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In this paper, a variational data assimilation approach is used to assimilate the rain rate (RR) data together with precipitable water (PW) measurements from the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) (4–5 January 1989; IOP-4 cyclone). The PW and RR, which are assimilated into the Pennsylvania State University–NCAR Mesoscale Model version 5 (MM5), are computed from the Special Sensor Microwave/Imager (SSM/I) raw data—brightness temperatures—via a statistical regression method. The SSM/I-derived RR and PW at 0000 UTC and/or 0930 UTC are assimilated into the MM5. The data at 2200 UTC are used for verification of the prediction results. Numerical experiments are performed using the MM5. Two horizontal resolutions of 50 km and 25 km are used in the authors’ studies. Comparisons are made between the experiments with and without SSM/I-measured PW and RR observations. Results from these experiments showed the following. 1) The MM5 simulated a well-behaved but slightly less...

Rainfall data from the Denver, Colorado, Urban Drainage and Flood Control District Automated Local Evaluation in Real Time (ALERT) network were used to identify heavy rainfall alarms for the period 1999–2003. Twenty-nine heavy rainfall-rate alarms were identified. Cloud-to-ground (CG) lightning flash data from the National Lightning Detection Network (NLDN) were analyzed for the 90 min prior to each heavy rainfall alarm. Spatial patterns from NLDN data were extracted using a point-polygon topology developed with basic Geographic Information System procedures. The information extracted from the polygons was used to calculated summary statistics for rainfall rates, CG flash rates, and CG flash duration. Heavy rainfall episodes were divided into two groups based on latitude, longitude, and elevation. Heavy rainfall episodes in the higher elevations of the study area produced an average of 29 mm of rainfall per episode and 1095 CG flashes in the 90 min prior to the rainfall-rate alarm. Only five polygons, all closely proximal to the alarm sites, produced significant CG flash rates prior to the rainfall alarms, and areas with CG flash durations greater than 25 min were clustered near the rainfall-rate alarm sites. In the second group (the lower elevation stations) the mean event produced a total of 33 mm of rainfall and 1182 CG flashes during the 90 min prior to the rainfall alarm. Four polygons saw consistent CG flash rates in the 90 min prior to the heavy rainfall alarms and CG flash duration was at its greatest in areas just west of the ALERT stations.

Observations from northern California during the California Landfalling Jets (CALJET) experiment are used to examine the mean characteristics of precipitation and their variances as functions of synoptic and topographic regimes. Ten cases involving the landfall of extratropical cyclones are analyzed with radar and rain gauge data collected at two sites: one in the coastal mountains north of San Francisco (CZD) and the other in the Central Valley just west of Sacramento (KDAX). Aside from the melting-layer bright band, the most striking feature in the 10-case composite vertical profile of radar reflectivity at CZD was a distinct change in slope about 2.5 km above the bright band. This “shoulder” is thought to represent a change in the growth rate of hydrometeors. Although the bright band was quite distinct, about one-third of the profiles in the composite did not exhibit this feature. These nonbrightband (NBB) profiles had a low-level slope where reflectivity increased with decreasing altitude, a structure suggesting that collision–coalescence was the primary growth process. The relationship between surface rainfall rate and low-level radar reflectivity implies that all profiles were composed of larger numbers of small drops than expected from a Marshall–Palmer drop size distribution, a trend that was especially apparent for NBB profiles. Synoptic variability of precipitation characteristics at CZD were examined by identifying five distinct regimes (cold sector, warm front, warm sector, cold front, and cool sector) based on a simplified conceptual model. The shoulder remained approximately 2.5 km above the bright band in each regime. Rainfall intensity was highest during the cold-frontal regime and NBB rainfall was most common during the warm-frontal, warm-sector, and cool-sector regimes. Topographic variability of precipitation characteristics was investigated by comparing results at CZD and KDAX. A shoulder structure located about 2.5 km above the bright band was also evident in the KDAX profiles, suggesting that this feature is related to large-scale dynamic, thermodynamic, and microphysical processes rather than orographic effects. The relationship between surface rainfall rate and low-level radar reflectivity near KDAX closely followed a trend expected for a Marshall–Palmer drop size distribution, implying the presence of relatively larger raindrops than observed at CZD and indicating that NBB rainfall occurs less frequently near KDAX.

