Showing papers by "Sharon L. Vadas published in 2015"

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

Abstract: In 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 N 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 T′ 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 T′ 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 T′ at z = 250 km is ∼9, 22, and 40 K for σz = 1, 2, and 4 m, respectively.