Mesoscale Precipitation Systems Research Articles

A bias correction method for precipitation through recognizing mesoscale precipitation systems corresponding to weather conditions

Accurate estimations of local precipitation are necessary for assessing water resources and water-related disaster risks. Numerical models are typically used to estimate precipitation, but biases can result from insufficient resolution and incomplete physical processes. To correct these biases, various bias correction methods have been developed. Recently, bias correction methods using machine learning have been developed for improved performance. However, estimating local hourly precipitation characteristics remains difficult due to the nonlinearity of precipitation. Here, we focused on precipitation systems that could be reproduced by numerical models, and estimated the spatial distribution of local precipitation by recognizing the relationship between simulated and observed precipitation with a resolution of 0.06 degrees using a machine learning method. We subsequently applied a quantile mapping method to modify the precipitation amounts. Validation showed that our method could significantly reduce bias in numerical simulations, especially the spatial distribution of hourly precipitation frequency. However, the bias in the temporal distribution of hourly precipitation did not improve. Spatial autocorrelation analysis showed that this method can predict precipitation systems with spatial scales of 2500 to 40000 km2, which are associated with large-scale disturbances (e.g., cold fronts, warm fronts, and low-pressure systems). The high accuracy of these estimates indicates that the spatial distribution of hourly precipitation frequency is strongly dependent on precipitation systems with these spatial scales. Accordingly, our method shows that the relationship between the spatial distribution of precipitation systems and local precipitation is strong, and by recognizing this relationship, the spatial distribution of local hourly precipitation can be accurately estimated.

ИССЛЕДОВАНИЕ РАДИОЛОКАЦИОННЫХ ХАРАКТЕРИСТИК ОБЛАЧНЫХ СИСТЕМ ПРИ ВЫПАДЕНИИ СИЛЬНЫХ ДОЖДЕЙ

The paper analyzes radar characteristics of mesoscale precipitation systems associated with heavy precipitation in Western Urals. The characteristics under study, obtained from the Doppler weather radar, include the maximum height of the radar echo of clouds and precipitation, meteorological phenomena, speed and direction of the radar echo movement. An attempt was made to classify mesoscale precipitation systems with respect to their horizontal scales and geometrical features as well as precipitation patterns. Statistical features of radar characteristics of cloud systems causing heavy rain were calculated taking into account their classification by horizontal scales. Radar meteorological characteristics were obtained from instruments in the Izhevsk city and Ufa city for the warm period of 2016–2017. The results can be used during nowcasting of heavy precipitation events.

Mesoscale precipitation systems and their role in the rapid development of a monsoon depression over the Bay of Bengal

AbstractThe structure of mesoscale precipitation within monsoon depressions is still not as well‐known as the synoptic‐scale composite cloud and precipitation structure. Here, using observational data from multi‐satellite sensors and a cloud‐resolving regional model, we investigate the three‐dimensional structure of mesoscale precipitation systems in the different stages of the life cycle of a monsoon depression. Effects of latent heating from the precipitation systems and the Bay of Bengal (BoB) on the development of the monsoon depression are also evaluated in sensitivity experiments with the model. A typical monsoon depression developed on 17 August 2016 over the BoB. In the rapid development phase, satellite observations reveal mesoscale convective systems with deep convective precipitation cells and stratiform precipitation near the head of the BoB. Extremely deep and intense convective cells appear along a ring‐like rain band when a closed cyclonic circulation becomes obvious around the northernmost part of the BoB. The deep convection appears frequently, particularly along the western‐to‐southwestern side of the low, a convergence‐prone area between northerlies with air masses of large convective available potential energy (CAPE) that makes up the western–southwestern part of the closed cyclonic circulation, and strong monsoon westerlies with relatively stable air masses to the south of the low. Sensitivity experiments reveal that both cloud/precipitation processes and evaporation from the BoB are essential for the rapid development of the monsoon depression over the BoB. Evaporation from the BoB adds a large amount of moisture to the atmospheric boundary layer near the low. Southwesterlies and southerlies on the eastern side of the low draw in warm, humid boundary‐layer air to the closed cyclonic circulation, which maintains a large‐CAPE environment in the low and enhances deep convection. A possible positive feedback process including moist convection that leads to the rapid intensification of monsoon depressions over the BoB is discussed.

