The Evolution of Multi-Cell Convection During Northward IMF with B_Z/B_Y > 1

Chao-Song HUANG, George SOFKO, A. V. KOUSTOV and Dieter ANDRE
University of Saskatchewan, Canada
J. M. RUOHONIEMI and R. A. GREENWALD
The Johns Hopkins University/Applied Physics Laboratory, USA.
M. R. HAIRSTON
University of Texas at Dallas, USA.

In this talk, the evolution of the convection pattern during northward IMF conditions in response to changes in B_Z/B_Y on Nov. 11/98 is followed. Symmetric four-cell convection, with two normal cells at lower latitudes and two reverse cells at high latitude, occurs for B_Z/B_Y7. The four-cell pattern is shown to persist when B_Z/B_Y falls to about 2.3, but the reverse cells shift toward earlier magnetic local time (MLT) for negative B_Y and toward later MLT for positive B_Y. When B_Z/B_Y decrease to ~1.7, the convection appears as a three-cell pattern, with two normal cells and a single reverse cell focused near noon. The normal cells are focused at quite high latitudes (from 76 60 80 MLAT), with a large latitudinal spatial extent of about 10 - 15 MLAT (1000-1500 km). It is notable that DMSP data shows sunward convection over the southern hemisphere polar cap and four-cell convection at the same time that the HF radars see the patterns in the northern hemisphere. An illustrated model of the evolution of the convection patterns with changing B_Z/B_Y is shown.

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