Showing papers on "Precipitation published in 1995"

Climatological Characterization of Three-Dimensional Storm Structure from Operational Radar and Rain Gauge Data

Abstract: Three algorithms extract information on precipitation type, structure, and amount from operational radar and rain gauge data. Tests on one month of data from one site show that the algorithms perform accurately and provide products that characterize the essential features of the precipitation climatology. Input to the algorithms are the operationally executed volume scans of a radar and the data from a surrounding rain gauge network. The algorithms separate the radar echoes into convective and stratiform regions, statistically summarize the vertical structure of the radar echoes, and determine precipitation rates and amounts on high spatial resolution. The convective and stratiform regions are separated on the basis of the intensity and sharpness of the peaks of echo intensity. The peaks indicate the centers of the convective region. Precipitation not identified as convective is stratiform. This method avoids the problem of underestimating the stratiform precipitation. The separation criteria are...

Trends in high-frequency climate variability in the twentieth century

Abstract: HIGH-FREQUENCY climate variability is a fundamental aspect of climate. Understanding climate change demands attention to changes in climate variability and extremes1, but knowledge of the recent behaviour of these variables has been limited by the unavailability of long-term high-resolution data. Climate simulations incorporating increased greenhouse-gas concentrations2-9 indicate that a warmer climate could result in a decrease in high-frequency temperature variability (analogous to the decrease in variability observed from the poles to the tropics, and from winter to summer10) and an increase in the proportion of precipitation occurring in extreme events. Here we analyse high-frequency temperature and precipitation data from hundreds of sites spread over Australia, China, the former Soviet Union and the United States over the past 30 to 80 years. Day-to-day temperature variability is seen to have decreased in the Northern Hemisphere, and-at least within the United States-the proportion of total precipitation contributed by extreme, one-day events has increased significantly. We find that although the notion of a recent increase in interannual temperature variability is supported by data from the past few decades11, the longer data records indicate that this trend is an aberration.

A Seasonal Snow Cover Classification System for Local to Global Applications

Abstract: A new classification system for seasonal snow covers is proposed. It has six classes (tundra, taiga, alpine, maritime, prairie, and ephemeral, each class defined by a unique ensemble of textural and stratigraphic characteristics including the sequence of snow layers, their thickness, density, and the crystal morphology and grain characteristics within each layer. The classes can also be derived using a binary system of three climate variables: wind, precipitation, and air temperature. Using this classification system, the Northern Hemisphere distribution of the snow cover classes is mapped on a 0.5° lat × 0.5° long grid. These maps are compared to maps prepared from snow cover data collected in the former Soviet Union and Alaska. For these areas where both climatologically based and texturally based snow cover maps are available, there is 62% and 90% agreement, respectively. Five of the six snow classes are found in Alaska. From 1989 through 1992, hourly measurements, consisting of 40 thermal and...

Long-Term Radar Observations of the Melting Layer of Precipitation and Their Interpretation

Abstract: In this study, 600 h of vertically pointing X-band radar data and 50 h of UHF boundary layer wind profiler data were processed and analyzed to characterize quantitatively the structure and the causes of the radar signature from melting precipitation. Five classes of vertical profiles of reflectivity in rain were identified, with three of them having precipitation undergoing a transition between the solid and liquid phase. Only one of them, albeit the most common, showed a radar brightband signature. In-depth study of the bright band and its dependence on precipitation intensity reveals that the ratio of the brightband peak reflectivity to the rainfall reflectivity is constant at 8 dB below 0.5 mm h−1 and then increases to reach 13 dB at 2.5 mm h−1 and 16 dB at 5 mm h−1. The equivalent reflectivity factor of snow just above the melting layer is on average 1–2 dB below the reflectivity of rain just below the melting layer, independent of precipitation intensity. The classical brightband explanation...

