Open AccessSpin‐down circulation of high‐latitude ion drag‐driven gyres
Author(s) -
Walterscheid R. L.,
Brinkman D. G.
Publication year - 2008
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2007ja012682
Subject(s) - ocean gyre , drag , anticyclone , circulation (fluid dynamics) , physics , forcing (mathematics) , atmospheric sciences , mechanics , jet (fluid) , subtropics , fishery , biology
We have used a model of thermospheric gyres with simplified geometry (azimuthally symmetric cylindrical coordinates) to study the spin‐down of high‐latitude gyres spun‐up into rapid motion by ion drag. Winds are spun‐up for an hour subject only to circumgyre ion‐drag forcing from strong radial electric fields with peak values of ±75 mV m −1 centered at a radial distance of 1500 km. The winds in the core of the jets approach 500 ms −1 . After the forcing ceases the winds begin to diminish owing to viscous forces. Ekman forcing drives a strong divergent circulation in the radius‐height plane that continues for several hours after ion‐drag forcing has ceased. This radial circulation is opposite to the circulation driven by agradient forcing during spin‐up. The circulation is significantly stronger for cyclonic rather than anticyclonic gyres. This caused peak wind for the circumgyre flow to be different for cyclonic and anticyclonic gyres, but the difference is not too marked. However, the location of the maximum and the wind at fixed altitudes below the peak can be quite different. The jet in the cyclonic gyre peaks higher, and the gradients in the anticyclonic gyre below the jet core are much better maintained.