Momentum Flux of Convective Gravity Waves Derived from an Offline Gravity Wave Parameterization. Part I: Spatiotemporal Variations at Source Level

Abstract

Spatiotemporal variations in momentum flux spectra of convective gravity waves (CGWs) at the source level (cloud top), including nonlinear forcing effects, are examined based on calculations using an offline version of CGW parameterization and global reanalysis data for a period of 32 years (1979–2010). The cloud-top momentum flux (CTMF) is not solely proportional to the convective heating rate but is affected by the wave-filtering and resonance factor and background stability and temperature underlying the convection. Consequently, the primary peak of CTMF is in the winter hemisphere midlatitudes, associated with storm tracks, where a secondary peak of convective heating exists, whereas the secondary peak of CTMF appears in the summer hemisphere tropics and intertropical convergence zone (ITCZ), where the primary peak of convective heating exists. The magnitude of CTMF fluctuates largely with 1-yr and 1-day periods in major CTMF regions. At low latitudes and Pacific storm-track regions, a 6-month period is also significant, and the decadal cycle appears in the southern Andes. The equatorial eastern Pacific region exhibits a substantial interannual to decadal scale of variabilities. The correlation between convective heating and the CTMF is relatively lower in the equatorial region than in other regions. The CTMF in 10°N–10°S during the period of the pre-Concordiasi campaign approximately follows a lognormal distribution but with a slight underestimation in the tail of the probability density function. In Part II, the momentum flux and drag of CGW in the stratosphere will be examined.

Inertia‐Gravity Waves Revealed in Radiosonde Data at Jang Bogo Station, Antarctica (74°37′S, 164°13′E): 2. Potential Sources and Their Relation to Inertia‐Gravity Waves

“…There are two major factors that result in the seasonal variations in the occurrence frequency of GWs: (i) variations in the GW source itself and (ii) wave propagation conditions from the source to the observation altitude (i.e., impact of background wind and stability) (Kang et al, 2017). For a stationary mountain source, seasonal variation of orographic GWs is due mainly to (ii) depending on the transient background atmosphere around the mountain.…”

Intercomparison of Gravity Waves in Global Convection-Permitting Models

“…The generation of GWs by convection is affected by many parameters, including lower-level wind shear, the width and depth of convective cells (Beres et al 2004(Beres et al , 2005, and resonance between wave modes and latent heating (Kang et al 2017). At the model resolutions considered here, parameterizations for deep convection are turned off (with the exception of IFS-9), but deep convection is still underresolved.…”

Short response to RC3

“…It is worth noting here that even large horizontal-scale phenomena may not be well represented at low latitudes in the reanalysis data because they are not balanced with well-observed quantities such as temperature due to small f . In fact, there is a large discrepancy in horizontal winds in the equatorial stratosphere among reanalysis datasets (Kawatani et al, 2016;Podglajen et al, 2014). It is also discussed by Kim and Chun (2015) that amplitudes of large horizontal-scale equatorial waves may be underestimated because the vertical grid spacing of the model is too coarse to resolve short vertical wavelengths that the equatorial waves may have in the strong vertical shear of the mean zonal wind of the QBO.…”