Precipitation Characteristics over East Asia in Early Summer: Effects of the Subtropical Jet and Lower-Tropospheric Convective Instability

Abstract A quasi-stationary front, called the baiu front, often appears during the early-summer rainy season in East Asia (baiu in Japan). The present study examines how precipitation characteristics during the baiu season are determined by the large-scale environment, using satellite observation three-dimensional precipitation data. Emphasis is placed on the effect of subtropical jet (STJ) and lower-tropospheric convective instability (LCI). A rainband appears together with a deep moisture convergence to the south of the STJ. Two types of mesoscale rainfall events (REs; contiguous rainfall areas), which are grouped by the stratiform precipitation ratio (SPR; stratiform precipitation over total precipitation), are identified: moderately stratiform REs (SPR of 0%–80%) representing tropical organized precipitation systems and highly stratiform REs (SPR of 80%–100%) representing midlatitude precipitation systems associated with extratropical cyclones. As the STJ becomes strong, rainfall from both types of mesoscale precipitation systems increases, with a distinct eastward extension of a midtropospheric moist region. In contrast, small systems appear regardless of the STJ, with high dependency on the LCI. The results indicate that the STJ plays a role in moistening the midtroposphere owing to ascent associated with secondary circulation to the south of the STJ, producing environments favorable for organized precipitation systems in the southern part of the rainband. The horizontal moisture flux convergence may also contribute to precipitation just along the STJ. On the other hand, the LCI plays a role in generating shallow convection. In high-LCI conditions, deep convection can occur without the aid of mesoscale organization.

Use of Multiple Verification Methods to Evaluate Forecasts of Convection from Hot- and Cold-Start Convection-Allowing Models

Abstract This study uses both traditional and newer verification methods to evaluate two 4-km grid-spacing Weather Research and Forecasting Model (WRF) forecasts: a “cold start” forecast that uses the 12-km North American Mesoscale Model (NAM) analysis and forecast cycle to derive the initial and boundary conditions (C0) and a “hot start” forecast that adds radar data into the initial conditions using a three-dimensional variational data assimilation (3DVAR)/cloud analysis technique (CN). These forecasts were evaluated as part of 2009 and 2010 NOAA Hazardous Weather Test Bed (HWT) Spring Forecasting Experiments. The Spring Forecasting Experiment participants noted that the skill of CN’s explicit forecasts of convection estimated by some traditional objective metrics often seemed large compared to the subjectively determined skill. The Gilbert skill score (GSS) reveals CN scores higher than C0 at lower thresholds likely due to CN having higher-frequency biases than C0, but the difference is negligible at higher thresholds, where CN’s and C0’s frequency biases are similar. This suggests that if traditional skill scores are used to quantify convective forecasts, then higher (>35 dBZ) reflectivity thresholds should be used to be consistent with expert’s subjective assessments of the lack of forecast skill for individual convective cells. The spatial verification methods show that both CN and C0 generally have little to no skill at scales <8–12Δx starting at forecast hour 1, but CN has more skill at larger spatial scales (40–320 km) than C0 for the majority of the forecasting period. This indicates that the hot start provides little to no benefit for forecasts of convective cells, but that it has some benefit for larger mesoscale precipitation systems.

Eastward-Propagating Property of Large-Scale Precipitation Systems Simulated in the Coarse-Resolution NICAM and an Explanation of its Appearance

Using the Non-hydrostatic ICosahedral Atmospheric Model (NICAM) on an aqua-planet with a uniform longitudinal sea surface temperature, precipitation systems (PSs) with coarse horizontal resolutions are studied. An eastward-propagating (EP) property of the PSs is seen even though the horizontal resolution becomes coarser to 112 km, as long as the vertical stratification is kept conditionally unstable. The appearance or disappearance of the EP property is explained in comparison with mesoscale (100 km) and large-scale (1,000 km) PSs, a non-precipitation system (NPS), and a system simulated by a dry model with positive-only wave CISK heating (DP). By assuming that the height and the updraft intensity of convection are common in these systems, the turnover times of representative convections are estimated. Compared with the time scale of the equatorial beta (Tβ), where its effect essentially works and the distinct EP property appears, the turnover times of the large-scale PS and DP are longer than Tβ, producing the EP property, whereas those of the NPS and mesoscale PSs are shorter, inducing no EP property. These results are consistent with observations and model outputs (Nakazawa 1988; Nasuno et al. 2007, 2008).

