Excitation of gravity waves by ocean surface wave packets: Upward propagation and reconstruction of the thermospheric gravity wave field

Abstract

AbstractIn this paper, we derive the atmospheric gravity waves (GWs) and acoustic waves excited by an ocean surface wave packet with frequency ωF and duration χ in an f plane, isothermal, windless, and inviscid atmosphere. This packet is modeled as a localized vertical body force with Gaussian depth σz. The excited GW spectrum has discrete intrinsic frequencies (ωIr) at ωF and ωF±2π/χ (“sum” and “difference”) and has a “continuum” of frequencies for ωIr<ωF+2π/χ. The momentum flux spectrum peaks at ωIr∼ωF and decreases rapidly as ωIr decreases. To simulate the effect these GWs have on the thermosphere, we present a new scheme whereby we sprinkle GW spectra in the ocean wave packet region, ray trace the GWs, and reconstruct the GW field. We model the GWs excited by ocean wave packets with horizontal wavelengths of λH = 190 km, periods of τF = 2π/ωF = 14 − 20 min and χ = 30 − 50 min. The excited GWs begin to arrive at z = 250 km at t ∼ 75 − 80 min. Those with the largest temperature perturbations have large ωIr and arrive at t ∼ 90 − 130 min. If |α|=ωF+2π/χ is a solution of the GW dispersion relation and |α| is less than the buoyancy frequency at z = 250 km, the sum and highest‐frequency continuum GWs have much larger phase speeds and arrive 50–60 min earlier with larger than the GWs with frequency ωF. For a packet with λH = 190 km, τF = 14 min, χ = 30 min, and height h0=1.3 m, the maximum at z = 250 km is ∼9, 22, and 40 K for σz = 1, 2, and 4 m, respectively.