Search Results
You are looking at 1 - 4 of 4 items for :
- Author or Editor: K. Krishna x
- Monthly Weather Review x
- Refine by Access: All Content x
Abstract
It is shown that, in any secant polar stereographic projection, a small circle on a sphere projects into a circle. This property provides a simple relationship between KH , the horizontal component of curvature of a horizonal curve and K H ′, the curvature of its projection on a secant polar stereographic map. KH can be computed by subtracting from thc map factor times K H ′ the earth's curvature multiplied by a correction factor that depends only on the latitude of the place and inclination of the curve to the latitude circle. This factor vanishes if the curve is along a meridian but takes an extreme value if it is along a latitude. For a given orientation of the curve, the value of this factor increases gradually as the location of the curve moves from the Pole to the Equator and more rapidly after it crosses the Equator. It is less than 1 in the Northern Hemisphere but can exceed unity in the Southern Hemisphere.
Abstract
It is shown that, in any secant polar stereographic projection, a small circle on a sphere projects into a circle. This property provides a simple relationship between KH , the horizontal component of curvature of a horizonal curve and K H ′, the curvature of its projection on a secant polar stereographic map. KH can be computed by subtracting from thc map factor times K H ′ the earth's curvature multiplied by a correction factor that depends only on the latitude of the place and inclination of the curve to the latitude circle. This factor vanishes if the curve is along a meridian but takes an extreme value if it is along a latitude. For a given orientation of the curve, the value of this factor increases gradually as the location of the curve moves from the Pole to the Equator and more rapidly after it crosses the Equator. It is less than 1 in the Northern Hemisphere but can exceed unity in the Southern Hemisphere.
A NUMERICAL STUDY OF THE DIURNAL VARIATION OF METEOROLOGICAL PARAMETERS IN THE PLANETARY BOUNDARY LAYER
I. DIURNAL VARIATION OF WINDS
Abstract
The diurnal variation of various meteorological parameters in the Planetary Boundary Layer at different latitudes was studied adopting the basic framework of the simple one dimensional model of Estoque and modifying it in the light of the latest theories of atmospheric turbulence. Following are the results concerning the variation of wind: i) The phase angle of the diurnal wind speed wave shifts with height, the rate of shift varying with latitude. The latter is negative at latitudes north of 30°N., zero at about 30°N., and becomes positive south of 30°N. ii) Low level wind maximum occurs before midnight in midlatitudes, slightly after midnight at 30°N., at sunrise at 17.5°N., and later farther south. iii) The amplitude of the diurnal wind speed wave increases from north to south, reaches a maximum a little below 3O°N., and then decreases rapidly. The super-geostrophic winds are strongest between 40°N. and 20°N., suggesting that these latitudes are more favorable for the occurrence of low level jet than any others. The height of the low level wind maximum is below 500 m. north of 30°N., at about 550 m. between 30°N., and 12.5°N. and higher farther south. iv) The winds attain an absolute minimum value by sunrise north of 30°N., and only a relative minimum by about sunset south of 30°N. v) A semidiurnal oscillation of wind speed occurs in the layers below 400 m. north of 30°N., but is not noticed at latitudes south of say 30°N. vi) The Ekman layer appears to be shallower in latitudes south of 30°N. than in more northern latitudes.
Abstract
The diurnal variation of various meteorological parameters in the Planetary Boundary Layer at different latitudes was studied adopting the basic framework of the simple one dimensional model of Estoque and modifying it in the light of the latest theories of atmospheric turbulence. Following are the results concerning the variation of wind: i) The phase angle of the diurnal wind speed wave shifts with height, the rate of shift varying with latitude. The latter is negative at latitudes north of 30°N., zero at about 30°N., and becomes positive south of 30°N. ii) Low level wind maximum occurs before midnight in midlatitudes, slightly after midnight at 30°N., at sunrise at 17.5°N., and later farther south. iii) The amplitude of the diurnal wind speed wave increases from north to south, reaches a maximum a little below 3O°N., and then decreases rapidly. The super-geostrophic winds are strongest between 40°N. and 20°N., suggesting that these latitudes are more favorable for the occurrence of low level jet than any others. The height of the low level wind maximum is below 500 m. north of 30°N., at about 550 m. between 30°N., and 12.5°N. and higher farther south. iv) The winds attain an absolute minimum value by sunrise north of 30°N., and only a relative minimum by about sunset south of 30°N. v) A semidiurnal oscillation of wind speed occurs in the layers below 400 m. north of 30°N., but is not noticed at latitudes south of say 30°N. vi) The Ekman layer appears to be shallower in latitudes south of 30°N. than in more northern latitudes.
