Regional Climate System Model Research Articles

Regional model simulation of summer rainfall over the Philippines: Effect of choice of driving fields and ocean flux schemes

The latest version of the Abdus Salam International Centre for Theoretical Physics (ICTP) regional model RegCM is used to investigate summer monsoon precipitation over the Philippine archipelago and surrounding ocean waters, a region where regional climate models have not been applied before. The sensitivity of simulated precipitation to driving lateral boundary conditions (NCEP and ERA40 reanalyses) and ocean surface flux scheme (BATS and Zeng) is assessed for 5 monsoon seasons. The ability of the RegCM to simulate the spatial patterns and magnitude of monsoon precipitation is demonstrated, both in response to the prominent large scale circulations over the region and to the local forcing by the physiographical features of the Philippine islands. This provides encouraging indications concerning the development of a regional climate modeling system for the Philippine region. On the other hand, the model shows a substantial sensitivity to the analysis fields used for lateral boundary conditions as well as the ocean surface flux schemes. The use of ERA40 lateral boundary fields consistently yields greater precipitation amounts compared to the use of NCEP fields. Similarly, the BATS scheme consistently produces more precipitation compared to the Zeng scheme. As a result, different combinations of lateral boundary fields and surface ocean flux schemes provide a good simulation of precipitation amounts and spatial structure over the region. The response of simulated precipitation to using different forcing analysis fields is of the same order of magnitude as the response to using different surface flux parameterizations in the model. As a result it is difficult to unambiguously establish which of the model configurations is best performing.

Simulation of the Taiwan climate using the Hadley Centre PRECIS regional climate modelling system: The 1979-1981 results

In this paper we describe the simulation of Taiwan's climate for the period 1979-1981 using the Hadley Centre PRECIS (Providing Regional Climates for Impact Studies) regional climate modeling system. The PRECIS simulations of surface precipitation and temperature have been compared in detail with the Central Weather Bureau measurements, and also with outputs from the IPCC global climate models such as the HadCM3, the CCSR, and the NCEP 50-year reanalysis data. Our results show that the very complicated spatial patterns of surface rainfall as revealed from the measurements can only be reproduced using the PRECIS model. The inter-annual variability in rainfall has shown to be well reproduced by the PRECIS model. The PRECIS model also demonstrates a good capability in simulating the spatial distribution of surface temperature over the whole of Taiwan, especially over Taiwan's Central Mountain Range. Since the PRECIS simulations were produced in combination with the ERA-15 global model results, our results show that a good way forward in conducting regional climate modeling at the national level requires the use of both global climate models and high resolution regional climate models.

A Study of the Antarctic Surface Energy Budget Using a Polar Regional Atmospheric Model Forced with Satellite-Derived Cloud Properties

Abstract Cloud properties from the newly extended Advanced Very High Resolution Radiometer (AVHRR) Polar Pathfinder (APP-x) dataset were incorporated into the atmospheric component of the Arctic Regional Climate System Model (ARCSyM) in order to improve the simulation of the Antarctic surface energy balance. A method for using the APP-x cloud properties in 48-h model simulations is presented. In the experiments, the model cloud fields were altered via the water vapor mixing ratio using cloud properties from the APP-x dataset. Significant improvements in monthly mean downwelling longwave radiation at the surface were observed relative to surface measurements. In the austral summer, the use of the APP-x dataset resulted in improvements as large as 30 W m−2 at the South Pole when compared to model results without APP-x clouds. However, only a very small improvement was seen in the turbulent heat fluxes and the surface temperature. It was also found that the satellite data can be used to shorten the model “sp...

The Swedish Regional Climate Modelling Programme, SWECLIM: A Review

The Swedish Regional Climate Modelling Programme, SWECLIM, was a 6.5-year national research network for regional climate modeling, regional climate change projections and hydrological impact assessment and information to a wide range of stakeholders. Most of the program activities focussed on the regional climate system of Northern Europe. This led to the establishment of an advanced, coupled atmosphere-ocean-hydrology regional climate model system, a suite of regional climate change projections and progress on relevant data and process studies. These were, in turn, used for information and educational purposes, as a starting point for impact analyses on different societal sectors and provided contributions also to international climate research.

