Thunderstorm Rain Research Articles

A Systematic Climatology Report of Aviation Weather Hazards on Yangon Airport Region

The primary goal of the research was to examine the aviation climatology analysis of the thunderstorms and fog on study area based on the statistical evaluation of the meteorological station's observation data. Weather is a critical factor in aviation, profoundly affecting aircraft operations and safety. The global aviation industry, with a staggering economic impact of $3.5 trillion and contributing 4.1 percent of global GDP, relies heavily on weather data and analysis. Study used METAR data from Myanmar's Yangon International Airport (VYY). Analysis of METAR, flight delay and accident data revealed that the influence of thunderstorms and fog might have had a direct or indirect impact on most accidents over study area. The frequency analysis method were primarily used in this study and the new method of fog event analysis came out. The two meteorological occurrences, thunderstorm rain (TSRA) and fog (FG), are also high frequency at VYY in a year and TSRA is a larger risk than FG for aviation operation due to its relative other weather phenomena. The July is the maximum TSRA occurrence month and total annual frequency analysis revealed that TSRA days are becoming more common year by year because of study. In addition, the total number of days with fog varies from 23 to 91 per year, with the most frequent time of day being between 2300 and 01:00 UTC. The conditions where the fog was most likely to form were those when the minimum temperature fell between 16 and 27 °C (liquid fog). The study raises a new question and a new possibility for viewing climatology from a new perspective. The insights gained from this report can contribute to the development of tailored weather forecasting and alert systems for pilots and airport personnel. Further deep study for systematic prediction of each hazards are leaved for future work.

Analysis of the Most Common Aviation Weather Hazard and Its Key Mechanisms over the Yangon Flight Information Region

The aviation industry has a global economic impact of $2.7 trillion (including direct, indirect, induced, and tourism catalytic effects) and contributes 3.6 percent of global GDP. Weather is one of the most essential elements impacting how an aircraft runs and how safely it can fly. The correlation coefficient is the most significant index explaining the relationship between variables and can result in teleconnection patterns of climate indices. El Nino-Southern Oscillation (ENSO) and India Ocean Dipole (IOD) were used in this study based on the ERA5 reanalysis dataset for 30 years (1991–2020). Myanmar’s Yangon International Airport has recorded more than 119874 times of observation data from 2009 to 2019. The mean percentage of occurrences of weather elements is calculated for each month and each season. Analysis of flight delay and accident data was obtained statistically from the Aviation Safety Network (ASN). According to the monthly delay index, July, August, and March are the maximum delay index months, and the correlation value between aircraft movement and delays is maximum in July and August and minimum in January and February. After examining numerous characteristics of Yangon International Airport, we identified which elements had a big impact on operations through vital interviews with operators, the accident case study section, and climatology analysis. As a result, we identified two meteorological occurrences: thunderstorm rain (TSRA) and fog (FG) are of high frequency and TSRA poses a larger risk than FG for aviation operation. The maximum frequency (%) of thunderstorm occurrences was 22% in July and the minimum was 1% in January. Annual frequency analysis revealed that TSRA days are becoming more common year after year as a result of global climate change. According to a spatial gridded analysis by ERA5 reanalysis data (1991–2020), the annual convective available potential energy (CAPE) values over local airport regions, the Bay of Bengal (BOB), the western equatorial Pacific, and the South China Sea show a positive correlation with convective rainfall. In contrast, negative convective inhibition (CIN) anomalies have been observed over the same areas as above, except for the western part of BOB along the Indian Coast. The primary innovation is that we look at the effects of thunderstorms on airport operations before determining their link with ENSO and the IOD individually and then combining them during their full phases. This raises a new question and a new possibility for viewing climatology from a new perspective.