Simulation and Interpretation of the Genesis of Tropical Storm Gert (2005) as Part of the NASA Tropical Cloud Systems and Processes Experiment

Abstract Several hypotheses have been put forward for the mechanisms of generation of surface circulation associated with tropical cyclones. This paper examines high-resolution simulations of Tropical Storm Gert (2005), which formed in the Gulf of Mexico during NASA’s Tropical Cloud Systems and Processes Experiment, to investigate the development of low-level circulation and its relationship to the precipitation evolution. Two simulations are examined: one that better matches available observations but underpredicts the storm’s minimum sea level pressure and a second one that somewhat overintensifies the storm but provides a set of simulations that encapsulates the overall genesis and development characteristics of the observed storm. The roles of convective and stratiform precipitation processes within the mesoscale precipitation systems that formed Gert are discussed. During 21–25 July, two episodes of convective system development occurred. In each, precipitation system evolution was characterized by intense and deep convective upward motions followed by increasing stratiform-type vertical motions (upper-level ascent, low-level descent). Potential vorticity (PV) in convective regions was strongest at low levels while stratiform-region PV was strongest at midlevels, suggesting that convective processes acted to spin up lower levels prior to the spinup of middle levels by stratiform processes. Intense vortical hot towers (VHTs) were prominent features of the low-level cyclonic vorticity field. The most prominent PV anomalies persisted more than 6 h and were often associated with localized minima in the sea level pressure field. A gradual aggregation of the cyclonic PV occurred as existing VHTs near the center continually merged with new VHTs, gradually increasing the mean vorticity near the center. Nearly concurrently with this VHT-induced development, stratiform precipitation processes strongly enhanced the mean inflow and convergence at middle levels, rapidly increasing the midlevel vorticity. However, the stratiform vertical motion profile is such that while it increases midlevel vorticity, it decreases vorticity near the surface as a result of low-level divergence. Consequently, the results suggest that while stratiform precipitation regions may significantly increase cyclonic circulation at midlevels, convective vortex enhancement at low to midlevels is likely necessary for genesis.

Retrieval of High-Resolution Wind Fields over the Southern Korean Peninsula Using the Doppler Weather Radar Network

Abstract The performance of a radar network for retrieving high-resolution wind fields over South Korea is examined. The network consists of a total of 18 operational radars. All of the radars possess the Doppler capability and carry out plan position indicator (PPI) volume scans comprising 6–15 elevation steps at every 6 or 10 min. An examination of the coverage of the radar network reveals that the radar network allows the retrieval of three-dimensional high-resolution wind fields over the entire area of the southern Korean Peninsula as well as nearby oceans above a height of approximately 3 km. After the quality control procedures of the radar measurements, the high-resolution wind fields (a few kilometers) are extracted using multiple-Doppler wind synthesis in the Custom Editing and Display of Reduced Information in Cartesian Space (CEDRIC) package developed by NCAR. The radar-retrieved winds are evaluated using the following two rain events: 1) Typhoon Ewiniar in 2006, which resulted in strong winds and heavy rainfall over the entire southern Korean Peninsula, and 2) a well-developed hook echo with a relatively small-scale diameter of about 30 km. The wind fields retrieved from the radar network exhibit counterclockwise rotation around the typhoon center and a general structure around a hook echo such as a cyclonically rotating updraft (i.e., mesocyclone). Comparisons with the wind measurements from four UHF wind profilers for the typhoon case reveal that the u- and υ-wind components retrieved from the radar network deviate by standard deviations of 3.6 and 4.5 m s−1 over ranges from −30 to 20 m s−1 and from 0 to 40 m s−1, respectively. Therefore, it is concluded that the operational radar network has the potential to provide three-dimensional high-resolution wind fields within the mesoscale precipitation systems over almost the entire area of the southern Korean Peninsula.