An African easterly wave (AEW) and associated mesoscale convective systems (MCSs) dataset has been created and used to evaluate the propagation of MCSs, AEWs, and, especially, the propagation of MCSs relative to the AEW with which they are associated (i.e., wave-relative framework). The thermodynamic characteristics of AEW–MCS systems are also analyzed. The analysis is done for both AEW–MCS systems that develop into tropical cyclones and those that do not to quantify significant differences. It is shown that developing AEWs over West Africa are associated with a larger number of convective cloud clusters (CCCs; squall-line-type systems) than nondeveloping AEWs. The MCSs of developing AEWs propagate at the same speed of the AEW trough in addition to being in phase with the trough, whereas convection associated with nondeveloping AEWs over West Africa moves faster than the trough and is positioned south of it. These differences become important for the intensification of the AEW vortex as this slower-moving convection (i.e., moving at the same speed of the AEW trough) spends more time supplying moisture and latent heat to the AEW vortex, supporting its further intensification. An analysis of the rainfall rate (MCS intensity), MCS area, and latent heating rate contribution reveals that there are statistically significant differences between developing AEWs and nondeveloping AEWs, especially over West Africa where the fraction of extremely large MCS areas associated with developing AEWs is larger than for nondeveloping AEWs.

The relationship of tropical cyclone (TC) future intensity change to current intensity and current axisymmetricity deduced from hourly Global Satellite Mapping of Precipitation (GSMaP) data was investigated. Axisymmetricity is a metric that correlates positively with the magnitude of the axisymmetric component of the rainfall rate and negatively with the magnitude of the asymmetric component. The samples used were all of the TCs that existed in the western North Pacific basin during the years 2000–15. The results showed that, during the development stage, the intensification rate at the current time, and 6 and 12 h after the current time was strongly related to both the current intensity and axisymmetricity. On average, the higher the axisymmetricity, the larger the intensity change in the next 24 h for TCs with a current central pressure (maximum sustained wind) between 945 and 995 hPa (85 and 40 kt). The mean value of the axisymmetricity for TCs experiencing rapid intensification (RI) was much higher than that for non-RI TCs for current intensities of 960–990 hPa. The new observational evidence for the intensification process presented here is consistent with the findings of previous theoretical studies emphasizing the role of the axisymmetric component of diabatic heating.

The structural evolution of the inner core and near environment throughout the life cycle of Hurricane Edouard (2014) is examined using a synthesis of airborne and satellite measurements. This study specifically focuses on the precipitation evolution and thermodynamic changes that occur on the vortex scale during four periods: when Edouard was a slowly intensifying tropical storm, another while a rapidly intensifying hurricane, during the initial stages of weakening after reaching peak intensity, and later while experiencing moderate weakening in the midlatitudes. Results suggest that, in a shear-relative framework, a wavenumber-1 asymmetry exists whereby the downshear quadrants consistently exhibit the greatest precipitation coverage and highest relative humidity, while the upshear quadrants (especially upshear right) exhibit relatively less precipitation coverage and lower humidity, particularly in the midtroposphere. Whether dynamically or precipitation driven, the relatively dry layers upshear appear to be ubiquitously caused by subsidence. The precipitation and thermodynamic asymmetry is observed throughout the intensification and later weakening stages, while a consistently more symmetric distribution is only observed when Edouard reaches peak intensity. The precipitation distribution, which is also discussed in the context of the boundary layer thermodynamic properties, is intimately linked to the thermodynamic symmetry, which becomes greater as the frequency, areal coverage, and, in particular, rainfall rate increases upshear. Although shear is generally believed to be detrimental to intensification, observations in Edouard also indicate that subsidence warming from mesoscale downdrafts in the low- to midtroposphere very near the center may have contributed favorably to organization early in the intensification stage.

In order to collect further information about recent microclimatic changes in urban areas, an analysis of the secular variations of rainfall intensity has been worked out. A significant increase in rainfall due to urbanization process has been ascertained in the last years. A detailed investigation was performed by studying the records of rainfalls, both showery and continuous, in Naples. The rainfalls were separately examined because of their different effect on the city: the former being more localized, the latter generally extending over wide areas. The analysis shows that a major portion of variance in continuous rainfall rate, in cases of static instability and low surface wind intensity, exhibits a persistence that can be described by a first-order Markov process. Moreover, for the continuous rainfalls, a method for possible prediction of the total mean rainfall rate is indicated.

