A climatology of open and closed mesoscale cellular convection over the Southern Ocean derived from Himawari-8 observations

Abstract

Abstract. Marine atmospheric boundary layer clouds cover vast areas of the Southern Ocean (SO), where they are commonly organized into mesoscale cellular convection (MCC). Using 3 years of Himawari-8 geostationary satellite observations, open and closed MCC structures are identified using a hybrid convolutional neural network. The results of the climatology show that open MCC clouds are roughly uniformly distributed over the SO storm track across midlatitudes, while closed MCC clouds are most predominant in the southeast Indian Ocean, with a second maximum along the storm track. The ocean polar front, derived from ECMWF-ERA5 sea surface temperature gradients, is found to be aligned with the southern boundaries for both MCC types. Along the storm track, both closed and open MCCs are commonly located in post-frontal, cold air masses. The hourly classification of closed MCC reveals a pronounced daily cycle, with a peak occurring late night/early morning. Seasonally, the diurnal cycle of closed MCC is most intense during the summer months (December–February; DJF). Conversely, almost no diurnal cycle is evident for open MCC.

A Characterization of Clouds and Precipitation Over the Southern Ocean From Synoptic to Micro Scales During the CAPRICORN Field Campaigns

“…While non-precipitating clouds prevail in the shallow cloud regime, there are strong radar reflectivities (greater than 5 dBZ) associated with strong negative Doppler velocities (smaller than −2 ms −1 ) between −10 and 0°C, consistent with the formation of large particles (Figures 2n and 2p). Such characteristics are congruent with in-situ observations in the Hallett-Mossop temperature zone (rime splintering between −8 and −3°C) shown in several previous studies for a similar synoptic environment (Huang et al, 2017(Huang et al, , 2021, commonly associated with the open mesoscale cellular convection (Lang et al, 2021(Lang et al, , 2022. Surface Note.…”

“…These clouds have been reported to be most poorly simulated in weather and climate model at all scales, constituting a leading contributor to the previously noted shortwave radiative biases (Bodas-Salcedo et al, 2012, 2014. However, it is worth noting that recent research has documented the frequent presence of both the open and closed Mesoscale Cellular Convective (MCC) clouds in this environment (Lang et al, 2021(Lang et al, , 2022, with contrasting cloud phase composition and precipitation rates (Ahn et al, 2017;Huang et al, 2017Huang et al, , 2021. Further analysis into the oceanic and atmospheric conditions would be necessary to refine our understanding of the associated cloud controlling factors.…”

“…The high-pressure cluster M1 (Figures2e-2h) features the lowest cloud occurrence (CF 62%, see Table2). A discontinuous dipole-like structure is evident in the CFTD/CFADs, representing two dominant disconnected cloud types: non-/lightly precipitating boundary layer clouds (likely closed mesoscale cellular convection as reported inLang et al (2020),Lang et al (2022)) with Doppler velocities between 0 and −2 ms −1 ; and mid-level clouds with in-cloud precipitation that does not reach the lower troposphere. The latter features a high concentration around −20°C and −5 dBZ, which suggests small precipitation-size particles, possibly mixed phase.…”

Inferring the Properties of Snow in Southern Ocean Shallow Convection and Frontal Systems Using Dual-Polarization C-Band Radar

“…As an example, we take the measurements collected by the OceanPol radar over the Southern excluded. If microphysical differences are found, more automated techniques, such as that proposed in Lang et al (2022), could be used to classify the large-scale conditions and feed that information to DPSR. All the requirements noted above in analysis of the case studies were also applied.…”

Southern Ocean precipitation: Toward a process‐level understanding

“…The cold air advection supports shallow convection, which is widespread across the lower latitudes of the SO (Lang et al, 2022;McCoy et al, 2017;Muhlbauer et al, 2014;Rampal & Davies, 2020). Vast tracts of shallow convection are commonly observed over these latitudes of the SO, covering tens of thousands of square kilometers.…”