oscillates each year with remarkable regularity but the interannual variability associated with the monsoon is not fully understood although much progress has been made in recent years. This study examines and evaluates the mean state and the interannual variability of the West African climate as simulated by the International Centre for Theoretical Physics (ICTP) Regional Climate Model version 3 (RegCM3) over the period 1979 through 1990 using the National Center for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis data as lateral boundary conditions.

Validation of simulated precipitation patterns over Ireland for the period 1961–2000

The Rotated Empirical Orthogonal Function (REOF) method was used to analyse the annual and interannual variability of the precipitation patterns over Ireland as simulated by the Rossby Centre Regional Climate Model Version 2 (RCA2) for the period 1961–2000. The annual and monthly precipitation results show that the model captures the major spatial pattern of each month, but the simulation shows a larger percentage of the variance explained by the leading spatial pattern and tends to have a less pronounced seasonal cycle compared to the observations. The simulation for the wet winter season is in slightly better agreement with the observations compared with the drier summer season. Spatial analysis of the monthly precipitation over a 40-year period shows two major patterns. The first, showing a precipitation maximum in the southwest, is well simulated; the second, showing a maximum in the west and northwest, shows a strongly increasing trend, which is slightly underestimated in the model simulation. Both patterns show seasonal and interannual variability. The wavelet energy density analysis shows that the interannual variability is more important than the seasonal one. In general, the model captures the major spatial and seasonal patterns observed between 1961 and 2000 but slightly overestimates monthly average precipitation levels. Copyright © 2005 Royal Meteorological Society.

Preliminary Simulation Research of Direct Radiative Forcing of Mineral Dust Aerosol Over East Asia Region

To research the direct radiative effect of dust aerosols over East Asia region, a dust emission scheme, a transport model and a radiative scheme of dust aerosol have been added into Regional Climate Model Version 3(RegCM3). Based on the simulation between March 2001 to February 2002, it is found that Northwest China and Mongolia are the main dust sources of East Asia, where the emission rates exceed 1μg/(m2·s) with the maximum value of 90μg/(m2·s). The maximum column burden of dust aerosol is about 5g/m2, which emerges over Taklimakan desert and Qinling Mountains; The direct radiative forcing at TOA is positive over land and negative over sea, and its regional average values in Spring, Summer, Autumn, Winter are 1.08, 0.88, 0.37, 0.40W/m2 respectively. The solar radiative forcing is also positive over land and negative over sea, but the infrared radiative forcing is positive in all modeling region; The radiative forcing values at surface for four seasons are –5.64, –2.25, –1.37, –1.87W/m2 respectively. Radiative forcing can be affected deeply by the change of single scattering albedo of dust aerosol.

Origin and Propagation of a Disturbance Associated with an African Easterly Wave as a Precursor of Hurricane Alberto (2000)

Abstract In this study, it is proposed that mesoscale convective complexes (MCCs) and a mesovortex (MV) were embedded within a wavelike disturbance over North Africa that led to the genesis of Hurricane Alberto (2000). The wavelike disturbance observed may be classified as an African easterly wave (AEW). Based on the cloud-top area and brightness values observed from infrared satellite data, four genesis and three lysis stages are identified within a cycle of moist convection associated with the pre-Alberto disturbance. The availability of water vapor is the most essential factor controlling the convective cycle of the pre-Alberto disturbance over the African continent. The presence of significant topography also contributes to the generation or decay of the associated MCCs through regulation of the water vapor supply. Further analysis of Meteosat satellite imagery reveals that the incipient disturbances for 23 of 34 eastern Atlantic tropical cyclones originated from the Ethiopian highlands (EH) region during the period of 1990–2001. The pre-Alberto disturbance was found to have exhibited characteristics of an AEW. At the EH, there existed two modes of disturbance development: a stationary mode and a propagating mode. The stationary mode corresponded with the generation of moist convection over the EH triggered by diurnally variant sensible heating, while the propagating mode corresponded with the generation and propagation of MVs and mesoscale convective systems (MCSs) from the lee side of the EH over a period of about 2 to 3 days. These components of the disturbance propagated westward together within an AEW train at an average speed of 11.6 m s−1. The average wavelength was roughly estimated to be about 2200 km. To prove that disturbances generated at the EH are indeed AEWs, the NCAR Regional Climate Model Version 3.0 is adopted to simulate the event. The simulated fields showed that both the propagating wave and stationary mountain wave modes were present, the convection was generated over the EH, and the pre-Alberto disturbance was generated near the lee of the EH. In addition, the convective cycle detected from NCEP reanalysis data was also reflected in the simulated fields. The simulated AEW possesses similar wave characteristics as the observed pre-Alberto disturbance.

