Abstract

Abstract. Gravity wave drag (GWD) is an important driver of the middle atmospheric dynamics. However, there are almost no observational constraints on its strength and distribution (especially horizontal). In this study we analyze orographic GWD (OGWD) output from Canadian Middle Atmosphere Model simulation with specified dynamics (CMAM-sd) to illustrate the interannual variability in the OGWD distribution at particular pressure levels in the stratosphere and its relation to major climate oscillations. We have found significant changes in the OGWD distribution and strength depending on the phase of the North Atlantic Oscillation (NAO), quasi-biennial oscillation (QBO) and El Niño–Southern Oscillation. The OGWD variability is shown to be induced by lower-tropospheric wind variations to a large extent, and there is also significant variability detected in near-surface momentum fluxes. We argue that the orographic gravity waves (OGWs) and gravity waves (GWs) in general can be a quick mediator of the tropospheric variability into the stratosphere as the modifications of the OGWD distribution can result in different impacts on the stratospheric dynamics during different phases of the studied climate oscillations.

Highlights

  • The internal gravity wave (GW) sourcing, propagation and breaking is governed to some extent by processes in the stratosphere, there is a significant portion of the gravity waves (GWs) spectra created in the troposphere

  • As we show in the first section of results, the CMAM-sd orographic GWD (OGWD) climatological horizontal distribution at 100, 50, 30 and 10 hPa is highly zonally asymmetric and OGWD tends to be distributed in local hotspots

  • In the first section we show the simulated climatological OGWD distribution at 100, 50, 30 and 10 hPa levels and estimate its interannual variability to be about half of the climatological OGWD value at the major hotspots

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Summary

Introduction

The internal gravity wave (GW) sourcing (e.g., adjustment processes; Plougonven and Zhang, 2014), propagation and breaking is governed to some extent by processes in the stratosphere, there is a significant portion of the GW spectra created in the troposphere (mostly orography and convection; Alexander et al, 2009). From sensitivity simulations with a mechanistic model, Šácha et al (2016) demonstrated the dynamical impact of the artificially enhanced GWD in the stratosphere and most importantly the significant impact of the spatial GWD distribution This can open new horizons for research on teleconnections between tropospheric (e.g., El Niño–Southern Oscillation, North Atlantic Oscillation, Pacific Decadal Oscillation) and stratospheric (e.g., polar vortex stability) phenomena taking into account that the tropospheric variability can affect the distribution of GW sources and the GWD distribution (and strength) in the stratosphere. This is the main hypothesis that we investigate in this study. It is not possible to compute the GWD from current satellite

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