No abstract

The East Asian monsoon circulation during the El Nino episodes of '86/87 and '91/92 is studied diagnostically. It is found that a southerly wind anomaly appeared in the lower troposphere along the coast of the East Asia during the mature phases of these two El Nino events. In the case of '86/87, the mature phase covered the boreal summer and the East Asian summer monsoon was intensified. On the other hand, in the case of '91/92, the northern winter was within the mature phase and the East Asian winter monsoon was weakened.Examination of the circulation features suggests that the effects of the El Nino events on the East Asian monsoon are felt through the variation of convective activities over the western equatorial Pacific. Convections in this area are strongly influenced by the evolution of sea surface temperature anomalies in the equatorial Pacific and are strongly suppressed during the mature phase, which exerts significant influences on the direct monsoonal circulation over the western tropical Pacific and the East Asia.The relationship between the East Asian monsoon and El Nino in its mature phase is also confirmed by a historical 850hPa wind dataset that covers 6 events prior to the '86/87 event. The dataset also suggests that an inverse relationship does not hold during the La Nina periods.

The importance of the El Nino-Southern Oscillation phenomenon in year-to-year fluctuations of the global climate has led to efforts to improve the real-time ocean observing system in the tropical Pacific. One element of this improved system is the TOGA-TAO (Tropical Atmosphere-Ocean) Array of wind and upper ocean thermistor chain moorings. This array, the result of an international effort, has already provided the rudiments of a basin-wide, real-time observing system and plans call for a major enhancement during the second half of the TOGA decade. The development of the TAO array is discussed, recent results from the pilot measurements are described, and plans for the expanded array are presented.

Diagnostic analysis is made to investigate features of the moisture circulation over East Asian during the El Niñ o episode in northern winter, spring and autumn. It is found that in all these seasons, the anomalies of precipitation in China, atmospheric precipitable water, water vapor transport and moisture divergence over East Asia in the El Niñ o mature phase, differ from those in the rest of the phases. In the El Niñ o mature phase, positive precipitation anomalies occur in the southern part of China. More northeastward water vapor transport appears around the southeastern coast of East Asia, where moisture converges, and precipitable water is above normal, which are consistent with the precipitation anomalies. The physical process through which El Niñ o affects the East Asian climate, is also identified. Differing from the rest of the phases in the El Niñ o episode, the mature phase is characterized by strong convective cooling anomalies in the atmosphere, in the area (0-15 N, 110 E-150 E) over the western tropical Pacific. As a Rossby wave response of the tropical atmosphere to the cooling anomalies, an anomalous low-level anticyclone forms to the north of the maritime continent. This anticyclonic anomaly not only transports more water vapor to the area around the southeastern coast of East Asia, but also strengthens the western Pacific subtropical high, and shifts it to the south of the mainland China, which are favorable for more precipitation in the southern part of China.

[1] The winter dipole anomaly (DA) in the Arctic atmosphere and its contribution to sea ice export are investigated by using a high-resolution coupled global general circulation model. The spatial distributions of the first two leading EOF modes of winter mean sea level pressure (SLP) and geopotential height at 500 hPa north of 70°N obtained by the long-term simulation (1900 -2010) are highly similar to those derived from the National Center for Environmental Prediction and the National Center for the Atmospheric Research (NCEP/NCAR) reanalysis datasets (1948 -2004). The first-leading mode corresponds to the Arctic Oscillation (AO). The DA is defined as the second-leading mode. The AO and DA account for 59% and 19% of the total variance, respectively. Composite spatial patterns of SLP, sea ice thickness and velocity in the extreme years when both the absolute values of principal component (PC1 and PC2) exceed 1.0 standard deviation indicate that the DA plays a great important role in sea ice export from the Arctic Ocean to the Greenland Sea due to its strong meridionality. Sea ice export is highly promoted (restricted) in the positive (negative) DA phase. The dependence of sea ice export on the DA is comparable to or rather larger than that on the AO. Citation: Watanabe, E., J. Wang, A. Sumi, and H. Hasumi (2006), Arctic dipole anomaly and its contribution to sea ice export from the