Impact of 4DVAR assimilation of rainfall data on the simulation of mesoscale precipitation systems in a mei-yu heavy rainfall event

The multi-scale weather systems associated with a mei-yu front and the corresponding heavy precipitation during a particular heavy rainfall event that occurred on 4{5 July 2003 in east China were successfully simulated through rainfall assimilation using the PSU/NCAR non-hydrostatic, mesoscale, numerical model (MM5) and its four-dimensional, variational, data assimilation (4DVAR) system. For this case, the improvement of the process via the 4DVAR rainfall assimilation into the simulation of mesoscale precipitation systems is investigated. With the rainfall assimilation, the convection is triggered at the right location and time, and the evolution and spatial distribution of the mesoscale convective systems (MCSs) are also more correctly simulated. Through the interactions between MCSs and the weather systems at difierent scales, including the low-level jet and mei-yu front, the simulation of the entire mei-yu weather system is significantly improved, both during the data assimilation window and the subsequent 12-h period. The results suggest that the rainfall assimilation flrst provides positive impact at the convective scale and the in∞uences are then propagated upscale to the meso- and sub-synoptic scales. Through a set of sensitive experiments designed to evaluate the impact of difierent initial variables on the simulation of mei-yu heavy rainfall, it was found that the moisture fleld and meridional wind had the strongest efiect during the convection initialization stage, however, after the convection was fully triggered, all of the variables at the initial condition seemed to have comparable importance.

Impacts of initial condition errors on mesoscale predictability of heavy precipitation along the Mei‐Yu front of China

AbstractSummertime heavy precipitation associated with the quasi‐stationary Mei‐Yu front often causes severe flooding along the Yangtze river basin in China. This study explores the mesoscale predictability of one such event near Wuhan, the capital city of Hubei Province. The 20–21 July rainfall event contributed to making the 1998 flood season the worst in this region since 1954. Various sensitivity experiments were performed to examine the impact of both realistic and idealized initial condition uncertainties of different scales and amplitudes on the prediction of the mesoscale precipitation systems along the Mei‐Yu front. While it is found that mesoscale model simulations initialized with global analyses at a 36‐h lead time can depict the evolution of the synoptic environment reasonably well, there are large variations between different experiments in the prediction of the mesoscale details and heavy precipitation of this event. It was also found that larger‐scale, larger‐amplitude initial uncertainties generally led to larger forecast divergence than did uncertainties of smaller scales and small amplitudes. However, the forecast errors induced by perturbations of the same amplitude but at different scales are very similar if the initial error is sufficiently small. Error growth is strongly nonlinear and small‐amplitude initial errors, which are far smaller than those of current observational networks, may grow rapidly and quickly saturate at smaller scales. They subsequently grow upscale, leading to significant forecast uncertainties at increasingly larger scales. In agreement with previous studies, moist convection is found to be the key to the rapid error growth leading to limited mesoscale predictability. These findings further suggest that, while there is significant scope for improving forecast skill by improving forecast models and initial conditions, mesoscale predictability of such a heavy precipitation event is inherently limited. Copyright © 2007 Royal Meteorological Society

Vertical moisture transport above the mixed layer around the mountains in western Sumatra

A remarkable increase in moisture frequently occurred in August afternoon radio soundings in 2001 in the layer up to 1000 m above the mixed layer (ML) near the mountains of western Sumatra, Indonesia. This moisture enhancement was also apparent in the monthly mean diurnal cycle. The mixing ratio is not vertically uniform in this layer, suggesting that turbulent mixing cannot be a major mechanism of the vertical moisture transport. A climatological numerical study using a cloud‐resolving model suggests that thermally‐induced upslope winds converge over the mountain summits during daytime, forming a moist air band along the mountain range. Ambient winds above the mountain range then advect the moist air into the surroundings, moisturizing the air above the ML over the leeward terrain. This mechanism is important for producing diurnal mesoscale precipitation systems over a wide area of the Indian Ocean, as documented by previous studies analyzing TRMM and GMS observational data.

