13 research outputs found
Dynamic characteristics of Atmospheric boundary Layer during different phases of Monsoon
Atmospheric Boundary layer (ABL) is the layer just above the earth surface and is influenced by the surface forcing within a short period of an hour or less. In this thesis, characteristics of the boundary layer over ocean, coastal and inland areas of the atmosphere, especially over the monsoon regime are thoroughly studied. The study of the coastal zone is important due to its high vulnerability mainly due to sea breeze circulation and associated changes in the atmospheric boundary layer. The major scientific problems addressed in this thesis are diurnal and seasonal variation of coastal meteorological properties, the characteristic difference in the ABL during active and weak monsoons, features of ABL over marine environment and the variation of the boundary layer structure over an inland station.
The thesis describes the various features in the ABL associated with the active and weak monsoons and, the surface boundary layer properties associated with the active and weak epochs. The study provides knowledge on MABL and can be used as the estimated values of boundary layer parameters over the marine atmosphere and to know the values and variabilities of the ABL parameters such as surface wind, surface friction, drag coefficient, wind stress and wind stress curl
Long term trends of seasonal and monthly rainfall in different intensity ranges over Indian subcontinent
In general Indian summer monsoon rainfall did not show any significant trend in all Indian summer monsoon rainfall series, however, it was reported that the ISMR is subjected to spatial trends. This paper made an attempt to bring out long term trends of different intensity classes of summer monsoon rainfall in different regions of Indian subcontinent. The long term trend of seasonal and monthly rainfall were also made using the India Meteorological Department gridded daily rainfall data with a spatial resolution of 1° × 1° latitude-longitude grid for the period from 1st January, 1901 to 31st December, 2003. The summer monsoon rainfall shows an increasing trend in southeast, northwest and northeast regions, whereas decreasing trend in the central and west coastal regions. In monthly scale, July rainfall shows decreasing trend over west coastal and central Indian regions and significant increasing trend over northeast region at 0.1% significant level. During the month August, decreasing trend is observed in the west coastal stations at 10% significant level. In most of the stations, mean daily rainfall shows an increasing trend for low and very high intense rainfall. For the moderate rainfall, the trend is different for different regions. In the central and southern regions the trend of moderate and moderately high classes show increasing trend. And for the high and very high intensity classes, the trend is decreasing significantly. In the northeastern regions, above 10 mm/day rainfall shows significantly increasing trend with 0.1% significant level.CUSAT AND CSIRMAUSAM, 64, 3 (July 2013), 481-48
Rainfall Climatology over Middle East Region and its Variability
A better understanding of the rainfall climatology of the Middle East region identifying the
mechanisms responsible for the rain producing systems is essential for effective utilization of the water
resources over the arid region. A comprehensive analysis on the rainfall climatology of the Middle East region
is carried out to bring out the spatial and temporal variation of rainfall and mechanisms responsible for the
rain events. The study was carried out utilizing rainfall, OLR, wind and humidity data sets procured from
TRMM, NOAA and NCEP-NCAR. Climatology of annual rainfall brings out two areas of alarmingly low rainfall
in the Middle East region: one in Egypt, Jordan and adjoining areas and the other in the southern part of Saudi
Arabia. Daily rainfall analysis indicates that northern region gets rainfall mainly during winter and spring
associated with the passage of Mediterranean low pressure systems whereas rain over the southern region is
caused mainly by the monsoon organized convection, cross equatorial flow and remnants of low pressure
systems associated with the monsoon during the summer season. Thermodynamic structure of the atmosphere
reveals that the region does not have frequent local convection due to insufficient moisture content.
The sinking motion associated with the sub tropic high pressure system and subsidence associated with the
Walker circulation are responsible for maintaining warm and dry air over the region.CUSAT AND CSIRInternational Journal of Water Resources and Arid Environments 1(3): 180-192, 201
Spatial and temporal characteristics of rain intensity in the peninsular Malaysia using TRMM rain rate
The present study is focused on the intensity distribution of rainfall in different classes and their
contribution to the total seasonal rainfall. In addition, we studied the spatial and diurnal variation
of the rainfall in the study areas. For the present study, we retrieved data from TRMM (Tropical Rain
Measuring Mission) rain rate available in every 3 h temporal and 25 km spatial resolutions. Moreover,
station rainfall data is used to validate the TRMM rain rate and found significant correlation
between them (linear correlation coefficients are 0.96, 0.85, 0.75 and 0.63 for the stations Kota
Bharu, Senai, Cameron highlands and KLIA, respectively). We selected four areas in the Peninsular
Malaysia and they are south coastal, east coastal, west coastal and highland regions. Diurnal variation
of frequency of rain occurrence is different for different locations. We noticed bimodal variation
in the coastal areas in most of the seasons and unimodal variation in the highland/inland area. During
the southwest monsoon period in the west coastal stations, there is no distinct diurnal variation.
The distribution of different intensity classes during different seasons are explained in detail in the
resultsCUSAT AND CSIRJournal of Hydrology 387 (2010) 312–31