Data from the Nimbus 5 electrically scanning microwave radiometer (ESMR) are used to make calculations of the latent heat release (L.H.R.) and the distribution of rainfall rate in a tropical cyclone as it grows from a tropical disturbance to a typhoon. The L.H.R. (calculated over a circular area of 4 deg latitude radius) increases during the development and intensification of the storm from a magnitude of 2.7 X 10 to the 21st power ergs/s (in the disturbance stage) to 8.8 X 10 to the 21st power ergs (typhoon stage). The latter value corresponds to a mean rainfall rate of 2.0 mm hr/s. The more intense the cyclone and the greater the L.H.R., the greater the percentage contribution of the larger rainfall rates to the L.H.R. In the disturbance stage the percentage contribution of rainfall rates less than or minus 6 mm hr/s is typically 8%; for the typhoon stage, the value is 38%. The distribution of rainfall rate as a function of radial distance from the center indicates that as the cyclone intensifies, the higher rainfall rates tend to concentrate toward the center of the circulation.

A better understanding of how the precipitation budget operates in tropical convective systems is a prime objective of the GATE research effort. Measurement of rainfall rate with shipboard radar is the principal method by which precipitation from tropical clouds that develop within the GATE B-scale array will be determined. Knowledge of the relationship between radar reflectivity (Z) and rainfall rate (R) is essential for an accurate interpretation of precipitation data derived through the use of radar technology. The Z-R relationship is determined through application of a least-squares linear regression to data points derived by appropriate integration of the third and sixth moments of a series of raindrop size spectra. Drop spectra measurements were obtained during GATE by means of a foil impactor operated at cloud-base level on board the NOAA DC-6 aircraft. A total of 107 Z-R data points are available, representing showers occurring on 12 days. The best-fit Z-R relationship for the cloud-base ...

Mesoscale heat and moisture budget calculations from the April 10-11 AVE-SESAME central U.S. region are calculated in order to diagnose the effect of midlatitude organized convection on its environment. When averaged over an area greater than the observational scale, the noise levels of 5 C/day for the heat budget and 2 g/kg per day for the moisture budget are considerably reduced. The credibility of such area-averaged budget results is indicated by the general agreement obtained between the observed rainfall rate and the vertically integrated heat sources and moisture sinks. The vertical convective heating that is diagnosed from this organized midlatitude convection differs significantly from tropical structures diagnosed on much larger temporal and spatial scales. A time lag of several hours between the moisture convergence and rainfall rate is noted.

A general theoretical expression for the rainfall rate and the total evaporation rate as a function of the distance below cloud base is developed, and is then specialized to the gamma raindrop size distribution. The theoretical framework is used to analyze the data of Rosenfeld and Mintz (1988) on the radar observations of the rainfall rate as a function of the distance below cloud base, for rain falling from continental convective cells in central South Africa, obtaining a parameterization for the evaporation of rainfall.

Surface mesonet observations were used to document the structure of prominent cold pools associated with two convective outer rainbands of Tropical Storm Hanna on 5 September 2008. The developing rainbands were located ~400 km north of the storm center as they crossed the Carolina coastline and passed over the mesonet. The combination of moderate CAPE, moderate low-level cross-band vertical shear, and dry midlevel air provided an environment supportive of surface cold pool formation and long-lived quasi-linear convection. Both rainbands exhibited multiple outward-tilting convective cells and discrete line segments centered within a narrow zone of nearly continuous stratiform precipitation. The mesonet observations provided a unique along- and cross-band perspective of discrete cold pools situated beneath and behind the convection portions of each rainband. Prominent cold pools extended 40–80 km behind the rainband’s leading edge and exhibited maximum potential temperature, mixing ratio, and equivalent potential temperature deficits of 2–4 K, 1–2 g kg−1, and 4–10 K, respectively. In the cross-band direction, convergence of storm-relative inflow along the cold pool leading edge was coincident with a modest high pressure anomaly, while inflow divergence prevailed through the cold pool and rainfall maxima. Several cold pools expanded along-band while being advected downband by the prevailing cyclonic flow. Cold pool wakes were observed more than 50 km behind the rainband leading edge and up to 20 km downband from intense convection. Variations in cold pool intensity were not well correlated with convective intensity, rainfall rate, or the degree of midlevel dryness. Implications of prominent cold pools on tropical cyclone convection, size, and intensity are discussed.

