Dynamics and Electrodynamics of an Ultra‐Fast Kelvin Wave (UFKW) Packet in the Ionosphere‐Thermosphere (IT)

Abstract

AbstractNumerical experiments are performed using a suite of general circulation models that enable the interaction between a Kelvin wave packet and the ionosphere‐thermosphere (IT) to be elucidated. 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%. The combination of positive and negative responses, and their relative magnitudes, depends on the phasing of the UFKW as it moves zonally relative to the Sun‐synchronous diurnal variation of the ionosphere, in addition to its changing amplitude between DOY 266 and 282. Modifications of order 10 ms−1 and −7% to zonal‐mean zonal winds and NmF2, respectively, also result from dissipation of the UFKW packet.