The tropical cyclone (TC) center position is often needed in the study of the innercore processes although there is currently no consensus on the definition of the TC center. While previous studies evaluated center-detecting methods in terms of the center position, vertical tilt and decomposed symmetric and asymmetric circulations, this study used the 1-km resolution output of the predicted Hurricane Wilma (2005) at 5minute intervals to evaluate the four TC centers that are frequently used in the diagnostic analysis of the inner-core dynamics processes: the pressure centroid center (PCC), the potential vorticity (PV) centroid center (PVC), the maximum tangential wind center (MTC) and the minimum pressure variance center (MVC) by focusing on the evolution of the small-scale track oscillation and vortex tilt. The differences in the detected center position and vertical tilt are generally small during the course of rapid intensification and eyewall replacement. The four methods all lead to similar small-scale track oscillations that rotate cyclonically around the mean track. While the MVC and PVC lead to a relatively smooth rotation, abrupt changes exist in the track oscillation of the MTC; the track oscillation of the PCC contains amplified embedded rotations that are associated with the PV mixing in the eye region. The tracks of the MVC and PVC relative to the lower-level center (vertical tilt) are generally smooth, while the relative tracks of the MTC and PCC contain abrupt changes. The MVC also leads to the strongest symmetric structure in the tangential wind, PV, and radial PV gradient in the eyewall region. This study suggests that the MVC should be selected in the study of inner-core processes.
Using the data from ERA‐interim, the Hadley Centre Global Sea Surface Temperature data set, and the Climate Prediction Center Merged Analysis of Precipitation, after removing the simultaneous El Niño and Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) signals, we have investigated variations of anomalous convergence around Kalimantan Island in lower troposphere in associations with the East Asian summer and Australian winter monsoons. Results indicate that when negative sea surface temperature anomalies appear in the western Pacific on both sides of the equator, the atmospheric cooling over the northwestern Pacific and from the South Pacific Convergence Zone (SPCZ) to Australia is favorable for the maintenance of anticyclonic anomalies over the areas from the western Pacific to the South China Sea and from the south of the equator to the northeast of Australia. These anomalous anticyclonic circulations can induce equatorial easterly anomalies, which subsequently facilitate the maintenance of anomalous convergence around Kalimantan Island. In turn, the anomalous convergence in Kalimantan Island is favorable for the maintenance of anomalous anticyclonic over the northwestern Pacific and SPCZ and thereby intensifies both the western Pacific subtropical high and the Australian High, inducing concurrent intensifications of the East Asian summer monsoon and Australian winter monsoon. Related to the anomalous convergence over Kalimantan Island, precipitation and temperature decrease from the western Pacific to SPCZ but increase from the Indian Ocean to western Maritime Continent and Australia, while temperature is lower than normal in Kalimantan. The above results have remarkable implications for in‐depth understanding of the mechanism behind anomalies of the East Asian summer monsoon and Australian winter monsoon.
The East Asian summer monsoon (EASM) and the Australian winter monsoon (AWM) are two important components of the Asian-Australian monsoon system during boreal summer. The simultaneous variations of these two monsoons would have remarkable impacts on climate in the Asian-Australian region. Using the reanalysis datasets, we investigate the mechanisms of variation and impacts of East Asian-Australian Monsoons (EAAMs). The singular value decomposition (SVD) is performed of the June-July-August (JJA) mean anomalous zonal wind for AWM as left field and JJA mean anomalous meridional wind for EASM as the right field after both El Niño-Southern Oscillation (ENSO) and India Ocean Dipole (IOD) signals are filtered out. Our results demonstrate that AWM and EASM are closely related to each other as revealed by the first leading SVD mode. The anomalously strong (weak) EAAMs correspond to anomalously strong (weak) AWM and EASM to the south of 30°N. When EAAMs are anomalously strong, cold sea surface temperature anomaly (SSTA) appears in regions near northern and northeastern coasts of Australia whereas the warmer SSTA appears in the northwestern tropical Pacific and South China Sea. The colder SSTA is associated with the upwelling of cold water from below induced by equatorial easterly anomalies, reinforcing the anticyclonic circulation over Australia through the Matsuno/Gill-type response whereas warm SSTA appears in the northwestern tropical Pacific and South China Sea as a result of oceanic response to the intensified northwest Pacific subtropical anticyclonic circulation. The EASM couples with AWM via the anomalous easterlies near equator in the Maritime Continent (MC) region and the slanted vertical anomalous circulations. In the years with strong EAAMs, precipitation decreases in northern Australia and over areas from the western Pacific to Bohai Sea 3 and Yellow Sea of China. Meanwhile, the western MC and the southeastern China experience more than normal precipitation.
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