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

In this paper, we derive the atmospheric gravity waves (GWs) and acoustic waves excited by an ocean surface wave packet with frequency. omega(F) and duration chi in an f plane, isothermal, windless, and inviscid atmosphere. This packet is modeled as a localized vertical body force with Gaussian depth sigma(z). The excited GW spectrum has discrete intrinsic frequencies (omega(Ir)) at.omega(F) and omega(F)+/- 2 pi/chi (sum and difference) and has a continuum of frequencies for omega(Ir) < omega(F) + 2 pi/chi. The momentum flux spectrum peaks at omega(Ir) similar to omega(F) and decreases rapidly as omega(Ir) 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 lambda(H) = 190 km, periods of tau(F) = 2 pi/omega(F) = 14 - 20 min and chi = 30 - 50 min. The excited GWs begin to arrive at z = 250 km at t similar to 75 - 80 min. Those with the largest temperature perturbations T' have large omega(Ir) and arrive at t similar to 90 - 130 min. If vertical bar alpha vertical bar = omega(F) + 2 pi/chi is a solution of the GW dispersion relation and vertical bar alpha vertical bar 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 omega(F). For a packet with lambda(H) = 190 km, tau(F) = 14 min, chi = 30 min, and height h(0) = 1.3 m, the maximum T' at z = 250 km is similar to 9, 22, and 40 K for sigma(z) = 1, 2, and 4 m, respectively.