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Zhan R.,Shanghai Typhoon Institute of China Meteorological Administration | Wang Y.,University of Hawaii at Manoa | Wen M.,Chinese Academy of Meteorological Sciences
Journal of Climate | Year: 2013

The sea surface temperature gradient (SSTG) between the southwestern Pacific Ocean (40°-20°S, 160°E-170°W) and the western Pacific warm pool (0°-16°N, 125°-165°E) in boreal spring has been identified as a new factor that controls the interannual variability of tropical cyclone (TC) frequency over the western North Pacific Ocean (WNP). This SSTG can explain 53% of the total variance of the WNP TC genesis frequency during the typhoon season for the period 1980-2011. The positive SSTG anomaly produces an anomalous cross-equatorial pressure gradient and thus anomalies in low-level southward cross-equatorial flow and tropical easterlies over the central-western Pacific. The anomalous easterlies further produce local equatorial upwelling and seasonal cooling in the central Pacific, which in turn maintains the easterly anomalies throughout the typhoon season. These dynamical/thermodynamical effects induced by the positive SSTG anomaly lead to a reduced low-level cyclonic shear, increased vertical wind shear, and weakened monsoon trough over the WNP, greatly suppressing WNP TC genesis during the typhoon season. This implies that the spring SSTG could be a good predictor for WNP TC genesis frequency. © 2013 American Meteorological Society.

Ying M.,Shanghai Typhoon Institute of China Meteorological Administration | Wu G.,CAS Institute of Atmospheric Physics | Liu Y.,CAS Institute of Atmospheric Physics | Sun S.,CAS Institute of Atmospheric Physics
Science China Earth Sciences | Year: 2012

In general, the tropical cyclone (TC) activity is considered to be influenced by the heat content of underlying ocean, vertical shear of horizontal wind, vorticity in the low troposphere, moisture in the troposphere, and favorable condition for deep convection development. However, these factors by nature merely present the internal factors of either atmosphere or ocean which influence the TC activity. In fact, the energy budget of the Earth system and its variation, modulated by the land-sea thermal contrast, are the intrinsic reasons responsible for the variation of TC activity. Here we investigate the modulation of diabatic heating distribution associated with the land-sea thermal contrast on the distribution of TC activity energy source and sink as well as the seasonality. An accumulated energy increment index (AEI) is defined using the TC best track data, and the energy sources and sinks of TC activity are then diagnosed effectively and practically according to the distribution of AEI. Results show that the thermal contrast of land and ocean is the primary reason for asymmetric distribution of TC activity about the Equator as well as the zonally asymmetric distribution of TC activity. The energy sources of TC activity are dominated by condensation heating of deep convection or double-dominant heating, which includes the condensation heating and cooling of longwave radiation (LO), while the sink areas are dominated by LO. The large scale diabatic heating associated with land-sea thermal contrast results in more favorable conditions for TC activity over the west part of oceans than those over the east parts. Moreover, the intensity of interaction of different diabatic heating over the west and east parts of ocean is also affected by the zonal scale of the oceans, which induces the difference of TC activity over the western North Pacific (WNP) and North Atlantic (ATL). The favorable westerlies and anticyclonic vertical shear associated with the tropical zonally asymmetric diabatic heating also contribute to the most intense TC activity over the WNP. The variation of large scale diabatic heating modulates the annual cycle of TC energy sources and sinks. In particular, the annual cycle over the WNP is the most typical one among the three basins (the WNP, the south Indian Ocean, and western South Pacific) that are characterized by the meridional shift of the energy sources and sinks. However, sources over the eastern North Pacific tend to extend westward and withdraw eastward associated with the variation of LO, while over the ATL, sources always merge from small pieces into a big one as the different diabatic heating over its west and east parts interacts with each other. Over the boreal Indian Ocean, the subcontinental scale land-sea heating contrast modifies the large scale circulation, and consequently contributes to the bimodal annual cycle of TC activity. In summary, TC activities are closely related to the interaction among various components of the climate system more than the atmosphere and ocean. © 2012 Science China Press and Springer-Verlag Berlin Heidelberg.

