Regional Rain Research Articles

Melting layer characteristics at different climatic conditions in the Indian region: Ground based measurements and satellite observations

Melting layer height, which is normally assumed to be the limits of rain region, is an important parameter to consider the performance of earth space communication link above 10 GHz. In this paper, the variation of melting layer observed by a vertically looking Micro Rain Radar (MRR) for 3 years has been presented for two different climatic locations in Indian tropical region — Shillong (25°34′ N, 91°53′ E, 1050 m) and Trivandrum (8°29′ N, 76°57′ E, 4 m). The analyses show that the variation is quite significant for different months in Shillong but not for Trivandrum. The height of melting layer shows a strong correlation with ground temperature of these locations. The results agree well with the long term Tropical Rainfall Measuring Mission (TRMM) measurements of melting layer indicating suitability of using TRMM data for such study. A comparison of MRR with the nearest Radiosonde measurement indicates that MRR can have potential application in the study of zero degree isotherm height in rainy conditions. Results also clearly indicate that the assumption of constant rain height is not a valid one for all tropical locations.

FUZZY WEIGHT CONTROLLER BASED CELL-SITE DIVERSITY FOR RAIN FADING MITIGATION IN LMDS NETWORKS IN THE TROPICS

Local multipoint distribution service (LMDS) is a broadband wireless access technology that operates at microwave frequencies above 25GHz. However, severe attenuation due to excessive rain in tropical regions presents a major challenge for achieving reliable communication over such frequencies. To overcome this problem, cell-site diversity (CSD) can be deployed in cellular- type LMDS networks. In this paper, we address the problem of reliable communication for LMDS networks in heavy rain regions by proposing a fuzzy weight controller based cell-site diversity (FWC- CSD) scheme. Rain cells are randomly simulated in an LMDS network to analyze the system performance using the proposed FWC-CSD scheme. Simulation results show that the proposed scheme yields improved performance in terms of average outage probability and throughput while maintaining the overall quality of service.

Dayside field‐aligned current source regions

The source regions of region‐0 (R0), region‐1 (R1), and region‐2 (R2) field‐aligned currents (FACs) were statistically determined using DMSP particle precipitation and magnetometer data. Each FAC sheet originates from more than one region in the magnetosphere, depending on the latitude and the magnetic local time (MLT). R2 originates mostly from the central plasma sheet (CPS) and boundary plasma sheet (BPS) in the morning and from the CPS, BPS, and inner magnetosphere in the afternoon, all of which are on closed field lines. Near noon, some R2 may originate from the low‐latitude boundary layer (LLBL), which is located near the magnetopause and can be open or closed. R1 mostly maps to the BPS, hence on closed field lines, in morning and afternoon, but near noon, it maps mostly to the LLBL. The LLBL source region can be found more frequently in the dawn–noon sector than in the noon–dusk sector. On the other hand, R0 is located mostly on open field lines and is associated mostly with mantle precipitation. However, the mantle precipitation has a dependency on the polarity of R0. Within up‐flowing R0, sometimes an upward field‐aligned electric field, which accelerates electron downward and retards ion precipitation, modifies mantle distribution to look more like those of polar rain or BPS. This electric field has the opposite polarity to the background electric field that maintains charge‐quasi‐neutrality and that limits some solar wind electrons from entering the magnetosphere in the mantle and polar rain regions. Implications to current generation mechanisms are discussed.

