Weather monitoring equipment/instruments
By
Ashok Jaswal, India Meteorological Department, On October 1, 2011
By
Ashok Jaswal, India Meteorological Department, On May 22, 2011
Abstract
Climate normals are used to describe the average climatic conditions of a particular place and are computed by National Meteorological Services of all countries. The World Meteorological Organization (WMO) recommends that all countries prepare climate normals for the 30-year periods ending in 1930, 1960, 1990 and so on, for which the WMO World Climate Normals are published. Recently, Climatological Normals for the period 1961-1990 have been prepared by India Meteorological Department (IMD) which will change the baseline of comparison from 1951-1980. In this paper, preparation of the 30-year Climatological Normals of India for the period 1961 to 1990 and spatial patterns of differences of annual means of temperatures, relative humidity, clouds, rainfall and wind speed from the previous normals (1951-1980) are documented.
The changes from earlier climatological normals indicate increase in annual means of maximum temperature, relative humidity and decrease in annual means of minimum temperature, cloud amount, rainfall, rainy days and wind speed over large parts of the country during 1961-1990. The spatial patterns of changes in dry bulb temperatures and relative humidity are complementary over most parts of the country. Compared with 1951-1980 climatology, there are large scale decreases in annual mean rainfall, rainy days and wind speed over most parts of the country during 1961-1990. The decrease in wind speed may be partly due to changes in exposure conditions of observatories due to urbanization.
By
Ashok Jaswal, India Meteorological Department, On May 21, 2011
Abstract
This study analyses near-surface wind speed changes in India during 1961 to 2008. Consisting of monthly wind speed data of 171 stations, the results show that most of the stations in India have experienced significant weakening of wind speed, both at monthly and annual timescales. All-India averaged annual mean wind speed has decreased from 9.7 kmph in 1961 to 5.0 kmph in 2008 resulting in a 49% decline. Averaged rate of decrease in annual mean wind speed is -0.88 kmph/decade. The largest rate of decline is in June (-1.33 kmph per decade) and the smallest is in October (-0.60 kmph per decade). Spatially, large declines are found in western India, south peninsula and the coastal areas while central, southeast and northeast India have the lesser change in wind speed. Significant weakening of wind speed has occurred primarily in regions along Gujarat, Maharashtra, Tamil Nadu, north Karnataka, and coastal Orissa and West Bengal which also have higher annual mean wind speed. Annual mean wind speeds exceeding 15 kmph are observed only over Gujarat and south Tamil Nadu. Some parts of Rajasthan, west Madhya Pradesh, Maharashtra, north Karnataka and adjoining Andhra Pradesh and the coastal belts experience wind speeds of 10-15 kmph. Stations having annual mean wind speed exceeding 10 kmph are rare in northern India.
The study evaluates climatology of winds and its long-term trends over India where wind power can be profitably utilised. The prominent regions are in Gujarat and adjoining Madhya Pradesh, south Rajasthan, north Maharashtra, north Karnataka, south Tamil Nadu, coastal Andhra Pradesh and along the west coast from Gujarat to Goa and along the east coast from Kolkata to Nagapatinam.
By
Ashok Jaswal, India Meteorological Department, On May 21, 2011
Annual and seasonal trends in specific humidity, relative humidity and dry bulb temperature based upon 215 stations across India are studied. The results of trend analysis show evidence of an increase in air moisture content over India during 1969-2007 with more than 90% stations showing increasing trends in specific humidity. Climatological means of specific humidity and relative humidity for the country are 14.1 g/kg and 63.9% respectively and trends are significantly increasing for all periods except for relative humidity in monsoon season. Annual trends in specific humidity, relative humidity and dry bulb temperature are +0.23 g/kg per decade, +0.85% per decade and +0.04° C per decade respectively. Seasonal trends in specific humidity, relative humidity and dry bulb temperature are statistically significant and highest in summer (+0.30 g/kg per decade), winter (+1.49% per decade) and monsoon (+0.11° C per decade) respectively. Spatially, the increasing trends in specific humidity and relative humidity are more coherent over north, northwest, central and southeast India. Spatial patterns of trends in relative humidity and dry bulb temperature are complementary and strongly correlated. Relative humidity trends are consistently decreasing over Jammu and Kashmir and northeast India.
Increasing trends in summer season relative humidity and monsoon season dry bulb temperature over large parts of the country contribute significantly to upward trend in human discomfort. The spatial patterns of discomfort index show that the aerial extent of uncomfortable conditions increases both north and westwards as season progresses from summer to monsoon.
By
Ashok Jaswal, India Meteorological Department, On May 21, 2011
Based upon 172 well distributed surface meteorological stations over India, annual and seasonal trends in total cloud cover and associated climatic variables diurnal temperature range and rainy days are investigated for 1961-2007. The data analysis indicates a general decrease in total cloud cover over most parts of India during winter, summer and monsoon. On monthly scale, statistically significant decrease in total cloud cover has occurred during April (3% per decade), June to September (2% per decade) and December (5% per decade). Seasonally, the declining trends in total cloud cover are significant for summer and monsoon (2% per decade). Spatial analysis of trends suggests coherent decrease in total cloud cover over central India (all seasons) and south peninsula (except post monsoon).
All India averaged monthly, annual and seasonal trends in diurnal temperature range and rainy days are mixed and weak. Spatially, trends in diurnal temperature range are decreasing over north and increasing over south peninsula while trends in rainy days are decreasing over large number of stations during winter and monsoon and increasing in summer and post monsoon seasons. However, the sizes of the same trend regions show considerable variability between seasons. Monsoon season total cloud cover and Nino3.4 sea surface temperature anomalies are significantly negatively correlated over all regions of the country except northeast indicating a strong relationship between them.
By
, On September 13, 2010
By
, On September 13, 2010
This article has been written to the participants of DST sponsored SERC School on Ocean-atmosphere Interactions and Global change during 14July-3August 2010conducted by Department of Meteorology & oceanography, Andhra University, by prof.A.S.N.MURTY,Berhampur University
