The Impact Of Arctic Oscillation And ENSO On The Extreme Climate Events In North China

The precipitation in North China has exhibited a decreasing trend concurrently with therecent global warming over the past decades, which resulted in a frequent warming anddrought event in this region and caused a negative impact on the local agriculture and naturalecosystems. The interannual variability of the Artic oscillation (AO) and ENSO has shown agreat impact on the year-to-year climate anomaly in North China. Therefore, theunderstanding of the joint impact of AO and ENSO on the extreme climate events in NorthChina is a very important issue. In present study, based on the station-observed precipitationand temperature, NCEP/NCAR reanalyzed datasets, this article firstly analyzed thespatial-temporal variations of extreme climate events in China, then discussed the jointlyimpact of AO and ENSO on the extreme drought in North China during the cold season of2010, and further explored the impact of AO and ENSO on the extreme climate events inNorth China on the basis of the historical records. The main results are summarized asfollows:(1) The maximum and the minimum temperature have shown upward trends in Chinaover the past five decades. However, the trend of precipitation has shown quite differentregional characteristics. The frequency of extreme high temperature (EHT) events hasexhibited an increased trend and the abrupt change is found around1990s. In contrast, thefrequency of extreme low temperature (ELT) events has shown a decreased trend andexhibited a suddenly change around the1970-80s. The frequency and intensity of extreme precipitation have exhibited the complex characteristics in the area and timing. The frequencyof EHT has shown an increased trend during the winter, but the ELT has exhibited andecreased feature in North China. In contrast to the intensity, the frequency of extremeprecipitation has shown a roubust interannual variability with a decreasing linear trend inNorth China.(2)The extreme drought occurred in North China during the cold season spanning2010-2011in North China is possibly impacted by its linear downward trend, but it is mainlyaffected by the negative phase of AO, and the stronger La Nina event. Statistical analysissuggests that during the negative phase of AO, the geopotential height at500hPa decreasesaround the Lake Baikal, the Ural blocking high develops, and the meridional circulationanomalies prevails over East Asia. Such high-latitude circulation may enhance the clod surgearound Lake Baikal southward shift and indirectly result in a cold and dry climate in NorthChina. During the La Nina year, however, the cooling of SST in the Nino3.4region weakensthe western North Pacific subtropical high and directly prevents the southward moisture fluxsupply. In contrast to the historical drought cases, the stronger and the persistent negativephase of AO and the La Nina event caused the cold front is much south and jointly resulted inthe persistent drought event in North China during the cold season of2010.(3) The precipitation anomaly is affected by the jointly impact of AO and ENSO, and thewet and drought is decided by the phase of AO and ENSO. A warming winter usually occursin North China corresponding to the positive phase of AO, in contrast, the precipitation wouldreduce in a stronger La Nina year, but it will increase when El Nino or weak La Nina occurs.The surface air temperature drops during the negative phase of AO, an extreme drought willoccur when a La Nina event prevails. As a result, the winter SSAT in North China isdependent on the phase of AO, but the precipitation anomaly is jointly dependent on the phase and intensity of AO and ENSO.