Predicting the effects of climate change on water yield and forest production in the northeastern United States

Abstract: Rapid and simultaneous changes in temperature, precipitation and the atmospheric concentration of CO2 are predicted to occur over the next century. Simple, well-validated models of ecosystem function are required to predict the effects of these changes. This paper describes an improved version of a forest carbon and water balance model (PnET-II) and the application of the model to predict stand- and regional-level effects of changes in temperature, precipitation and atmospheric CO2 concentration. PnET-II is a simple, generalized, monthly time-step model of water and carbon balances (gross and net) driven by nitrogen availability as expressed through foliar N concentration. Improvements from the original model include a complete carbon balance and improvements in the prediction of canopy phenology, as well as in the computation of canopy structure and photosynthesis. The model was parameterized and run for 4 forest/site combinations and validated against available data for water yield, gross and net carbon exchange and biomass production. The validation exercise suggests that the determination of actual water availability to stands and the occurrence or non-occurrence of soil-based water stress are critical to accurate modeling of forest net primary production (NPP) and net ecosystem production (NEP). The model was then run for the entire NewEngland/New York (USA) region using a 1 km resolution geographic information system. Predicted long-term NEP ranged from -85 to +275 g C m-2 yr-1 for the 4 forest/site combinations, and from -150 to 350 g C m-2 yr-1 for the region, with a regional average of 76 g C m-2 yr-1. A combination of increased temperature (+6*C), decreased precipitation (-15%) and increased water use efficiency (2x, due to doubling of CO2) resulted generally in increases in NPP and decreases in water yield over the region.

Chemical and Isotopic Methods for Quantifying Ground‐Water Recharge in a Regional, Semiarid Environment

Abstract: The High Plains aquifer underlying the semiarid Southern High Plains of Texas and New Mexico, USA was used to illustrate solute and isotopic methods for evaluating recharge fluxes, runoff, and spatial and temporal distribution of recharge. The chloride mass-balance method can provide, under certain conditions, a time-integrated technique for evaluation of recharge flux to regional aquifers that is independent of physical parameters. Applying this method to the High Plains aquifer of the Southern High Plains suggests that recharge flux is approximately 2% of precipitation, or approximately 11 ± 2 mm/y, consistent with previous estimates based on a variety of physically based measurements. The method is useful because long-term average precipitation and chloride concentrations in rain and ground water have less uncertainty and are generally less expensive to acquire than physically based parameters commonly used in analyzing recharge. Spatial and temporal distribution of recharge was evaluated by use of δ2H, δ18O, and tritium concentrations in both ground water and the unsaturated zone. Analyses suggest that nearly half of the recharge to the Southern High Plains occurs as piston flow through playa basin floors that occupy approximately 6% of the area, and that macropore recharge may be important in the remaining recharge. Tritium and chloride concentrations in the unsaturated zone were used in a new equation developed to quantify runoff. Using this equation and data from a representative basin, runoff was found to be 24 ± 3 mm/y; that is in close agreement with values obtained from water-balance measurements on experimental watersheds in the area. Such geochemical estimates are possible because tritium is used to calculate a recharge flux that is independent of precipitation and runoff, whereas recharge flux based on chloride concentration in the unsaturated zone is dependent upon the amount of runoff. The difference between these two estimates yields the amount of runoff to the basin.

The Effect of Eurasian Snow Cover on the Indian Monsoon

Abstract: The authors successfully model and simulate the observed evidence that anomalously high winter/spring Eurasian snow cover is linked to weak rainfall in the following summer Indian monsoon. It is shown that excessive snow cover in February reduces June to September precipitation over India. The excessive snow cover is associated with a weak monsoon characterized by higher sea level pressure over India, a weaker Somali jet, weaker lower tropospheric westerlies, and weaker upper tropospheric easterlies. The weak monsoon is also associated with weaker secondary circulations. The remote response to excessive Eurasian snow cover is to reduce the strength of trade winds in the eastern equatorial Pacific Ocean. Energy used in melting excessive snow reduces the surface temperature over a broad region centered around the Tibetan Plateau. Reduced surface sensible heat flux reduces the midtropospheric temperature over the Tibetan Plateau. The result is to reduce the midtropospheric meridional temperature gra...

Winter Weather Forecasting throughout the Eastern United States. Part IV: Lake Effect Snow

Abstract: This article is the final installment of a four-part series that examines the challenge of forecasting winter weather throughout the eastern United States. This paper examines the problems and challenges of forecasting lake effect snows. The climatology of lake-induced snowfall is reviewed, and an overview of the characteristics and evolution of these mesoscale precipitation bands is presented. The atmospheric conditions associated with five different types of lake snow bands are discussed. The abilities of remote sensors to resolve, and dynamical models to simulate, these mesoscale events are also explored. Finally, several techniques designed to improve operational forecasts of lake effect snow are described in detail, along with representative case studies.