A summer simulation of biogenic contributions to ground‐level ozone over the continental United States

The role of biogenic emissions in the production of ground‐level ozone has been the subject of considerable scientific investigation. However, because existing studies generally draw their conclusions from simulations of episodes lasting days to a week, there is a need to evaluate the biogenic impact over a relatively long timescale. Moreover, the magnitude of synergistic interaction between anthropogenic and biogenic emissions should be carefully quantified, and this issue is not accounted for in most previous investigations. In this study, we performed a summer seasonal (June to August 1995) model evaluation of surface ozone across the continental United States. A three‐dimensional regional climate, emissions, and air quality modeling system was used to do the simulations. The factor separation (FS) technique was applied to quantify the contributions from biogenic emissions alone and those from the synergy between anthropogenic and biogenic emissions. In the first step of this study, U.S. Environmental Protection Agency's National Emission Trends (NET) 1996 and 2020 “control case” raw anthropogenic emissions inventories were processed through Sparse Matrix Operator Kernel Emissions (SMOKE), an emissions model, to generate the speciated, gridded, and hourly emissions data needed for the air quality model. Next, six air quality simulations were carried out assuming zero emissions, biogenic only emissions, 1995 anthropogenic only emissions, biogenic plus 1995 anthropogenic emissions, 2020 anthropogenic only emissions, and biogenic plus 2020 anthropogenic emissions. The model results show that ground‐level ozone concentrations decrease moderately under the EPA's 2020 emissions scenario for many areas within the continental United States, with large reductions in vast areas of the eastern United States. They also show that the 1995 summer average “total biogenic contribution” to daily maximum surface ozone concentrations can reach 34 ppb. Biogenic emissions are associated with at least 20% of surface ozone concentrations for the most areas of the continental United States, with the peaks reaching more than 40% in California coastal areas, the southeastern states, and northeastern areas. A sizable portion of this “total biogenic contribution,” however, (up to 80% in some areas) is due to the synergy between anthropogenic and biogenic emissions and would thus be influenced by controls on anthropogenic source emissions.

Evaluation of basin-scale hydrologic response to a multi-storm simulation

Understanding how hydrologic systems of large river basins respond to atmospheric forcing is crucial to regional climate and hydrology studies. A hydrologic model system (HMS) was linked to a regional climate model (RCM) to model a series of storm events passing over the Susquehanna River Basin and to simulate various hydrologic processes in soil hydrology, land surface hydrology, and ground-water hydrology using observed and modeled storm events. The RCM is designed to link to general circulation models and to provide fine spatiotemporal output for hydrologic and other applications. The hydrologic models were calibrated to the observed data (e.g. soil moisture and streamflow) at the basin and subbasin-scales. The HMS-simulated hydrologic response to observed precipitation from a six-storm sequence compares well to the observed. The subgrid-scale spatial variability in precipitation and hydraulic conductivity is included in HMS simulations with RCM-modeled precipitation. Nested 108–36–12km RCM domains are used for the multi-storm simulation. The 12km RCM-modeled precipitation is then downscaled to a 1km hydrologic grid resolution for HMS simulation. Simulations of the six-storm sequence by the RCM produce precipitation fields that appear realistic in general, but that diverge in detail from observed precipitation in both time and space. HMS proves to be sensitive to these details, so the simulated streamflow does not accurately reproduce observed streamflow. The results suggest potential value in improving on the current versions of RCM and HMS for regional climate and hydrology system modeling.

Coupled Precipitation-Streamflow Simulations at the GAME/HUBEX Site: Sixian Basin.

As a contribution to the GAME/HUBEX program, we used historical data and the Regional Climate System Model (RCSM) to analyze and simulate precipitation and streamflow in the Xixian basin. Historical data for the period 1982 to 1988 indicates that peak precipitation and streamflow occurs during the summer and early fall, when this region is affected by the East Asian summer monsoons and typhoons, respectively. In preparation for long-term coupled atmospheric and streamflow model simulations, we calibrated the RCSM’s semi-distributed hydrologic model (TOPMODEL) for the Xixian basin using observations from 1982 to 1984 and validated for the period 1985 to 1988 with good results. Long-term hydroclimate simulations generated for the period January 1979 to December 1983 using the RCSM captured important hydroclimate characteristics of the region. The simulated seasonal precipitation and streamflow variations agree well with observations during late fall to spring. Summertime precipitation and streamflow were overestimated in the hindcast. The over-estimated precipitation may be due to the input large-scale forcing and the difficulty in simulating convertive precipitation during the monsoon season using a mesoscale atmospheric model. Coupled modeling of regional climate and streamflow is a relatively new capability. Implementation of this technique to river basins in the East Asia region will result in an increased predictability of water resources for this region.