Variational Assimilation of TMI Rain Type and Precipitation Retrievals into Global Numerical Weather Prediction

Improvement in forecast accuracy is expected to result from the incorporation of rain type and precipitation retrieved from the TRMM Microwave Imager (TMI) into numerical weather prediction (NWP) models, especially in the tropics, where latent heating is the main energy source of atmospheric motion. A One-dimensional Variational Method (1DVAR) was developed in the present study for the assimilation of convective and stratiform rain flags, and precipitation retrieved from TMI into a Japan Meteorological Agency (JMA) global NWP system. In order to simplify the observational operators of the 1DVAR, it was assumed that the rain flags (precipitation) were functions of total water content (divergence) alone. Using these operators, the 1DVAR sought the optimal total water content (divergence), by minimizing a cost function that consists of a background total water content (divergence) term, and observation terms for the retrieved rain flags (precipitation). The impact of the TMI rain flags and precipitation assimilation on the NWP forecasts was examined in a case study of meso-scale precipitation systems over the Indian Ocean around 06 UTC 16 July 1998. The 1DVAR made deep (mid-tropospheric) moist layers with strong (moderate) updrafts in the TMIretrieved heavy rain areas (stratiform rain areas). This assimilation enabled the NWP to spin-up heavy precipitation in correspondence with the TMI retrievals, and to maintain the heavy rain areas for 24 hours. The creation of deep moist layers was essential to maintain these heavy rain areas. The assimilation also induced model stratiform precipitation around the TMI-retrieved stratiform rain areas, although the model rain areas lasted for the first several hours only. The impacts of the assimilation were also examined by including the 1DVAR into the forecastanalysis cycle of the global NWP system for July 1998. The results show that the assimilation improved large-scale patterns of precipitation, convective and stratiform rain areas, and precipitable water content over tropical oceans. It was also found that the assimilation changed double-peak profiles of diabatic heating around inter-tropical convergence zones, into more realistic mid-tropospheric peak profiles. This change was mainly ascribable to the enhancement of tall convection and suppression of low-level convection by the 1DVAR. The Hadley circulation was strengthened (weakened) in the upper to mid- (lower-) troposphere in accordance with the changes in diabatic heating.

Airflow and Precipitation Fields within Deep Alpine Valleys Observed by Airborne Doppler Radar*

Abstract Although airborne Doppler radar is increasingly relied upon to provide detailed descriptions of mesoscale precipitation systems in remote and complex meteorological settings, the utility of these observations has often been limited by the considerable difficulty in their manual processing to remove ground clutter and other sources of contamination, which is a prerequisite to synthesis of reliable airflow and reflectivity fields. This difficulty is further magnified over mountainous terrain, where these sources of contamination take on increased spatial extent and geometric complexity. Removal of such contamination has traditionally required tedious and time-consuming manual editing. As such, routine retrieval of near-surface airflow and precipitation characteristics over steep orography and within hydrologically critical zones, such as deep valleys cutting through mountainous regions (along which population and transportation corridors are frequently concentrated), has been impractical. A new app...

The Influence of Carl—Gustaf Rossby on Mesoscale Weather Prediction and an Outlook for the Future

Abstract This article presents an overview of the advances in mesoscale prediction from the time of Rossby to the present and an outlook for the future. The first part traces the evolution of research and forecasting based upon the conservation of certain properties on isentropic coordinates. It begins with Rossby's use of these properties to identify and follow air masses and concludes with current use of the isentropic/potential vorticity framework to define air motions and to describe cyclones, fronts, and associated mesoscale precipitation systems, as well as numerical weather prediction in isentropic coordinates. Highlights of this historical research on mesoscale prediction are presented. Regarding future advances in mesoscale observations and prediction, the authors suggest that, for the next decade, the prospects for global mesoscale datasets are not encouraging: Researchers will have to be content with datasets with resolutions considerably below the resolution that is likely to be available from...