Relation between century-scale Holocene arid intervals in tropical and temperate zones

Abstract: CLIMATE records from lake sediments in tropical Africa, Central America and west Asia show several century-scale arid intervals during the Holocene1–10. These may have been caused by temporary weakening of the monsoonal circulation associated with reduced northward heat transport by the oceans7 or by feedback processes stimulated by changes in tropical land-surface conditions10. Here we use a lake-sediment record from the montane Mediterranean zone of Morocco to address the question of whether these events were also felt in temperate continental regions. We find evidence of arid intervals of similar duration, periodicity and possibly timing to those in the tropics. But our pollen data show that the forest vegetation was not substantially affected by these events, indicating that precipitation remained adequate during the summer growing season. Thus, the depletion of the groundwater aquifer that imprinted the dry events in the lake record must have resulted from reduced winter precipitation. We suggest that the occurrence of arid events during the summer in the tropics but during the winter at temperate latitudes can be rationalized if they are both associated with cooler sea surface temperatures in the North Atlantic.

Freshwater outflow and Subtropical Convergence influence on phytoplankton biomass on the southern Brazilian continental shelf

Abstract: The present study discusses the role of different continental shelf water masses on inorganic nutrient levels and on phytoplankton biomass along the southern Brazilian coast during October 1987 and September 1988. In this productive area, variability of phytoplankton biomass has been related to the seasonal latitudinal displacement of the Subtropical Convergence and to the freshwater outflow of La Plata River and Patos Lagoon. Very distinct precipitation rates, as a consequence of the ENSO (El Nin˜o-Southern Oscillation) cycle, preceding the two sampled periods of this study, allowed a first evaluation of the impact of this event on freshwater outflow and shelf phytoplankton biomass. The amount of chlorophyll in shelf waters was directly related to nutrients supplied by the Coastal Water (i.e. freshwater outflow), Subtropical and Subantarctic Waters. Comparing the results of this study with previous cruises performed in the area, it was found that high chl a concentrations are common features during periods of elevated precipitation rates. Apart from nutrient input by freshwater and the consequent changes in the vertical profiles of density, the extreme precipitation rates are also associated with different wind patterns, which, in turn, control the presence of particular water masses in the euphotic zone. Our results suggest that ENSO events have an important impact on the variability of phytoplankton production, and thus should affect biogeochemical cycles in the southern Brazilian coastal areas.

The climate-carbon isotope relationship in tree rings and the significance of site conditions

Abstract: Considerable complexity exists regarding the relationship between tree ring δ 13 C and climate. We proceed from the theoretically derived and experimentally confirmed finding that the relative humidity of the atmosphere but also the soil water content can influence the stomatal opening of plant leaves and consequently the δ 13 C of photosynthetically fixed carbon. Therefore, the potential to reconstruct humidity variations by δ 13 C in tree rings should depend on the water conditions at the site where the trees are growing. We analysed δ 13 C series (3-year ring samples) of cellulose of beech trees ( Fagus silvatica ) covering the time period from 1934 to 1989 for 3 sites in Switzerland: a relatively dry and a humid site close together and another dry site 30 km distant. The δ 13 C series from the two dry sites are closely interrelated and are inversely correlated to the total precipitation amount of the months May + June + July This is most expressed for first differences, i.e., differences of consecutive values, while the long-term trends are more strongly influenced by biological effects. A multivariate analysis shows that at the dry sites, δ 13 C is relatively high for dry/warm summers and low for cool/wet summers. The respective correlations for the humid site are less distinct. In addition, we compared average δ 13 C values for beech, pine and spruce trees from sites differing in soil moisture conditions. For all species we found that the drier the sites the more positive the tree δ 13 C values are. We conclude that at relatively dry sites in temperate-moist climatic conditions, short-term precipitation variations can be reconstructed by δ 13 C measurement on tree rings of beech and probably also of the conifers pine and spruce. DOI: 10.1034/j.1600-0889.47.issue3.4.x

Analysis of daily variability of precipitation in a nested regional climate model : comparison with observations and doubled CO2 results, Global Planet

