地球流体セミナー/ Workshop on Climate Modeling and Satellite Observations

Development of Tropical Circulation in Response to an Equatorial Warm SST Anomaly Revealed by an switch-on Ensemble Aqua-planet GCM

Department of Earth and Planetary Sciences, Kushu University
Kensuke Nakjima
kensuke@geo.kyushu-u.ac.jp
22nd, Jan., 2002


Contens


Introduction: where does rain fall occur in toropics?


Introduction: Why do we use aqua-planet GCM?


Introduction: previous studies which used aqua-planet GCM.


Introduction: observations of SST and precipitation distributions






Result obtained by Gill (1980).


Result obtained by Heckley and Gill (1984).


Question: How about can the results of Gill (1980) be modified ?


Description of our numerical model: GFD Dennou Club AGCM ver. 5


Boundary condition: SST distribution
  • put warm patch on the equator, where temperature anomaly is 4 K.


Reslut: horizontal distribution of precipitation (after 2000 day and 50 days mean).


Reslut: horizontal distribution of surface pressure (after 2000 day and 50 days mean).


Steady state responce
  • west of the warm SST patch: Kelvin response
  • east of the warm SST patch: Rossby response ?


Time averaged structure
  • upper left : horizontal wind and geopotential hight anomaly at σ=0.175
  • upper right: temperature anomaly at σ=0.175
  • lower left : zonal and vertical wind and temperature anomaly at equator
  • lower right: horizontal wind and surface pressure anomaly at σ=0.995


Moisture flux
  • upper left : qu at equator (longitude-hight cross section)
  • upper right: qv at 138 E (latitude-hight cross section)
  • lower left : qv at 180 E (latitude-hight cross section)
  • lower right: qv at 278 E (latitude-hight cross section)


Summary of the steady state response.




Outline of the ensemble experiment (1)


Resluts of the ensemble experiment (1)



Summay of the ensemble experiment (1)


Outline of the ensemble experiment (2)


Resluts of the ensemble experiment (2)



Resluts of the ensemble experiment (2) [mpeg movie]



Summary of the ensemble experiment (2)
  • Kelvin response is clearly observed, but Rossby response is obscure.
  • Why ?
    • The negative heating due to drying in the west region of the warm SST patch weakens the Rossby wave which is excited by the warm SST patch.
    • Dispersion relation of the equatorial Rossby wave: The group velocity of short equatorial Rossby wave is eastward.
    • Gill (1980) and Heckley and Gill (1984) use long wave approximation (re-calculation result of Heckley and Gill (1984) without long wave approximation is hear).


Dispersion relation of the equatorial wavw
  • The group velocity of short equatorial Rossby wave is eastward.


Summary


Future ploblem (1)


Future ploblem (2)


References


References

  • Gill, A. E., 1980: Some simple solutions for heat-induced tropical circulation. Quart. J. Roy. Meteorol. Soc., 106, 447-462.
  • Heckley, W. A., and A. E. Gill, 1984: Some simple analytical solutions to the problems of forced equatorial long waves. Quart. J. Roy. Meteorol. Soc., 110, 203-217.
  • Hayashi, Y.-Y. and A. Sumi, 1986: The 30-40 day oscillations simulated in an ``aqua planet'' model. J. Meteor. Soc. Japan, 64, 451-467.
  • Hosaka, M., M. Ishiwatari, S. Takehiro, K. Nakajima, and Y.-Y. Hayashi, 1998: Tropical precipitation patterns in response to a local warm SST area placed at the equator of an Aqua planet. J. Meteor. Soc. Japan, 76, 289-305.
  • Numaguti, A., and Y.-Y. Hayashi, 1991: Behavior of cumulus activity and the structures of circulations in an aqua planet mode. 2. Eastward-moving planetary scale structure and the intertropical convergence zone. J. Meteor. Soc. Japan, 69, 563-579.
  • Numaguti, A., 1992: Numerical experiments on the large scale structure of cumulus activity in the tropics. Ph.D. Thesis, University of Tokyo. (in Japanese).
  • Numaguti, A., 1993: Dynamics and energy-balance of the Hadley circulation and the tropical precipitation zones - significance of the distribution of evaporation. J. Atmos. Sci., 50, 1874-1887.
  • Kodama, Y. M., 1999: Roles of the atmospheric heat sources in maintaining the subtropical convergence zones: An aqua-planet GCM study. J. Atmos. Sci., 56, 4032-4049.
  • Takayabu, Y. N., 1994: Large-scale cloud disturbances associated with equatorial waves. 1. Spectral features of the cloud disturbances, J. Meteor. Soc. Japan, 72, 433-449.
  • Takayabu, Y. N., 1994: Large-scale cloud disturbances associated with equatorial waves. 2. Weastward-propagating inertio-grabity waves, J. Meteor. Soc. Japan, 72, 451-465.
  • Toyoda, E., K. Nakajima, M. Ishiwatari, and Y,-Y. Hayashi, 1999: Response of the tropical atmosphere to a localized warm SST area: Time-development observed in an aqua-planet ensemble experiment. Nagare Multimedia http://www.nagare.or.jp/mm/99/toyoda/.
  • Wheeler M, G. N. Kiladis, and P. J. Webster, 2002: Large-scale dynamical fields associated with convectively coupled equatorial waves, J. Atmos. Sci., 57, 613-640.
  • TRMM: http://www.eorc.nasda.go.jp/TRMM/Gallery/tev/pdf/tev_11.pdf


Odaka Masatsugu 2002-01-20