Hye‐Yeong Chun

Gravity wave momentum flux induced by thermal forcing representing latent heating due to cumulus convection is investigated analytically from a viewpoint of a subgrid-scale drag for the large-scale flow, and a possible way to parameterize the momentum flux in large-scale models is proposed. For the formulations of the momentum flux and its vertical derivative, two-dimensional, steady-state, linear perturbations induced by thermal forcing in a uniform basic-state wind are considered. The calculat

Abstract In this study, we estimate atmospheric turbulence in the free atmosphere in terms of the Thorpe scale ( L T ) and eddy dissipation rate ( ε ) using U.S. high vertical‐resolution radiosonde data over 4 years (September 2012 to August 2016) at 68 operational stations. In addition, same calculations are conducted for 12 years (October 2005 to September 2017) at four stations among the 68 stations. These high vertical‐resolution radiosonde data have a vertical resolution of approximately 5

A convective gravity‐wave parameterization (GWP) is introduced in the Met Office Unified Model (MetUM) in addition to the existing GWPs, and the tropical quasi‐biennial oscillation (QBO) is simulated. We replace a significant amount of momentum flux, which is originally launched by the background GWP, with the convective gravity‐wave (CGW) momentum flux with a broad wave spectrum that is explicitly determined by the convective sources. Compared to the experiment without the CGW parameterization,

Abstract The contributions of the equatorial waves to the quasi‐biennial oscillation (QBO) are investigated using Hadley Centre Global Environment Model version 2 (HadGEM2). A gravity wave parameterization that couples its source spectrum to the convection is used. The equatorial wave modes are identified in the spectral domain, based on their distinct characteristics associated with momentum and heat fluxes. The Kelvin waves and parameterized gravity waves (PGWs) transport westerly momentum int

Gravity waves generated by convective clouds are numerically simulated using a two‐dimensional mesoscale model that extends to the upper mesosphere (physical model top of 105 km), and characteristics of the waves are investigated before and after wave breaking occurred in the mesosphere. Gravity waves generated by convective clouds have wide spectrum corresponding to their sources, but large portions of the waves with short horizontal and vertical wavelengths are reflected, trapped, and filtered

An updated parameterization of gravity wave drag forced by subgrid-scale cumulus convection (GWDC) in large-scale models is proposed. For an analytical formulation of the cloud-top wave stress, two-dimensional, steady-state, linear perturbations induced by diabatic heating are found in a two-layer structure with a piecewise constant shear with a critical level in the lower layer, a uniform flow in the upper layer, and piecewise constant buoyancy frequencies in each layer. The dynamical frame con

A parameterization of gravity wave drag forced by subgrid-scale cumulus convection (GWDC) proposed by Chun and Baik is implemented into the National Center for Atmospheric Research Community Climate Model (NCAR CCM3) and its effect on perpetual January and July climate is investigated. The cloud-top gravity wave stress is concentrated in the intertropical convergence zone where persistent deep cumulus clouds exist. The resultant zonal wind acceleration due to the breaking of convectively forced

A parameterization scheme of gravity wave drag induced by cumulus convection (GWDC) is implemented in the Yonsei University atmospheric general circulation model (GCM) and the effects of GWDC on the zonal-mean flow and planetary waves are investigated through perpetual July simulations. The GWDC parameterization scheme used in this study includes a momentum gain in the cloud region to conserve the momentum. The gravity wave stress at the cloud top is concentrated in the intertropical convergence

Using observational data from Korean Air Lines (KAL) Boeing (B) 737-800, B777-200 and B777-300 flights from January to December 2012, the derived equivalent vertical gust velocity (DEVG) was calculated as a turbulence indicator. Based on 1 min flight segments using the calculated DEVG, the highest frequency of moderate-or-greater (MOG) turbulence occurred in the Northern Hemisphere winter, whereas the lowest frequency occurred in the Northern Hemisphere summer. Spatially, the KAL turbulence enco

Abstract In the present study, the authors propose a way to include a nonlinear forcing effect on the momentum flux spectrum of convectively forced internal gravity waves using a nondimensional numerical model (NDM) in a two-dimensional framework. In NDM, the nonlinear forcing is represented by nonlinear advection terms multiplied by the nonlinearity factor (NF) of the thermally induced internal gravity waves for a given specified diabatic forcing. It was found that the magnitudes of the waves a

Abstract We propose near-cloud turbulence (NCT) diagnostics for use in aviation turbulence forecasting, using a convective gravity wave drag (CGWD) parameterization scheme. The NCT diagnostics are obtained based on (i) CGWD and (ii) minimum Richardson number including the effects of convective gravity waves (CGWs). The feasibility of the NCT diagnostics is examined using numerical simulation results of real turbulence cases related to the breaking of CGWs, which occurred over eastern Missouri an