Abstract: Abstract We analyze daily mean, variability, and frequency of precipitation in two continuous 3 1 2 year long climate simulations over the continental U.S., one for present conditions and one for conditions under doubled carbon dioxide concentration, conducted with a regional climate model (RegCM) nested in a general circulation model (GCM). The purpose of the work is to analyze model errors and limitations in greater detail than previously done and to calculate quantities that eventually will be used to form climate change scenarios that account for changes in daily variability of precipitation. The models used are a version of the NCAR Community Climate Model (CCM) and the climate version (RegCM) of the NCAR/Penn State mesoscale model (MM4) at 60 km horizontal grid point spacing. Model output is compared with a 30-year daily observational data set for mainly two regions of the U.S.: the Northwest, and the central Great Plains. Statistics compared include mean daily precipitation, mean daily intensity, frequency, transition probabilities, quantiles of precipitation intensity, and interquartile ranges. We discuss how different measures of daily precipitation lead to different conclusions about the quality of the control run. For example, good agreement between model and observed data regarding mean daily precipitation usually results from compensating errors in the intensity and frequency fields (too high frequency and too low intensity). We analyze how detailed topographic features of the RegCM enhance the simulation of daily precipitation compared to the CCM simulation. In general, errors in all measures are smallest at the Northwest grid points, and the damping of the seasonal cycle of mean daily precipitation from the coast to inland Oregon is basically well reproduced. However, some errors in the frequency and intensity fields can be traced to inadequate representation of topography, even with a horizontal resolution of 60 km. Differences in the control and doubled CO2 runs (for both RegCM and CCM) for these regions are also presented. The most significant changes for the RegCM grid points is increased variability of daily precipitation under doubled CO2 conditions. Areas with significant changes (both increases and decreases) of precipitation frequency and intensity are found. There are some areas where frequency decreases, but precipitation mean daily amounts increase. Such changes, which would be masked by more traditional analyses of precipitation change, are important from a climate impacts point of view. The limitations on the analyses posed by small sample sizes are discussed.

Simulation and Diagnosis of the Regional Summertime Precipitation Climatology of South America

Abstract: The regional precipitation climatology of South America during austral summer is studied by means of an R30 general circulation model (GCM). Results from perpetual January experiments, which differ only in their distributions of topography and sea surface temperature (SST), are presented. The precipitation field of the most realistic experiment compares well with the observed January precipitation climatology of South America. reproducing, in particular, five regions of maximum precipitation. To understand how structure in the surface conditions is mapped onto the precipitation field. the results of the three GCM experiments are compared. Continentality, through the generation of a thermal low, is responsible for much of the structure in the modeled precipitation field of South America. Topography introduces orographic precipitation maxima in the Central and Southern Andes and modifies precipitation rates elsewhere. Longitudinal structure in SSTs, which is also largely an expression of continenta...

Stochastic characterization of regional circulation patterns for climate model diagnosis and estimation of local precipitation

Abstract: Two statistical approaches for linking large-scale atmospheric circulation patterns and daily local rainfall are applied to GCM (general circulation model) climate simulations. The ultimate objective is to simulate local precipitation associated with altered climate regimes. Two regions, one in the Pacific-American sector (western region) and one in the American-Mid-Atlantic sector (eastern region), are explored. The first method is based on Classification and Regression Trees (CART) analysis. The CART method classifies observed daily sea level pressure (SLP) fields into weather types that are most strongly associated with the presence/absence of rainfall at selected index stations. After applying this method to historical SLP observations, precipitation simulations associated with GCM SLP output were validated in terms of probability of occurrence and survival time of the weather states identified by the CART analysis. Daily rainfall time series were then generated from weather classes derived b...

Analysis of daily variability of precipitation in a nested regional climate model: comparison with observations and doubled CO2 results

