Monthly Highlights

Climate in China

During June 2007, monthly mean surface air temperature for China was the second highest for June in record. Temperatures were 1℃ below normal in parts of Qinghai and Tibet, while temperatures were near or above normal in the remainder of China, with temperatures 2-4℃ above normal in northern North China, most of Northeast China, southern Xinjiang, eastern and western Inner Mongolia.

For the month, precipitations were observed 30-200% above normal in most of South China, parts of the middle reaches of the Yangtze River, the lower valleys of both the Huaihe River and the Yellow River, western Hetao area, the upper reaches of the Yellow River, northwestern and southern Xinjiang. Meanwhile, precipitations were more than 30% below normal in the remainder of China.

Climate in the World

During June 2007, monthly mean surface air temperatures were observed above normal in most of the Northern Hemisphere. Temperatures were more than 2℃ above normal in coast regions of northeastern Russia, northern China, most of Mongolia, middle and southern Europe, southwestern West Africa, northern Algeria, parts of northern USA, middle and eastern South America, with temperatures more than 4℃ above normal in Northeast China and parts of Mongolia. Meanwhile, temperatures were more than 2℃ below normal in middle and western Russia and middle Australia (fig.1).

For the month, precipitations were observed 50-200% more than normal in middle and northern Russia, West Europe, coast regions around the Mediterranean Sea, most South Africa and East Africa, middle and southern USA, parts of northern South America, northeastern Australia, the southern Indian Peninsula, and middle East Asia. Meanwhile, precipitations were 50-100% less than normal in southern and western Australia, northern East Asia, most of Middle Asia, Europe, northern Africa, western USA and most of South America (fig.2).

General Circulation Features

Northern Hemisphere: During June 2007, the mean 500hPa geopotential height field exhibited a weak 5-wave pattern at the mid-high latitudes, with the troughs over the West Siberian Plain, the oceans south to the Kamchatka Peninsula, the oceans west to Canada, the Newfoundland Island and the northwestern North Atlantic Ocean. In the 500hPa height anomaly field, positive anomalies above 4 dam covered the northern North Atlantic Ocean to southeastern Canada, Greenland, the Bering Sea and most of the North Arctic Ocean, with center above 12 dam. Meanwhile, negative anomalies below -4 dam covered parts of the northeastern and northwestern North Atlantic Ocean, the Ural Mountains, and parts of the northeastern North Pacific Ocean, with center below -8 dam (fig.4). For the month, the Northwest Pacific subtropical high was larger and stronger than normal, and extended slightly more westward and its ridge line position was more southward than normal.

Southern Hemisphere: For the month, meridional circulation was much obvious at the mid-high latitudes. In the 500hPa height anomaly field, positive anomalies above 4 dam covered most of the Indian Ocean south of 60°S and Antarctica, middle and south of the South Pacific, with center above 16 dam. Meanwhile, negative anomalies below -8 dam covered middle of the South Indian Ocean around 40°S, southmost South America and the oceans around it, and oceans southeast to New Zealand. Heights were near normal in other regions.

Tropical Features

Sea Surface Temperatures (SSTs)

During June 2007, SSTs still exhibited a pattern of “cold in the east and warm in the west” in the equatorial Pacific. Positive SST anomalies above 0.5℃ covered most of the equatorial western Pacific, which enlarged compared with last month. Negative SST anomalies in the equatorial eastern Pacific weakened and withdrew eastward to the region east of 120ºW, with central values below -2.0℃ in the far eastern equatorial Pacific. SST anomaly indices of NINO Z, NINO 3.4, NINO 4, NINO 3 and NINO 1+2 were -0.3℃, 0.1℃, 0.3℃, -0.6℃ and -1.4℃, with raises of 0.1℃, 0.3℃, 0.1℃, 0.1℃ and 0.1℃ from last month, respectively. Meanwhile, SST anomalies were 0.5-1.0℃ above normal in most of the equatorial Indian Ocean.

Subsurface Temperatures

During June 2007, comparing with last month, the area of anomalously warm subsurface waters in the western equatorial Pacific rose up and extended eastward, with central value weakened. Meanwhile, anomalously cold subsurface waters in the equatorial eastern Pacific weakened and withdrew eastward.

Warm Pools

During June 2007, areas of the western Pacific and Indian Ocean warm pools were above normal and both of their intensities were stronger than normal.

Wind Field

For the month, at the lower troposphere (850hPa), weak easterly anomalies covered the equatorial Pacific near the Date Line with central values below -4 m·s^-1, while zonal winds were near normal over other regions of the equatorial Pacific. Easterly anomalies covered the equatorial Indian Ocean with central values below –4 m·s^-1. At the upper troposphere (200hPa), zonal winds were near normal over most regions of the equatorial Pacific.

Southern Oscillation

For the month, Southern Oscillation Index (SOI) was 0.4, with an ascend of 0.6 from last month.

Convection over the Tropics

During June 2007, the anomalous outgoing longwave radiation (OLR) showed that convections were near normal over most of the equatorial Pacific. In the lower troposphere (850hPa) divergent wind field, a convergent center was observed over 140ºE, 5ºN, and a divergent center was located in 90ºW, 25ºS. Correspondingly, at the upper troposphere (200hPa), the divergent center was found over 155ºE, 15ºS, and the convergent center was over 115ºW, 25ºS.

ENSO Monitoring and Prediction

(1) SST still exhibited a pattern of “cold in the east and warm in the west” in the equatorial Pacific during June, while all of SST anomaly indices of NINO Z, NINO 3.4, NINO 4, NINO 3 and NINO 1+2 ascended from last month. NINO Z was -0.2℃.

(2) The area of anomalously warm subsurface waters in the western equatorial Pacific rose up and extended eastward, with central values weakened compared with last month, while anomalously cold subsurface waters in the eastern equatorial Pacific weakened..

(3) Southern Oscillation Index (SOI) was 0.4.

(4) At the lower troposphere (850hPa), wind field was near normal in most of the central and eastern equatorial Pacific, while weak easterly anomalies covered parts of the western equatorial Pacific.

(5) Convections were near normal over the equatorial Pacific.

(6) Most of models predicted that the SST anomalies in the equatorial eastern Pacific could drop and come into La Nina status in the following 1-3 months.

In conclusion, the anomalously SSTs in the equatorial Pacific appeared to be the ENSO-neutral conditions in the mid-eastern Pacific, and it is expected to maintain in the following 1-2 months.