During
May, mean surface air temperatures were near normal in most of China except
northern Xinjiang, most of Tibet and the regions south to the Yangtze River
where temperatures were 1~2℃
above normal. In this month, rainfall totals were 50~90% less than normal in
western Tibet, eastern Xinjiang and eastern Inner Mongolia. Meanwhile, in the
rest of China, rainfall totals were near or more than normal, with 50%~100%
above normal in western and northern Xinjiang, central Qinghai, central Tibet,
most of Yunnan, northwestern North China, most of Shandong and northern
Northeast China.
During
May, the mean surface air temperatures were 2~4℃
above normal in
West Siberia, eastern Far East of Russia, western Alaska and central America,
with center values of above 4℃
more than normal in
central West Siberia, while temperatures were 2℃
below normal in
north-central Algeria, northern Center Siberia, most of Canada and south-central
South America, with center values of 4~7℃
below normal in part of Canada.
In
this month, rainfall totals were 50%~100% more than normal in most of East
Europe, Alps Mts., the southern Indian Peninsula, part of Asia, Far East of
Russia, Alaska, northeastern America, northwestern Australia and part of South
America. In the rest of the world, rainfall totals were near or less than
normal, with no rain in part of Sahara, southeastern Africa, the coast of the
southeastern Arabia Peninsula, the southeastern Iran Plateau, southwestern
America and central Brazil.
Northern Hemisphere: During
May, the mean 500hPa geopotential height field exhibited a 4-wave pattern at the
mid-high latitudes. In the anomaly field, negative anomalies dominated northern
North America, most of Europe and Stanovoi Mts., with center values below –8
dam over north-central North America. Meanwhile, most of other regions were
controlled by positive anomalies, with center values above 8 dam over the
northeastern Pacific and West Siberia. In this month, the polar vortex was
weaker than normal. In Eurasia, meridional circulation was stronger than normal,
while zonal circulation was near normal. The Northern Hemisphere subtropical
high was obviously stronger than normal, and the Northwest Pacific subtropical
high was stronger and larger than normal.
Southern Hemisphere: In this month, the mean 500 hPa geopotential height field exhibited a 3-wave pattern at the mid-high latitudes. In the height anomaly field, positive anomalies above 4 dam covered Antarctica, southernmost South America and the sea areas around it, offshore of southern South Africa and parts of the south-central South Pacific. Meanwhile, negative anomalies controlled most of other regions, with center values below 8 dam over the southeastern South Pacific.
Sea
Surface Temperatures (SSTs): During
May, negative SST anomalies in the eastern part of the eastern equatorial
Pacific enhanced obviously, but mainly localized within the regions east to 120°W,
with center values below -2.5℃.
Meanwhile, above 0.5℃
SST anomalies dominated most of the western and central equatorial Pacific.
Correspondingly, the SSTa index of NINO 4 was 0.5℃,
with a rise of 0.3℃
from last month, while the SSTa indices of NINO 3 and NINO 1+2 were 0.3℃
and -1.3℃,
with drops of 0.3℃
and 1.0℃
from last month, respectively. In addition, SSTs were obviously greater than
normal within the Kuroshio Current.
Subsurface
Temperatures: During
May, the location of the positive anomaly center in the equatorial Pacific
shifted eastward to 160ºW.
Compared with that of last month, the area and intensity of positive anomalies
shrunk and weakened obviously. Meanwhile, the area and location of the negative
anomalies in the eastern equatorial Pacific shrunk and rose.
Warm
Pools: In
this month, the western equatorial Pacific warm pool was stronger and larger
than normal, with its intensity index being 2.0. The equatorial Indian Ocean
warm pool was larger than normal.
Southern
Oscillation: During
May, the Southern Oscillation Index was 0.5.
ENSO
Monitoring
a)
Compared with that of last month, negative SST anomalies in the eastern
part of the eastern equatorial Pacific enhanced obviously, but mainly localized
within the regions east to 120°W.
Meanwhile, above 0.5℃
SST anomalies dominated most of the western and central equatorial Pacific.
b)
Positive anomalies in the central equatorial Pacific weakened obviously.
Meanwhile, the area and location of the negative anomalies in the eastern
equatorial Pacific shrunk and rose.
c)
The Southern Oscillation Index was near normal.
d)
At the lower troposphere (850hPa) and upper troposphere (200hPa), zonal
winds were near normal over the equatorial Pacific.
e)
The convections enhanced obviously over the western equatorial Pacific.
The
above features exhibited that during May tropic ocean and atmosphere showed ENSO-neutral
conditions.
ENSO
Forecasting
There
are four statistical models: the analogue prediction model, the optimum
filtering assembly model, the maximum entropy singular spectrum analysis and the
principal component canonical correlation analysis, and two ensemble schemes:
assessment ensemble scheme and recursion ensemble scheme that are routinely run
by Climate System Diagnostics and Prediction Division of NCC.
These
predictions of the eastern Pacific SST suggested that ENSO-neutral conditions
are expected to continue for the next 2~3 months.
Considering
the uncertainty of model predictions, it suggested that the prediction should to
be used cautiously.