Tahereh Alinejadtabrizi

The orographic precipitation enhancement (OPE) generated within wintertime post‐frontal air masses is a prominent climate feature of Tasmania. This study investigates a passage of a cold sector of a mid‐latitude cyclone over the Southern Ocean (SO) and Western Tasmania (WTAS) observed from 2100 UTC 11 July to 0300 UTC 13 July. The in situ and remote sensing observations have been used to study clouds and precipitation over the SO and WTAS. Those observations include Optical Particle Size Velocity disdrometers and Micro Rain Radars implemented during a winter field campaign implemented in 2019, 27 rain gauges operated by Hydro Tasmania, C‐band weather radar and satellite‐based observations. ERA5 reanalysis was used to analyze the synoptic meteorology and thermodynamic conditions. Deep convection reaching heights of 8 km was observed over the SO and Tasmania and was triggered by a post‐frontal trough. The microphysical properties of these deep convective clouds were substantially different from those for the shallow open mesoscale cellular convection, which is commonly observed over the SO. The deep convective clouds and OPE produced heavy precipitation exceeding 55 mm over WTAS according to in situ observations during the post‐frontal period (over 30 hr). The GPM‐IMERG satellite‐based precipitation product captured the spatial pattern of the OPE over WTAS though rain gauge calibration induced overestimation of heavy precipitation at some sites. The analysis of C‐band radar observations suggests that orographic convection invigoration and convective‐to‐stratiform transition mechanisms produced OPE over WTAS.

Global climate models perform particularly poorly over the Southern Ocean, resulting in persistent cloud and radiation biases. This is in part driven by incomplete understanding of the aerosol formation and transformations over the Southern Ocean and their influence cloud formation and properties. Oxidation of volatile sulfur compounds, in particular dimethyl sulfide (DMS), and the subsequent secondary particle formation, is an important source of aerosols in the Southern Ocean atmosphere (and in marine environments in general). This presentation will focus on terminal oxidation products of volatile sulfur compounds, namely sulfuric acid (SA) and methanesulfonic acid (MSA), in both gas and particle phase observed during the 2024 Multidisciplinary Investigations of the Southern Ocean (MISO) voyage (Jan – March 2024) aboard the Australian Research Vessel Investigator and covering the western Pacific sector of the Southern Ocean (110o – 150o E). These species are investigated and will be presented in the context of air mass origin and synoptic meteorology.A notable feature of the voyage were periods of elevated gaseous MSA south of ~62o S, coinciding with increased particulate sulfate and MSA, as well as enhanced cloud condensation nuclei (CCN) concentrations. These periods were found to be associated with Antarctic continental outflow and the air masses to have free tropospheric origin. By using E-AIM thermodynamic modelling we show that aerosol particles during MISO voyage were highly acidic (pH < -1) and that the elevated gaseous MSA is a result of evaporation from these highly acidic particles. Evaporation of MSA from highly acidic aerosols during Antarctic continental outflow has already been reported for the 2018 CAPRICORN-2 voyage which covered a very similar geographical region (Miljevic et al., 2025). The recent MISO voyage further highlights long range transport as an important pathway for biogenically dominated CCN and brings into focus MSA gas-particle partitioning as a relevant process in the marine sulfur cycle.Reference:Miljevic, B., Mallet, M. D., Osuagwu, C. G., Ristovski, Z. D., Humphries, R. S., Selleck, P., Taylor, S., & Keywood, M. D. (2025). Aerosol acidity controls methanesulfonic acid evaporation from aerosols during Antarctic katabatic outflow. Communications Earth & Environment, 6(1), 1057. https://doi.org/10.1038/s43247-025-03041-2

Precipitation from marine boundary layer clouds is a critical yet highly uncertain feature of post‐frontal conditions over the Southern Ocean (SO), where shallow convection dominates. This study evaluates whether satellite retrievals (GPM‐IMERG and CloudSat) and reanalysis (ERA5) represent the contrasting precipitation between open and closed mesoscale cellular convection (MCC) observed over the SO, from limited in situ records. Substantial discrepancies are found across data sets. While ERA5 captures the expected contrast, GPM‐IMERG underestimates precipitation, especially from open MCCs, and fails to reflect morphological distinction. Both CloudSat products detect higher mean precipitation for open MCCs, though with differences in intensity distribution. Using observed precipitation rates and occurrence frequencies, open MCCs are estimated to contribute 9%–13% and closed MCCs 1%–11% of the annual precipitation between 40°S and 50°S. These results highlight the importance of improving the representation of marine atmospheric boundary layer cloud morphologies in models and observational data sets to better constrain the SO water cycle.