STUDY OF SOME OF THE TECHNICAL AND ECONOMICAL INDICATORS FOR DIFFERENT MECHANIZATION SYSTEMS IN THE SEMI QUARANTEED RAIN REGION

This study was conducted in Nineveh, Humaedat region which located in the semi guaranteed rain region, for the 2004-2005 agricultural season, to see some indicators of economic assessment and technological indicators, by taking data from the four companies (different mechanization systems) to plant wheat and barley crops for making comparison among them for tillage, planting and harvesting to find the values of these indicators of the total agricultural operations and the average of these companies and to compare with some universal values. The average values of the four companies in the total agricultural operation, showed that the fuel consumption was 24.8 L/ha, 21.3 L/hr, specific fuel consumption 0.17 L/kw.hr. The percentage of fuel costs from the total costs 7.8% and the percentage of the fuel cost of mechanization costs 17.5%.While one kw serving area of land 0.76 hectares, the share of the tractors and harvesters of the earth 589 ha/tractor, 688 ha/harvester respectively. the Average of the time work of tractors and harvesters per year 529 and 419 hr/year respectively. The average productivity of the season 0.42 ha/hr, actual productivity 0.85 ha/hr. The work efficiency of the agricultural season was 48%, and the human effort 3.07 man.hr/ha. The agricultural worker share of the land 41.72 ha/man. The cost of mechanization to planting one hectare was 14382 ID. The percentage of mechanization cost of total costs 44%. The effectiveness of total capital was 1.48. The effectiveness of mechanization capital was 3.61 where yields were 264.2 kg/ha.

Light rain events change over North America, Europe, and Asia for 1973–2009

AbstractAnalysis of daily precipitation data reveals diverse long‐term trends of light rain events in North America (NA), Europe (EU), and Asia (AS), but overall a decreasing trend is found from 1973–2009, especially over East Asia, where a remarkable shift from light to heavy rain events has been observed. Although it has been argued that global warming may lead to a shift from light to heavy rain, regionally little correspondence is found between light rain trends and temperature/precipitable water (PW) trends. This argues for the need to include other factors such as atmospheric circulation and aerosol changes that affect regional rain rates and cloud processes. Copyright © 2010 Royal Meteorological Society

Pollen–vegetation relationships for pine and spruce in southeast Poland on the basis of volumetric and Tauber trap records

The aim of the study was to determine the pollen–vegetation relationship for Pinus and Picea. Pollen deposition was monitored using Tauber traps in the Roztocze region of Poland. The pine and spruce pollen sums obtained were compared with annual sums recorded in volumetric samplers in the cities of Lublin and Rzeszów. Average values of pollen deposition were compared to a detailed inventory of vegetation within a radius of 1 km of the monitoring sites. A more robust vegetation survey, conducted at a distance of 15 km, was used to estimate the proportion of pine and spruce pollen in regional pollen rain. The occurrence of high and low pollen deposition years was studied. Between 2001 and 2006, the data from Lublin and Roztocze produced similar trends in the high or low Pinus pollen sums. The representation of pine in the pollen spectra was very high, due to both its abundance in the regional vegetation and the prevalence of long-distance transport of pine pollen. Comparison of pollen and vegetation data indicates that, in the case of spruce, the distance from the monitoring site and forest structure are the most important factors influencing pollen representation. The problems associated with estimating pollen productivity of both pine and spruce in relation to Poaceae is discussed.

Convective scale structure and evolution of a squall line observed by C-band dual Doppler radar in an arid region of northwestern China

A long-lived and loosely organized squall line moved rapidly across Urumqi, the capital city of Xinjiang Uygur Autonomous Region of China on 26 June 2005, generating hail and strong winds. The squall line was observed by a dual Doppler radar system in a field experiment conducted in 2004 and 2005 by the Chinese Academy of Meteorological Sciences and the local meteorological bureau in northwestern China. The 3D wind fields within the squall line were retrieved through dual Doppler analyses and a variational Doppler radar analysis system (VDRAS). The formation and structure of the squall line as well as the genesis and evolution of embedded convective cells were investigated. During its life period, the squall line consisted of six storm cells extending about 100 km in length, and produced hail of about 25 mm in diameter and strong surface winds up to 11 m s−1. Radar observations revealed a broad region of stratiform rain in a meso-β cyclone, with the squall line located to the west of this. Two meso-γ scale vortices were found within the squall line. Compared to typical squall lines in moist regions, such as Guangdong Province and Shanghai, which tend to be around 300–400 km in length, have echo tops of 17–19 km, and produce maximum surface winds of about 25 m s−1 and temperature variations of about 8°C this squall line system had weaker maximum reflectivity (55 dBZ), a lower echo top (13 km) and smaller extension (about 100 km), relatively little stratiform rainfall preceding the convective line, and a similar moving speed and temperature variation at the surface.