Performance of Resource Management Techniques for Weather-Impacted Satellite Networks

Signals transmitted via satellite networks at high frequency in the Ka,Q, andVbands are susceptible to degradation due to rain attenuation. Adaptive transmission techniques are usually employed to mitigate the effect of rain and improve users’ quality of service (QoS) but the effectiveness of these techniques hinges on the accuracy with which rain attenuation on the link is known. Commonly, most techniques rely on predicted attenuation along the link for selection of optimal transmission parameters. This paper proposes an efficient approach to predict the rain attenuation experienced by sources of multimedia connections in rain-impacted satellite networks. The proposed technique is based on three Markov models for widespread, shower, and thunderstorm rain events and predicts the attenuation experienced at different periods within the duration of a user’s connection. It relies on an adaptive modulation and coding (AMC) scheme to dynamically mitigate rain attenuation and a call admission control (CAC) policy to guarantee the satisfaction of users’ QoS requirements.

OLAP technology and Machine learning as the tools for validation of the Numerical Models of Convective Clouds

In the present work we use the technologies of machine learning and OLAP for more accurate forecasting of such phenomena as a thunderstorm, hail, heavy rain, using the numerical model of convective cloud. Three methods of machine learning: support vector machine, logistic regression and ridge regression are used for making the decision on whether or not a dangerous convective phenomenon occurs at present atmospheric conditions. The OLAP technology is used for development of the concept of multidimensional data base intended for distinguishing the types of the phenomena (thunderstorm, heavy rainfall and light rain). Previously developed complex information system is used for collecting the data about the state of the atmosphere and about the place and at the time when dangerous convective phenomena are recorded.

Regime Analysis of Critical Raindrop Diameters for Rainfall Attenuation in Southern Africa

The influence of critical raindrop diameters on the specific rainfall attenuation in Durban (29o52'S, 30o58'E), South Africa using various rainfall regimes is analyzed in this paper. Different rain rate values representing drizzle, widespread, shower and thunderstorm are selected for the purpose of analysis over the measured raindrop size distribution. The three-parameter lognormal and gamma DSD models with shape parameter of 2 are used to estimate the parameters required to investigate the drop sizes which produce a major contribution to the total specific rainfall attenuation for the selected rain rate values. The computed total specific attenuation increases with increasing frequencies and rain rates. The highest and prevailing contribution to the specific attenuation occurs at for the stratiform (drizzle or widespread) and convective (shower or thunderstorm) rain types for the models considered. The total percentage fraction formed by drops in the diameter range 0.5 mm ≤ D ≤ 2.5 mm and 1.0 mm ≤ D ≤ 3.0 mm are found to be most critical for the specific rain attenuation for the stratiform (drizzle and widespread) and convective (shower and thunderstorm) rainfall types especially at higher frequencies.

Below-cloud scavenging of aerosol particles by precipitation in a typical valley city, northwestern China

To fill the blank information for aerosol precipitation-scavenging research in north-west of China, the aerosol particle and raindrop size distributions were measured simultaneously during 1 September 2012 to 31 August 2013 in urban Lanzhou. The scavenging coefficients of thunderstorm and non-thunderstorm rain and snow events were studied and presented on the basis of nine selected precipitation cases including 3 snow and 6 rain events. The variation of scavenging coefficients of snowfall across the size distribution clearly exhibited a trough of lower values for particles of 1000 nm–2000 nm in diameter, while the particles smaller than 500 nm were scavenged efficiently by non-thunderstorm rain, and thunderstorm rain more effectively scavenged the particles in 500–1000 nm. The snow scavenging coefficients varied between 3.11 × 10−7 s−1 and 1.18 × 10−3s−1 in the 10–10,000 nm size range. The scavenging coefficients of thunderstorm (non-thunderstorm) rain were between 8.25 × 10−7s−1 (7.48 × 10−6s−1) and 1.23 × 10−3s−1 (7.46 × 10−4s−1). Additionally, the number of particles in 10–50 nm was more sensitive to duration of snow, while snowfall intensity was more responsible for particle number concentrations in 50–100 nm and 100–1000 nm. The longer period of precipitation with lower raindrop velocity can more effectively scavenge the particles in the size range of 10–50 nm.

