A unified approach to trace surface heat and cold events by using height anomaly

After decomposing an atmospheric field into climatic and anomalous components, a maximum height anomaly (MHA) in upper troposphere is found to be closely associated with surface anomalous temperature episodes. Thus, a unified method has been proposed to trace both heat and cold events as well as surface temperature anomalies through the following four aspects of this study. (1) First, a global daily MHA database from 1980 to 2010 is derived and its long-term variation is analyzed. (2) The general relationship between surface air temperature anomaly (SATA) and MHA is then studied. Following the hydrostatic balance, positive (negative) MHA center often corresponds well to positive (negative) SATA or heat (cold) event. (3) Potential capability of using MHA signal to extend predictability of SATA events is further examined. It is found that signals in MHA are stronger and appear earlier than that in temperature field. Positive or negative MHA centers can often be traced 9 days ahead on average for many SATA events. The earliest MHA signal to indicate a heat (cold) event can be traced 20 (26) days back in an upstream region. (4) Some challenges in applying MHA to early warning SATA events are discussed, mainly from the irregularity of MHA tracks, the location uncertainty of downward extension of upper air temperature anomaly including missing and false alarm issue, and the inability in quantifying intensity. Therefore, the forecast capability of MHA signal will strongly depend on the quality of an operational model forecasts.National Natural Science Foundation of China [41375073]; Chinese Academy of Sciences [201306032, XDA0509400]SCI(E)ARTICLEyutian4ever@163.com5-61647-16644