1. Climate in China
In March 2014, the surface air temperature averaged over China was 5.3ºC, which was 1.2ºC above normal (4.1ºC) and ranked the 6th highest since 1961. The mean precipitation over China was 29.1 mm, which was basically nearly same as normal (29.5mm). For the month, extremes of Consecutive Non-Precipitation Days (CNPD), Daily Temperature Drop (DTD), Consecutive Precipitation (CP) and Consecutive Precipitation Days (CPD) were observed in China.
2. General Circulation Features
Northern Hemisphere: During March 2014, in the mean 500hPa geopotential height anomaly field, positive anomalies above 4 dam covered the central North Atlantic Ocean, East Europe, and regions from Mongolia to the arctic through the central Siberia. Meanwhile, negative anomalies below -4 dam covered the northwestern West Siberia nearby, the eastern North Pacific, and northeastern North America, with central values below -16 dam over parts of northeastern North America. For the month, the area of northwestern Pacific subtropical high was largger than normal. The position of its west ridge shifted further westward than normal.
Southern Hemisphere: For the month, in the mean 500hPa geopotential height anomaly field, positive anomalies over 4 dam were observed over the southern South Pacific, the central South Atlantic Ocean, and the southern South Indian Ocean. Meanwhile, negative anomalies below -4 dam were observed over the southwestern South Atlantic Ocean, and the ocean south of South Africa.
3. Tropical Features
Sea Surface Temperatures (SSTs): During March 2014, SSTs were 0.5℃ nearby above normal in the western equatorial Pacific, with central values of at least 1.0℃ above normal locating near the Date Line, and SSTs were near average in the central and eastern equatorial Pacific. Niño1+2, Niño3, Niño4, Niño3.4 and NiñoZ indices were -0.9℃, -0.3℃, 0.5℃, -0.2℃ and 0℃, respectively. SSTs were slightly above normal in the tropical South Indian Ocean, but they were slightly below normal in the tropical North Indian Ocean. The Indian Ocean basin-wide index (IOBW) was 0.1℃. SSTs were near normal in the tropical Atlantic Ocean.
Subsurface Temperatures: During March 2014, anomalously warm subsurface water dominated the most equatorial Pacific, with central values at least6℃above normal near 160ºW. Meanwhile, anomalously cold subsurface water remained in the far eastern Pacific, with central values below -2℃ near 95ºW.
Warm Pools: For the month, the area of both Indian Ocean and western Pacific warm pools were near normal, with the intensity of the Indian Ocean warm pool slightly above normal and that of the western Pacific warm pool significantly above normal.
Wind Field: For the month, at lower troposphere (850hPa), westerly anomalies covered the most equatorial Pacific, with central values at least 4 m/s above normal near the Date Line. At upper troposphere (200hPa), westerly anomalies dominated the eastern equatorial Pacific, with central values above 12 m/s. Easterly anomalies controlled the central and western equatorial Pacific. In the tropical Indian Ocean, easterly anomalies controlled the mid – west, but westerly anomalies controlled the east.
Southern Oscillation: For the month, the Southern Oscillation Index (SOI) was -0.8.
Convections over the Tropics: During March 2014, the anomalous outgoing longwave radiation (OLR) showed that convection was active over the central equatorial Pacific near the Date Line, with central values below -15W/m2. However, convection was suppressed near the Marine continent, with central values at least 15W/m2. Meanwile, convection was active over the most equatorial Indian Ocean with central values at least 15W/m2.
4. ENSO Monitoring and Outlook
Since the mid of February 2014, sea surface temperature (SST) in large portions of the equatorial eastern Pacific has increased, and then by the mid of March, the positive SST anomalies has covered most of Nino regions except Nino 1+2 and correspondingly the subsurface warm water has dominated the eastern equatorial Pacific. Meanwhile the twice strongly westerly burst events occurred in early the year, which led to weaken the northeasterly trade wind and intensify the convection activities near dateline. In the mid of April 2014, a new westerly anomalies that is beneficial to El Nino event appeared to develop in the western tropical Pacific. In addition, the studies showed that both signal factors of the past winter negative SST anomalies in the northwestern Pacific and the last spring air temperature difference between over the eastern and western tropical Pacific all favor an El Niño event since summer 2014.
Considering the prediction of models and current development trend of the sea and atmospheric status, the current ENSO-neutral with slightly warm conditions is expected to transition to the El Niño conditions in summer 2014 and furthermore probably to shape into an El Niño event during the rest of 2014.
Therefore, we will closely monitor the development of ENSO conditions and update our ENSO wrap-up in time.