Characteristics of Gravity Waves from Convection and Implications for Their Parameterization in Global Circulation Models

Abstract

Characteristic properties of gravity waves from convection over the continental United States are derived from idealized high-resolution numerical simulations. In a unique modeling approach, waves are forced by a realistic thermodynamic source based on observed precipitation data. The square of the precipitation rate and the gravity wave momentum fluxes both show lognormal occurrence distributions, with long tails of extreme events. Convectively generated waves can give forces in the lower stratosphere that at times rival orographic wave forcing. Throughout the stratosphere, zonal forces due to convective wave drag are much stronger than accounted for by current gravity wave drag parameterizations, so their contribution to the summer branch of the stratospheric Brewer-Dobson circulation is in fact much larger than models predict. A comparison of these forces to previous estimates of the total drag implies that convectively generated gravity waves are a primary source of summer-hemisphere stratospheric wave drag. Furthermore, intermittency and strength of the zonal forces due to convective gravity wave drag in the lower stratosphere resemble analysis increments, suggesting that a more realistic representation of these waves may help alleviate model biases on synoptic scales. The properties of radar precipitation and gravity waves seen in this study lead to a proposed change for future parameterization methods that would give more realistic drag forces in the stratosphere without compromising mesospheric gravity wave drag.

Secondary Gravity Waves Generated by Breaking Mountain Waves Over Europe

“…Through dissipation mechanisms such as viscosity, critical level filtering, and wave breaking, waves can deposit their energy and momentum into the mean state causing localized forcing of the mean winds and heating/cooling of the atmosphere (Fritts & Alexander, ; Heale et al, , ; Hickey et al, ; Holton, ; Holton & Alexander, ; Lund & Fritts, ; McFarlane, ; Vadas, ; Vadas et al, ; Vadas & Fritts, ). The influence of gravity wave forcing contributes to atmospheric phenomena such as the quasi‐biennial oscillation (QBO) (Alexander & Holton, ; Baldwin et al, ; Dunkerton, ; Ern et al, ; Piani et al, ), the summer branch of the Brewer‐Dobson circulation (Alexander & Rosenlof, ; Stephan et al, ), and the cold summer mesopause (Alexander & Rosenlof, ; Garcia & Solomon, ; Holton & Alexander, ).…”

How does knowledge of atmospheric gravity waves guide their parameterizations?

“…For illustrative purposes the example of intermittency was recalled. Demonstrated from observations as a robust feature (Alexander et al ., ; Hertzog et al ., ; Wright et al ., ; Stephan et al ., ), its introduction into parameterizations appears to be beneficial (Bushell et al ., ; de la Cámara et al ., ). It redistributes the resulting forcing through the stratosphere and mesosphere, in a way that lies outside the possible outcomes of parameterizations with constant sources for non‐orographic waves.…”

Multilayer Observations and Modeling of Thunderstorm‐Generated Gravity Waves Over the Midwestern United States

“…Deep convection, for example, thunderstorms, Mesoscale Convective Complexes, and Mesoscale Convective Systems (MCSs), represents important sources of GWs, especially at tropical and midlatitudes during local summer (Gong et al, ; Hoffmann & Alexander, ; Perwitasari et al, ; Tsuda et al, ). Convectively generated GWs contribute to the summer branch of the Brewer‐Dobson Circulation (Alexander & Rosenlof, ; Stephan et al, ) and drive the Quasi‐Biennial Oscillation (Alexander & Holton, ; Piani et al, ), and the Semi‐Annual Oscillation (Ern et al, ; Garcia et al, ). In the mesosphere and lower thermosphere (MLT), convectively generated GWs can be subject to significant breaking leading to secondary wave generation (Horinouchi et al, ; Snively & Pasko, ; Vincent et al, ) and have significant impacts on mean winds and temperature structure (Vadas & Liu, ; Vadas et al, ).…”

“…However, high‐resolution observations of middle‐atmospheric GWs cannot yet be reproduced efficiently in cloud‐resolving models, using simple sources initialized from soundings, nor GW‐resolving numerical weather prediction and general circulation models. As a simpler strategy, Grimsdell et al (), Stephan and Alexander (), and Stephan et al () used Doppler radar observations of precipitation rates to infer latent heating rates that drive their simulations. This has been shown advantageous in being able to replicate observations at lower computational expense.…”