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The Representation of Spiral Gravity Waves in a Mesoscale Model With Increasing Horizontal and Vertical Resolution.

Authors :
Nolan, David S.
Onderlinde, Matthew J.
Source :
Journal of Advances in Modeling Earth Systems. Aug2022, Vol. 14 Issue 8, p1-22. 22p.
Publication Year :
2022

Abstract

Recent observational and numerical studies have investigated the dynamics of fine‐scale gravity waves radiating horizontally outward from tropical cyclones. The waves are wrapped into spirals by the tangential wind of the cyclone and are described as spiral gravity waves. This study addresses how well numerical simulations of these waves compare to observations as the horizontal grid spacing is decreased from 2.0 to 1.0 to 0.5 km, and the number of vertical levels changes from 25 to 50 to 100. Spectral filtering is applied to separate the fine‐scale waves in vertical velocity (w) and the larger‐scale waves in pressure (p) from moist updrafts and downdrafts in the eyewall and rainbands. As the grid spacing decreases, the radial wavelengths of the w waves decrease from 20 to 7 km, approaching observed values. For grid spacing 1.0 km, the p waves become well‐resolved with wavelength 70 km. The outward phase speeds range from 15 to 30 ms−1 for the w waves and 50 to 70 ms−1 for p waves. Analysis of the upper‐level outflow region finds that the spiral w waves propagate 5–10 ms−1 faster due to radial advection, but also finds what appear to be different classes of larger‐amplitude, slow‐moving spiral waves. Similar waves can be seen in satellite images, which appear to be caused by dynamical instability of the strongly vertically sheared radial and tangential winds in the TC outflow. Plain Language Summary: Tropical cyclones—known also as hurricanes, typhoons, and cyclones—cause some of the most significant weather impacts around the world. Recent work has found that these storms causes oscillations in the atmosphere that radiate outward in expanding spirals. These are called spiral gravity waves. This paper investigates how well computer models reproduce these waves as the pixel sizes used by the model become smaller (requiring more computer power). As the pixels decrease to 1.0 km or less, the waves become increasingly realistic. The simulations show two types of spiral gravity waves, which can be seen either in vertical motion or in the atmospheric pressure field. The vertical motion waves are 5–10 km wide and move outward at 90 km hr−1, while the pressure waves are 60–80 km wide and move outward at 220 km hr−1. Focusing on the cloud shield at the top of the cyclone (what we see in satellites) reveals a new class of slow‐moving, spiral waves that are distinct from the gravity waves. Key Points: Computer simulations of tropical cyclones show the detailed structures of outward propagating spiral gravity wavesAs resolution increases, the wave properties come close to, but do not converge to observed valuesA new class of waves is identified in the upper‐level outflow, which are slow‐moving spiral waves due to dynamical instabilities [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
19422466
Volume :
14
Issue :
8
Database :
Academic Search Index
Journal :
Journal of Advances in Modeling Earth Systems
Publication Type :
Academic Journal
Accession number :
158791021
Full Text :
https://doi.org/10.1029/2022MS002989