Estimation of Gravity Wave Momentum Flux and Phase Speeds from Quasi-Lagrangian Stratospheric Balloon Flights. Part I: Theory and Simulations

Abstract

A methodology for estimating gravity wave characteristics from quasi-Lagrangian observations provided by long-duration, superpressure balloon flights in the stratosphere is reviewed. Wavelet analysis techniques are used to detect gravity wave packets in observations of pressure, temperature, and horizontal velocity. An emphasis is put on the estimation of gravity wave momentum fluxes and intrinsic phase speeds, which are generally poorly known on global scales in the atmosphere. The methodology is validated using Monte Carlo simulations of time series that mimic the balloon measurements, including the uncertainties associated with each of the meteorological parameters. While the azimuths of the wave propagation direction are accurately retrieved, the momentum fluxes are generally slightly underestimated, especially when wave packets overlap in the time-frequency domain, or for short-period waves. A proxy is derived to estimate by how much momentum fluxes are reduced by the analysis. Retrievals of intrinsic phase speeds are less accurate, especially for low phase speed waves. A companion paper (Part II) implements the methodology to observations gathered during the Vorcore campaign that took place in Antarctica

Sensitivity study for mesoscale simulations of gravity waves above Antarctica during Vorcore

“…intrinsic frequencies are high; Boccara et al, 2008), and in a large part (for the present case) because the sampling frequency (every 15 min) is such that waves with intrinsic periods shorter than 1 h are not well observed. The simulated fluxes are also expected to be underestimated, due to the limited resolution (e.g.…”

Effect of gravity wave temperature fluctuations on homogeneous ice nucleation in the tropical tropopause layer

“…Superpressure balloons are advected by the wind on isopycnic (constant-density) surfaces and therefore behave as quasi-Lagrangian tracers of atmospheric motions. A further remarkable property of superpressure balloons is their sensitivity to atmospheric gravity waves (Massman, 1978;Nastrom, 1980;Boccara et al, 2008;Vincent and Hertzog, 2014). The sampling frequency of the balloon position, atmospheric pressure, and temperature during the campaign is every 30 s.…”

“…Instead, we infer the temperature disturbances from the balloon vertical displacements (ζ b ). The isentropic air parcel vertical displacement (ζ ) is linked to that of the isopycnic balloon through (Boccara et al, 2008), where g is the gravitational acceleration, c p is the specific heat at constant pressure, R a is the gas constant for air, and ∂T /∂z is the vertical gradient of the background temperature. We use the European Centre for Medium-range Weather Forecasts (ECMWF) operational analyses to diagnose ∂T /∂z at the balloon position in the above equation.…”

Gravity wave reflection and its influence on the consistency of temperature- and wind-based momentum fluxes simulated above Typhoon Ewiniar

“…Note that the sign of m is negative for upward propagating waves and positive for downward propagating waves, with the sign convention of non-negative ω. For the calculation of F T in this study, we take the sign of m to be negative, based on the assumption that the temperature variance stems from upward propagating waves, which is often made in other studies as well (e.g., Espy et al, 2004;Boccara et al, 2008;Hertzog et al, 2008;Li et al, 2011).…”