Low-Cloud, Boundary Layer, and Sea Ice Interactions over the Southern Ocean during Winter

Wall, Casey J.; Kohyama, Tsubasa; Hartmann, Dennis L.

doi:10.1175/jcli-d-16-0483.1

Cited by 19 publications

(37 citation statements)

References 52 publications

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“…The number concentration of Antarctic aerosols -of which the INPs will be a subset -has been shown to have a seasonal cycle that is well documented. For instance, Weller et al (2011) and Kim et al (2017) documented the monthly variation in the total aerosol concentration at the coast in the Weddell Sea sector (Neumayer Station) and at the northern tip of the Antarctic Peninsula (King Sejong Station), respectively. They found that the maximum concentrations occurred in February (Kim et al, 2017, their Fig.…”

Section: On the Marine Origin Of The (Biological) Inpsmentioning

confidence: 99%

Antarctic clouds, supercooled liquid water and mixed phase, investigated with DARDAR: geographical and seasonal variations

et al. 2019

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Abstract. Antarctic tropospheric clouds are investigated using the DARDAR (raDAR/liDAR)-MASK products between 60 and 82∘ S. The cloud fraction (occurrence frequency) is divided into the supercooled liquid-water-containing cloud (SLC) fraction and its complementary part called the all-ice cloud fraction. A further distinction is made between SLC involving ice (mixed-phase clouds, MPC) or not (USLC, for unglaciated SLC). The low-level (<3 km above surface level) SLC fraction is larger over seas (20 %–60 %), where it varies according to sea ice fraction, than over continental regions (0 %–35 %). The total SLC fraction is much larger over West Antarctica (10 %–40 %) than it is over the Antarctic Plateau (0 %–10 %). In East Antarctica the total SLC fraction – in summer for instance – decreases sharply polewards with increasing surface height (decreasing temperatures) from 40 % at the coast to <5% at 82∘ S on the plateau. The geographical distribution of the continental total all-ice fraction is shaped by the interaction of the main low-pressure systems surrounding the continent and the orography, with little association with the sea ice fraction. Opportunistic comparisons with published ground-based supercooled liquid-water observations at the South Pole in 2009 are made with our SLC fractions at 82∘ S in terms of seasonal variability, showing good agreement. We demonstrate that the largest impact of sea ice on the low-level SLC fraction (and mostly through the MPC) occurs in autumn and winter (22 % and 18 % absolute decrease in the fraction between open water and sea ice-covered regions, respectively), while it is almost null in summer and intermediate in spring (11 %). Monthly variability of the MPC fraction over seas shows a maximum at the end of summer and a minimum in winter. Conversely, the USLC fraction has a maximum at the beginning of summer. However, monthly evolutions of MPC and USLC fractions do not differ on the continent. This suggests a seasonality in the glaciation process in marine liquid-bearing clouds. From the literature, we identify the pattern of the monthly evolution of the MPC fraction as being similar to that of the aerosols in coastal regions, which is related to marine biological activity. Marine bioaerosols are known to be efficient ice-nucleating particles (INPs). The emission of these INPs into the atmosphere from open waters would add to the temperature and sea ice fraction seasonalities as factors explaining the MPC fraction monthly evolution.

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Section: On the Marine Origin Of The (Biological) Inpsmentioning

confidence: 99%

Antarctic clouds, supercooled liquid water and mixed phase, investigated with DARDAR: geographical and seasonal variations

et al. 2019

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“…The relationship between clouds and sea ice also differs by season. In winter and fall, there is an apparent increase in low cloud cover with decreasing sea ice concentration (as in Wall, Kohyama, et al, 2017). During spring and summer, low cloud cover does not appear as closely related to sea ice concentration.…”

Section: Seasonal Sea Ice Concentration and Low Cloud Covermentioning

confidence: 99%

“…Surface-independent observations of temperature and cloud phase help constrain potential mechanisms underlying the observed cloud response to varying sea ice conditions. One potential mechanism leading to increased cloud opacity when sea ice retreats is an increase in air-sea coupling strength (Kay & Gettelman, 2009;Morrison et al, 2018;Wall, Kohyama, et al, 2017). Air-sea coupling contributes to low cloud formation and maintenance as moisture is transferred from the sea surface to the atmosphere to promote cloud formation (Klein & Hartmann, 1993).…”