Evaluation of Indian summer monsoon rainfall features using TRMM and KALPANA-1 satellite derived precipitation and rain gauge observation

The study provides a concise and synthesized documentation of the current level of skill of the satellite (3B42RT, 3B42V-6, KALPANA-1) products over Indian regions based on the data gathered during the summer monsoon seasons of 2006, 2007 and 2008. The inter-comparison of satellite products with the rain gauge observations suggests that the TRMM 3B42V6 product could distinctly capture characteristic features of the summer monsoon, such as north–south oriented belt of heavy rainfall along the Western Ghats with sharp gradient of rainfall between the west coast heavy rain region and the rain shadow region to the east, pockets of heavy rainfall along the location of monsoon trough, over the east central parts of the country, over north-east India, along the foothills of Himalayas and over the north Bay of Bengal. The KALPANA-1 and 3B42RT products reproduce only the broadest features of mean monsoon seasonal rainfall. The near real-time products 3B42RT and KALPANA-1 underestimate the orographic heavy rainfall along the Western Ghats of India. The precipitation estimates from TRMM 3B42V6 product, when accumulated over the whole season, could reproduce the observed pattern. However, the TRMM 3B42RT and KALPANA-1 estimates are comparatively lower than the observed rainfall over most parts of the country during the season. Inter comparison reveals that the TRMM 3B42V6 product showed better skill in estimating the daily and seasonal mean rainfall over all India and also over four homogeneous regions of India.

The 11 August 2006 squall‐line system as observed from MIT Doppler radar during the AMMA SOP

AbstractOn the evening of 9 August 2006, a mesoscale convective system (MCS) having a north‐south oriented squall‐line organization formed over the border between Chad and Nigeria. It propagated westward, intensified over Nigeria on 10 August, and reached Niamey (Niger) at 0320 UTC on 11 August. Its passage over Niamey was accompanied by dust lifting and was well tracked by the Massachusetts Institute of Technology (MIT) Doppler radar. The three‐dimensional structure of the airflow and precipitation pattern is investigated from regular radar volume scans performed every ten minutes between 0200 and 0321 UTC. The 3D wind components are deduced from the multiple‐Doppler synthesis and continuity adjustment technique (MUSCAT) applied to a set of three volume scans obtained over a time period of one hour, which are equivalent to a three‐radar observation of the squall line when considering a reference frame moving with the system and the hypothesis of a stationary field.Results of the wind synthesis reveal several features commonly observed in tropical squall lines, such as the deep convective cells in front of the system, fed by the monsoon air and extending up to 15 km altitude, and the well‐marked stratiform rain region at the rear, associated with mesoscale vertical motions. Forward and trailing anvils are clearly identified as resulting from the outflow of air reaching the tropopause and transported to this level by the sloping convective updraughts occurring in a sheared environment. In the northern part, a deeper and stronger front‐to‐rear flow at mid‐levels is found to contribute to the rearward deflection of the leading line and to promote a broader (over 300 km) stratiform cloud region. Eddy vertical transports of the cross‐line momentum mainly accounts for the mid‐level flow acceleration due to a momentum redistribution from low to higher levels. The height distribution of hydrometeors and their associated production terms derived from a one‐dimensional microphysical retrieval model indicate the distinct roles of the convective and stratiform regions in the formation of graupel and rain, and the respective contributions of cold (riming) and warm (coalescence, melting) processes. Cooling from melting, and heating/cooling from condensation/evaporation processes yield a net decrease and increase of the potential temperature at low and mid‐to‐upper levels, respectively, with respect to an environmental thermodynamic profile taken three hours ahead of the analysis. Finally, the upper‐level rearward flow could convey the non‐negligible proportion of ice particles farther from the leading deep convection to the trailing stratiform region, thereby favouring the extent of this region. Copyright © 2009 Royal Meteorological Society