Abstract
To study the climatological structure of the atmospheric fields during the onset phase of the Indian summer monsoon, a composite analysis of different meteorological parameters over Indian stations is carried out. The composites are constructed relative to a uniform set of onset dates over south Kerala. Over the peninsular Indian stations, the rainfall composites show sudden and sharp increases with onset except in the case of east coast stations, where rainfall does not substantially change with the onset of the summer monsoon. The composite wind analysis demonstrates how the upper-tropospheric subtropical westerlies weaken and shift poleward and the tropical easterlies strengthen and spread north with the onset of the monsoon. The onset vortex that takes the monsoon northward along the west coast in many years is clearly discernible between 600 and 400 hPa in the composite streamline charts. The relative humidity builds up suddenly in the vertical a few days before the onset at the respective stations. The vertically integrated zonal moisture transport at individual stations over the peninsula increases sharply with respect to the south Kerala onset, with appropriate lag in time. The composite outgoing longwave radiation fields over the north Indian Ocean show rapid buildup of convective activity over the southeast Arabian Sea and east Bay of Bengal with the approach of the monsoon.
Abstract
To study the climatological structure of the atmospheric fields during the onset phase of the Indian summer monsoon, a composite analysis of different meteorological parameters over Indian stations is carried out. The composites are constructed relative to a uniform set of onset dates over south Kerala. Over the peninsular Indian stations, the rainfall composites show sudden and sharp increases with onset except in the case of east coast stations, where rainfall does not substantially change with the onset of the summer monsoon. The composite wind analysis demonstrates how the upper-tropospheric subtropical westerlies weaken and shift poleward and the tropical easterlies strengthen and spread north with the onset of the monsoon. The onset vortex that takes the monsoon northward along the west coast in many years is clearly discernible between 600 and 400 hPa in the composite streamline charts. The relative humidity builds up suddenly in the vertical a few days before the onset at the respective stations. The vertically integrated zonal moisture transport at individual stations over the peninsula increases sharply with respect to the south Kerala onset, with appropriate lag in time. The composite outgoing longwave radiation fields over the north Indian Ocean show rapid buildup of convective activity over the southeast Arabian Sea and east Bay of Bengal with the approach of the monsoon.
Abstract
The impact on tropical cyclone (TC) prediction from assimilating Doppler weather radar (DWR) observations obtained from the TC inner core and environment over the Bay of Bengal (BoB) is studied. A set of three operationally relevant numerical experiments were conducted for 24 forecast cases involving 5 unique severe/very severe BoB cyclones: Sidr (2007), Aila (2009), Laila (2010), Jal (2010), and Thane (2011). The first experiment (CNTL) used the NCEP FNL analyses for model initial and boundary conditions. In the second experiment [Global Telecommunication System (GTS)], the GTS observations were assimilated into the model initial condition while the third experiment (DWR) used DWR with GTS observations. Assimilation of the TC environment from DWR improved track prediction by 32%–53% for the 12–72-h forecast over the CNTL run and by 5%–25% over GTS and was consistently skillful. More gains were seen in intensity, track, and structure by assimilating inner-core DWR observations as they provided more realistic initial organization/asymmetry and strength of the TC vortex. Additional experiments were conducted to assess the role of warm-rain and ice-phase microphysics to assimilate DWR reflectivity observations. Results indicate that the ice-phase microphysics has a dominant impact on inner-core reflectivity assimilation and in modifying the intensity evolution, hydrometeors, and warm core structure, leading to improved rainfall prediction. This study helps provide a baseline for the credibility of an observational network and assist with the transfer of research to operations over the India monsoon region.
Abstract
The impact on tropical cyclone (TC) prediction from assimilating Doppler weather radar (DWR) observations obtained from the TC inner core and environment over the Bay of Bengal (BoB) is studied. A set of three operationally relevant numerical experiments were conducted for 24 forecast cases involving 5 unique severe/very severe BoB cyclones: Sidr (2007), Aila (2009), Laila (2010), Jal (2010), and Thane (2011). The first experiment (CNTL) used the NCEP FNL analyses for model initial and boundary conditions. In the second experiment [Global Telecommunication System (GTS)], the GTS observations were assimilated into the model initial condition while the third experiment (DWR) used DWR with GTS observations. Assimilation of the TC environment from DWR improved track prediction by 32%–53% for the 12–72-h forecast over the CNTL run and by 5%–25% over GTS and was consistently skillful. More gains were seen in intensity, track, and structure by assimilating inner-core DWR observations as they provided more realistic initial organization/asymmetry and strength of the TC vortex. Additional experiments were conducted to assess the role of warm-rain and ice-phase microphysics to assimilate DWR reflectivity observations. Results indicate that the ice-phase microphysics has a dominant impact on inner-core reflectivity assimilation and in modifying the intensity evolution, hydrometeors, and warm core structure, leading to improved rainfall prediction. This study helps provide a baseline for the credibility of an observational network and assist with the transfer of research to operations over the India monsoon region.