Section: Potential Mechanisms For Increasing Opaque Cloud Fractionmentioning

confidence: 99%

The Combined Influence of Observed Southern Ocean Clouds and Sea Ice on Top‐of‐Atmosphere Albedo

et al. 2018

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When sea ice concentration decreases, surface albedo decreases. Yet the impact of Southern Ocean sea ice concentration decreases on top‐of‐atmosphere albedo is uncertain. Why? The cloud cover and opacity response to Southern Ocean sea ice variability has been challenging to quantify. Here we use observations to constrain the cloud response to Southern Ocean sea ice variability and assess the combined influence of sea ice and clouds on top‐of‐atmosphere albedo. We focus on the spring and summer seasons that dominate the high‐latitude shortwave energy budget. To isolate the influence of sea ice concentration on clouds, we analyze spaceborne light detection and ranging (LIDAR) observations in regions where present‐day sea ice concentration varies. During spring, low cloud cover is slightly (4%) higher over open water compared to sea ice. During summer, sea ice variability does not affect low cloud cover. During both spring and summer, cloud opacity is larger over open water than over sea ice due to a cloud phase shift from ice toward liquid with warming. Independent ship‐based visual and radiosonde observations available during summer corroborate the LIDAR results. Even with the cloud response, satellite‐observed top‐of‐atmosphere albedo is lower over open water than over sea ice. The observations show the cloud response to sea ice retreat with warming will not mask the surface albedo decrease. In other words, more shortwave radiation will be absorbed when Southern Ocean sea ice is lost.

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“…Ra phael (2003) demonstrated the Southern Hemisphere atmospheric response to the summertime sea-ice in crease over the entire Antarctic using a CGCM. More recently, by analyzing observational data and CGCM model output, Wall et al (2017) revealed that the atmospheric boundary layer in the Weddell Sea is stable over the sea ice during austral winter because sea ice inhibits heat and moisture transport from the ocean to the atmosphere, while the boundary layer is unstable and cloudy over open water.…”

Section: Introductionmentioning

confidence: 99%

Role of Weddell Sea ice in South Atlantic atmospheric variability

Morioka¹,

Engelbrecht²,

Behera³

2017

Clim. Res.

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We investigated the role of Weddell Sea ice in atmospheric variability over the South Atlantic by conducting observational data analysis and coupled general circulation model (CGCM) experiments. Weddell Sea ice exhibits a pronounced interannual variability in early austral summer (November−January). Low sea-ice concentration (SIC) anomalies in the Weddell Sea are strongly associated with anticyclonic atmospheric circulation anomalies in the South Atlantic. Composite analysis reveals that the low SIC anomalies in the Weddell Sea may be attributed to increased solar radiation and northwesterly wind anomalies. The low SIC anomalies, in turn, contribute to warmer skin temperature in the band of 60−70°S and enhance the near-surface atmospheric stability north of this band, implying favorable conditions for sustaining the anticyclonic circulation anomalies in the South Atlantic. This intriguing association between the SIC and atmospheric circulation anomalies is also simulated in CGCM experiments, e.g. when the interannual sea surface temperature variability in the tropics and mid-latitudes is suppressed. These results suggest that Weddell Sea ice, which may undergo interannual variation via air−sea−ice interactions in the high latitudes, influences atmospheric variability over the South Atlantic.

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Low-Cloud, Boundary Layer, and Sea Ice Interactions over the Southern Ocean during Winter

Cited by 19 publications

References 52 publications

Antarctic clouds, supercooled liquid water and mixed phase, investigated with DARDAR: geographical and seasonal variations

Antarctic clouds, supercooled liquid water and mixed phase, investigated with DARDAR: geographical and seasonal variations

The Combined Influence of Observed Southern Ocean Clouds and Sea Ice on Top‐of‐Atmosphere Albedo

Role of Weddell Sea ice in South Atlantic atmospheric variability

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