Measurements and Simulations of Nadir-Viewing Radar Returns from the Melting Layer at X and W Bands

AbstractSimulated radar signatures within the melting layer in stratiform rain—namely, the radar bright band—are checked by means of comparisons with simultaneous measurements of the bright band made by the ER-2 Doppler radar (EDOP; X band) and Cloud Radar System (CRS; W band) airborne Doppler radars during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida-Area Cirrus Experiment (CRYSTAL-FACE) campaign in 2002. A stratified-sphere model, allowing the fractional water content to vary along the radius of the particle, is used to compute the scattering properties of individual melting snowflakes. Using the effective dielectric constants computed by the conjugate gradient–fast Fourier transform numerical method for X and W bands and expressing the fractional water content of a melting particle as an exponential function in particle radius, it is found that at X band the simulated radar brightband profiles are in an excellent agreement with the measured profiles. It is also found that the simulated W-band profiles usually resemble the shapes of the measured brightband profiles even though persistent offsets between them are present. These offsets, however, can be explained by the attenuation caused by cloud water and water vapor at W band. This is confirmed by comparisons of the radar profiles made in the rain regions where the unattenuated W-band reflectivity profiles can be estimated through the X- and W-band Doppler velocity measurements. The brightband model described in this paper has the potential to be used effectively for both radar and radiometer algorithms relevant to the satellite-based Tropical Rainfall Measuring Mission and Global Precipitation Measuring Mission.

Estimating the potential of rainfed agriculture in India: Prospects for water productivity improvements

Abstract A detailed district and agro-ecoregional level study comprising the 604 districts of India was undertaken to (i) identify dominant rainfed districts for major rainfed crops, (ii) make a crop-specific assessment of the surplus runoff water available for water harvesting and the irrigable area, (iii) estimate the efficiency of regional rain water use and incremental production due to supplementary irrigation for different crops, and (iv) conduct a preliminary economic analysis of water harvesting/supplemental irrigation to realize the potential of rainfed agriculture. A climatic water balance analysis of 225 dominant rainfed districts provided information on the possible surplus runoff during the year and the cropping season. On a potential (excluding very arid and wet areas) rainfed cropped area of 28.5 million ha, a surplus rainfall of 114 billion m 3 (Bm 3 ) was available for harvesting. A part of this amount of water is adequate to provide one turn of supplementary irrigation of 100 mm depth to 20.65 Mha during drought years and 25.08 Mha during normal years. Water used in supplemental irrigation had the highest marginal productivity and increase in rainfed production above 12% was achievable even under traditional practices. Under improved management, an average increase of 50% in total production can be achieved with a single supplemental irrigation. Water harvesting and supplemental irrigation are economically viable at the national level. Net benefits improved by about threefold for rice, fourfold for pulses and sixfold for oilseeds. Droughts have very mild impacts on productivity when farmers are equipped with supplemental irrigation.

Improving Global Model Precipitation Forecasts over India Using Downscaling and the FSU Superensemble. Part I: 1–5-Day Forecasts

Abstract The availability of daily observed rainfall estimates at a resolution of 0.5° × 0.5° latitude–longitude from a collection of over 2100 rain gauge sites over India provided the possibility for carrying out 5-day precipitation forecasts using a downscaling and a multimodel superensemble methodology. This paper addresses the forecast performances and regional distribution of predicted monsoon rains from the downscaling and from the addition of a multimodel superensemble. The extent of rainfall prediction improvements that arise above those of a current suite of operational models are discussed. The design of two algorithms one for downscaling and the other for the construction of multimodel superensembles are both based on the principle of least squares minimization of errors. That combination is shown to provide a robust forecast product through day 5 of the forecast for regional rains over the Indian monsoon region. The equitable threat scores from the downscaled superensemble over India well exceed those noted from the conventional superensemble and member models at current operational large-scale resolution.