Monitoring of Mesoscale Precipitation Systems in the Alps and the Northern Alpine Foreland by Radar and Rain Gauges

Mesoscale convective precipitation systems in the Alpine region are studied by analyzing radar and rain gauge data. The data from weather radars in Austria, France, Germany, and Switzerland are combined into a composite. Availability of radar data restricts the study mainly to the northern part of the Alpine region. Mesoscale convective systems (MCS) occur often in this region and are comparable to large systems observed in the USA. Seven precipitation events lasting one to six days from the years 1992–1996 are examined in detail. They all moved west to east and showed no diurnal preference in formation or dissipation. They reach sizes of 2 − 6 · 104 km2. MCS with leading-line trailing-stratiform structure tended to be larger and more intense. A 25-year set of rain gauge data indicates that a giant MCS (covering more than 4 · 104 km2 with more than 30 mm/day) occurs every 6 years in the northern Alpine region. MCS occur more frequently in the southern Alpine region.

A Modeling Case Study of Heavy Rainstorms along the Mei-Yu Front

On 12‐13 June 1991, a series of convective rainstorms (defined as mesoscale precipitation systems with rainfall rates exceeding 10 mm h21) developed successively along the Mei-Yu front. During this event, new rainstorms formed to the east of preceding storms at an interval of approximately 300‐400 km. The successive development and eastward propagation of these rainstorms produced heavy rainfall over the Jiang-Huai Basin in eastern China, with a maximum 24-h accumulation of 234 mm. This study presents the results of a numerical simulation of this heavy rainfall event using the Penn State‐NCAR Mesoscale Model Version 5 (MM5) with a horizontal resolution of 54 km. Despite the relatively coarse horizontal resolution, the MM5, using a moist physics package comprising an explicit scheme and the Grell cumulus parameterization, simulated the successive development of the rainstorms. The simulated rainstorms compared favorably with the observed systems in terms of size and intensity. An additional sensitivity experiment showed that latent heat release is crucial for the development of the rainstorms, the mesoscale low-level jet, the mesolow, the rapid spinup of vorticity, and the Mei-Yu frontogenesis. Without latent heat release, the maximum vertical motion associated with the rainstorm is reduced from 70 to 6 cm s 21. Additional model sensitivity experiments using the Kain‐Fritsch cumulus parameterization with grid sizes of 54 and 18 km produced results very similar to the 54-km control experiment with the Grell scheme. This suggests that the simulation of Mei-Yu rainstorms, the mesoscale low-level jet, and the mesolow is not highly sensitive to convective parameterization and grid resolution. In all the full-physics experiments, the model rainfall was dominated by the resolvable-scale precipitation. This is attributed to the high relative humidity and low convective available potential energy environment in the vicinity of the Mei-Yu front. The modeling results suggest that there is strong interaction and positive feedback between the convective rainstorms embedded within the Mei-Yu front and the Mei-Yu front itself. The front provides a favorable environment for such rainstorms to develop, and the rainstorms intensify the Mei-Yu front.

The Mesoscale Structure of Severe Precipitation Systems in Switzerland

Abstract The structures of severe mesoscale precipitation systems (MPS) in Switzerland have been classified by analyzing radar images obtained over a 5-yr period. Severe MPSs were defined to be those producing most of the damage on days on which at least 5 (out of 2400) communities reported water and/or at least 20 reported hail damage. Of 94 MPSs selected, 82 had radar reflectivity of 47 dBZ or greater and were referred to as mesoscale convective systems (MCS). The 12 remaining MPSs consisted of less intense, long-lasting, and widespread frontal or orographic rainfall. Subclasses of MCSs were defined according to their internal arrangements of cell complexes (CC). A CC was defined as an echo contour of 40 dBZ surrounding echo maxima of at least 47 dBZ. Four general categories of organization were found: isolated CC, a group of CCs, and a broken or continuous line of CCs. All categories can be purely convective at the mature stage, or the CCs may be juxtaposed with a stratiform precipitation area, usually...