Abstract: We analyze daily mean, variability, and frequency of precipitation in two continuous 3 1 2 year long climate simulations over the continental U.S., one for present conditions and one for conditions under doubled carbon dioxide concentration, conducted with a regional climate model (RegCM) nested in a general circulation model (GCM). The purpose of the work is to analyze model errors and limitations in greater detail than previously done and to calculate quantities that eventually will be used to form climate change scenarios that account for changes in daily variability of precipitation. The models used are a version of the NCAR Community Climate Model (CCM) and the climate version (RegCM) of the NCAR/Penn State mesoscale model (MM4) at 60 km horizontal grid point spacing. Model output is compared with a 30-year daily observational data set for mainly two regions of the U.S.: the Northwest, and the central Great Plains. Statistics compared include mean daily precipitation, mean daily intensity, frequency, transition probabilities, quantiles of precipitation intensity, and interquartile ranges. We discuss how different measures of daily precipitation lead to different conclusions about the quality of the control run. For example, good agreement between model and observed data regarding mean daily precipitation usually results from compensating errors in the intensity and frequency fields (too high frequency and too low intensity). We analyze how detailed topographic features of the RegCM enhance the simulation of daily precipitation compared to the CCM simulation. In general, errors in all measures are smallest at the Northwest grid points, and the damping of the seasonal cycle of mean daily precipitation from the coast to inland Oregon is basically well reproduced. However, some errors in the frequency and intensity fields can be traced to inadequate representation of topography, even with a horizontal resolution of 60 km. Differences in the control and doubled CO2 runs (for both RegCM and CCM) for these regions are also presented. The most significant changes for the RegCM grid points is increased variability of daily precipitation under doubled CO2 conditions. Areas with significant changes (both increases and decreases) of precipitation frequency and intensity are found. There are some areas where frequency decreases, but precipitation mean daily amounts increase. Such changes, which would be masked by more traditional analyses of precipitation change, are important from a climate impacts point of view. The limitations on the analyses posed by small sample sizes are discussed.

Global atmospheric water balance and runoff from large river basins

Abstract: Atmospheric vapour flux convergence is introduced for the estimation of the water balance in a river basin. The global distribution of vapour flux convergence, - ΔH · Q is estimated using the European Centre for Medium-Range Weather Forecasts global analysis data for the period 1980-1988. From the atmospheric water balance, the annual mean - ΔH · Q can be interpreted as the precipitation minus evaporation. The estimated - ΔH · Q is compared with the observed discharge data in the Chao Phraya river basin, Thailand. The mean annual values are not identical, but their seasonal change corresponds very well. The four year mean - ΔH · Q is also compared with the climatological runoff of nearly 70 large rivers. The multi-annual mean runoff is calculated from the Global Runoff Data Centre data set and used for the comparison. There is generally a good correspondence between the atmospheric water balance estimates and the runoff observations on the ground, especially in the mid- and high latitudes of the northern hemisphere. However, there are significant differences in many instances. The results emphasize the importance of accurate routine observations in both the atmosphere and river runoff. The global water balance of the zonal mean is compared with prior estimates, and the estimated value from this study is found to be smaller than previous estimates. The annual water balance in each ocean and each continent are also compared with previous estimates. Generally, the global runoff estimation using the conventional hydrological water balance is larger than the result by the atmospheric water balance method. Annual freshwater transport is estimated by atmospheric water balance combined with geographical information. The results show that the same order of freshwater is supplied to the ocean from both the atmosphere and the surrounding continents through rivers. The rivers also carry approximately 10% of the global annual freshwater transport in meridional directions as zonal means.

Physical interpretations of regional variations in the scaling exponents of flood quantiles

Abstract: The concepts of simple scaling and multiscaling provide a new theoretical framework for the study of spatial or regional flood frequency relations and their underlying physical generating mechanisms. In particular, the scaling exponents in the power law relationship between flood quantiles and drainage areas contain a ‘basic signature of invariance’ regarding the spatial variability of floods, and therefore suggest different hypotheses regarding their physical generating mechanisms. If regional floods obey simple scaling, then the slopes do not vary with return periods. On the other hand, if regional floods obey multiscaling, then the slopes vary with return periods in a systematic manner. This premise is expanded here by investigating the empirical variations in the scaling exponents in three states of the USA: New York, New Mexico and Utah. Distinct variations are observed in the exponents among several regions within each state. These variations provide clear empirical evidence for the presence of both simple scaling and multiscaling in regional floods. They suggest that snowmelt-generated floods exhibit simple scaling, whereas rainfall-generated floods exhibit multiscaling. Results from a simple rainfall-runoff experiment, along with the current research on the spatial scaling structure of mesoscale rainfall, are used to give additional support to these physical hypotheses underlying two different scaling structures observed in floods. In addition, the rainfall-runoff experiment suggests that the behaviour of the flood exponents in small basins is determined by basin response rather than precipitation input. This finding supports the existence of a critical drainage area, as has been reported for the Appalachia flood data in the USA, such that the spatial variability in floods in basins larger than the critical size is determined by the precipitation input, and in basins smaller than the critical size is determined by the basin response.