Effects of precipitation variation on severe acid rain in southern China

Acid rain has been recognized as a serious environmental problem in China since the 1980s, but little is known about the effects of the climatic change in regional precipitation on the temporal and spatial variability of severe acid rain. We present the effects of the regional precipitation trend change on the area and intensity of severe acid rain in southern China, and the spatio-temporal distribution characteristics of SO2 and NO2 concentrations are analyzed on the basis of SO2 and NO2 column concentration data. The results are as follows. (1) The emission levels of SO2 and NO2 have reached or passed the precipitation scavenging capacity in parts of southern China owing to the emission totals of SO2 and NO2 increasing from 1993 to 2004. (2) Notable changes in the proportion of cities subject to severe acid rain occurred mainly in the south of the middle-lower reaches of the Yangtze River during 1993–2004. With an abrupt change in 1999, the severe acid rain regions were mainly located in central and western China during 1993–1999 and moved obviously eastward to the south of the lower-middle reaches of the Yangtze River with the proportion of cities subject to severe acid rain increasing significantly from 2000 to 2004. (3) The spatial distribution and variation in the seasonal precipitation change rate of more than 10 mm/10a are similar to those of severe acid rain in southern China. An abrupt change in 1999 is seen for winter and summer precipitation, the same as for the proportion of cities subject to severe acid rain in southern China. The significant increase in summer storm precipitation from 1991 to 1999 mitigated the annual precipitation acidity in the south of the Yangtze River and reduced the area of severe acid rainfall. On the other hand, the decrease in storm rainfall in summer expanded the area of severe acid rainfall in the south of the Yangtze River in 2000–2006. Therefore, the change in seasonal precipitation is an important factor in the severe acid rain regions moving eastward and expanding in southern China.

Evidence of mineral dust altering cloud microphysics and precipitation

Abstract. Multi-platform and multi-sensor observations are employed to investigate the impact of mineral dust on cloud microphysical and precipitation processes in mesoscale convective systems. For a given convective strength, small hydrometeors were more prevalent in the stratiform rain regions with dust than in those regions that were dust free. Evidence of abundant cloud ice particles in the dust sector, particularly at altitudes where heterogeneous nucleation of mineral dust prevails, further supports the observed changes of precipitation. The consequences of the microphysical effects of the dust aerosols were to shift the precipitation size spectrum from heavy precipitation to light precipitation and ultimately suppressing precipitation.

Baroclinicity Influences on Storm Divergence and Stratiform Rain: Subtropical Upper-Level Disturbances

Abstract Divergence structures associated with the spectrum of precipitating systems in the subtropics and midlatitudes are not well documented. A mesoscale model is used to quantify the relative importance different baroclinic environments have on divergence profiles for storms primarily caused by upper-level disturbances in southeastern Texas, a subtropical region. The divergence profiles simulated for a subset of the modeled storms are consistent with those calculated from an S-band Doppler radar. Realistic convective and stratiform divergence signals are also generated when applying a two-dimensional convective–stratiform separation algorithm to reflectivities derived from the mesoscale model, although the model appears to underestimate stratiform rain area. Divergence profiles from the modeled precipitating systems vary in magnitude and structure across the wide range of baroclinicities common in southeastern Texas. Barotropic storms more characteristic of the tropics generate the most elevated divergence (and thus diabatic heating) structures with the largest magnitudes. In addition, stratiform rain regions in barotropic storms contain thicker, more elevated midlevel convergence signatures than more baroclinic storms. As the degree of baroclinicity increases, stratiform area fractions generally increase while the levels of nondivergence (LNDs) decrease. However, some weakly baroclinic storms contain stratiform area fractions and/or divergence profiles with magnitudes and LNDs that are similar to barotropic storms, despite having lower tropopause heights and less deep convection. Additional convection forms after the passage of barotropic and weakly baroclinic storms that contain elevated divergence signatures, circumstantially suggesting that heating at upper levels may cause diabatic feedbacks that help to drive regions of persistent convection in the subtropics.

