Highlights

General Circulation Features

Northern Hemisphere

During June 2004, the mean 500hPa geopotential height field exhibited a 4-wave pattern at mid-high latitudes. Negative anomalies covered most of northern Europe, mid-eastern Siberia and the regions from the western Atlantic Ocean to eastern North America, with center values below -8 dam. Positive departures controlled most of other regions with departures above 8 dam over the regions from the northwestern North America to the Polar and the northwestern Pacific. For the month, the Northwest Pacific subtropical high was weaker than normal and shifted eastward compared with the normal position.

Southern Hemisphere

For the month, a 3-wave pattern appeared in the mid-high latitudes at the mean 500hPa geopotential height field. Positive departures covered most of the regions, with the maximum greater than 12 dam over the southwestern Atlantic Ocean. Meanwhile, negative anomalies of -4~-12 dam were observed in the southern Pacific.

Climate for China

During June, the mean surface air temperatures were 1~2℃ above average in Northwest China and along the coast of Guangdong, and 2~ 4℃ above average in most of the Northeast and the eastern Inner Mongolia. Temperatures were 1~2℃ lower than average in northern Yunnan, Sichuan basin and the central North China Plain. For the month, rainfall totals were 50~100% more than normal in southern Hebei, northwestern Shandong, western Tibet and western Inner Mongolia, and even 200~400% more than normal locally. Rainfall totals were observed 30~90% below normal in northeastern Inner Mongolia, the northern Northeast, most of the three regions of Northwest, South China and East China.

Tropical Features

Sea Surface Temperatures (SSTs)

During June, near-normal sea surface temperatures were observed in much of the eastern equatorial Pacific but lower than -0.5℃below average in the offshore of South America. The positive SST anomalies around 0.5℃ were found in the central and western equatorial Pacific. Correspondingly, the SST indices of NINO 4, NINO 3 and NINO 1+2 regions were 0.5℃, -0.1℃ and -1.5℃, respectively. In addition, positive anomalies around 0.5℃ controlled the central and eastern equatorial India Ocean, and negative anomalies below -0.5℃ controlled the western Indian Ocean.

Circulation

Wind Field

For the month, at the lower troposphere (850hPa), westerly anomalies of 2~4 m/s covered most of the equatorial Pacific, with center values above 8 m/s in the western equatorial Pacific. The zonal winds closed to normal in the equatorial India Ocean. At the upper troposphere (200hPa), weak easterly anomalies were found in the most of the equatorial Pacific and the equatorial Indian Ocean except that weak westerly anomalies in the central equatorial Pacific and the central equatorial Indian Ocean.

Southern Oscillation

During June, the Southern Oscillation Index was -1.5.

Convection over the Tropics

During June, the anomalous outgoing longwave radiation (OLR) distribution exhibited that enhanced convections were over the western equatorial Pacific and near the dateline, and suppressed convections were over the Indonesia. In the lower troposphere (850hPa) divergent wind field, the convergent center was over 145°E, 10°N, and the divergent center was around 80°W, 25°S. Correspondingly, the divergent and the convergent centers at the upper troposphere (200hPa) were over 140°E, 10°N and around 105°W, 20°S, respectively.