Response of the seasonal carbon cycle in high latitudes to climate anomalies

Many observational studies have demonstrated that the amplitude of the seasonal carbon cycle in high latitudes is increasing and advancing in phase. Several hypotheses related to natural and anthropogenic landscape disturbance and climate change have been proposed to explain these observations. This study employs a regional atmosphere‐biosphere model (the Arctic Regional Climate System Model (ARCSyM)) to investigate the impacts of the climatic effects of elevated carbon dioxide on terrestrial carbon exchange over Alaska. A perturbation experiment, driven by a “transient” global climate scenario at the point at which atmospheric carbon dioxide has doubled, is compared to a validated present‐day simulation. The focus of this paper is on the role of physical climate in seasonal carbon exchange between the atmosphere and the terrestrial biosphere at regional scales. In the present‐day simulation the ARCSyM reproduces most observed features of climate and the surface energy budget and simulates a clearly defined growing season in the seasonal cycle of carbon dioxide exchange. In the perturbation experiment, the model atmosphere shows a generally warmer and wetter climate, with increased permafrost thaw. Two dominant biomes, tundra and boreal forest, are analyzed in detail for their responses to the perturbed climate. The amplitudes of the seasonal carbon dioxide cycle for Alaskan boreal forest and tundra increase 12 and 8%, respectively, with phase advances of ∼7 and 2 days, respectively. The forcing of photosynthetic productivity by soil moisture changes is a dominant contributor to the simulated changes in net ecosystem exchange. Boreal forest ecosystem is more sensitive to moisture anomalies due to a drier soil, whereas in the tundra regions, which are often close to saturation, changes are forced primarily by temperature variations. Thus in the event of a northward migration of tree line, sensitivity of regional carbon exchange to climate perturbations could increase.

Retrospective simulation of a storm event: A first step in coupled climate/hydrologic modeling

Global and regional climate models are valuable tools for assessing the effects of natural and anthropogenic perturbations to climate and hydrology. Results of a coupled regional climate and hydrologic model system, designed for the integrated assessment of climate‐hydrologic impacts at regional scales demonstrate that (a) simulated precipitation in a storm event is sensitive to the spatial resolution of the regional climate model and (b) spatial variability of precipitation and hydraulic variables must be accounted for in order to realistically capture the basin‐scale hydrologic response to a storm event. The regional climate model (with a spatial resolution of 4 to 36 km) can be driven either by global climate model output (with resolutions at the order of 100 km) or by observed climate data. The meteorological fields simulated over the mid‐Atlantic region of the USA were disaggregated to drive the basin‐scale hydrologic model (with a resolution of 1 km). With the improved treatment of spatial variability, the simulated streamflow at the basin outlet compares well with observations. These results from coupled climate‐hydrologic models at regional scales suggest that climate‐hydrology modeling studies that do not allow for spatial variability may be misleading.

A Seasonal Precipitation and Stream Flow Hindcast and Prediction Study in the Western United States during the 1997/98 Winter Season Using a Dynamic Downscaling System

Abstract The authors present a seasonal hindcast and prediction of precipitation in the western United States and stream flow in a northern California coastal basin for December 1997–February 1998 (DJF) using the Regional Climate System Model (RCSM). In the seasonal hindcast simulation, in which the twice-daily National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis was used for the initial conditions and time-dependent boundary forcing, RCSM has simulated realistically the temporal and spatial variations of precipitation in California and stream flow in a northern California coastal basin. For the headwater basin of the Russian River in the northern California Coast Ranges, the Topography-Based Hydrologic Model (TOPMODEL) forced by observed daily precipitation resulted in a correlation coefficient of 0.88 between observed and simulated DJF stream flow. In the coupled stream flow hindcast, the authors obtained a correlation coefficient of 0.7 between simulated and...

Summer Differences among Arctic Ecosystems in Regional Climate Forcing

Biome differences in surface energy balance strongly affect climate. However, arctic vegetation is considered sufficiently uniform that only a single arctic land surface type is generally used in climate models. Field measurements in northern Alaska show large differences among arctic ecosystem types in summer energy absorption and partitioning. Simulations with the Arctic Regional Climate System Model demonstrate that these variations in land surface parameters and ecological processes cause variation in surface fluxes that is sufficiently large to affect the regional climate. Plausible changes in arctic vegetation in response to high-latitude warming would feed back positively to local summer warming. This local warming could extend into the boreal zone. Climate feedbacks that operate during the growing season are particularly likely to impact vegetation and ecosystem properties. These field and model results suggest that vegetation changes within a biome could be climatically important and warrant consideration in regional climate modeling.