Lidar profiling of aerosol scavenging parameters at a tropical station, Pune, India

In this study, we deal with observations of aerosol column content (height integration of vertical distribution of aerosol number density) that have been carried out using an Ar+ lidar for three different measurement cycles (each cycle consisting of three experimental days associated with non-rain, rain, and non-rain, respectively) of weekly spaced observations for pre-monsoon (March/April 1994), monsoon (September 1991), and post-monsoon (October 1998). Based on these observed profiles of aerosol number concentration on rainy days with respect to those on non-rainy days, vertical distributions of scavenging collection efficiencies (SCEs) are computed and discussed in this article. The SCE is found to decrease from 0.3 to 0.01 between the heights, 100 and 800 m for thunderstorm rain in April 1994, and during monsoon, it increases from 0.1 to 0.7. In the October 1998 episode, SCE was found to increase initially from 0.35 to 0.75 for heights between 40 and 200 m and thereafter decrease to 0.35 in the height interval of 200–800 m. For the rainfall intensity increase from 1 to 10 mm hour−1, the corresponding scavenging coefficient (SC) for atmospheric layer 50–100 m varies from 4 × 10−6 to 4 × 10−5 s−1 for thunderstorm in April 1994 and between 5 × 10−6 and 5 × 10−5 s−1 in October 1998, respectively. During monsoon, these values vary from 3 × 10−5 to 5 × 10−4 s−1. They lie in the range of those observed in the earlier field studies. The results are found useful to establish links between aerosols and cloud properties, and the influence of such interactions on weather and climate.

Below-thunderstorm rain scavenging of urban aerosols in the health hazardous modes

A very high number concentration of aerosols in urban locations has a wide impact on health and ecosystem. The evolutions of urban aerosol distributions at elapse-time 30 and 60 min are simulated at rainfall rates, 0.5 and 0.9 mm h−1 applying scavenging coefficients to initial aerosols number concentrations (before rain). We show how thunderstorm rain scavenges number concentrations of urban aerosols in the ultrafine and fine modes. Elapsed-time evolutions of urban aerosols presented in this work show washout of about 50–60 and 70–80% number concentrations of particles in the diameter range 0.02 μm ≤ D p ≤ 0.1 μm after 30 and 60 min of thunderstorm rain when compared to initial number concentrations (before rain). Assuming 37 and 24% Sulfate and Organic Carbon particles in aerosol distributions in the urban environment and by applying scavenging coefficients to these initial number concentrations, elapse-time evolutions after 30 and 60 min of thunderstorm rain are presented in this work. The health impact is addressed in terms of depositions of particles within respiratory system by deposition fractions as a function of particle size. For D p ≤ 0.1 μm, 33 and 41% of initial number concentrations of Sulfate and Organic Carbon particles deposits within respiratory system. Whereas elapsed-time evolutions show 60 and 80% cleansing of initial number concentrations of Sulfate and Organic Carbon particles after 30 and 60 min of thunderstorm rain.

Study of scavenging of submicron-sized aerosol particles by thunderstorm rain events

Observed scavenging coefficients for 0.013–0.75 μm particles are between 1.08×10 −5 and 7.58×10 −4 s −1. Based on observed results a correlation between scavenging coefficient and rain intensity is obtained to study below thundercloud scavenging of atmospheric aerosols during thunderstorm rain events. When the rain intensity increases from 5.24 to 45.54 mm h −1, the corresponding scavenging coefficient increases from 0.5×10 −5 to 4×10 −5 s −1 for thunderstorm rain episodes. The overall scavenging coefficients for 0.02 – 10 μm particles at different rainfall rates are estimated from contributions of Brownian diffusion, directional interception, inertial impaction, thermophoresis, diffusiophoresis and electrical forces during thunderstorms. The evolutions of PSD are predicted at different time intervals with theoretical scavenging rates. Comparison of observed evolutions of PSD during thunderstorm rain events with predicted evolutions of PSD shows an order of discrepancy between the observed and model results. Possible causes for discrepancy are discussed in terms of uncertainties in observed data and shortcomings in theoretical approach. The present results are useful for recommendations for the type of experimental setup essential for the field study of precipitation scavenging and improvements in theoretical approach close to atmospheric conditions during thunderstorm rain events.

