Thumree Sarkar

Bio: Thumree Sarkar is an academic researcher from University of Calcutta. The author has contributed to research in topics: Cirrus & Disdrometer. The author has an hindex of 2, co-authored 7 publications receiving 38 citations. Previous affiliations of Thumree Sarkar include Indian Institute of Technology Delhi.

Comparative assessment of a near‐global view of individual cloud types from space‐borne active and passive sensors and ground‐based observations

Abstract: The World Meteorological Organizations' International Cloud Atlas recognizes 10 basic cloud genera for classifying clouds. Many of these have been used for over 200 years and are based on cloud appearance and base altitude as seen from surface. Over the satellite era, several missions and programs provide public products that classify clouds into these cloud genera. Here, we provide the first comparison of three such satellite climatologies of cloud genera with surface observations. Specifically, we analyse 10 years (2007–2016) of CloudSat, 4 years (2007–2010) of joint CloudSat‐CALIPSO, 13 years (2000–2012) of ISCCP‐H, and 11 years (1998–2008) of the EECRA data between 50°N and 50°S for eight cloud genera. Averaged over this latitude range, the total cloud amounts for these datasets range from 0.56 to 0.65, with Cumulus (Cu) ranging from 0.06 to 0.14; Stratus (St) from 0.14 to 0.38; Altostratus (As) from 0.05 to 0.13; Altocumulus (Ac) from 0.07 to 0.17; Nimbostratus (Ns) from 0.03 to 0.06; Cirrus (Ci) from 0.1 to 0.19; and Deep‐convective (Dc) from 0.01 to 0.04. The largest disagreement among the sensors is observed for Dc cloud with the coefficient of variation of 44%. On the other hand, the cloud datasets show the best agreement for Ci cloud with the coefficient of variation of 24.1%. Regionally, however, the level of agreement and disagreement can vary drastically. For example, in Indian summer monsoon region (ISM 60°–90°E, 10°–30°N) Ci cloud shows a variation of 28%, whereas the Dc cloud shows 16% variation, which is the opposite of their near‐global feature. The observed discrepancies in cloud genera are discussed in terms of observing characteristics, including instrument, methods, and sampling. Greater effort is still required to reduce discrepancies among these datasets, and the assessment provided here can act as a guide for their use in climate studies.

Dependence of rain integral parameters on measured rain drop velocities at a tropical location

Abstract: A study using a Laser Precipitation Monitor (LPM) for several rain events spanning the monsoon season of 2013 at Kolkata, India, reflects the effect of velocity measurements on Z-R and A-R relationship for both convective and stratiform events. Laser precipitation monitor measures ground based drop size distribution and drop velocity simultaneously. The presence of high velocity small drops (super-terminal) and low velocity large drops (sub-terminal) is abundantly experienced during different types of rain in the tropical region as observed by a Laser precipitation monitor (LPM). The number fraction of these drops is higher in convective rain than in stratiform rain. As the observed drop velocities show significant variation from the theoretically derived velocities, it is possible to get noticeable difference in rain rate calculations, Z-R and A-R relationships. The study involves a comparison of Z-R and A-R relations using both Gunn-Kinzer (GK) and actual observed velocity in convective and stratiform rain regimes separately as there was significant difference in number fraction of high velocity and low velocity rain drops in both the cases.

Raindrop Size Distribution in a Midlatitude Continental Squall Line Measured by Thies Optical Disdrometers over East China

Abstract: Disdrometer data measured by ground-based optical disdrometers during a midlatitude continental squall line event on 18 August 2012 in Shandong Province, eastern China, are analyzed to study characteristics of raindrop size distribution (DSD). Four disdrometers simultaneously performed continuous measurements during the passage of the convective line. The convective line was partitioned into three regions: the convective center, leading edge, and trailing edge. Results show distinct differences in DSDs and integral rainfall parameters between the convective-center and the edge regions. The convective center has higher drop concentrations, larger mean diameters, and wider size distributions when compared with the edge regions. The leading and trailing edges have similar drop concentrations, but the latter has larger mean diameters and wider size distributions. The shape of DSD for the convective center is convex down, whereas it is convex upward in tropical continental squall lines, as reported in ...

Impacts of Instrument Limitations on Estimated Raindrop Size Distribution, Radar Parameters, and Model Microphysics during Mei-Yu Season in East China

Abstract: Instrumentation limitations on measured raindrop size distributions (DSDs) and their derived relations and physical parameters are studied through a comparison of the DSD measurements during mei-yu season in east China by four collocated instruments, that is, a two-dimensional video disdrometer (2DVD), a vertically pointing Micro Rain Radar (MRR), and two laser-optical OTT Particle Size Velocity (PARSIVEL) disdrometers (first generation: OTT-1; second generation: OTT-2). Among the four instruments, the 2DVD provides the most accurate DSD and drop velocity measurements, so its measured rainfall amount has the best agreement with the reference rain gauge. Other instruments tend to miss more small drops (D < 1 mm), leading to inaccurate DSDs and a lower rainfall amount. The low rainfall estimation becomes significant during heavy rainfall. The impacts of instrument limitations on the microphysical processes (e.g., evaporation and accretion rates) and convective storm morphology are evaluated. This is...

Propagation research in Europe using the OLYMPUS satellite : Propagation effects on sattelite communication links

Abstract: Since the inception of commercial satellite communications, the prediction of propagation impairments has been as a key element in the design of ground stations. In the last decade, satellite communication systems started to migrate from trunk telephony using large groundstations towards flexible video, data, and voice communications employing very small apertue terminals (VSAT's) at frequencies between 11 and 30 GHz

Statistical characteristics of raindrop size distribution during rainy seasons in the Beijing urban area and implications for radar rainfall estimation

Abstract: . Raindrop size distribution (DSD) information is fundamental in understanding the precipitation microphysics and quantitative precipitation estimation, especially in complex terrain or urban environments which are known for complicated rainfall mechanism and high spatial and temporal variability. In this study, the DSD characteristics of rainy seasons in the Beijing urban area are extensively investigated using 5-year DSD observations from a Parsivel 2 disdrometer located at Tsinghua University. The results show that the DSD samples with rain rate 1 mm h −1 account for more than half of total observations. The mean values of the normalized intercept parameter ( log 10Nw ) and the mass-weighted mean diameter ( Dm ) of convective rain are higher than that of stratiform rain, and there is a clear boundary between the two types of rain in terms of the scattergram of log 10Nw versus Dm . The convective rain in Beijing is neither continental nor maritime, owing to the particular location and local topography. As the rainfall intensity increases, the DSD spectra become higher and wider, but they still have peaks around diameter D∼0.5 mm. The midsize drops contribute most towards accumulated rainwater. The Dm and log 10Nw values exhibit a diurnal cycle and an annual cycle. In addition, at the stage characterized by an abrupt rise of urban heat island (UHI) intensity as well as the stage of strong UHI intensity during the day, DSD shows higher Dm values and lower log 10Nw values. The localized radar reflectivity ( Z ) and rain rate ( R ) relations ( Z=aRb ) show substantial differences compared to the commonly used NEXRAD relationships, and the polarimetric radar algorithms R(Kdp) , R(Kdp , ZDR) , and R(ZH , ZDR) show greater potential for rainfall estimation.