The role of synoptic-scale features and advection in prolonged warming and generation of different forms of precipitation at Dome Fuji station, Antarctica, following a prominent blocking event

摘要

abstract_textpA blocking event over the East Antarctic ice sheet during June 1997 generated the highest surface air temperature (which increased from around -70 degrees C to around -30 degrees C) and pressure of that year at the Dome Fuji station (77.5 degrees S, 40 degrees E). Following the blocking event, the anomalously high air temperature (around -50 degrees C to -60 degrees C) and pressure were maintained at the surface for about 1 week. This study investigates how these warm conditions were maintained and documents the sequential occurrence of two forms of synoptic-scale high-pressure systems with conditions that produced precipitation by different processes in each case. In the first half of the warm period, a solitary high-pressure system (the Solitary High) formed over the Dome Fuji station and traveled west over East Antarctica after being cut off from the tip of the preceding blocking ridge. During this phase, tropospheric temperatures were higher, and surface-based temperature inversions were more intense than during the following period. While a dry-out developed in the troposphere below about 300 hPa, the precipitation of ice crystals in the surface-based temperature inversion layer was generated by deposition of moisture that had become trapped in the boundary layer after being transported onto the continent by the previous blocking ridge. This mechanism has not been previously reported elsewhere. During the second half of the warm period, a ridge of high pressure (the Transcontinental Ridge) traversed East Antarctica almost completely, and its western section was amplified by the merging of the Solitary High with a preceding quasi-stationary Rossby wave train propagating along the Southern Ocean. This ridge allowed an intrusion of warm, moist air from the Weddell Sea toward the station, which generated precipitation throughout the whole troposphere by orographic uplift once again, and ended the dry-out. This represents the typical mechanism of both moisture transportation and the generation of precipitation, and this mechanism was the same as that associated with the preceding blocking ridge./p/abstract_text