Sea surface estimates of local winds, waves, and rain-rate conditions are crucial to complement infrared/visible satellite images in estimating the strength of tropical cyclones (TCs). Satellite measurements at microwave frequencies are thus key elements of present and future observing systems. Available for more than 20 years, passive microwave measurements are very valuable but still suffer from insufficient resolution and poor wind vector retrievals in the rainy conditions encountered in and around tropical cyclones. Scatterometer and synthetic aperture radar active microwave measurements performed at the C and Ku band on board the European Remote Sensing (ERS), the Meteorological Operational (MetOp), the Quick Scatterometer (QuikSCAT), the Environmental Satellite (Envisat), and RadarSat satellites can also be used to map the surface wind field in storms. Their accuracy is limited in the case of heavy rain and possible saturation of the microwave signals is reported. Altimeter dual-frequency measurements have also been shown to provide along-track information related to surface wind speed, wave height, and vertically integrated rain rate at about 6-km resolution. Although limited for operational use by their dimensional sampling, the dual-frequency capability makes altimeters a unique satellite-borne sensor to perform measurements of key surface parameters in a consistent way. To illustrate this capability two Jason-1 altimeter passes over Hurricanes Isabel and Wilma are examined. The area of maximum TC intensity, as described by the National Hurricane Center and by the altimeter, is compared for these two cases. Altimeter surface wind speed and rainfall-rate observations are further compared with measurements performed by other remote sensors, namely, the Tropical Rainfall Measuring Mission instruments and the airborne Stepped Frequency Microwave Radiometer.

The Indian mesosphere–stratosphere–troposphere (MST) radar observations during the passage of 37 convective systems are utilized to investigate the characteristics of vertical air velocity w in different convection categories (shallow, deep, and decaying) and also the differences in draft core statistics from the wet to dry spell. The radar and optical rain gauge measurements show pronounced differences in core statistics (in terms of their vertical structure, draft strength, size, number, and the elevation angle) and surface rainfall characteristics from the dry to wet spell. The shallow convective cores are preponderant in the dry spell. Composite w profiles, retrieved from all deep cases and also from individual convection cases, depict an upper-tropospheric peak in the wet spell and a bimodal distribution (peaks at 5 and 11–13 km) in the dry spell, illustrating that they are characteristic features of wet and dry spells. The average vertical extents of the cores are nearly equal (about 8 km) in both spells of the monsoon; however, the core-base (and top) altitudes are different. In both wet and dry spells, the composite w profile for all cores show similar vertical variation to that of for updraft cores, while the composite w for downdraft cores do not show much variation with altitude, indicating that the updraft cores dictate the vertical structure of composite w. The core size varies considerably (a factor of 2) with altitude in both spells of the monsoon. Although nearly equal in the lower troposphere in both phases of the monsoon, the core size is larger by 1–2 km in the dry spell in the middle and upper troposphere. Consistent with the longer lifetime (bigger core size) of cores in the dry spell, the cores are more inclined (with a mean elevation angle of 30°) in the dry spell. The surface rainfall distribution is wider and has large number of intense rainfall rates in the wet spell. The mean rainfall rate for the wet spell is also larger by a factor of 2, consistent with earlier studies.

The Indian Mesosphere–Stratosphere–Troposphere radar (IMSTR), Lower Atmospheric Wind Profiler (LAWP), and Joss–Waldvogel (JW) disdrometer measurements during the passage of two distinctly different (in terms of total rain and rainfall rate) convective storms are utilized to understand the nature and origin of the multipeak raindrop size distribution (MRDSD). Important issues, such as the preferential stage and height at which bi- or multimodal rain distribution occurs in a mesoscale convective system (MCS) are addressed. For both of the storms, the MRDSD is observed during the transition period from convection to stratiform rain. The pattern and variation of the MRDSD during this period is strikingly similar in both of the storms. The MRDSD is first observed above the freezing level in the presence of heavy riming. The subsequent spectra have shown bimodal distribution below the freezing level, and the bimodality is attributed to the coexistence of ice and supercooled droplets. Interestingly, the bimodal distribution has not varied much with altitude when it is produced because of the coexistence of ice and supercooled droplets. The MRDSD is also observed at few range gates and for a short duration. Such a type of MRDSD is seen during the transition period between decaying and intensifying rain.