Construction of a 1961-1990 European climatology for climate change modelling and impact applications

Abstract: A 1961–1990 mean monthly climatology for a ‘greater European’ region extending from 32°W to 66°E and from 25° to 81°N has been constructed at a resolution of 0.5°latitude by 0.5° longitude for a suite of nine surface climate variables: minimum, maximum, and mean air temperature; precipitation totals; sunshine hours; vapour pressure; wind speed; and (ground) frost day and rain day ( > 0.1 mm) frequencies. This climatology has been constructed from observed station data distributed across the region. Station frequencies range from 936 (wind speed) to 3078 (precipitation). Over 95 per cent of these data are based on observations between 1961 and 1990 and over 90 per cent were supplied by individual national meteorological agencies (NMAs) on specific request. For four variables, some standardization of the data had to be performed because different countries supplied data under different definitions. Thus cloud cover had to be converted to sunshine hours, relative humidity to vapour pressure, air frost days to ground frost days and rain days > 1 mm to rain days > 0.1 mm. The interpolation of the station data to the grid used elevation as one of the predictor variables and thus enabled three climate surfaces to be produced for each variable, reflecting the minimum, mean, and maximum elevation within each 0.5° by 0.5° cell. Subsets of stations were used for the interpolation of each variable, the selection being based on optimizing the spatial distribution, source priority and length of record. The accuracy of the various interpolations was assessed using validation sets of independent station data (i.e. those not used in the interpolation). Estimated mean absolute errors (MAE) ranged from under 4 per cent for vapour pressure to about 10 per cent for precipitation and up to 20 per cent for wind speed. The accuracy of the interpolated surfaces for minimum and maximum temperature was between 0.5°C and 0.8°C. We believe these results constitute the first climatology that has been constructed for this extensive European region at such a fine spatial resolution (0.5° by 0.5°) from relatively dense station networks, for three different elevation surfaces and for a wide range of surface climate variables, all expressed with respect to a standard 30-year period. The climatology is already being used by researchers for applications in the areas of ecosystem modelling, climate change impact assessment and climate model validation, and is available from the authors.

Global climate sensitivity to tropical deforestation

Abstract: Regional to global-scale climate sensitivity to tropical deforestation is simulated using a modified version of the NCAR Community Climate Model (CCM1-Oz) which includes a mixed-layer ocean model, a 3-layer sea-ice model and BATS (the Biosphere-Atmosphere Transfer Scheme). A fourteen-year control integration is followed by a six year deforestation experiment in which the tropical moist forest throughout the Amazon Basin, S.E. Asia and tropical Africa is replaced by scrub grassland. The three deforested regions sustain different impacts on their regional climates. The largest disturbances occur in the Amazon Basin where total precipitation decreases by −437 mm yr −1 , evaporation decreases by −231 mm yr −1 and a marked decrease in moisture convergence is clear, although the surface temperature increases by 0.3 K. In S.E. Asia, surface temperature decreases in 11 months with an annual average cooling of −0.7 K; total evaporation decreases all the year by 130 mm yr −1 ; while the sign of the precipitation changes is strongly seasonal. The African region is least affected by deforestation, although surface net radiation decreases year-round and there is a detectable decrease in moisture convergence in the dry season. Regional responses to deforestation differ because regional circulation patterns are affected differently. For example, while ground surface temperatures increase in the Southern Amazon and over this basin as a whole, the northern Amazon, S.E. Asia and Africa all exhibit decreases in ground surface temperatures. The modification of atmospheric circulation patterns over deforested tropical regions prompts climate responses distant from the disturbance. Impacts of tropical deforestation include a disturbance of the Asian monsoon and small but statistically significant changes in climate in the middle and high latitudes.

Relative contributions of land and ocean processes to precipitation variability

Abstract: A series of general circulation model simulations are used to quantify the relative contributions of land surface and ocean variability to variability in precipitation. The simulations show that land surface processes contribute significantly to the variance of annual precipitation over continents. In contrast, ocean processes acting alone have a much smaller effect, particularly in midlatitudes. The precipitation variability reflects local evaporation variability and associated hydrological persistence, and it responds most strongly to the land surface during summer, when moist convection dominates.