観測船啓風丸によりTOGA COARE集中観測期間中、1992年11月に観測された赤道付近の対流

During the TOGA COARE IOP (Tropical Ocean-Global Atmosphere, Coupled Ocean-Atmosphere Response Experiment, Intensive Observation Period), 7.5-minute-interval weather radar observations and 6-hourly radiosonde observations were conducted by the Keifu Maru, a research vessel of the Japan Meteorological Agency (JMA) at a point of (0.5S, 154.5E), near the center of the Intensive Flux Array (IFA), from 3 to 16 November, 1992. The radar echo intensity is digitized on a 2.5km mesh over a square of 500km×500km.The observed equatorial convection was documented focusing on mesoscale precipitation systems (MPSs). According to the radar echo coverage, the observation period was divided into four periods. On 3-4 November, convection was inactive and organization of MPSs was suppressed. On 5-8 November, convection was activated and echoes were organized into MPSs with a horizontal scale of about 100-300km. The convection showed diurnal variation with enhancement in the midnight to early morning (14-20 UTC, 00-06 Local Time (LT)). Major MPSs formed as convective cells at early night around 10 UTC (20 LT) and matured into large echoes with embedded strong echoes around midnight to early morning (14-20 UTC, 00-06 LT), then dissipated into scattered weak echoes by the morning around 23 UTC (09 LT). Life histories of major MPSs were similar those of mesoscale precipitation features (MPFs) presented by Leary and Houze (1979). On 10-12 November, an active convective event containing larger MPSs occurred for 1.5 days associated with the westward passage of a large (1500-2000km) scale rapid westward-moving cloud disturbance. The MPSs moved eastward but the field of development of the MPSs seemed to move westward, corresponding to the westward passage of the large-scale cloud disturbance. The MPSs took the form of a multiple-line structure oriented northeast to southwest with a length over 300-500km in the developing stages. The longer lifetime of MPSs covered up the diurnal variation of convection. On 13-14 November, convection was completely suppressed.The nighttime enhancement of convection on 5-8 November suggests that even over an open warm water pool region, intense convection circumstantially behaves as diurnal cyclic through the nighttime appearances of MPSs depending on large-scale conditions. Tightly bound and successively westward appearances of eastward-moving MPSs on 10-12 November implies an interaction between the grouped MPSs and the westward-moving large-scale cloud disturbance. Characteristics of the large-scale cloud disturbance were examined.

Use of satellite soundings in monitoring mesoscale precipitation systems

An attempt was made to use TOVS retrievals in the precipitation forecasting at the Hungarian Meteorological Service. Some of the retrieved parameters are indispensable for the estimation of the precipitation. The spatial resolution of the satellite soundings in many cases makes it possible to monitor precipitation systems on a meso-alpha and larger meso-beta scale. This is especially important in certain late spring synoptic situations when extra large amount of precipitation can fall on the catchment areas of the Hungarian rivers. The weaker temporal resolution of the retrievals, however, implies that ground, radar and geostationary satellite observations also have to be used. In the paper evaluation of the effect of the application of TOVS soundings upon the accuracy of the precipitation forecasting is presented on the basis of case studies.

Subsynoptic-Scale Structure in a Major Synoptic-Scale Cyclone

Abstract An analysis of a major cyclone over the eastern United States in late February 1984 revealed the presence of several embedded well-defined mesoscale structures, including a low-level jet, a long-lived snowband and a strong upper-level front. Understanding the importance of these mesoscale features to the evolution of the synoptic-scale cyclone is the basis for this paper. Evidence is presented that a period of weakening after initial surface cyclogenesis was the result of decoupling of the upper-level trough from the surface cyclone, as a consequence of the development of peripheral mesoscale precipitation systems. Redevelopment on the western side of the Appalachians occurred where orographic subsidence was amplified by a strong mesoscale low-level jet. Further intensification then took place when a strong upper-level frontal zone approached the surface cyclone. An incidental finding is that one of the mesoscale precipitation systems was a snowband, driven by strong synoptic-scale frontogenetica...