Gravity‐wave forcing in the stratosphere: Observational constraints from the Upper Atmosphere Research Satellite and implications for parameterization in global models

Global models that include parameterized gravity‐wave effects have an excessively broad range of tuning parameters to choose from that allow a very broad range of gravity‐wave momentum forcing distributions. We derive a set of constraints on gravity‐wave characteristics near the tropopause from databased estimates of gravity‐wave effects in the stratosphere. We use 5.6 years of Upper Atmosphere Research Satellite data and UK Met Office‐analyzed wind and temperature fields to first derive estimates of the gravity‐wave mean flow forcing in the stratosphere. We then compare these estimates to a suite of gravity‐wave model calculations to infer the constraints on the gravity‐wave characteristics near the tropopause. These constraints apply to the portion of the gravity‐wave spectrum that dissipates in the stratosphere and does not include those that dissipate and drive the mesosphere. We focus on equatorial and extratropical regions separately and find substantially different wave characteristics between the two. We also find a seasonal variation in gravity‐wave characteristics in the extratropics. Near the equator, gravity waves assist in driving the quasibiennial and semiannual oscillations, and our constraints on “gravity waves” likely include a blend of characteristics of both ordinary gravity waves and some Kelvin‐wave modes. In the extratropics, gravity‐wave forcing primarily assists in the annual winter‐to‐summer transition from westward‐to‐eastward winds.