Role of Wind Filtering and Unbalanced Flow Generation in Middle Atmosphere Gravity Wave Activity at Chatanika Alaska

Colin Triplett,Kim Nielsen,Richard Collins,Kohei Mizutani,V Harvey

doi:10.3390/atmos8020027

Abstract

The meteorological control of gravity wave activity through ﬁltering by winds and generation by spontaneous adjustment of unbalanced ﬂows is investigated. This investigation is based on a new analysis of Rayleigh LiDAR measurements of gravity wave activity in the upper stratosphere-lower mesosphere (USLM,40–50km)on 152 nights at Poker Flat Research Range (PFRR), Chatanika, Alaska (65◦ N, 147◦ W), over 13 years between 1998 and 2014. The LiDAR measurements resolve inertia-gravity waves with observed periods between 1 h and 4 h and vertical wavelengths between 2 km and 10 km. The meteorological conditions are deﬁned by reanalysis data from the Modern-Era Retrospective Analysis for Research and Applications (MERRA). The gravity wave activity shows large night-to-night variability, but a clear annual cycle with a maximum in winter,and systematic interannual variability associated with stratospheric sudden warming events. The USLM gravity wave activity is correlated with the MERRA winds and is controlled by the winds in the lower stratosphere through ﬁltering by critical layer ﬁltering. The USLM gravity wave activity is also correlated with MERRA unbalanced ﬂow as characterized by the residual of the nonlinear balance equation. This correlation with unbalanced ﬂow only appears when the wind conditions are taken into account, indicating that wind ﬁltering is the primary control of the gravity wave activity.

Highlights

Gravity waves are an essential component of the atmospheric circulation [1,2,3]
We first consider the stability of the upper stratosphere-lower mesosphere (USLM) and show the buoyancy period averaged over the first consider thea stability and in show the buoyancy period overaveraged the
We have documented the USLM gravity wave activity (40–50 km) over 14 years based on uniform processing of a high-quality set of Rayleigh LiDAR observations

Summary

Introduction

Gravity waves are an essential component of the atmospheric circulation [1,2,3]. How these waves affect the circulation of the stratosphere is a focus of the Stratospheric Processes and theirRole in Climate (SPARC) program [4] and the recent Deep Propagating Gravity Wave Experiment (DEEPWAVE) campaign [5]. Atmosphere 2017, 8, 27 into the mesosphere and contribute to the recovery of the circulation (e.g., [6,7,8,9,10]) During these events, there is significant ageostrophic imbalance in the flows as the tropospheric and stratospheric jets depart from geostrophic balance. More recent studies of gravity waves have studied the generation of gravity waves through spontaneous adjustment of unbalanced flows that include the contributions of mesoscale phenomena, such as jets and fronts [14]. In the absence of convection during the winter, unbalanced flows (associated with ageostrophic flows, jets and fronts) are expected to be a significant source of gravity waves [15,16,17]

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