Several years of long-term high temporal resolution ocean ambient noise data from the tropical Pacific Ocean are analyzed to detect oceanic rainfall. Ocean ambient noise generated by rainfall and wind are identified through an acoustic discrimination process. Once the spectra are classified, wind speed and rainfall rates are quantified using the empirical algorithms. Rainfall-rate time series have temporal resolutions of 1 min. These data provide a unique opportunity to study the rainfall events and patterns in two different climate regions, the intertropical convergence zone (ITCZ) of the tropical eastern Pacific (10° and 12°N, 95°W) and the equatorial western Pacific (0°, 165°E). At both locations the rain events have a mean rainfall of 15 mm h−1, but the events are longer in the eastern Pacific. After the rain event is defined, the probability that a rain event can be detected using the change in air–sea temperature often associated with the rainfall is investigated. The result shows that the rain event accompanied by the decrease of air temperature is a general feature, but that using the temperature difference to detect the rainfall has a very high false alarm rate, which makes it unsuitable for rainfall detection.

This paper investigates the effects of cloud microphysics parameterizations on simulations of warm-season precipitation at convection-permitting grid spacing. The objective is to assess the sensitivity of summertime convection predictions to the bulk microphysics parameterizations (BMPs) at fine-grid spacings applicable to the next generation of operational numerical weather prediction models. Four microphysical parameterization schemes are compared: simple ice (Dudhia), four-class mixed phase (Reisner et al.), Goddard five-class mixed phase (Tao and Simpson), and five-class mixed phase with graupel (Reisner et al.). The experimentation involves a 7-day episode (3–9 July 2003) of U.S. midsummer convection under moderate large-scale forcing. Overall, the precipitation coherency manifested as eastward-moving organized convection in the lee of the Rockies is insensitive to the choice of the microphysics schemes, and the latent heating profiles are also largely comparable among the BMPs. The upper-level condensate and cloudiness, upper-level radiative cooling/heating, and rainfall spectrum are the most sensitive, whereas the domain-mean rainfall rate and areal coverage display moderate sensitivity. Overall, the three mixed-phase schemes outperform the simple ice scheme, but a general conclusion about the degree of sophistication in the microphysics treatment and the performance is not achievable.

A regional atmospheric model (RegCM) developed at the International Pacific Research Center (IPRC) is used to investigate the effect of assumed fractional convective entrainment/detrainment rates in the Tiedtke mass flux convective parameterization scheme on the simulated diurnal cycle of precipitation over the Maritime Continent region. Results are compared with observations based on 7 yr of the Tropical Rainfall Measuring Mission (TRMM) satellite measurements. In a control experiment with the default fractional convective entrainment/detrainment rates, the model produces results typical of most other current regional and global atmospheric models, namely a diurnal cycle with precipitation rates over land that peak too early in the day and with an unrealistically large diurnal range. Two sensitivity experiments were conducted in which the fractional entrainment/detrainment rates were increased in the deep and shallow convection parameterizations, respectively. Both of these modifications slightly delay the time of the rainfall-rate peak during the day and reduce the diurnal amplitude of precipitation, thus improving the simulation of precipitation diurnal cycle to some degree, but better results are obtained when the assumed entrainment/detrainment rates for shallow convection are increased to the value consistent with the published results from a large eddy simulation (LES) study. It is shown that increasing the entrainment/detrainment rates would prolong the development and reduce the strength of deep convection, thus delaying the mature phase and reducing the amplitude of the convective precipitation diurnal cycle over the land. In addition to the improvement in the simulation of the precipitation diurnal cycle, convective entrainment/detrainment rates also affect the simulation of temporal variability of daily mean precipitation and the partitioning of stratiform and convective rainfall in the model. The simulation of the observed offshore migration of the diurnal signal is realistic in some regions but is poor in some other regions. This discrepancy seems not to be related to the convective lateral entrainment/detrainment rate but could be due to the insufficient model resolution used in this study that is too coarse to resolve the complex land–sea contrast.

A high-resolution tropical cyclone model with explicit cloud microphysics has been used to investigate the dynamics and energetics of tropical cyclone rainbands. As a first step, the model rainbands have been qualitatively compared with observed rainband characteristics. The model-generated rainbands show many of the mesoscale and convective-scale features of observed tropical cyclone rainbands. Sensitivity studies of numerically simulated tropical cyclone convection to ice-phase microphysical parameters showed that the model was most sensitive to changes in the graupel fall speed parameters. Increasing the fall speeds saw graupel being confined to the convective regions and producing higher rain rates in the inner core of the storm. A greater region of stratiform precipitation was produced when the efficiency for the collection of snow and cloud ice by graupel was reduced and when the mean size of graupel was reduced. Both of these simulations resulted in a higher concentration of snow being transported into the stratiform region. Although the precipitation structure changed across the simulations, the surface rainfall rate and the fundamental dynamical variables showed little sensitivity to the parameter variations.

