Dynamics and electrodynamics of an ultra-fast kelvin wave (UFKW) packet in the ionosphere-thermosphere (IT)

Focus is on an eastward-propagating ultra-fast Kelvin wave (UFKW) packet with periods between 2 and 4 days and zonal wavenumber s =−1 during day of year (DOY) 266–281, 2009. Dissipative processes modify the classic UFKW dynamics (equatorially trapped, small meridional wind component) in three ways: (1) molecular diffusion acts to spread the UFKW zonal (u ) and meridional (v ) wind fields meridionally, pole to pole, as u and v , respectively, decay and grow with increasing height; (2) due to molecular diffusion, the UFKW spectrum at longer periods and with shorter vertical wavelengths preferentially dissipates with height; and (3) interaction with the diurnally varying IT introduces a westward-propagating s =+2 component to the wind field that significantly modifies its longitude-UT structure to include a diurnal modulation.

The F-region ionosphere also responds with s =+2, which originates from the influence of diurnally varying E-region conductivity on E ×B drifts. Additional spectral peaks in v and ionospheric parameters arise due to longitude variations in the magnetic field. Maximum excursions in NmF2 (as compared with those from a simulation without UFKW forcing) achieve values as large as ±50% but more commonly occur in the range of ±20-30%.