Researchers from the Environmental Physics Laboratory (EphysLab), CIM-UVigo, participated in a pioneering study that presents a climatology for the period 1980-2015 of the main sources of moisture for each of the seas that make up the Antarctic Ocean, focusing on the relationships between transported moisture and sea ice concentration and using a Lagrangian approach, a technique in which this group from the Ourense campus is a specialist.
The work was developed in the last year and a half together with two Brazilian research groups, specifically from the federal universities of São Paulo and Itajubá, within the projects of the São Paulo Research Foundation. It was attended by EphysLab members Luis Gimeno and Raquel Nieto, who carried out a research stay at the São Paulo academic institution, and Marta Vázquez, an expert on moisture transport in the Arctic region. On the Brazilian side, Michelle Simões Reboita, Rosmeri P. da Rocha and Anita Drumond participated. The results of the study were recently published in the latest issue of the journal Atmosphere under the title Characterization of moisture sources for austral seas and relationship with sea ice concentration.
“In this study, the Flexpart particle dispersion model is used to locate the main sources of moisture that affect the seas of the Southern Ocean,” explain EphysLab. This model, the researchers explain, allows the trajectories of particles to be followed and the variations in their specific humidity to be analyzed, making it possible to geographically locate where they gain or lose moisture and therefore relate the sources and sinks.
Sources of humidity and ice concentration
Regarding the results of the study, Nieto and Gimeno indicate that it was found that “in the different seas of the region, the main sources of moisture correspond to the main areas of passage of cyclones in mid-latitudes, with maximum evaporation occurring between winter and austral spring”. However, they add, the contribution of moisture from sources over the austral seas “seems to be more effective in the last months of summer and autumn, with greater moisture contributions appearing over these regions at these times”. As the researchers detail, this greater contribution seems to be modulated to some extent by the atmospheric circulation pattern known as the “southern annular mode”, producing an increase in moisture transport from the sources in its positive phase, for example to the Weddell Sea. “After analyzing the sources of moisture, this was related to the concentration of sea ice and it was seen how the variability of the moisture contribution from the main sources seems to be related to this concentration. The maximum moisture contributions generally coincide with minimums in the ice extent and it was found that in this relationship there is a maximum lag of two months,” they comment.
The moisture transport analyses carried out by EphysLab were also completed with studies of other variables by researchers from Brazil. “To focus on a specific region, over the Weddell Sea, it was found, for example, that in addition to the moisture that reaches the region, the variability of ice concentration also depends on the interrelationship of this mechanism and temperature”, indicate the researchers from Ourense. Thus, they detail, it was determined that at times of maximum moisture supply, the atmospheric circulation pattern in the area is modified and consequently a decrease in temperature occurs, contributing to a decrease in ice concentration over the Weddell Sea, and vice versa.
The importance of sea ice
Regarding the relevance of undertaking the study of the research object, EphysLab recalls how “sea ice and any form of ice found in the sea that originates from the freezing of seawater is one of the components of the climate system, causing a great influence on the Earth’s climate”. The extent and concentration of sea ice, they detail, not only depend on the seasons of the year but also respond to many different interactive processes in the atmosphere and the ocean, to the modes of atmospheric circulation on a large scale, as well as to the processes associated with climate change. Among the multiple atmospheric and oceanic controllers that control the variability of sea ice, indicate Raquel Nieto and Luis Gimeno, “little attention has been paid to the transport of moisture from the extratropics to the Southern Ocean, a relevant mechanism that plays a crucial role in atmospheric hydrology in the Arctic and with implications for the extent of Arctic sea ice”. Thus, they emphasize, “the transport of atmospheric moisture is a primary source of water in the polar regions and through radiative cloud forcing directly or indirectly affects snow, sea ice and the ice sheet.”
