There is a dominant seesaw pattern in summertime precipitation between northeast Asia and Siberia. Examined here is a mechanism of the seesaw mode, focusing on quasi-stationary Rossby waves propagating on two upper-tropospheric waveguides along the Asian jet and over northern Eurasia. Empirical orthogonal function (EOF) analysis to the low-frequency (10-day low-pass filtered) variation during summer reveals wave-propagation patterns on both of the waveguides. The time evolution of the two composite fields, constructed using the obtained EOF modes for each phase of the seesaw mode, was investigated by the wave-activity flux. In both composite fields, eastward-propagating Rossby waves originating from the North Atlantic-European sector branch off around eastern Europe onto the two waveguides, which become out of phase toward the east because of the difference in longitudinal wavelengths along them. This results in opposite phase anomalies of meridional winds over northeast Asia and Siberia. Budget analyses of vorticity, heat, and water vapor on a day with significant wave patterns along the two waveguides revealed the main balances; the zonal advection of vorticity anomalies around the tropopause was partly balanced by an anomalous stretching effect over these two regions, and the adiabatic heating anomalies in the midtroposphere associated with the stretching effect around the tropopause were balanced with diabatic heating anomalies, explained by condensation heating related to the precipitation anomalies. These events occur frequently in July, when the climatological precipitation is the largest, particularly over northeast Asia.

This study investigated recent changes in the characteristics of explosively developing extratropical cyclones over the northwestern Pacific region in winter from 1979/80 to 2010/11 by using reanalysis data from the Japanese 25-yr Reanalysis/Japan Meteorological Agency Climate Data Assimilation System (JRA-25/ JCDAS). The results showed that the frequency of explosive cyclones increased in the northwestern Pacific region east of Japan. This increase was accompanied by a decrease in the number of slowly developing cyclones, indicating an increase in the cyclone growth rate. Moreover, most of the increased explosive cyclones east of Japan originated southwest of Japan. A comparison of the dynamical features and energy budgets of two composite cyclones in the earlier and later halves of the study period suggested that the increase was due to an enhancement of the low-level baroclinicity to the east of Japan and an increase in humidity associated with sea surface temperature warming and enhanced evaporation along the eastern shore of the Asian continent.

The summertime precipitation over northeast Asia (Mongolia and Inner Mongolia) increased from 1980 to the mid‐1990s, and low‐precipitation summers continued for 4 years from 1999. A vegetation index based on satellite observations shows a similar interannual change. The first EOF mode of the interannual change of July precipitation shows a seesaw pattern between northeast Asia and Siberia, and the time coefficient represents the summertime precipitation change over northeast Asia. This mode is associated with Rossby waves propagating eastward over the Eurasian continent, which accompany anomalous meridional winds over northeast Asia and Siberia, resulting in anomalous vertical flows. The vertical flows over these regions are connected with each other through the meridional circulation, which contributes to form the seesaw pattern by suppressing or enhancing the precipitation.

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[1] Transient and localized severe total ozone reduction events, ozone miniholes, have been sometimes observed in both hemispheres. Dynamical contributions to the minihole formation are estimated for 22 events and the mean features are explored in each hemisphere. For the estimation, global distributions of ozone mixing ratio are reconstructed dynamically by using three kinds of satellite ozone data and isentropic distributions of potential vorticity. As a result, most of the total ozone reductions are explained by dynamical processes in both hemispheres. On miniholes in the Northern Hemisphere, about a half of the dynamical reduction of column ozone in the upper troposphere and the stratosphere is due to isentropic transport of ozone-poor air which is poleward around the tropopause and equatorward in the middle stratosphere. The remaining half is explained by loss of air masses in isentropic layers, which is caused by vertical uplift of isentropes in the lower and middle stratosphere. The same type of miniholes is also found in the Southern Hemisphere. The other type in the Southern Hemisphere is caused by displacement or stretching of the Antarctic ozone hole toward midlatitudes, where the total ozone is reduced by the equatorward transport of ozone depleted polar air throughout the stratosphere, while the local uplift of isentropes due to the associated advection of cold temperature also contributes to reduce total ozone.