Hydrostatic and Non-Hydrostatic Simulations of Moist Convection

Abstract

Comparative experiments of moist convection using hydrostatic and non-hydrostatic models are performed to study the suitability of the hydrostatic approximation for a high-resolution model when the grid size falls below 20km. The moist convection in the models is treated by the use of an explicit warmrain process predicting cloud water and rainwater as well as by a semi-explicit scheme consisting of the warm-rain process and moist convective adjustment. The differences between the experiments with and without hydrostatic water loading are also examined and quantitatively compared with those between the hydrostatic and non-hydrostatic simulations.When the prognostic explicit scheme is used, the hydrostatic simulation overdevelops moist convection, overestimates the total amount of precipitation, and overexpands the area of precipitation as the grid size decreases. This overdevelopment alters substantially the structure of moist convection and precipitation patterns. The absence of hydrostatic water loading also alters the total amount and structure of precipitation. Hydrostatic water loading exerts more significant influences on simulated precipitation than the hydrostatic approximation. In the 20-km simulations, the hydrostatic simulation with hydrostatic water loading produces results that are comparable to the non-hydrostatic counterpart.The difference in the total amount of precipitation between the hydrostatic and non-hydrostatic simulations was not as large as that of the convective development. This can be explained by considering the total water budget, which includes simulated precipitation and water vapor flux through the lateral boundaries, i, e., the water-vapor flux in the hydrostatic simulation corresponds to that in the non-hydrostatic one.Although moist convective adjustment removes conditional instability and does not produce strong updrafts, the characteristics of the results in the comparative experiments of moist convection using hydrostatic and non-hydrostatic models were hardly changed by the incorporation of moist convective adjustment (the semi-explicit scheme). On the other hand, hydrostatic water loading exerts more significant influences on simulated precipitation with the semi-explicit scheme than that with the prognostic explicit scheme. Therefore, in developing 10-20km numerical weather prediction models, hydrostatic water loading should be evaluated in preference to adopting non-hydrostatic models.

Model intercomparison of COSMO 5.0 and IFS 45r1 at kilometer-scale grid spacing

“…One of the properties of hydrostatic systems is supposed to be the overestimation of convective precipitation amount and area compared to nonhydrostatic systems (Kato and Saito, 1995;Kato, 1997). When looking at total precipitation over land and comparing it with values from IMERG, it looks like IFS is overestimating convective precipitation.…”

“…But then again, Dudhia (1993) found only little differences between the hydrostatic and the nonhydrostatic solution for a cold front with grid spacing of 6.5 km. Kato and Saito (1995) performed idealized moist convection simulations with grid spacings of 20 km, 10 km, and 5 km and found that the hydrostatic model without parameterized deep convection overdevelops updrafts and overestimates convective precipitation amount and area. These results were later confirmed for a real-world case from Kato (1996).…”

Vertical Velocity in the Gray Zone

“…This paper seeks to address these questions through both analytical solutions to the relevant equations of motion as well as cloud‐resolving numerical simulations, run with an atmospheric model equipped with both hydrostatic and nonhydrostatic solvers. Of course, similar approaches have been taken by previous authors (W97; Kato & Saito, ; Morrison, ; Orlanski, ; Pauluis & Garner, ), so we must build on these prior studies in meaningful ways. We do so by first taking advantage of the aforementioned computer power to explore much finer resolutions ( ) than these previous studies ( km), ideally probing down to the inner edge of the gray zone.…”

Comparison of Simulated Tropical Cyclone Intensity and Structures Using the WRF with Hydrostatic and Nonhydrostatic Dynamical Cores

“…As might be expected, real-case simulations demonstrated that nonhydrostatic mesoscale models are superior to hydrostatic models in high-resolution precipitation forecasts [14][15][16][17]. However, it should be noted that such simulations were conducted with a grid spacing smaller than 10 km, which is traditionally considered the hydrostatic limit in the absence of latent heat release [18]. Meanwhile, Dudhia [19] identified a "gray zone" of the dynamics and it remains unclear whether nonhydrostatic dynamics should be applied within this zone.…”