Thunderstorm asthma.

Thunderstorms have often been linked to epidemics of asthma, especially during the grass flowering season; however, the precise mechanisms explaining this phenomenon are unknown. Evidence of high respirable allergen loadings in the air associated with specific meteorologic events combined with an analysis of pollen physiology suggests that rupture of airborne pollen can occur. Strong downdrafts and dry, cold outflows distinguish thunderstorm rain from frontal rain. The weather system of a mature thunderstorm likely entrains grass pollen into the cloud base, where pollen rupture would be enhanced, then transports the respirable-sized fragments of pollen debris to ground level where outflows distribute them ahead of the rain. The conditions occurring at the onset of a thunderstorm might expose susceptible people to a rapid increase in concentrations of pollen allergens in the air that can readily deposit in the lower airways and initiate asthmatic reactions.

Rainfall Measurement Error by WSR-88D Radars due to Variations inZ–RLaw Parameters and the Radar Constant

Abstract An investigation is made of the extent to which variations in Z–R (reflectivity factor–rainfall rate) relations can explain the systematically large offsets of radar-measured rainfall from rain gauge measurements as observed with some National Weather Service (NWS) WSR-88D radars. It is shown that theory predicts that the use by the NWS of the current default Z–R relation (Z = 300R1.4) should underestimate rainfall by about 25% in stratiform rain and overestimate it by about 33% in thunderstorm rain. Yet it is commonly observed that some WSR-88D radars systematically underestimate rainfall by a factor of 2 or more in stratiform rain and produce estimates of rainfall with acceptable accuracy for isolated thunderstorms. It is shown that variations in Z–R law parameters alone cannot explain these discrepancies, and it is proposed that their origin lies in a radar calibration offset. A comparison is made of reflectivity factors measured by the KGSP WSR-88D at Greer, South Carolina, with those determi...

