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)

Hovmöller diagram of precipitation anomaly at equator 1 run 8 run 16 run 32 run 64 run 128 run

Hovmöller diagram of surface prssuer anomaly at equator 1 run 8 run 16 run 32 run 64 run 128 run

horizontal distribution of precipitation anomaly 1 run 8 run 16 run 32 run 64 run 128 run

horizontal distribution of surface pressure 1 run 8 run 16 run 32 run 64 run 128 run

Summay of the ensemble experiment (1)

Outline of the ensemble experiment (2)

Hovmöller diagram of temperature anomaly at equator on σ=0.549 Hovmöller diagram of zonal wind anomaly at equator on σ=0.995 Hovmöller diagram of zonal wind anomaly at equator on σ=0.830 Hovmöller diagram of zonal wind anomaly at equator on σ=0.175 Hovmöller diagram of surface pressure anomaly at 15 N Hovmöller diagram of zonal wind anomaly at 15 N on σ=0.175 Hovmöller diagram of meridional wind anomaly at 15 N on σ=0.175

Horizontal distribution of precipitation anomaly Horizontal wind anomaly on σ=0.23 and temperature anomaly on middle level Horizontal wind anomaly distribution on σ=0.995 and surface pressure anomaly Horizontal distribution of precipitation anomaly and moisture flux anomaly on σ=0.995

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

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