Advertisement

Thermal and wind structure of the monsoon trough boundary layer

  • G. Rajkumar
  • R. Narasimha
  • S. P. Singal
  • B. S. Gera
Article
  • 26 Downloads

Abstract

Radiosonde data from Jodhpur, taken at 0530, 1730 and around 1100 hr IST during MONTBLEX 1990, reveal that the distribution of virtual potential temperature0 v below about 500 hPa has a structure characterized by up to three layers each of approximately constant gradient. We are thus led to introduce a characterization of the observed thermal structure through a sequence of the symbolsN, S andU, standing respectively for neutral, stable or unstable conditions in the different layers, beginning with the one closest to the ground. It is found that, of the 29 combinations possible, only the seven classes,S, SS′, SNS′, NS, NSS′, USS′ andUNS are observed, whereS′ stands for a stable layer with a different gradient of0 r. than in the layerS. It is also found that, in 90% of the launches at 0530 hr, 48% of the launches at 1730 hr and 69% of the launches around 1100 hr, the first radiosonde layer near the ground is stable; the classical mixed layer was found in only 11 % of the data set analysed, and, if present on other occasions, must have been less than 250 m in height, the first level at which radiosonde data are available. Supplementing the above data, sodar echograms, available during 82% of the time between June and August 1990, suggest a stable layer up to a few tens of metres 48% of the time. A comparative study of the radiosonde data at Ranchi shows that the frequent prevalence of stability near the surface at Jodhpur cannot be attributed entirely to the large scale subsidence known to be characteristic of the Rajasthan area. Further, data at Jodhpur reveal a weak low level jet at heights generally ranging from 400 to 900 m with wind speeds of 6 to 15 m/s. Based on these results, it is conjectured that the lowest layers in the atmosphere during the monsoons, especially with heavy clouding or rain, may frequently be closer to the classical nocturnal boundary layer than to the standard convective mixed layer, although often with shallow plumes that penetrate such a stable layer during daytime.