A Double-Moment Multiple-Phase Four-Class Bulk Ice Scheme. Part II: Simulations of Convective Storms in Different Large-Scale Environments and Comparisons with other Bulk Parameterizations

Abstract: Part I of this study described a detailed four-class bulk ice scheme (4ICE) developed to simulate the hydro-meteor profiles of convective and stratiform precipitation associated with mesoscale convective systems. In Part II, the 4ICE scheme is incorporated into the Goddard Cumulus Ensemble (GCE) model and applied without any “tuning” to two squall lines occurring in widely different environments, namely, one over the “Pica) ocean in the Global Atmospheric Research Program's (GARP) Atlantic Tropical Experiment (GATE) and the other over a midlatitude continent in the Cooperative Huntsville Meteorological Experiment (COHMEX). Comparisons were made both with earlier three-class ice formulations and with observations. In both cases, the 4ICE scheme interacted with the dynamics so as to resemble the observations much more closely than did the model runs with either of the three-class ice parameterizations. The following features were well simulated in the COHMEX case: a lack of stratiform rain at the s...

Interactions of Radiation and Convection in Simulated Tropical Cloud Clusters

Abstract: A two-dimensional cumulus ensemble model is used to study the interactions of radiation and convection in tropical squall cloud clusters. The model includes cloud-scale and mesoscale dynamics, an improved bulk ice microphysics parameterization, and an advanced interactive radiative transfer scheme. The life cycle of a tropical squall line is simulated over a 12-h period using thermodynamic and kinematic initial conditions as well as large-scale advective forcing typical of a GATE Phase III squall cluster environment. The focus is on the interaction and feedback between longwave (or IR) radiation and cloud processes. It will be shown that clew-sky IR cooling enhances convection and, hence, surface precipitation. Simulation results reveal an increase of surface precipitation by ∼15% (∼1.7 mm) over a 12-b period due to this clear-sky cooling. With fully interactive IR radiative heating, direct destabilization of clouds via IR radiative top cooling and base warming generates more turbulence and contr...

Climate, Snow Cover, Glaciers, and Runoff in the Tien Shan, Central Asia

Abstract: The Pica Shan, a mountainous region located on the northern periphery of central Asia, has a wide range of climatic and hydrological conditions. On the basis of long term data from 348 meteorological and glaciological stations, the annual distribution of precipitation in different regions and elevational zones of the Tien Shan was calculated. Major climatic features are the entrance of moisture during spring-summer, small winter precipitation, decrease of precipitation towards the east and the center of the mountains or with distance up valleys, and increase of precipitation with altitude up to crest-lines of ranges. Annual total evaporation from snow can be 50–60 mm per year, reaching 30 percent of snow accumulation. Four main groups of rivers were identified: rivers with mainly snow nourishment, rivers with mainly glacial nourishment, rivers with mainly rain nourishment, and rivers with mainly ground water nourishment. Coefficient of runoff variation in Tien Shan's rivers is about 0.20, and coefficient of glacial runoff variation is about 0.15. Glacial runoff is 15–20 percent of the total volume of river runoff.

Flashover problems caused by ice build up on insulators

Abstract: The number of single-phase faults in the transmission networks in wintertime increases substantially during cold atmosphere precipitation and after ice accretions followed by a rise in air temperature above 0/spl deg/C. >

Climate trends in the South-west Pacific

Abstract: Temperature and precipitation trends are described for newly homogenized historical climate data sets for the South-west Pacific. Regions that exhibit similar temperature and precipitation trends and variability are defined, and the temperature and precipitation time series aggregated according to these regions. Four temperature regions show distinctive trends: two regions south-west of the South Pacific Convergence Zone (SPCZ), which display steady climate warming; two regions north-east of the SPCZ, which cooled during the 1970s, and warmed in the 1980s. Annual anomalies differ in response to the El Nino-Southern Oscillation (ENSO) phenomena, depending on the region's position with respect to a pivotal line along the SPCZ. The climate warming apparent throughout much of the south-west Pacific comes from sites where there can be no question of any urban influence. Five main South-west Pacific precipitation regions show distinctive trends that are connected to the main climatological features. Four New Zealand precipitation subregions relate to the interaction of the main climatological features with local orography. Annual precipitation anomalies show marked variability and are also affected by ENSO in most regions. The pivotal line for the response of precipitation regions lies just to the north-east of the SPCZ. The ENSO relationships with precipitation appear consistent on both annual and interdecadal time-scales. From these climatic trends four climatic response regions are recognized in the South-west Pacific.