Characterization of Moisture Sources for Austral Seas and Relationship with Sea Ice Concentration

Abstract

In this study, the moisture sources acting over each sea (Weddell, King Haakon VII, East Antarctic, Amundsen-Bellingshausen, and Ross-Amundsen) of the Southern Ocean during 1980-2015 are identified with the FLEXPART Lagrangian model and by using two approaches: backward and forward analyses. Backward analysis provides the moisture sources (positive values of Evaporation minus Precipitation, E − P > 0), while forward analysis identifies the moisture sinks (E − P < 0). The most important moisture sources for the austral seas come from midlatitude storm tracks, reaching a maximum between austral winter and spring. The maximum in moisture sinks, in general, occurs in austral end-summer/autumn. There is a negative correlation (higher with 2-months lagged) between moisture sink and sea ice concentration (SIC), indicating that an increase in the moisture sink can be associated with the decrease in the SIC. This correlation is investigated by focusing on extremes (high and low) of the moisture sink over the Weddell Sea. Periods of high (low) moisture sinks show changes in the atmospheric circulation with a consequent positive (negative) temperature anomaly contributing to decreasing (increasing) the SIC over the Weddell Sea. This study also suggests possible relationships between the positive (negative) phase of the Southern Annular Mode with the increase (decrease) in the moisture that travels from the midlatitude sources to the Weddell Sea.

Present‐Day Regional Antarctic Sea Ice Response to Extratropical Cyclones

“…Excepting Δu 10 , we find that median maximum correlations between all variables in Figure 7 and ΔSIC are negative for all ETC time steps. This further confirms that northerly warm, moist airflow within the cyclone's warm sector leads to thermodynamic (relative to the climatology) and pushes the sea ice edge poleward (e.g., Pezza et al, 2012;Reboita et al, 2019) while southerly winds induce equatorward sea ice drift and enhance thermodynamic growth behind the cold front. We note that within-composite correlation variability is high (i.e., many Figure 7 boxes have negative and .…”

“…(2016)). Although the South Pacific region, where both Bellingshausen and Ross ETCs form, has been shown to contribute more moisture to the Antarctic than the South Indian and South Atlantic Oceans (H. Wang et al., 2020), we hypothesize that total moisture transport is larger for E. Antarctic and E. Weddell cyclones because they form at lower latitudes (Reboita et al., 2019). E. Antarctic and E. Weddell composite ETCs also exhibit greater meridional movement (Table 1), which has been shown to be an important factor for ETC‐induced moisture transport (Sinclair & Dacre, 2019).…”

“…We find that E. Antarctic and E. Weddell composite ETC warm sectors produce greater poleward moisture transport prior to Lysis (160 − 200 kg m −1 s −1 ) than Bellingshausen or Ross ETCs (140 − 160 kg m −1 s −1 ), despite greater regional sea ice cover (see Figure 1 in Hobbs et al (2016)). Although the South Pacific region, where both Bellingshausen and Ross ETCs form, has been shown to contribute more moisture to the Antarctic than the South Indian and South Atlantic Oceans (H. Wang et al, 2020), we hypothesize that total moisture transport is larger for E. Antarctic and E. Weddell cyclones because they form at lower latitudes (Reboita et al, 2019). E. Antarctic and E. Weddell composite ETCs also exhibit greater meridional movement (Table 1), which has been shown to be an important factor for ETC-induced moisture transport (Sinclair & Dacre, 2019).…”

“…ETCs form within the polar jet (Uotila et al., 2011) and move southeastward toward the Antarctic coast over the course of days. These storms are important to Antarctic climate because they are cumulatively responsible for the majority of all meridional moisture and energy transport between the middle and high latitudes (Tsukernik & Lynch, 2013; Gorodetskaya et al., 2014; Papritz et al., 2014; Kurita et al., 2016; Reboita et al., 2019; H. Wang et al., 2020; Naakka et al., 2021). Storm fronts circulate air masses around the low pressure center and affect regional cloud and precipitation processes, temperature, surface energy, and sea ice (Nicolas & Bromwich, 2011; Binder et al., 2017; Y. Wang et al., 2019; Alexander et al., 2021).…”

“…ETCs form within the polar jet (Uotila et al, 2011) and move southeastward toward the Antarctic coast over the course of days. These storms are important to Antarctic climate because they are cumulatively responsible for the majority of all meridional moisture and energy transport between the middle and high latitudes (Tsukernik & Lynch, 2013;Gorodetskaya et al, 2014;Papritz et al, 2014;Kurita et al, 2016;Reboita et al, 2019;H. Wang et al, 2020;Naakka et al, 2021).…”