Gully Migration on a Southwest Rangeland Watershed

Most rainfall and almost all runoff from Southwestern rangelands are the result of intense summer thunderstorm rainfall. Gully growth and headcutting are evident throughout the region. A large, active headcut on a Walnut Gulch subwatershed has been surveyed at irregular intervals from 1966 to present. Runoff at the headcut was estimated using a kinematic cascade rainfall-runoff model (KINEROS). The headcut sediment contribution was about 25% of the total sediment load measured downstream from the headcut; and the sediment contribution from the swale drainage above the headcut, as estimated from a depth-integrated pumping sampler, was about the same. Although more data are needed to quantify sediment contributions from other tributary watersheds, the total contribution from gully banks and headcuts on Walnut Gulch must be an important portion of the total sediment load. The 150-km2 Walnut Gulch Experimental Watershed, near Tombstone, Arizona, is typical of much of the semiarid rangeland in the southwestern United States. Walnut Gulch is a tributary of the San Pedro River. Most rainfall and almost all runoff from these rangelands are the result of intense summer thunderstorm rains of short duration and limited areal extent. Gully growth and headcutting have been evident throughout the region, including Walnut Gulch. In 1975, a project was initiated to determine the gullyand headcut contribution to sediment loads at several runoff-measuring stations on Walnut Gulch. One of the principal objectives of the program was to determine the rate of headcut development and the proportional headcut contribution to the total watershed sediment yield. The object of this study was to determine movement and sediment contribution of a major headcut on watershed 63.011, a subdrainage of Walnut Gulch. Historical Background The most intensive study of gully erosion in the United States was carried out by H.A. Ireland, C.F.S. Sharpe, and D.H. Eargle, and published in USDA Technical Bulletin 633 (1939). Although the study area was on the Piedmont of South Carolina, the report serves as a landmark effort in understanding gully erosion and headcut migration elsewhere. In their report, they stated: Almost all gullies result from the acceleration of runoff, or from an unnatural concentration of flowing water. Acceleration and concentration of water have been brought about in various ways, and gullies may be classified into several groups on the basis of their origin. Increased amounts of runoff result from overgrazing, burning, deforestation, or denuding of the land by cultivation. Concentration of the runoff is caused by construction of roads and railroads, with their accompanying ditches, by construction of terraces and terrace outlets, by contour plowing followed by breaking-over of furrows during heavy rains, and by stock paths which, in many cases, become rills and gullies. Acceleration of the movement of water in stream channels is sometimes brought about by clearing of brush from the banks, a practice which often results in accelerated bank erosion. The theory of erosional processes has been covered by many, including Beasley (1972) and Thormes (1980). The mechanisms of erosion and sediment movement from gullies have been reported by others, including Piest, Bradford, and Spomer (1975) and Piest, Bradford, and Wyatt (1975). However, most of the available data Authors are research hydraulic engineer and hydrologist, USDA-ARS, Southwest Rangeland Watershed Research Center, 2000 East Allen Road, Tucson, Ariz. 85719. Manuscript accepted 27 January 1986. on gully erosion is from farmlands, rather than rangelands. The southeastern Arizona geologic record indicates gullying has occurred in the past, but the most recent intense episode of accelerated gullying appears to have begun in the 1880's (Hastings and Turner 1965). Gullies in the 2 major stream channels of southeastern Arizona, the San Pedro and Santa Cruz Rivers, began because of man's activities in the flood plains and were accelerated by increased runoff from overgrazed tributary watersheds. From m andering perennial streams, both the San Pedro and Santa Cruz became incised ephemeral channels. The gullies proceeded to develop from the major channels upward into the tributary watersheds. Gullies migrated well into Walnut Gulch from the San Pedro. The advance of gullies has slowed as the amount of contributing runoff area to each decreased, but a few gullies are still very active. The most active gullies are those with large contributing areas remaining, a result of restricted headcutting at one or more times during the upward migration. Watershed Description Watershed 63.011 (824 hectares) is located in the upper part of Walnut Gulch Experimental Watershed. There are 10 weighingtype recording raingages located on, or immediately adjacent to, the watershed (Fig. 1). Runoff stage is measured with an A-35

Dust, Clouds, Rain Types, and Climatic Variations in Tropical North Africa

AbstractDust and processes of raindrop formation in the clouds play a very important role in the climatic evolution of tropical north Africa. Sedimentologic, stratigraphic, pedologic, geomorphologic, and palynologic data converge to show that a major environmental change occurred in tropical Africa about 7000 yr B.P. In the Sudanian and Sudano–Guinean zones (wet tropical zone), from 15,000 to 7000 yr B.P., rivers deposited mostly clay, while from 7000 to 4000 yr B.P. they deposited mostly sand. During the first period, pedogenesis was vertisolic (montmorillonite dominant), associated with pollen belonging mostly to vegetation typical of hydromorphic soils, while during the second period pedogenesis was of ferruginous type (kaolinite dominant) with pollen belonging mostly to vegetation typical of well-drained soils. The great change near 7000 yr B.P. is linked chiefly to a major hydrological change that appears related to a change in the size of raindrops: from fine rains associated with considerable atmospheric dust (raindrop diameter essentially less than 2 mm) to the second period associated with thunderstorm rains (raindrop diameter mostly greater than 2 mm). The size of raindrops is related particularly to cloud thickness and dust concentration in the troposphere. Thunderstorm activity is influenced also by fluctuations of the atmospheric electricity, modulated by the sun.

Shapes of Raindrop Size Distributions

Abstract The “instant” shape of raindrop size distributions (measured during 1 min or less) usually differs from the exponential, generally in the direction of monodispersity. Experimental results are presented for both widespread and thunderstorm rain. It is shown that the measured shape depends significantly on the sample size, and that adding many “instant” distributions from different conditions leads to an exponential distribution such as proposed by Marshall and Palmer. This transition is examined, as well as the sample size needed for a well-defined shape.