Development of an Antarctic Regional Climate System Model. Part I: Sea Ice and Large-Scale Circulation

Abstract A coupled atmosphere–ice regional model previously used for simulations in the Arctic has been implemented in the Antarctic. Three 14-month simulations were performed for 1988–89, with different oceanic specifications. The year 1988 was interesting as there were several sensible heat polynya events in the Cosmonaut Sea region, the investigation of which is the goal of future finer-resolution simulations. Overall, the regional climate model produces reasonable simulations of the Antarctic at 100-km resolution. Root-mean-square errors range from 4 hPa in surface pressure, 4 K in near-surface air temperature, and 3 m s−1 in near-surface winds, to 1 K in air temperature and 2 m s−1 in winds at the 500-hPa level. Tests of the coupled system response to oceanic heat flux suggest that the sea-ice simulation is more sensitive than the atmospheric circulation, but it could be expected that the atmosphere would respond to these changes in sea ice over longer time periods than those of interest here. This s...

Development of an Antarctic Regional Climate System Model. Part II: Station Validation and Surface Energy Balance

Abstract In this, the second part of the analysis of an Antarctic regional climate system model, the model results and analyses are compared to a series of observational data from automated weather stations at a number of Antarctic stations, radiosonde launches, and surface energy balance climatology. The observational analyses show significant biases in comparison with station data, which is attributable in part to the errors in and low resolution of the elevation dataset. This is a factor in model performance also. Further, a dominant factor in the generation of the model biases is the simulation of atmospheric water vapor and cloud. The known “cold” bias in the clear-sky longwave radiation scheme is amply compensated for by excessive cloudiness in many cases. The strong vertical moisture transport contributes to the excessive cloud formation. The biases explored in detail in this paper are common to regional and global simulations of the Antarctic region and highlight areas in which model development s...

Antarctic regional modelling of atmospheric, sea-ice and oceanic processes and validation with observations

AbstractHigh-latitude interactions of local-scale processes in the atmosphere-ice-ocean system have effects on the local, Antarctic and global climate. Phenomena including polynyas and leads are examples of such interactions which, when combined, have a significant impact on larger scales. These small-scale features, which are typically parameterized in global models, can be explicitly simulated using high-resolution regional climate system models. As such, the study of these interactions is well suited to a regional model approach and is considered here using the Arctic Regional Climate System Model (ARCSyM). This model has been used for many simulations in the Arctic, and is now implemented for the Antarctic. Observations of such processes in the Antarctic are limited, which makes model validation difficult. However, using the best available observations for an annual cycle, we have determined a suite of model parameterization which allows us to reasonably simulate the Antarctic climate. This work considers a fine-resolution (20 km) simulation in the Cosmonaut Sea region, with the eventual goal of elucidating the mechanisms in the formation and maintenance of the sensible-heat polynya which is a regular occurrence in this area. It was found in an atmosphere-sea-ice simulation that the ocean plays an important role in regulating the sea-ice cover in this region in compensating for the cold atmospheric conditions.

DOWNSCALED CLIMATE AND STREAMFLOW STUDY OF THE SOUTHWESTERN UNITED STATES1

ABSTRACT: Downscaling coarse resolution climate data to scales that are useful for impact assessment studies is receiving increased attention. Basin‐scale hydrologic processes and other local climate impacts related to water resources such as reservoir management, crop and forest productivity, and ecosystem response require climate information at scales that are much finer than current and future GCM resolutions. The Regional Climate System Model (RCSM) is a dynamic downscaling system that has been used since 1994 for short‐term precipitation and streamflow predictions and seasonal hindcast analysis with good skill. During the 1997–1998 winter, experimental seasonal forecasts were made in collaboration with the NOAA Climate Prediction Center and UCLA with promising results. Preliminary studies of a control and 2°CO2 perturbation for the southwestern U.S. have been performed.

Modeling clouds and radiation for the November 1997 period of SHEBA using a column climate model

A column version of the Arctic regional climate system model (ARCSYM) has been developed for testing general circulation model parameterizations in the Arctic. The ARCSYM column model has been employed for a 23‐day period in November to simulate conditions over a multiyear ice floe that has been the site of intensive observations as part of the Surface Heat Budget of the Arctic (SHEBA) project. The large‐scale tendencies of temperature, moisture, and wind are specified with values obtained from a special column data set obtained from the European Centre for Medium‐Range Weather Forecasting. Comparisons between the ARCSYM column simulations and SHEBA data reveal that modeled temperature profiles are too cold aloft and generally too warm in the boundary layer. The occurrence of low clouds is severely underpredicted while the high cloud fraction is over predicted. The modeled longwave radiative cooling at the surface is 1.5–3 times as large as that observed. Much of this bias is related to problems with the treatment of clear‐sky radiative transfer and in the simulated cloud optical properties. At the same time, the magnitude of modeled downward sensible heat flux at the surface is much too large. This has been related, in part, to the method for scaling temperature at the lowest modeled level to its surface air value under conditions of strong static stability. The importance of properly treating longwave radiative transfer under extremely cold, clear‐sky conditions is evident in the sensitivity studies. The best simulation of cloud properties was achieved by assuming liquid cloud processes and properties at temperatures above 255 K. This temperature is significantly colder than that used in many climate models. The occurrence of supercooled clouds in the simulation dramatically reduced longwave cooling at the surface due to increases in the optical depth and fractional coverage of clouds. Results from a coupled sea ice‐atmosphere simulation reveal that improvements in the atmospheric parameterizations are enhanced when the system is coupled.

