Abstract
Abstract. Effects of realistic propagation of gravity waves (GWs) on distribution of GW pseudomomentum fluxes are explored using a global ray-tracing model for the 2009 sudden stratospheric warming (SSW) event. Four-dimensional (4D; x–z and t) and two-dimensional (2D; z and t) results are compared for various parameterized pseudomomentum fluxes. In ray-tracing equations, refraction due to horizontal wind shear and curvature effects are found important and comparable to one another in magnitude. In the 4D, westward pseudomomentum fluxes are enhanced in the upper troposphere and northern stratosphere due to refraction and curvature effects around fluctuating jet flows. In the northern polar upper mesosphere and lower thermosphere, eastward pseudomomentum fluxes are increased in the 4D. GWs are found to propagate more to the upper atmosphere in the 4D, since horizontal propagation and change in wave numbers due to refraction and curvature effects can make it more possible that GWs elude critical level filtering and saturation in the lower atmosphere. GW focusing effects occur around jet cores, and ray-tube effects appear where the polar stratospheric jets vary substantially in space and time. Enhancement of the structure of zonal wave number 2 in pseudomomentum fluxes in the middle stratosphere begins from the early stage of the SSW evolution. An increase in pseudomomentum fluxes in the upper atmosphere is present even after the onset in the 4D. Significantly enhanced pseudomomentum fluxes, when the polar vortex is disturbed, are related to GWs with small intrinsic group velocity (wave capture), and they would change nonlocally nearby large-scale vortex structures without substantially changing local mean flows.
Highlights
Atmospheric gravity waves (GWs) play an important role in the momentum and energy budgets of global circulations in the middle and upper atmosphere
GW rays are launched every 3 h, and 3 d old rays are eliminated. These launch intervals and ray lifetimes are chosen considering computational time, the timescale of the large-scale flow, and elapsed time for rays launched in the troposphere to reach the upper mesosphere and lower thermosphere
In each ensemble member of Orographic GWs (OGWs) and number of rays for OGWs (NOGWs), a single GW packet is launched at a horizontal grid point, and properties of GW packets are randomly chosen from a precomputed set of parameters made based on previous GW parameterizations (GWPs) studies for OGWs and NOGWs
Summary
Atmospheric gravity waves (GWs) play an important role in the momentum and energy budgets of global circulations in the middle and upper atmosphere. Amemiya and Sato (2016) presented a quasi-columnar way of implementing a ray-based GWP in global models, ignoring time propagation of GWs It is not clear how ray-based GWPs can be formulated in a way that is consistent with theories on interactions between GW packets and slowly varying mean flows. Given that GW refraction and transient propagation cannot be considered in these models with conventional columnar GWPs, there may be limitations in the model-based assessment that is of relative importance between PWs and GWs in evolutions of SSWs and ESs. Satellite observations have presented evidence of substantial variations of GW activity around SSW onset dates. A summary and discussion is given in the last section
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