Abstract
Interannual variability of cyclones that are generated over the eastern Asian continent and passed over the Yellow, Bohai, and East China seas (YBE cyclones) in spring is analyzed using reanalysis datasets for the period of 1979–2017. Possible causes for the variability are also discussed. Results show that the number of YBE cyclones exhibits significant interannual variability with a period of 4–5 years. Developing cyclones are further classified into two types: rapidly developing cyclones and slowly developing cyclones. The number of rapidly developing cyclones is highly related to the underlying sea surface temperature (SST) anomalies (SSTA) and the atmospheric baroclinicity from Lake Baikal to the Japan Sea. The number of slowly developing cyclones, however, is mainly affected by the North Atlantic Oscillation (NAO) in the preceding winter (DJF); it works through the upper-level jet stream over Japan and the memory of ocean responses to the atmosphere. Positive NAO phase in winter is associated with the meridional tripole pattern of SSTA in the North Atlantic Ocean, which persists from winter to the following spring (MAM) due to the thermal inertia of the ocean. The SSTA in the critical mid-latitude Atlantic region in turn act to affect the overlying atmosphere via sensible and latent heat fluxes, leading to an increased frequency of slowly developing cyclones via exciting an anomalous eastward-propagating Rossby wave train. These results are confirmed by several numerical simulations using an atmospheric general circulation model.
Highlights
Extratropical cyclones are an essential component of the atmospheric circulation system in the extratropical region, which play an important role in maintaining the energy balance of the atmosphere by transferring energy and moisture poleward to reduce the meridional temperature gradient [1].In the Northern Hemisphere, extratropical cyclones are mainly located over Kuroshio in the Pacific, subtropical Northwest American coast, East Pacific, Southeast Greenland, and Barents sea in winter [2].On the interannual time scale, there exists an obvious correlation between Atlantic storm frequency and the North Atlantic Oscillation (NAO) [2,3]
It may act to work through the change of atmospheric circulation instead
YBE spring cyclones are classified into two types to reveal their interannual variability and possible causes based on reanalysis datasets and numerical simulations
Summary
In the Northern Hemisphere, extratropical cyclones are mainly located over Kuroshio in the Pacific, subtropical Northwest American coast, East Pacific, Southeast Greenland, and Barents sea in winter [2]. On the interannual time scale, there exists an obvious correlation between Atlantic storm frequency and the North Atlantic Oscillation (NAO) [2,3]. While the eastern Pacific cyclone frequency is related to the Pacific-North American (PNA) pattern [2]. Atmosphere 2019, 10, 40; doi:10.3390/atmos10010040 www.mdpi.com/journal/atmosphere (AO) index is positively correlated with the frequency of extratropical cyclones at the high latitudes in the Northern Hemisphere, whereas a negative correlation appears at the low latitudes. Changes in long-term trends of extratropical cyclones over the Northern Hemisphere have gained many attentions due to global warming [5,6,7,8,9,10,11,12].
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