Earlier warnings may be possible with tornado Doppler

Tornadoes in severe thunderstorms were detected by a powerful Doppler radar in Norman, Oklahoma, more than 20 minutes before they became visible to ground observers, adding at least 10 minutes to the time available for tornado warnings. These experimental observations were part of a cooperative effort by NOAA and the Air Force to test the tornado‐detecting performance of an experimental Doppler radar.Donald W. Burgess of the NOAA National Severe Storms Laboratory, Donald R. Devore of the Oklahoma City Weather Service Forecast Office, and Capt. Joel D. Bonewitz of the Air Weather Service also found that the Doppler radar and its hightechnology data handling and display systems showed unexpected promise in detecting conditions associated with the heavy thunderstorm rains that can produce lethal flash floods.

Potential of Convective Cloud Seeding in the Southwest

ADSTRACT WATER users in the Southwest can be divided generally into those who use stored water (reservoir and/or groundwater) and those who depend upon rain-fall for range forage and for livestock watering. These groups may or may not view weather modification simi-larly. The principal purposes for increasing precipitation in the Southwest are: (a) to increase the surface and subsurface water stored for municipal, industrial, mining, and irrigated agriculture users, and (b) to increase range forage for beef production. The former users are most interested in moving the most possible water from the watersheds into reservoirs and ground-water storage; the latter users are most interested in retaining as much water as possible on the land to improve range conditions. Much of the land surface of Arizona and New Mexico is arid or semiarid, and in these lands, thunderstorms are the major runoff source. On rangelands in south-eastern Arizona, for example, about 70 percent of the rainfall and almost all runoff results from intense thun-derstorm rains in July, August, and early September (Dorroh, 1960; Osborn and Hickok, 1968). However, winter storms are significant sources of water supply for mountainous watersheds, such as parts of the Salt River System (the water supply for the greater Phoenix area).

Characteristics of Raindrop Charge and Associated Electric Field in Different Types of Rain

Simultaneous measurements of raindrop charge, atmospheric electric field and rain intensity were made at Poona using fast response, continuous recording surface instruments during four types of rain: pre-monsoon (thunderstorm rain), monsoon rain type I (tight intermittent rain), monsoon rain type II (heavy continuous rain) and post-monsoon (thunderstorm rain). Measurements were also made of the conductivity of rainwater samples collected during the monsoon season. On some days of this period data on cloud thickness as obtained from the aircraft flights in the region were also available. The electric field associated with negatively charged raindrops was less negative than that associated with positively charged drops. The raindrop charge spectrum showed different characteristics during the four types of rain studied. It was broadest during the pre-monsoon rain when the convective activity was a maximum. It followed a log-normal distribution during the monsoon rain type I and it was peaked and skewed to the positive side during the monsoon rain type II. Rainwater conductivity was inversely correlated with the cloud vertical thickness. The results of the present study support the warm cloud charge generation mechanism proposed by Takahashi (1974).

Thunderstorm Water Contents and Rain Fluxes Deduced from Radar

Abstract Total instantaneous water contents of several intense thunderstorms were calculated from smoothed representations drawn from quantitative radar observations; values typically ranged from 108–109 kg. Rain rates and accumulations were obtained from reflectivity measurements near the surface. The rainfall rates of the storms were about 105–106 kg sec−1 with total accumulations averaging 109–1010 kg. Dimensions and durations of the storms are also given.

Size distribution of Raindrops-Part -VI

A.C. Best has fo1lnd an empirical formula for the size distribution of raindrops. If F (x) is the fraction of liquid water in the air comprised by drops of diameter less than x, 1 -F = exp [-(x/a)n ], where a and n are constants for any particular rainfall. Contrary to the general supposition that the above formula, applies to the average size distribution of a number of samples of rain, it has boon found that the formula holds for individual samples, in 90 out of 104 cases of general monsoon rains and in 134 out of 169 cases of thundersturm rains recorded at Poona. The formula fails where the liquid water distribution is multimodal (generally bimodal) or is J-shaped.
 
