Masatake E. Hori

The Role of Barents Sea Ice in the Wintertime Cyclone Track and Emergence of a Warm-Arctic Cold-Siberian Anomaly

AbstractSea ice variability over the Barents Sea with its resultant atmospheric response has been considered one of the triggers of unexpected downstream climate change. For example, East Asia has experienced several major cold events while the underlying temperature over the Arctic has risen steadily. To understand the influence of sea ice in the Barents Sea on atmospheric circulation during winter from a synoptic perspective, this study evaluated the downstream response in cyclone activities with respect to the underlying sea ice variability. The composite analysis, including all cyclone events over the Nordic seas, revealed that an anticyclonic anomaly prevailed along the Siberian coast during light ice years over the Barents Sea. This likely caused anomalous warm advection over the Barents Sea and cold advection over eastern Siberia. The difference in cyclone paths between heavy and light ice years was expressed as a warm-Arctic cold-Siberian (WACS) anomaly. The lower baroclinicity over the Barents Se...

A polar low embedded in a blocking high over the Pacific Arctic

A polar low (PL) is a short-lived phenomenon involving strong winds that occurs over polar oceans. In October 2009, the R/V Mirai encountered a PL with a 600-km-wide, comma-shaped cloud that developed over the Chukchi Sea. A shipboard Doppler radar and radiosondes were used to understand the fine structure of this PL. Analyses of low-level winds and the thermodynamic structure indicated that the development of the PL was decoupled from sea surface thermal forcing. The PL was likely triggered by an intrusion of a potential vorticity (PV) anomaly at the tropopause. A southerly warm advection associated with a blocking high over Alaska resulted in rapid development of the PL in front of the cold dome induced by the upper-level PV anomaly. The westerly winds after passage of the PL seemed to modify the upper-ocean structure dramatically.

Cold air formation and advection over Eurasia during “dzud” cold disaster winters in Mongolia

Large negative temperature anomalies due to cold air advection have been observed over the Eurasian continent in recent years. During the 2009/2010 winter, a large amount of snow accumulated across Central Asia and China, which along with a strong cold air outbreak, resulted in extremely high livestock mortality in Mongolia. The present study examined the surface inversion development over the Eurasian continent in terms of the cold air advection, accumulation, and breaking processes at ground level. Meteorological analyses shown trends toward earlier onsets of snow and subsequent cold air advection from the Arctic through western Siberia during the last decade, which is a possible driver of the persistent enhanced surface cooling observed in mid-winter in Mongolia. Cyclones are shown to be drivers of early snowfall onset at the beginning of winter and the subsequent migration of cold air from the Arctic, and are thus the key to understanding and predicting the frequency and intensity of persistent surface cooling, which is a substantial physical precursor for the cold disaster in Mongolia “dzud.”