Impacts of diurnal radiative forcing on flow and rainfall patterns during summer flood and drought conditions (1993 and 1988, respectively) in the central United States were investigated using a regional climate model. The modeling approach, which included evaluation of sensitivity to modification in the solar hour, enabled evaluation of the impact on an event-by-event basis. The effect of the solar hour forward shift of 12 h on boundary layer wind speed over north-central Texas, which is often related to rainfall in the central United States through northward moisture advection, followed almost exactly the shift in solar hour. Domain-averaged daily rainfall in the central United States simulated with 12-h solar shift frequently showed in the flood year a backward or forward time shift of ∼12 h in the timing of its peak, an increase or decrease of rainfall rate, and on a few occasions noticeable formation of short-lived rainfall events. This pattern suggests relatively high sensitivity to the tim...

Regional summertime atmospheric conditions of 1993 are analyzed with the University of Utah Local Area Model (ULAM) by nudging boundary values and large internal scales of the local model toward values produced by the Nested Grid Model (NCEP/NOAA) initial analyses and forecasts archived at 6-h intervals. The approach allows the local ULAM to develop finer-scale structures in the precipitation and circulation forecasts than those resolved by the NGM. The study focuses on the influence of surface evaporation upon rainfall and low-level flow in regional simulations. Much of the rainfall simulated in the control experiment occurred from the late afternoon to early morning hours, with a pronounced midday minimum over the flood region. The moisture flux from the south due to the low-level jet (LLJ) provides much of the moisture source for the precipitation, and it is shown that the net moisture influx is significantly larger than the rainfall rate over the flood region. As a consequence, modifications ...

An algorithm converting satellite-measured microwave radiances to rainfall rates was used to analyze the rainfall patterns of western North Pacific tropical cyclones (typhoons) mainly of the 1987 season. Having realized that these rainfall rates were reasonable and compared favorably with those existing in the tropical cyclone climatology, they were correlated to the 24-h Dvorak intensifies of typhoons in search of diagnostic insights and prognostic aids. Special Sensor Microwave/Imager rainfall rates from 27 map times of 12 typhoons were computed. Mean rainfall rates were computed for various rectangular areas within a typhoon. Those storms filled the mean areal rainfall-rate distributions along an x axis that showed several maxima. Rain volume rates within boxes of various sizes centered an the storms correlated differently with the future 24-h pressures. Correlation between these two parameters was −0.68 for a 444-km box, −0.38 for a 666-km box, and 0.10 for a 888-km box. Results further showe...

Statistics of echoes observed on day 261 of GATE, using the radar aboard the Canadian ship Quadra, are described. This is a case in which detailed observations have been obtained from many sensors during the growth of a cloud cluster. Dividing the radar field of view into many “bins,” it was found that rainfall rates and echo top heights were log-normally distributed UP to a certain limit, with a few additional high values. After identifying echo cores, bounded by a reflectivity threshold 24 dB above 1 mm6 m−3, their area were found to be distributed in a similar manner. Upper limits of log-normality before (and during) the growth of the cluster were about 5 (and 30) mm h−1 for rainfall rate, 7 (and 7) km for echo top height (at the 29 dB level of intensity) and 100 (and 400) km2 for area (within contours of intensity 24 dBZ). To echoes organized on a length scale of about 100 km for more, one attributes maximum rainfall rates reaching roughly 50 mm h−1, peak heights reaching 14 km, and maximum a...

Data from the Nimbus-5 Electrically Scanning Microwave Radiometer (ESMR-5) were used to calculate latent heat release and other rainfall parameters for over 70 satellite observations of 21 tropical cyclones in the tropical North Pacific Ocean. The results indicate that the ESMR-5 measurements can be useful in determining the rainfall characteristics of these storms and appear to be potentially useful in monitoring as well as predicting their intensity. The ESMR-5 derived total tropical cyclone rainfall estimates agree favorably with previous estimates for both the disturbance and typhoon stages. The mean typhoon rainfall rate (1.9 mm h(-1)) is approximately twice that of disturbances (1.1 mm h(-1)).