Impact of climate change on surface ozone and deposition of sulphur and nitrogen in Europe

Abstract The potential impact of regional climate change on the distribution and deposition of air pollutants in Europe has been studied using a regional chemistry/transport/deposition model, MATCH. MATCH was set up using meteorological output from two 10-year climate change experiments made with the Rossby Centre regional Atmospheric climate model version 1 (RCA1). RCA1 was forced by boundary conditions from two different global climate models using the IPCC IS92a (business as usual) emission scenario. The global mean warming in both the GCMs was 2.6 K and was reached in the period 2050–2070. Simulations with MATCH indicate substantial potential impact of regional climate change on both deposition of oxidised nitrogen and concentrations of surface ozone. The simulations show a strong increase in surface ozone expressed as AOT40 and mean of daily maximum over southern and central Europe and a decrease in northern Europe. The simulated changes in April–September AOT40 are significant in relation to inter-annual variability over extended areas. Changes in deposition of oxidised nitrogen are much smaller and also less coherent due to the strong inter-annual variability in precipitation in the RCA1 simulations and differences in the regional climate change simulated with RCA1 in the two regional scenarios. Changes in simulated annual deposition are significant in relation to inter-annual variability only over small areas. This indicates that longer simulation periods are necessary to establish changes in deposition.

Investigating the Effect of Seasonal Plant Growth and Development in Three-Dimensional Atmospheric Simulations. Part II: Atmospheric Response to Crop Growth and Development

Abstract The authors examine the effect of seasonal crop development and growth on the atmospheric boundary layer in the warm season over the central Great Plains region of North America. They introduced daily crop development and growth functions into the Biosphere–Atmosphere Transfer Scheme (BATS) coupled to the National Center for Atmospheric Research Regional Climate Model version 2 (NCAR RegCM2). Coupled RegCM/BATS simulations were performed over the conterminous United States for a dry (1988) and favorably moist (1991) growing seasons at a spatial resolution of 90 km × 90 km. Largest differences between the control and interactive runs occurred in 1988, when up to 45% differences in surface latent and sensible heat fluxes were simulated in response to different Leaf Area Index (LAI) parameterizations employed by the models (in June and July, LAI was about 5 in the control cases and between 1 and 2 in the interactive cases). Two to four °C differences in air temperatures resulted in response to such ...

Development of a Second-Generation Regional Climate Model (RegCM2). Part I: Boundary-Layer and Radiative Transfer Processes

Abstract During the last few years the development of a second-generation regional climate modeling system (RegCM2) has been completed at the National Center for Atmospheric Research (NCAR). Based upon the National Center for Atmospheric Research-Pennsylvania State University Mesoscale Model (MM4), RegCM2 includes improved formulations of boundary layer, radiative transfer, surface physics, cumulus convection, and time integration technique, which make it more physically comprehensive and more computationally efficient than the previous regional climate model version. This paper discusses a number of month-long simulations over the European region that were conducted to test the new RegCM2 boundary-layer parameterization (the scheme developed by Holtsag et al.) and radiative transfer formulation [the package developed for the NCAR Community Climate Model 2 (CCM 2)]. Both schemes significantly affect the model precipitation, temperature, moisture, and cloudiness climatology, leading to overall more realist...