Roles of Cloud Microphysics on Cloud Responses to Sea Surface Temperatures in Radiative‐Convective Equilibrium Experiments Using a High‐Resolution Global Nonhydrostatic Model

Abstract

The high‐cloud amount responses to sea surface temperature (SST) changes were investigated based on simulations with radiative‐convective equilibrium configuration using a high‐resolution nonhydrostatic icosahedral atmospheric model. The radiative‐convective equilibrium was calculated using a nonrotating sphere with Earth radius and a 14‐km horizontal mesh with uniform SSTs of 300 and 304 K. Two types of cloud microphysics schemes (single‐ and double‐moment bulk schemes) and two types of vertical layer configurations (38 and 78 layers) were tested. The radiatively driven circulation weakens with increasing SST in all simulation pairs due to the increase in the static stability, as suggested in previous studies. In contrast, the high‐cloud amount increases in three simulation pairs and decreases in one pair. These indicate that the weakening of radiatively driven circulation with increasing SST does not always accompany the high‐cloud amount decrease. We determined that the tropopause layer was wet (dry) in simulations that showed positive (negative) high‐cloud cover responses. The radiatively driven upward moisture transport just below the wet tropopause layer increases with increasing SST in the simulation pairs with positive high‐cloud amount responses, and this causes the supply of ice condensate to the lower layer through the sedimentation process, while this feedback was not observed in the simulation pair with the negative response. These indicate that the high‐cloud cover response depends on the occurrence of the feedback and there is a feedback threshold among the variety of simulations. And furthermore, these speculate that whether the feedback mechanism is effective or not has the large impact on high‐cloud responses in the real atmosphere.

Fine Vertical Resolution Radiative‐Convective Equilibrium Experiments: Roles of Turbulent Mixing on the High‐Cloud Response to Sea Surface Temperatures

“…After initial shocks with relatively large amplitudes, the precipitation rate suddenly decreased to less than 0.15 mm/hr in the simulations with SSTs of 300 and 304 K. Then, the precipitation rate gradually increased and became constant after an integration time of approximately 80 days, although fluctuations with relatively small amplitudes were observed. These results are consistent with those obtained by Ohno and Satoh () using a finer horizontal grid spacing, although the precipitation rates in this work are ∼0.01–0.02 mm/hr larger than those reported by Ohno and Satoh (). Similar trends are observed for the other variables, such as the outgoing longwave radiation (OLR) at the top of the atmosphere.…”

“…With this configuration, the vertical grid spacing gradually increases from the surface to the top of the atmosphere. The vertical grid spacings in the other vertical layer configurations are similar to that of L38 in the lower atmosphere; however, from the lower troposphere to a height of approximately 20 km, the vertical grid spacings are 400, 200, 100, and 50 m for L78, L126, L214, and L398, respectively, similar to the spacings used in previous studies (Ohno & Satoh, , ; Seiki et al, ). Above 20 km, the vertical layer depth gradually increases again.…”

“…The horizontal grid spacing used in the present study is 28 km, twice the value used by Ohno and Satoh (). This horizontal grid is coarser than those typically used for CRMs in smaller domains; however, a number of previous studies demonstrated a qualitative similarity of results among simulations using 7‐ and 3.5‐km and even finer horizontal grid spacings (Iga et al, ; Kajikawa et al, ; Miyamoto et al, ; Noda et al, ; Satoh & Matsuda, ; Sato et al, ; Tomita, ).…”

“…The use of RCE configurations enables researchers to more easily focus on investigating the resolution dependency of high‐cloud responses, as long as the response in the RCE is similar to those observed in simulations with more realistic configurations. Ohno and Satoh () validated the similarity of the high‐cloud response in simulations for both realistic and RCE configurations using the NICAM. In the next section, descriptions of the model and experimental design are provided.…”

What Drives the Life Cycle of Tropical Anvil Clouds?

“…As the simulations of anvil cloud evolution were found to be very sensitive to details in the description of microphysics (Ohno & Satoh, ; Powell et al, ), we perform several microphysical sensitivity tests. In particular, we vary the upper limit of IC number concentration and implement a more realistic freezing scheme for temperatures below the homogeneous freezing temperature of water.…”