Zhan R.,Shanghai Typhoon Institute of China Meteorological Administration | Wang Y.,University of Hawaii at Manoa | Tao L.,Nanjing University of Information Science and Technology
Journal of Climate | Year: 2014

Arecent finding is the significant impact of the sea surface temperature anomaly (SSTA) over the east Indian Ocean (EIO) on the genesis frequency of tropical cyclones (TCs) over the western North Pacific (WNP). In this study it is shown that such an impact is significant only after the late 1970s. The results based on both data analysis and numerical model experiments demonstrate that prior to the late 1970s the EIO SSTA is positively correlated with the equatorial central Pacific SSTA and the latter produces an opposite atmospheric circulation response over theWNP to the former.As a result, the impact of the EIOSSTAon the TCgenesis over theWNP is largely suppressed by the latter. After the late 1970s, the area coverage of the EIO SSTA is expanding. This considerably enhances the large-scale circulation response over the WNP to the EIO SSTA and significantly intensifies the impact of the EIOSSTAon TCgenesis frequency over theWNP. The results fromthis study have great implications for seasonal prediction of TC activity over the WNP. © 2014 American Meteorological Society.

Li J.,Environment Canada | Chylek P.,Los Alamos National Laboratory | Zhang F.,Chinese Academy of Meteorological Sciences | Zhang F.,Shanghai Typhoon Institute of China Meteorological Administration
Journal of the Atmospheric Sciences | Year: 2014

The physical characteristics of extratropical cyclones are investigated based on nonequilibrium thermodynamics. Nonequilibrium thermodynamics, using entropy as its main tool, has been widely used in many scientific fields. The entropy balance equation contains two parts: the internal entropy production corresponds to dissipation and the external entropy production corresponds to boundary entropy supply. It is shown that dissipation is always present in a cyclone and the dissipation center is not always coincident with the low-pressure center, especially for incipient cyclones. The different components of internal entropy production correspond to different dissipation processes. Usually the thermal dissipation due to turbulent vertical diffusion and convection lags geographically the dynamic dissipation due to wind stress. At the incipient stage, the dissipation is mainly thermal in nature. A concept of temperature shear is introduced as the result of thermal dissipation. The temperature shear provides a useful diagnostic for extratropical cyclone identification. The boundary entropy supply and the entropy advection are also strongly associated with cyclones. The entropy advection is generally positive (negative) in the leading (trailing) part of a cyclone. A regional study in the western Pacific clearly demonstrates that the surface entropy flux and temperature shear are the most reliable early signals of cyclones in the cyclogenesis stage. © 2014 American Meteorological Society.

Zhang F.,Chinese Academy of Meteorological Sciences | Zhang F.,Shanghai Typhoon Institute of China Meteorological Administration | Shen Z.,Shanghai Climate Center | Li J.,University of Victoria | And 2 more authors.
Journal of the Atmospheric Sciences | Year: 2013

Although single-layer solutions have been obtained for the δ-four-stream discrete ordinates method (DOM) in radiative transfer, a four-stream doubling-adding method (4DA) is lacking, which enables us to calculate the radiative transfer through a vertically inhomogeneous atmosphere with multiple layers. In this work, based on the Chandrasekhar invariance principle, an analytical method of δ-4DA is proposed. When applying δ-4DA to an idealized medium with specified optical properties, the reflection, transmission, and absorption are the same if the medium is treated as either a single layer or dividing it into multiple layers. This indicates that δ-4DA is able to solve the multilayer connection properly in a radiative transfer process. In addition, the δ-4DA method has been systematically compared with the δ-two-stream doubling-adding method (δ-2DA) in the solar spectrum. For a realistic atmospheric profile with gaseous transmission considered, it is found that the accuracy of δ-4DA is superior to that of δ-2DA in most of cases, especially for the cloudy sky. The relative errors of δ-4DA are generally less than 1% in both the heating rate and flux, while the relative errors of δ-2DA can be as high as 6%. © 2013 American Meteorological Society.

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