On the Momentum Flux of Vertically Propagating Orographic Gravity Waves Excited in Nonhydrostatic Flow over Three-Dimensional Orography

• Type: Article in International Scientific Journal
• Date: 2021

Authors

Xu, X (Author) Other; Li, RQ (Author) Other; Teixeira, MAC (Author) Other; Lu, YX (Author) Other

Journal

The Journal is awaiting validation by the Administrative Services.

Title: JOURNAL OF THE ATMOSPHERIC SCIENCES

Vol. 78

Pages: 1807-1822

ISSN: 0022-4928

Indexing

ISI Web of Knowledge - 10 Citations

Scopus - 8 Citations

Other information

Authenticus ID: P-010-GBP

DOI: 10.1175/jas-d-20-0370.1

Abstract (EN): <jats:title>Abstract</jats:title><jats:p>This work studies nonhydrostatic effects (NHE) on the momentum flux of orographic gravity waves (OGWs) forced by isolated three-dimensional orography. Based on linear wave theory, an asymptotic expression for low horizonal Froude number (<jats:inline-formula /> where (<jats:italic>U</jats:italic>, <jats:italic>V</jats:italic>) is the mean horizontal wind, <jats:italic>¿</jats:italic> and <jats:italic>a</jats:italic> are the orography anisotropy and half-width and <jats:italic>N</jats:italic> is the buoyancy frequency) is derived for the gravity wave momentum flux (GWMF) of vertically-propagating waves. According to this asymptotic solution, which is quite accurate for any value of <jats:italic>Fr</jats:italic>, NHE can be divided into two terms (NHE1 and NHE2). The first term contains the high-frequency parts of the wave spectrum that are often mistaken as hydrostatic waves, and only depends on <jats:italic>Fr</jats:italic>. The second term arises from the difference between the dispersion relationships of hydrostatic and nonhydrostatic OGWs. Having an additional dependency on the horizontal wind direction and orography anisotropy, this term can change the GWMF direction. Examination of NHE for OGWs forced by both circular and elliptical orography reveals that the GWMF is reduced as <jats:italic>Fr</jats:italic> increases, at a faster rate than for two-dimensional OGWs forced by a ridge. At low <jats:italic>Fr</jats:italic>, the GWMF reduction is mostly attributed to the NHE2 term, whereas the NHE1 term starts to dominate above about <jats:italic>Fr</jats:italic> = 0.4. The behavior of NHE is mainly determined by <jats:italic>Fr</jats:italic>, while horizontal wind direction and orography anisotropy play a minor role. Implications of the asymptotic GWMF expression for the parameterization of nonhydrostatic OGWs in high-resolution and/or variable-resolution models are discussed.</jats:p>

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 16