Microphysical and Thermodynamic Structure and Evolution of the Trailing Stratiform Regions of Mesoscale Convective Systems during BAMEX. Part I: Observations

Abstract This study used airborne and ground-based radar and optical array probe data from the spiral descent flight patterns and horizontal flight legs of the NOAA P-3 aircraft in the trailing stratiform regions (TSRs) of mesoscale convective systems (MCSs) observed during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX) to characterize microphysical and thermodynamic variations within the TSRs in the context of the following features: the transition zone, the notch region, the enhanced stratiform rain region, the rear anvil region, the front-to-rear flow, the rear-to-front flow, and the rear inflow jet axis. One spiral from the notch region, nine from the enhanced stratiform rain region, and two from the rear anvil region were analyzed along with numerous horizontal flight legs that traversed these zones. The spiral performed in the notch region on 29 June occurred early in the MCS life cycle and exhibited subsaturated conditions throughout its depth. The nine spirals performed within the enhanced stratiform rain region exhibited saturated conditions with respect to ice above and within the melting layer and subsaturated conditions below the melting layer. Spirals performed in the rear anvil region showed saturation until the base of the anvil, near −1°C, and subsaturation below. These data, together with analyses of total number concentration and the slope to gamma fits to size distributions, revealed that sublimation above the melting layer occurs early in the MCS life cycle but then reduces in importance as the environment behind the convective line is moistened from the top down. Evaporation below the melting layer was insufficient to attain saturation below the melting layer at any time or location within the MCS TSRs. Relative humidity was found to have a strong correlation to the component of wind parallel to the storm motion, especially within air flowing from front to rear.

Microphysical and Thermodynamic Structure and Evolution of the Trailing Stratiform Regions of Mesoscale Convective Systems during BAMEX. Part II: Column Model Simulations

Abstract This study employed a nondynamic microphysical column model to evaluate the degree to which the microphysical processes of sublimation, melting, and evaporation alone can explain the evolution of the relative humidity (RH) and latent cooling profiles within the trailing stratiform region of mesoscale convective systems observed during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX). Simulations revealed that observations of a sharp change in the profile of RH, from saturated air with respect to ice above the melting layer to subsaturated air with respect to water below, developed in response to the rapid increase in hydrometeor fall speeds from 1–2 m s−1 for ice to 2–11 m s−1 for rain. However, at certain times and locations, such as the first spiral descent on 29 June 2003 within the notch of lower reflectivity, the air may remain subsaturated for temperatures (T) < 0°C. Sufficiently strong downdrafts above the melting level, such as the 1–3 m s−1 downdrafts observed in the notch of lower reflectivity on 29 June, could enable this state of sustained subsaturation. Sensitivity tests, where the hydrometeor size distributions and upstream RH profiles were varied within the range of BAMEX observations, revealed that the sharp contrast in the RH field across the melting layer always developed. The simulations also revealed that latent cooling from sublimation and melting resulted in the strongest cooling at altitudes within and above the melting layer for locations where hydrometeors did not reach the ground, such as within the rear anvil region, and where sustained subsaturated air is present for T < 0°C, such as is observed within downdrafts. Within the enhanced stratiform rain region, the air is typically at or near saturation for T < 0°C, whereas it is typically subsaturated for T > 0°C; thus, evaporation and melting result in the primary cooling in this region. The implications of these results for the descent of the rear inflow jet across the trailing stratiform region are discussed.