A 14-year climatology of the bulk sensible and latent heat fluxes (SHF and LHF) made from the Southern Ocean Flux Station (SOFS) is analysed with respect to the synoptic meteorology and mesoscale cellular convection (MCC). A K-means clustering algorithm identified five synoptic regimes: High Pressure/Ridging (HPR), Tasman Blocking High (TBH), Zonal, Frontal, and Cold Air Advection (CAA). Among these, the CAA regime exhibited the most pronounced air-sea coupling, with a mean SHF of −40.4 W m⁻² and LHF of −131.0 W m⁻², which are 3.5 and 2 times greater than the overall mean, respectively. For the Zonal, Frontal, and CAA regimes, a strong correlation between the surface fluxes and the M-index (surface − 850 hPa potential temperature difference) is observed, with an R² of 0.58 for the SHF and M-index relationship in the Zonal regime and an R² of 0.48 for the LHF and M-index in the CAA regime when the estimated inversion strength (EIS) is less than zero. Furthermore, the flux transfer rate demonstrates a two-fold increase with the M-index when the capping inversion weakens and collapses (EIS shifts from > 0 to < 0). The relationship between surface fluxes and the M-index is weak in the HPR and TBH regimes, which are characterised by stronger inversions at SOFS. Turning to open and closed MCC, relatively smaller differences in the fluxes are observed between these two cloud states at SOFS, indicating that SHF and LHF are not the primary drivers in the transition between these cloud types. However, the EIS and M-index exhibit considerable differences between the cloud types, which may be more significant for the morphology of open and closed MCCs, rather than the surface flux release. The SOFS measurements were employed to evaluate ERA5 fluxes, revealing that ERA5 accurately represents the observed bulk SHF and LHF with significant correlation coefficients of r = 0.9 (p < 0.01) and 0.92 (p < 0.01), respectively. A mean bias of 1.6 W m⁻² is noted for SHF and −6.2 W m⁻² for LHF in ERA5. The bias in SHF is attributed to the underestimation of wind speed (10 m) in ERA5, whereas the dry bias of specific humidity (2 m) leads to the overestimation of LHF.

A 14-year climatology of the bulk sensible and latent heat fluxes (SHF and LHF) made from the Southern Ocean Flux Station (SOFS) is analyzed with respect to the synoptic meteorology and mesoscale cellular convection (MCC). A K-means clustering algorithm identified five synoptic regimes: High Pressure/Ridging (HPR), Tasman Blocking High (TBH), Zonal, Frontal, and Cold Air Advection (CAA). Among these, CAA showed the strongest air-sea coupling, with mean SHF of -40.4 W/m² and LHF of -131.0 W/m², which are 3.5 and 2 times greater than the overall mean, respectively. This striking increase in fluxes during CAA is associated with a high marine cold-air outbreak index (M-index) and weak inversion coupled with cold and dry air transport towards SOFS by the strong south-westerly wind. The SOFS measurements are also employed to evaluate ERA5 fluxes, finding that ERA5 accurately represents the observed bulk SHF and LHF, with a mean bias of 1.6 W/m² for SHF and -6.2 W/m² for LHF, along with significant correlation coefficients of r=0.9 and 0.92, respectively. Turning to open and closed MCC, relatively weak differences in the fluxes are observed between these two states, suggesting that the SHF and LHF are not the primary drivers in the transition between open and closed MCC. In open MCC, SHF and LHF show a strong correlation with the M-index, while closed MCC is associated with a stable atmosphere with a strong inversion, where the M-index relationship with surface fluxes is weak.

A 14-year climatology of the bulk sensible and latent heat fluxes (SHF and LHF) made from the Southern Ocean Flux Station (SOFS) is analyzed with respect to the synoptic meteorology and mesoscale cellular convection (MCC). A K-means clustering algorithm identified five synoptic regimes: High Pressure/Ridging (HPR), Tasman Blocking High (TBH), Zonal, Frontal, and Cold Air Advection (CAA). Among these, CAA showed the strongest air-sea coupling, with mean SHF of -40.4 W/m² and LHF of -131.0 W/m², which are 3.5 and 2 times greater than the overall mean, respectively. This striking increase in fluxes during CAA is associated with a high marine cold-air outbreak index (M-index) and weak inversion coupled with cold and dry air transport towards SOFS by the strong south-westerly wind. The SOFS measurements are also employed to evaluate ERA5 fluxes, finding that ERA5 accurately represents the observed bulk SHF and LHF, with a mean bias of 1.6 W/m² for SHF and -6.2 W/m² for LHF, along with significant correlation coefficients of r=0.9 and 0.92, respectively. Turning to open and closed MCC, relatively weak differences in the fluxes are observed between these two states, suggesting that the SHF and LHF are not the primary drivers in the transition between open and closed MCC. In open MCC, SHF and LHF show a strong correlation with the M-index, while closed MCC is associated with a stable atmosphere with a strong inversion, where the M-index relationship with surface fluxes is weak.