Keywords

Atmospheric boundary layer monsoons thermodynamic structure 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Ananthakrishnan R and Soman M K 1992 Inconsistencies in the mean fields of temperature, geopotential height and winds over the Indian aerological network during July — August;Mausam 43 199–204Google Scholar
  2. Brown E H and Hall F F Jr. 1978 Advances in atmospheric acoustics;Rev. Geophys. Space Phys. 16 47–110CrossRefGoogle Scholar
  3. Das P K 1962 Mean vertical motion and non-adiabatic heat sources over India during the monsoon;Tellus 14 212–220CrossRefGoogle Scholar
  4. Findlater J 1969 A major low level air current near the Indian Ocean during the northern summer;Q. J. R. Meteorol. Soc. 95 362–280CrossRefGoogle Scholar
  5. Gamo M, Goyal P, Manjukumari, Mohanty U C and Singh M P 1994 Mixed layer characteristics as related to the monsoon climate of New Delhi, India;Boundary-Layer Meteorol. 67 213–227CrossRefGoogle Scholar
  6. Holt T and Raman S S 1978 A comparison of the significant features of the marine boundary layers over the east central Arabian Sea and the north Central Bay of Bengal during MONEX-79;Mausam 38 171–176Google Scholar
  7. Holt T and Raman S S 1985 Aircraft and ship observations of the mean structure of the marine boundary layer over Arabian Sea during MONEX-79;Boundary-Layer Meteorol. 33 259–282CrossRefGoogle Scholar
  8. Holzworth G C 1962 A study of air pollution potential for western United States;J. Appl. Meteorol. 1 366–382CrossRefGoogle Scholar
  9. Iribarne J V and Godson W L 1973 Atmospheric Thermodynamics;Geophysics and Astrophysics Monographs 6 pp. 222Google Scholar
  10. Joseph P V and Raman P L 1966 Existence of low level westerly jet stream over peninsular India during July;Indian J. Meteorol. Geophys. 17 407–410Google Scholar
  11. Kusuma G R, Raman S S and Prabhu A 1991 Boundary-layer heights over the monsoon trough region during active and break phases;Boundary-Layer Meteorol. 57 129–138CrossRefGoogle Scholar
  12. Padmanabhamurty B and Mandai B B 1976 A note on pollution potential at Delhi during October 1975 — March 1976;Vayu Mandai 6 58–60Google Scholar
  13. Padmanabhamurty B and Mandai B B 1979 Climatology of inversions, mixing depths and ventillation coefficients at Delhi;Mausam 30 473–478Google Scholar
  14. Parasnis S S and Goyal S B 1990 Thermodynamic features of the atmospheric boundary layer during the summer monsoon;Atmos. Environ. A24 743–752Google Scholar
  15. Parasnis S S and Morwal S B 1994 A convectively-driven boundary layer in the monsoon trough;Boundary-Layer Meteorol. 71 197–204CrossRefGoogle Scholar
  16. Raman S S 1982 Dynamics of the atmospheric boundary layer during the 1980 total solar eclipse;Proc. Indian National Sci. Academy A48 187–195Google Scholar
  17. Raman S S, Templeman B, Templeman S, Holt T, Murthy A B, Singh M P, Agarwaal P, Nigam S, Prabhu A and Ameenulla S 1990 Structure of the Indian southwesterly premonsoon and monsoon boundary layers observations and numerical simulations;Atmos. Environ. A24 723–734Google Scholar
  18. Rao Y P 1976 Southwest monsoon;Meteorological Monograph, Synoptic meteorology 1/1976 Indian Meteorological Department pp. 367Google Scholar
  19. Rudra Kumar S, Srinivasan H P, Satyadev H N, Ameenulla S and Prabhu A 1991 Surface data from MONTBLEX-90;Report no. 91MD2, Centre for Atmospheric Sciences, Indian Institute of Science, Bangalore 560012, IndiaGoogle Scholar
  20. Shaw N A 1974 Observations of atmospheric structure using an acoustic sounder; ANL/RER/75-2Radiological and Environmental Research Division, Argonne National Laboratory, IL 60439, USA, pp. 37Google Scholar
  21. Sikka D R and Narasimha R 1995 Genesis of the monsoon trough boundary layer experiment (MONTBLEX);Proc. Indian Acad. Sci. (Earth Planet. Sci.)104 157–187Google Scholar
  22. Singal S P 1989 Acoustic sounding stability studies;Encyclopedia of environment control technology: Air pollution control (ed) Cheremissinoff (Houston (Texas): Gulf Publishing)2 1003–1061Google Scholar
  23. Singal S P 1990 Need for acoustic sounding (SODAR) monitoring of the atmospheric boundary layer for environmental pollution management, in environmental planning and management in India;New world environment series, (New Delhi: Ashish Publishing House)1 77–105Google Scholar
  24. Singal S P 1993 Monitoring air pollution related meteorology using SODAR;Appl. Phys. B (Photo and Laser Chemistry)57 65–82CrossRefGoogle Scholar
  25. Singal S P and Gera B S 1982 Acoustic remote sensing of the boundary layer;Proc. Indian Acad. Sci. (Engg. Section)5 131–157Google Scholar
  26. Singal S P, Gera B S and Aggarwal S K 1983 Studies of the boundary layer at Delhi using sodar;Proc. 2nd Int. Symp. on Acoustic Remote Sensing of the Atmosphere and Oceans, Rome, Italy, 29th August — 1st Septemberxiii 1–8Google Scholar
  27. Singal S P, Gera B S and Aggarwal S K 1985 Studies of sodar-observed dot echo structures;Atmosphere-Ocean 23 304–312Google Scholar
  28. Singal S P, Lewthwaite E W D and Wratt D S 1989 Estimating atmospheric stability from monostatic acoustic sounder records;Atmos. Environ. 23 2079–2089CrossRefGoogle Scholar
  29. Singal S P, Gera B S and Ojha V K 1993 Sodar studies of the monsoon trough boundary layer at Jodhpur (India);Mausam 44 9–14Google Scholar
  30. Srivastav S K 1995 Synoptic meteorological observations and weather conditions during MONTBLEX-90;Proc. Indian Acad. Sci. (Earth Planet. Sci.)104 189–220Google Scholar
  31. Stull R B 1988 An introduction to boundary layer meteorology, Kluwer Academic Publishers, pp. 666Google Scholar
  32. Wamser C and Lykossov V N 1995 On the friction velocity during blowing snow;Beitr. Phys. Atmosph. 68 85–94Google Scholar

Copyright information

© Indian Academy of Sciences 1996

Authors and Affiliations

  • G. Rajkumar
    • 1
  • R. Narasimha
    • 1
  • S. P. Singal
    • 2
  • B. S. Gera
    • 2
  1. 1.Jawaharlal Nehru Centre for Advanced Scientific ResearchBangaloreIndia
  2. 2.National Physical LaboratoryNew DelhiIndia

Personalised recommendations