Monthly
Highlights
During January 2007, averaged
surface air temperature was generally above normal in China. Monthly mean
temperatures were over 1℃ above normal
in most of Tibet, northern Xinjiang, mid-eastern Inner Mongolia, Northeast
China, North China, northern East China, with 2-6℃ above normal in most of Northeast China, Tibet and
eastern Inner Mongolia. While temperatures were 1-2℃ below normal in Guizhou and western
Guangxi. Temperatures in other regions were near normal.
For the month, precipitations were near or below normal in
most of China with exception of precipitations 30-50% more than normal in most
of Northeast China and eastern Inner Mongolia, northern Xinjiang, Sichuan,
Chongqing, Guizhou and northern Hunan. Precipitations were 30-80% less than
normal in North China, the Huanghuai area, the Jianghuai area, southwestern
Yunnan, mot of the Tibet Plateau, and southern Xinjiang, with no precipitation
in parts of above regions.
During January 2007, monthly mean
temperatures were over 2℃ above
normal in most of Eurasia at the mid-high latitudes, most of the Tibet Plateau,
parts of northern Africa, northeastern America with temperatures 8-12℃ above normal in mid-western Russia. While
temperatures were 1-4℃ below normal in
mid-western America, parts of northeastern Siberia and western Australia.
For the month, precipitations were observed 50-100%
more than average in most of Europe, northern Russia, regions from southwestern
Baikal to northeastern China, locations in Africa, southwestern America,
central South America, central and southwestern Australia, with over 200% above
normal in locations. Meanwhile, precipitations were more than 50% below average
in Arabia, South Asia, the Tibet Plateau and southern Northwest China and most
North China, most of western Africa, and South Africa, northwestern America,
northern and southern South America and northwestern and southeastern Australia,
with no precipitation in parts of above regions.
General Circulation Features
Northern
Hemisphere: During January
2007, the mean 500hPa geopotential height field exhibited mainly a 3-wave
pattern at the mid-high latitudes. In the 500hPa height anomaly field, negative anomalies below -4 dam covered
regions from the northern North Atlantic Ocean to northern Europe, and from
northeastern Russia to the northern Pacific with central values below –12 dam
over North Europe. Meanwhile, positive anomalies above 4 dam covered a band
region from the mid-eastern North Atlantic Ocean east to the central North
Pacific via Eurasia, with central values above 12 dam in the southern
Mediterranean Sea, the Baikal and the northeastern North Pacific. Heights in
the rest regions were near normal. For the month, the Northwest Pacific
subtropical high was larger, stronger and extended farther west than normal.
Position of ridgeline located slightly further north than normal.
Southern
Hemisphere: For the month,
zonal circulation prevailed in the southern Hemisphere in the mean 500hPa
geopotential height field at the mid-high latitudes. In the 500hPa height anomaly field, obviously positive
anomalies were found over the polar regions with central values above 12 dam.
Meanwhile, negative anomalies about –4 dam were observed over the
southeastern South Pacific. Heights were near normal in the other regions.
Tropical Features
Sea Surface Temperatures (SSTs): During January 2007, positive SST anomalies above 0.5℃ maintained in the equatorial mid-eastern
Pacific but central values decreased obviously. Most of the NINO indices
decreased sharply with the exception of NINO1+2. NINO Z，NINO
3.4, NINO 3, NINO 4 and NINO 1+2 indices were 0.8℃, 0.8℃,0.9℃, 0.8℃ and
0.5℃, respectively. Meanwhile,
SSTs were about 0.5℃ above normal in the equatorial
western Indian Ocean.
Warm Pools: During January 2007, areas of the western Pacific and Indian Ocean warm pools were above
normal and their intensities were both stronger than normal.
Subsurface Temperatures: During January 2007, the anomalously subsurface warm
waters in the equatorial Pacific Ocean weakened and shrank to the equatorial
eastern Pacific. Meanwhile, the anomalously cold water in the central
equatorial Pacific enhanced and extended eastward compared with last
month.
Wind Field：During January 2007, at the lower troposphere (850hPa), westerly
anomalies covered the eastern equatorial Pacific and the eastern equatorial Indian
Ocean. Easterly anomalies or near normal wind were observed over the
mid-western equatorial Pacific. At the upper troposphere (200hPa), zonal winds
were near normal over most of the equatorial Pacific and westerly anomalies
were over the western equatorial Indian Ocean.
Southern Oscillation: For the month, Southern Oscillation Index (SOI) was -0.8,
with a decrease of 0.6 from last month.
Convection
over the Tropics:
During
January 2007, the anomalous
outgoing longwave radiation (OLR) showed that convections enhanced over the
mid-western equatorial Pacific and were suppressed over the eastern equatorial
Indian Ocean and southwestern Indonesia. In the lower troposphere (850hPa)
divergent wind field, a convergent center was observed over 150ºE, 5ºS, and a divergent center was located in 105ºW, 5ºS. Correspondingly, at the upper troposphere
(200hPa), the divergent center was found over 170ºE, 10ºS, and the convergent center was over 100ºW, 5ºS.
ENSO Monitoring and Prediction
(1) Positive SST anomalies
above 0.5℃ maintained in the equatorial mid-eastern Pacific but
central values decreased obviously. NINO Z is 0.8℃
(2) The anomalously subsurface warm waters in the
equatorial Pacific Ocean weakened and shrank to the equatorial eastern Pacific;
the anomalously cold water in the central equatorial Pacific enhanced and
extended eastward.
(3) At the lower troposphere (850hPa), westerly
anomalies covered the eastern equatorial Pacific and the eastern equatorial
Indian Ocean; easterly anomalies or near normal wind were observed over the
mid-western equatorial Pacific.
(4)
Southern Oscillation Index (SOI) was -0.8, with a decrease of 0.6 from last
month.
(5)
Convections enhanced over the mid-western equatorial Pacific and were
suppressed over the eastern equatorial Indian Ocean and Indonesia.
(6) Most
of models predicted that positive SST anomalies could decrease to be normal
during following 3-6 months.
In conclusion, tropical oceanic and atmospheric
conditions showed that the ENSO warm phase weakened obviously in this month.
The features of ENSO warm phase are expected to weaken obviously in the
following 1~2 months.