Spatial and temporal variability of snow accumulation rate and air transports at East Antarctic ice sheet in 1993–2010

Influenced by the steep shapes and surrounded by the ocean, Antarctica has a specific spatial distribution of snowfall and humidity. The coastal area has many snowfall and blizzard, whereas the interior area has a few heavy snow events but there are some influences by the diamond dust every day. The high altitudes and low temperature make the less humidity around the interior, the annual accumulation rate is very low. It is important to understand the spatial distribution of the accumulation rate and their interannual variations to estimate the mass balance of the ice sheet for predicting the future climate change, e.g. sea level rise. Snow stakes along the traverse routes have been observed for long term monitoring program 'the variation of ice sheet surface mass balance' from the 1960's by the Japanese Antarctic Research Expedition in Shirase glacier drainage basin, East Antarctica. During the traverse route between coastal S16 point (69°02'S, 40°03'E, 580m a.s.l.) to inland Dome Fuji (77°22'S, 39°42'E, 3,810m a.s.l.), the snow stake observations every 2 km have been carried out from 1993. Comparing the annual accumulation rates with AAO-indices (SAM), annual accumulation rate and AAO-index showed the positive correlation. We attempted to express the moisture transport using trajectory analysis by assumed that air parcels come from the outside of Antarctica would have rich moisture than the air parcels that traveled around the ice sheet. Air transports are calculated using the NITRAM trajectory model (Tomikawa and Sato, 2005) and ERA-Interim meteorological data set in 1993-2010. The time duration is 5 days from the lifecycle of synoptic disturbances and we suppose the origin of air parcel is the point of trajectory at 5 days ago in this study. The starting points are distributed from 69°S to 78°S per 1 degree along the 39°E and its altitude is 1,300m above the surface. The annual (averaged from 69°S to 78°S along 39°E) percentages of air parcels came from outside of Antarctica have a positive correlation with the annual averaged accumulation deviations in 2000s. However, in the 1990s, there is no significant phase as same as its relationship with AAO-indices. To discuss about this change from 1990s to 2000s, we compared the averaged monthly numbers of snowfall days at Syowa Station for those terms. These are not the amount of snowfall. They are only records whether the day had snowfall event or not. The total monthly snowfall days have a seasonal variation but there is a significant difference between 1990s and 2000s. In 1990s, they decreased in June and have a semiannual cycle. However, in 2000s, the decreasing has gone and the numbers don't change in through the winter. As in 1990s, the snowfall would concentrate in the early winter, especially Katabatic wind area, the annual accumulations tend to be low because we measure in summer. But in 2000s, it snows in late winter too. Moreover, the total annual snowfall days has increased and got larger amplitude in 2000s. Therefore the accumulation rates seems to be changed from 1990s to 2000s. Comparing the phases of AAO-indices and numbers of the air parcels came from the outside of Antarctica, we found a relationship between them. In 1990s, if SAM has a plus phase, the atmospheric circulation field tends to enhance the air parcels from outside of Antarctica to enter into the interior region. However, that relationship has gone in 2000s. We are trying to make it clear why the relationship has changed. We will discuss our interpretation for this relationship in the presentation.