A 14-year climatology of the bulk sensible and latent heat fluxes (SHF and LHF) made from the Southern Ocean Flux Station (SOFS) is analyzed with respect to the synoptic meteorology and mesoscale cellular convection (MCC). A K-means clustering algorithm identified five synoptic regimes: High Pressure/Ridging (HPR), Tasman Blocking High (TBH), Zonal, Frontal, and Cold Air Advection (CAA). Among these, CAA showed the strongest air-sea coupling, with mean SHF of -40.4 W/m² and LHF of -131.0 W/m², which are 3.5 and 2 times greater than the overall mean, respectively. This striking increase in fluxes during CAA is associated with a high marine cold-air outbreak index (M-index) and weak inversion coupled with cold and dry air transport towards SOFS by the strong south-westerly wind. The SOFS measurements are also employed to evaluate ERA5 fluxes, finding that ERA5 accurately represents the observed bulk SHF and LHF, with a mean bias of 1.6 W/m² for SHF and -6.2 W/m² for LHF, along with significant correlation coefficients of r=0.9 and 0.92, respectively. Turning to open and closed MCC, relatively weak differences in the fluxes are observed between these two states, suggesting that the SHF and LHF are not the primary drivers in the transition between open and closed MCC. In open MCC, SHF and LHF show a strong correlation with the M-index, while closed MCC is associated with a stable atmosphere with a strong inversion, where the M-index relationship with surface fluxes is weak.

A 14-year climatology of the bulk sensible and latent heat fluxes (SHF and LHF) made from the Southern Ocean Flux Station (SOFS) is analyzed with respect to the synoptic meteorology and mesoscale cellular convection (MCC). A K-means clustering algorithm identified five synoptic regimes: High Pressure/Ridging (HPR), Tasman Blocking High (TBH), Zonal, Frontal, and Cold Air Advection (CAA). Among these, CAA showed the strongest air-sea coupling, with mean SHF of -40.4 W/m² and LHF of -131.0 W/m², which are 3.5 and 2 times greater than the overall mean, respectively. This striking increase in fluxes during CAA is associated with a high marine cold-air outbreak index (M-index) and weak inversion coupled with cold and dry air transport towards SOFS by the strong south-westerly wind. The SOFS measurements are also employed to evaluate ERA5 fluxes, finding that ERA5 accurately represents the observed bulk SHF and LHF, with a mean bias of 1.6 W/m² for SHF and -6.2 W/m² for LHF, along with significant correlation coefficients of r=0.9 and 0.92, respectively. Turning to open and closed MCC, relatively weak differences in the fluxes are observed between these two states, suggesting that the SHF and LHF are not the primary drivers in the transition between open and closed MCC. In open MCC, SHF and LHF show a strong correlation with the M-index, while closed MCC is associated with a stable atmosphere with a strong inversion, where the M-index relationship with surface fluxes is weak.

A 14-year climatology of the bulk sensible and latent heat fluxes (SHF and LHF) made from the Southern Ocean Flux Station (SOFS) is analyzed with respect to the synoptic meteorology and mesoscale cellular convection (MCC). A K-means clustering algorithm identified five synoptic regimes: High Pressure/Ridging (HPR), Tasman Blocking High (TBH), Zonal, Frontal, and Cold Air Advection (CAA). Among these, CAA showed the strongest air-sea coupling, with mean SHF of -40.4 W/m² and LHF of -131.0 W/m², which are 3.5 and 2 times greater than the overall mean, respectively. This striking increase in fluxes during CAA is associated with a high marine cold-air outbreak index (M-index) and weak inversion coupled with cold and dry air transport towards SOFS by the strong south-westerly wind. The SOFS measurements are also employed to evaluate ERA5 fluxes, finding that ERA5 accurately represents the observed bulk SHF and LHF, with a mean bias of 1.6 W/m² for SHF and -6.2 W/m² for LHF, along with significant correlation coefficients of r=0.9 and 0.92, respectively. Turning to open and closed MCC, relatively weak differences in the fluxes are observed between these two states, suggesting that the SHF and LHF are not the primary drivers in the transition between open and closed MCC. In open MCC, SHF and LHF show a strong correlation with the M-index, while closed MCC is associated with a stable atmosphere with a strong inversion, where the M-index relationship with surface fluxes is weak.

A 14-year climatology of the bulk sensible and latent heat fluxes (SHF and LHF) made from the Southern Ocean Flux Station (SOFS) is analyzed with respect to the synoptic meteorology and mesoscale cellular convection (MCC). A K-means clustering algorithm identified five synoptic regimes: High Pressure/Ridging (HPR), Tasman Blocking High (TBH), Zonal, Frontal, and Cold Air Advection (CAA). Among these, CAA showed the strongest air-sea coupling, with mean SHF of -40.4 W/m² and LHF of -131.0 W/m², which are 3.5 and 2 times greater than the overall mean, respectively. This striking increase in fluxes during CAA is associated with a high marine cold-air outbreak index (M-index) and weak inversion coupled with cold and dry air transport towards SOFS by the strong south-westerly wind. The SOFS measurements are also employed to evaluate ERA5 fluxes, finding that ERA5 accurately represents the observed bulk SHF and LHF, with a mean bias of 1.6 W/m² for SHF and -6.2 W/m² for LHF, along with significant correlation coefficients of r=0.9 and 0.92, respectively. Turning to open and closed MCC, relatively weak differences in the fluxes are observed between these two states, suggesting that the SHF and LHF are not the primary drivers in the transition between open and closed MCC. In open MCC, SHF and LHF show a strong correlation with the M-index, while closed MCC is associated with a stable atmosphere with a strong inversion, where the M-index relationship with surface fluxes is weak.