Tropical regions can be characterized as large fields of convective clouds of all sizes. Latent heat released is
different for different precipitating systems like convective and stratiform. So we need to classify various precipitating
systems. In the present study, ground based observations of Joss-Waldvogel Disdrometer (JWD) which was installed at
Thumba (8.5°N, 76.9°E) under Ka band propagation experiment is used extensively to characterize the tropical rain. It
can be noticed that the JWD is placed at calm and noise-free places, in order to make it sensitive to smaller drops. The
JWD is a standard tool for precipitation measurements such as Drop Size Distribution (DSD), rainfall intensity, R, rain
accumulation and liquid water content, W, reflectivity factor, Z. The range of drop diameters that can be measured spans
from 0.3 to 5 mm with an accuracy of 5%. For present study Disdrometer data from June 2005 onwards are collected.
The main objective of the present study is to classify precipitation system into Convective, Transition (an intermediate
region) and stratiform. Since DSD integral parameters like rain rate (R), liquid water content (LWC), Reflectivity (Z) are
different for different precipitating systems, so we need to classify these systems. There is a dearth of raindrop Size data
and distribution models for the tropics, especially over Indian continent. Models for drop size distribution are required
for the evaluation of microwave and millimeter wave propagation effects due to rainfall. In the present paper various
DSD models namely gamma model and lognormal model with different combination of moments for observing the
characteristic features of tropical rain are studied.
KEYWORDS: Radar, Reflectivity, Liquids, Signal to noise ratio, Temporal resolution, Doppler effect, Spatial resolution, Signal attenuation, Particles, Classification systems
The Micro Rain Radar (MRR) a highly resolution radar operates at a frequency of 24 GHz installed at Thumba
(8.5°N, 76.9°E) under Ka band propagation experiment is used extensively to characterize the tropical rain. This radar
measurements of rain were obtained with fine spatial and temporal resolutions like One minute time resolution and 200
m height resolution. With this radar for the first time classification of precipitating systems are studied. With the
presence or absence of bright band a radar signature of melting layer one can classify particular rain type as convective
or stratiform. For present study MRR data from September 2005 onwards are collected. The main objective is to classify
precipitation system into Stratiform and Convective with the presence or absence of Bright band. Another potential of
this radar is ability to give information of vertical structure of fall velocity of hydrometeors. This also gives profiles of
number concentration of various ranges of Drop sizes, liquid water content and rain rate for different heights. These
results are compared with the collocated ground based Disdrometer. Attenuation at Microwave frequencies during the
presence of rain is a serious concern to the communication. Once temporal and spatial information of DSD is known
microwave attenuation can be studied. These results will be presented in this paper.
A case study of sea breeze circulation at a coastal region Thumba (8.5°N, 76.9°E) was carried out using Doppler Sodar,
surface wind, temperature, humidity measurements and radiosonde ascents. The analysis of surface meteorological data
showed that the onset of sea breeze on 12th April 2006 was at 0945 hrs. GPS sonde observation over sea at 1425 hrs and
Radiosonde observation over land at 1730 showed a well developed sea breeze circulation over Thumba coast by
afternoon hours. The vertical extent of sea breeze circulation was ~1000m over sea as well as on land. The Thermal
Internal Boundary Layer (TIBL) depth associated with sea breeze circulation was about 400m at 8 km away from coast.
The marine mixed layer height was ~500m about 12 km away from the coast. Numerical simulation of sea breeze was
made using HRM (High Resolution Model) and compared the results with the observations.
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