Daily Rainfall Variability over Northeastern Argentina in the La Plata River Basin

We did a brief description of the climatic behavior and after this we analyzed the temporal variation in the total number of days a year with rainfall and the number of days a year with rainfall above the 100 mm threshold at the rain gauging stations in northeastern Argentina south of the La Plata River basin. The results show an increase both in the frequency of daily rainfall, especially during the winter season, and the frequency of days with heavy rainfall starting in the early 1970s. The increase in frequency of occurrence is more significant in the case of heavy rainfall. The annual maximum rainfall was calculated for periods of 1, 3, 5, 7, and 10 consecutive days at regional rain gauging stations for the respective historical periods, and the rain intensity-duration-return period curves (IDT) were determined on a frequency analysis. The IDT curves were compared with rainfall intensity-duration data of critical storms occurring in the last decades. We noticed that the rain intensities of critical storms (mostly convective) widely exceeded the intensities given by the 100-year IDT curves, particularly for short durations. The increase in both the frequency of heavy rainfall occurrence and rain intensity from the 1970s onward shows an increase in frequency and intensity of the meso-scale convective systems in the region resulting from climatic change. These systems tend to produce rainfall of very high intensity that is spatially concentrated and which generally produces significant floods in the local rivers.

Climate variability, snow, and physiographic controls on storm hydrographs in small forested basins, western Cascades, Oregon

AbstractLarge floods are often attributed to the melting of snow during a rain event. This study tested how climate variability, snowpack presence, and basin physiography were related to storm hydrograph shape in three small (<1 km2) basins with old‐growth forest in western Oregon. Relationships between hydrograph characteristics and precipitation were tested for approximately 800 storms over a nearly 30‐year period. Analyses controlled for (1) snowpack presence/absence, (2) antecedent soil moisture, and (3) hillslope length and gradient. For small storms (<150 mm precipitation), controlling for precipitation, the presence of a snowpack on near‐saturated soil increased the threshold of precipitation before hydrograph rise, extended the start lag, centroid lag, and duration of storm hydrographs, and increased the peak discharge. The presence of a snowpack on near‐saturated soil sped up and steepened storm hydrographs in a basin with short steep slopes, but delayed storm hydrographs in basins with longer or more gentle slopes. Hydrographs of the largest events, which were extreme regional rain and rain‐on‐snow floods, were not sensitive to landform characteristics or snowpack presence/absence. Although the presence of a snowpack did not increase peak discharge in small, forested basins during large storms, it had contrasting effects on storm timing in small basins, potentially synchronizing small basin contributions to the larger basin hydrograph during large rain‐on‐snow events. By altering the relative timing of hydrographs, snowpack melting could produce extreme floods from precipitation events whose size is not extreme. Further work is needed to examine effects of canopy openings, snowpack, and climate warming on extreme rain‐on‐snow floods at the large basin scale. Copyright © 2008 John Wiley & Sons, Ltd.

Heavy rain events in the Western Mediterranean: an atmospheric pattern classification

Abstract. Heavy rain is one of the most important high-impact weather phenomena that occasionally affect Mediterranean areas. The aim of this study is to achieve a classification of atmospheric patterns related to heavy rain events in both French and Spanish Mediterranean regions. The classification is made on some atmospheric fields (geopotential at 1000 hPa and at 500 hPa and temperature at 850 hPa) of HIRLAM-INM-0.5° operational analysis, for heavy rain events included in the High Impact Weather MEDEX database. It covers a period of roughly 7 and a half years, from January 1997 to May 2004. A Principal Components Analysis was conducted to reduce the number of variables. After that, by means of a Cluster Analysis, the heavy rain events are classified into 8 atmospheric patterns. The results show a good relationship between regions affected by heavy rain and atmospheric patterns, in the sense that the same atmospheric patterns usually produce heavy rain in different regions, and heavy rain in different regions is usually due to specific atmospheric patterns.