Patterns in the horizontal distribution of integrated water vapor, integrated liquid water and rainfall rate derived from the Seasat Scanning Multichannel Microwave Radiometer (SMMR) during a September 10-12, 1978 North Pacific cyclone are studied. These patterns are compared with surface analyses, ship reports, radiosonde data, and GOES-West infrared satellite imagery. The SMMR data give a unique view of the large mesoscale structure of a midlatitude cyclone. The water vapor distribution is found to have characteristic patterns related to the location of the surface fronts throughout the development of the cyclone. An example is given to illustrate that SMMR data could significantly improve frontal analysis over data-sparse oceanic regions. The distribution of integrated liquid water agrees qualitatively well with corresponding cloud patterns in satellite imagery and appears to provide a means to distinguish where liquid water clouds exist under a cirrus shield. Ship reports of rainfall intensity agree qualitatively very well with SMMR-derived rainrates. Areas of mesoscale rainfall, on the order of 50 km x 50 km or greater are detected using SMMR derived rainrates.

A number of physical factors that influence the relation between measured radar reflectivity and surface rainfall are considered both theoretically and through detailed comparisons of radar and raingauge measurements. These factors include natural differences in raindrop-size distributions, enhancement of radar reflectivity by presence of hailstones or melting snow, diminution of reflectivity by downdrafts, and low-level changes in rainfall rate caused by accretion or evaporation. Results of 374 comparisons in twenty storms, which cover a wide variety of synoptic situations and rainfall patterns, are presented. Magnitudes of the effects of the different factors are estimated, and storm types where they are likely to be significant are pointed out. Also, some ways of compensating for the observed effects are suggested.

Rawinsonde data from CIATE were used to investigate further the relationships between deep convection and large-scale circulations. The data were analyzed at all of the individual observation times and with composites ~ on rainfall rate. The net latent heating rate was found to he strongly related to horizontal divergence between the surface and 700 mb and from 150 to 350 mb, but not to middle level divergence. It was also wrongly correlated with horizontal moisture convergence below 500 mb and with vertical velocity, particularly in the middle levels. The latter result is in close agreement with the findings of earlier studies which estimated convection from diagnostic models. Spectral analyses of radar-es6mated rainfall showed that the convection varied significantly only at frequencies corresponding to those of easterly waves and the diurnal cycle supporting the satellite data analyses of Murakami. Conditional instability averaged over the A/B array varied substantially with time and was poorl...

Fluctuations in the Australian summer monsoon over the period 1952–82 are described. The basis of the study is an objective definition of the major summer monsoon components based on the low-level zonal winds at Darwin; this is shown to be in good agreement with other large-scale indicators. Statistics are presented and discussed for the interannual variation in summer monsoon onset, extent, active and break conditions, circulation strength, and vertical structure. Some relationships with the Southern Oscillation are also described. These indicate that the Southern Oscillation Index (SOI) is highly correlated with the intensity and degree of convergence in the low-level monsoonal shear zone, and with the mean daily rainfall rate over northern Australia. There is also a significant correlation between the summer monsoon onset date and the SOI in the following spring, which has implications for El Nino teleconnections.

Meteorological data are analysed to determine the location and intensity of the rainstorms that led to flash flooding in the Las Vegas Valley and resulted in approximately $4.5 million in damages on 3 July 1975. The effective precipitation contributing to the flood was found to cover an area of 550 km2. Within this area two centers of heavy rainfall were found, one situated approximately 14 km southwest of the central business district and the other about 13 km north-northwest. Maximum rainfall amounts are estimated to be of the order of 3.0 inch. A maximum rainfall rate of 1.0 inch per hour was detected in a weighing-bucket raingage. Hail and surface wind gusts of about 50 kt were observed in the northwestern portion of the city. Furthermore, the area of heavy rainfall is shown to have developed over the Las Vegas Valley and not over the surrounding mountains. Integration of an isohyetal analysis shows that, at least, 2.3×107 m3 (1.9×104 acre ft) of water was available before infiltration. This ...

The interaction between a squall line and its environment is examined by using the model of Ogura and Cho (1973). This model incorporates a continuous spectrum of cumulus clouds that are distinguished by their entrainment rates. Conversion of liquid water droplets into raindrops has been included in the cloud microphysical process, but the ice phase has been neglected. By virtue of the cloud spectrum, convective transport terms in the larger scale heat and moisture equations appear as functions of vertical mass flux within the clouds. Once the larger-scale distributions are determined from observations, the vertical mass flux can be found from the budget equations. The cloud populations, i.e., fractional area covered by each cloud category, and the cumulative rainfall rate are functions of this vertical mass flux. A squall line observed in the National Severe Storms Laboratory (NSSL) network on 8 June 1966 is used to test the theory. This squall line encompassed approximately 10% of the area used...