Impact of tundra ecosystems on the surface energy budget and climate of Alaska

The sensitivity of regional terrestrial climate to the characteristics of tundra ecosystems has been investigated by a series of sensitivity experiments concentrating on the summer of 1995. Validation of the NCAR Land Surface Model and the Arctic Regional Climate System Model for this season indicate their adequacy for this study. Comparisons of the simulated climate in response to a wet meadow tundra or a dry heath tundra results in an expected cooling and moistening of both the local area and the adjoining sea ice and forested regions. The impact of atmospheric cloud‐radiation feedbacks is to reduce the cooling as the summer progresses, although moistening continues, associated with increased precipitation in some areas. The spatial variability of the response is dependent upon prevailing synoptic conditions, which act to enhance moisture advection in certain areas. This study indicates that vegetation variation within the Arctic has substantial climatic effects that extend beyond the Arctic. In addition, the perturbations in the summer season could have profound implications of Arctic wintertime climate and issues of snow‐albedo feedback and spring melt.

Five‐minute, 1/2°, and 1° data sets of continental watersheds and river networks for use in regional and global hydrologic and climate system modeling studies

A major shortcoming of the land surface component in climate models is the absence of a river transport algorithm. This issue becomes particularly important in fully coupled climate system models (CSMs), where river transport is required to close and realistically represent the global water cycle. The development of a river transport algorithm requires knowledge of watersheds and river networks at a scale that is appropriate for use in CSMs. These data must be derived largely from global digital topographic information. The purpose of this paper is to describe a new data set of watersheds and river networks, which is derived primarily from the TerrainBase 5′ Global DTM (digital terrain model) and the CIA World Data Bank II. These data serve as a base map for routing continental runoff to the appropriate coast and therefore into the appropriate ocean or inland sea. Using this data set, the runoff produced in any grid cell, when coupled with a routing algorithm, can easily be transported to the appropriate water body and distributed across that water body as desired. The data set includes watershed and flow direction information, as well as supporting hydrologic data at 5′, 1/2°, and 1° resolutions globally. It will be useful in fully coupled land‐ocean‐atmosphere models, in terrestrial ecosystem models, or in stand‐alone macroscale hydrologic‐modeling studies.

Eastern Asian hydrometeorology simulation using the Regional Climate System Model

We present the hydrometeorology of eastern Asia during April 1995 simulated by the Regional Climate System Model. The amount and location of simulated monthly precipitation agrees well with observations. Soil water content variation was closely correlated with precipitation. Land-surface evaporation and the surface energy budget were strongly controlled by soil moisture content. A sensitivity test with reduced initial soil moisture content suggested that near-surface soil moisture spins up quickly after heavy precipitation events. However, variations in the initial soil moisture field may alter details of the simulated precipitation which can introduce further complexity in climate simulations.

Snow‐albedo feedback and the spring transition in a regional climate system model: Influence of land surface model

Using the Arctic regional climate system model (ARCSYM), we investigate the spring seasonal transition and mechanisms controlling snowmelt over a domain covering the northern half of Alaska. Annual simulations for 1992 comparing the Biosphere‐Atmosphere Transfer Scheme (BATS) and the land surface model scheme (LSM) show that the BATS experiment enters the spring transition with respect to the large‐scale atmospheric regime approximately one month earlier than observed climate and the LSM experiment transitions a month later than observed, even though the air temperature in the LSM experiment is generally warmer than in the BATS experiment. A more detailed examination reveals that each simulation commences and completes the snowmelt period at about the same time but that the LSM snowmelt is more rapid than in the BATS experiment. Controlling the snowmelt is the initial snowpack depth and the surface energy budget, both of which involve a complex series of feedbacks between shortwave and longwave radiation, cloud, surface turbulent fluxes, and vegetation. The snowmelt over tundra regions dominates the more rapid snowmelt seen in the LSM simulation. It is determined that the most crucial differences between the BATS and the LSM schemes are the partitioning of net ground heat flux between patches of snow and bare ground and the formulation of snow albedo.