 The parameters a and n are found to be independent for general rains but are connected by the average relation a n = 7.1 mm for thunderstorm rains. There is also a correlation between the intensity of precipitation I and the parameter n For general rains the average rell1,tioll found is I = 6.9 exp [-0.14 (n-5.5)2] and that fur thundorsturm rains is I = 975 exp (-n).
 --
 ~
 .."
 
 Introduction and Results ;,~; identIcal value of the intensity of precipitation,
 
 ..' viz., 3.3 mm/hr, having very different diameter
 Best(1950)ha8s~own.tha.t m?st ?i,the avaIlable spectra of liquid water. The averttge values for
 dt,l.tt~ on t~e ,ili'op-s1Ze dlBtnbutIonIs 111 aGGordance these two 8amples were calculated and a similar ::.:
 wIth the formulae --graph was plotted. It was found that the graph :':
 1-1!' = exp [ -(xla)n ] and a = AlP was a str.aig~t line for each of the individu~1
 I sample8 WIth Its own valnes of a and n ~s shown ill
 where F is the fraction of liquid water in the air Figs. l(a) and l(b). For the average values, how-
 comprised by drop8 of diallleter less than x; a aud ever, the plot showed a sharp kink so that two
 1t are constants for a particular rainfall. I!~rom the straight lines with different slopes were obtall1ed as
 first of these equations it follows that- shown in Fig. l(c). Realising that the individual
 I samples wcre more suitable and that there was a
 log loglo [l,(l-F)] = -0.36 + n (loglox-Ioglo(t) danger in calCulating averages of such heteroge-
 and that log log~o [lj(~-F») plotted against loglox neou~ ~aterial (very di~erent diame.te~ 8~c~tr~ ),
 should be a straIght Ime wIth 810pe rt. The value Bcst s Imes were plotted 1o1;' all the 1~9 1U~IVIdu,ll
 of a can be calculated from the intercept. sa1Uple8. It was foUlld that a straIght line was
 ..obtained for 134 samples, showing that Best's
 Followillg the usual practIce, the whole of the formula holds for individual samples. It was further
 data.on thu!l~erstor.m rains consisting of 169 sam- found that the 35 samples -for which the formula
 pies was dI':'lded mto 1~ groups a!ld aver~ge does not apply, could be divided into three cate-
 values obtamed. On usmg these for plottmg gories aB follows -
 log ~lO [lj(l-F)] against logloX' it was foUlld that
 in 9 cases a straight line was obtained, in 7 (;ases (a) Two straight line8 with the second line
 two strt\ight lines were obtained and in one case haying a higher slope were obtained in 21 cases.
 three straight lines were obtall1ed. Suspecting An exactly similar result was obtall1ed by Best
 .that this non-agreement was due to averaging of (1950) for the East -Hill data which he has atLribut-
 such heterogeneous ma~rial, Best's lines were ed to the small amount of data Gorresponding to
 plotted for :tw~ individual samples of raiu with that line.

Size distribution of Raindrops -Part V

Results of measurements of the size distribution of raindrops for thunderstorm rain recorded at Poona during August, September and October 1956 are described and compared with those for monsoon rain. The basic data are given in the form of a table showing the number of raindrops received per square metre per second, (grouped country at intervals of 0.25 mm in diameter) for various intensities of precipitation. The total momentum and kinetic energy of raindrops per square metre per sea have been determined as a function of the Intensity of precipitation. The concentration of raindrops and liquid water per cubic metre of air and their dictribution in different diameter groups is discussed. The radar reflectivity factor for individual rain periods has been calculated for monsoon as well as thunderstorm rain, Evidence for the breaking up of large raindrops is presented in the paper.