Characteristics of gravity waves generated in the jet-front system in a baroclinic instability simulation

Young-Ha Kim,Sang-Hun Park,Hyun-Joo Choi,In-Sun Song,Hye-Yeong Chun

doi:10.5194/acp-16-4799-2016

Abstract

Abstract. An idealized baroclinic instability case is simulated using a ∼ 10 km resolution global model to investigate the characteristics of gravity waves generated in the baroclinic life cycle. Three groups of gravity waves appear around the high-latitude surface trough at the mature stage of the baroclinic wave. They have horizontal and vertical wavelengths of 40–400 and 2.9–9.8 km, respectively, in the upper troposphere. The two-dimensional phase-velocity spectrum of the waves is arc shaped with a peak at 17 m s−1 eastward. These waves have difficulty in propagating upward through the tropospheric westerly jet. At the breaking stage of the baroclinic wave, a midlatitude surface low is isolated from the higher-latitude trough, and two groups of quasi-stationary gravity waves appear near the surface low. These waves have horizontal and vertical wavelengths of 60–400 and 4.9–14 km, respectively, and are able to propagate vertically for long distances. The simulated gravity waves seem to be generated by surface fronts, given that the structures and speeds of wave phases are coherent with those of the fronts.

Highlights

Gravity waves (GWs) at high latitudes have a significant impact on the shape and magnitude of the polar jet in the middle atmosphere by large-scale deposition of the momentum that they transport (Kim et al, 2003)
We investigate the spectral characteristics of GWs simulated in an idealized low-level baroclinic instability case
This section briefly describes the features of the simulated baroclinic wave before presenting the analysis of the GWs

Summary

Introduction

Gravity waves (GWs) at high latitudes have a significant impact on the shape and magnitude of the polar jet in the middle atmosphere by large-scale deposition of the momentum that they transport (Kim et al, 2003). The momentum deposited by mountain GW parameterization does not fully account for the momentum required to reproduce the observed polar jet structure in models (e.g., Sato et al, 2012; Choi and Chun, 2013). Several mechanisms of GW excitation in jet-front systems have been proposed, including spontaneous balanced adjustment, Lighthill radiation, unbalanced instability, and shear instability (see Plougonven and Zhang, 2014, and references therein). Further investigation of these proposed mechanisms is still ongoing to understand GW generation. Note that the GW characteristics estimated from measurements have some uncertainties because each measurement can detect only a portion of waves and the analysis

Results

Discussion

Conclusion