The Analysis of Typhoon Structures Using Advanced Microwave Sounding Unit Data and Its Application to Prediction

Abstract

In this study, the Advanced Microwave Sounding Unit (AMSU) data are used to retrieve the temperature and velocity fields of typhoons and assimilate them with the three-dimensional variational data assimilation (3DVAR) routines for uses in numerical model predictions for typhoons. The authors' procedure of an end-to-end typhoon prediction using an AMSU-based initial condition is similar to the framework developed by Zhu et al. in 2002 but differs from it by considering a downward integration approach in part of the retrieval process and with the starting point of the integration chosen as a constant 50-hPa field without any structure. The typhoon circulation from this retrieval is thus determined objectively from the AMSU observation alone, without a preimposed typhoon vortex structure, allowing an asymmetric structure even at the inner core of a typhoon. The results show that this procedure is capable of retrieving a reasonable typhoon circulation from the AMSU data. The impact of the AMSU data on the assimilated initial condition for prediction is shown to be especially notable in its modification of the upper-level circulation of the typhoons. With the downward integration, the error accumulates downward such that the current approach provides a relatively more accurate estimate of the upper-level circulation, important for the steering of a typhoon. Consistent with this, it is demonstrated that the inclusion of the AMSU data helps to improve the forecast of typhoon tracks for selected cases of typhoons. This approach is less satisfying in producing an accurate retrieval and prediction of the intensity of typhoons. The reasons for this shortcoming and possible future remedies are discussed.

Results from parallel observations of superconducting and absolute gravimeters and GPS at the Hsinchu station of Global Geodynamics Project, Taiwan

“…Flooding and increased soil moisture will also lead to additional gravity changes. Therefore, the gravity changes due to typhoons detected at HS can be used to validate models of density distribution within a typhoon system, e.g., the model of Chou et al [2008] that is based on three‐dimensional variational data assimilation (3DVAR) and the Advanced Microwave Sounding Unit (AMSU) data.…”

“…In addition to the spatial and temporal scales that result in different admittances for the typhoon and nontyphoon conditions, other factors may also affect the admittance during a typhoon, for example, the actual density of the central part of a typhoon. A typical Doppler radar image of typhoon (see, e.g., the real‐time radar images at Central Weather Bureau of Taiwan) shows that the precipitating water is not evenly distributed within the effective area of a typhoon and the convection within a typhoon can be asymmetric [see, e.g., Chou et al , 2008; Li et al , 2008]. In particular, condensation of water vapor contained in the moist air normally occurs at low altitudes.…”

Extreme Rainfall Mechanisms Exhibited by Typhoon Morakot (2009)

“…Among many studies, different methods have been used to improve the initial typhoon vortex, e.g., the vortex surgery method (Kurihara et al 1993(Kurihara et al , 1995, re-implantation of the model integrated vortex (e.g., Liu et al 1997), a powerful physical initialization scheme with complementary observations (Krishnamurti et al 1993), the inclusion of a Rankine vortex in the background analysis or by assimilation of 3DVAR (Xiao et al 2006(Xiao et al , 2009Chen 2007;Chou et al 2008;Hsiao et al 2010), bogus data assimilation (BDA) using 4DVAR Zou and Xiao 2000;Pu and Braun 2001;Park and Zou 2004;Wu et al 2006), or the recently developed method using an Ensemble Kalman Filter (EnKF) (e.g., Chen and Snyder 2007;Wu et al 2010a;Yen et al 2011). The insertion of a stronger vortex may help improve cyclone intensity forecasting since the model initial cyclone better captures the observed intensity and position.…”

The Cold Avoidance of Typhoons in Their North Turning Over the South China Sea

“…Peng et al (2014) revealed the cold-air intrusion from the northwest played a key role in the big turn of Megi through its adjustment to the large-scale circulation. In the lower layers, the northerly inflow of cold air tends to destroy the axisymmetric thermal structure of the TC, which may reduce the moving speed of the TC (Chou et al, 2008). Chen et al (1997) revealed that the asymmetry of the thermal structure and the strength of the thermal instability layer of the TCs could lead to the significant anomaly of the TC track.…”