The time variation of mass-integrated liquid water and latent heat release for a severe thunderstorm in marked vertical wind shear is investigated for an actual Oklahoma storm and for a two-dimensional numerical modeling experiment. For the actual storm, an approximate continuity equation for liquid water variation is used together with profiles of radar reflectivity. Empirical relationships are utilized to determine the rainfall rate (flux) and liquid water content from the radar reflectivity profiles. Estimates of total storm water mass are obtained from the reflectivity profiles for the volume swept by the radar beam in the vertical. The downdraft evaporation rate is parameterized on the basis of a previous study which estimated this quantity as a residual in the continuity equation for liquid water mass. To estimate latent heat release and total liquid water mass from the numerical model, the two-dimensional cloud is extended to a three-dimensional region whose horizontal cross sections are e...

Heat and moisture budgets associated with a midlatitude convective system (10–11 April 1979) are used to evaluate several versions of Kuo-type cumulus parameterization schemes on a semiprognostic basis. It is shown that the observed rainfall rate is closely related to the large-scale vertical advection of moisture and to a lesser extent to the large-scale moisture convergence. Both the Kuo and the Anthes schemes show considerable skill in reproducing the convective heating profile (Q1) when a moist adiabat is used to represent the cloud thermodynamic properties and the effect of eddy sensible heat flux is estimated by a steady-state cloud model. However, when a model cloud with a small radius is used to estimate the cloud's thermodynamic properties, both the Kuo and Authes schemes predict convective heating profiles with considerably lower levels of maximum heating than observed. This indicates that entrainment is not very important for the deep convection present in this case. Anthes' scheme is ...

For the summer of 1964, precipitation intensity in the vicinity of Montreal, observed by CPS-9 radar, was recorded on constant-altitude maps at six heights. To allow for attenuation (at λ = 3.2 cm) and other radar uncertainties, the distribution with rainfall rate R at 5,000 ft was matched to that for one rain gage at the surface. The extent (area × time) in excess of a given R decreased rapidly with increasing R and with increasing height: a factor 1000 from 0.4 to 100 mm hr–1, a factor 10 per 15,000 ft. The pattern in plan at any height (with resolution limited to about 2 mi in the recorded maps) can be described in terms of cells with intensity decreasing outward approximately exponentially. A logarithmic function of intensity was used: T = 1.66 log (R/R0) where R0 = 0.25 mm hr–1. The value of T for a contour bounding a central area A is given by T = Tc−x, where Tc is the maximum and x = (A/17.5 n.mi.2)1/3. (With this relation, one can estimate peak intensity from the area bounded by any given...

Airborne foil impactor measurements in Atlantic Hurricane Ginger (1971) show a raindrop size spectrum which is well represented by an exponential relation of the Marshall-Palmer type. No difference was observed between the spectral characteristics of the rainbands and those of the eyewall, but some dependence of the slope-rainfall rate relation on rainwater content was noted.

Monsoon depressions (MDs) bring substantial monsoon rainfall to northern and central India. These events usually form over the Bay of Bengal and travel across northern India toward Pakistan. Using European Centre for Medium-Range Weather Forecasts interim reanalysis, an MD-tracking algorithm, and an objective identification method, the authors find that about 40% of MDs interact with northerly intrusions of dry desert air masses as the MDs traverse the subcontinent. MD interactions with dry intrusions are often preceded by positive potential vorticity (PV) anomalies on the subtropical jet and low-level anticyclonic anomalies over the north Arabian Sea. Dry intrusions nearly halve the precipitation rate in the southwest quadrant of MDs, where MDs rain the most. However, dry intrusions increase the rainfall rate near the MD center. Similarly, ascent is reduced west of the MD center and enhanced at the MD center, especially in the upper troposphere. The reduced ascent west of MD centers is likely attributable to changes in vertical shear reducing differential cyclonic vorticity advection. Dry intrusions slightly reduce MDs’ propagation speed. For the mid- to upper-level vortex, this can be explained by anomalous westerlies reducing propagation by adiabatic advection. For the lower-tropospheric vortex, it is likely that reduced diabatic generation of PV plays a role in slowing propagation, along with reduced adiabatic advection.