Abstract
Abstract. The influence of environmental conditions on the intensity changes of tropical cyclones (TCs) over the western North Pacific (WNP) is investigated through examination of 37 TCs during 2000–2011 that interacted directly with the western North Pacific subtropical high (WNPSH). Comprehensive composite analysis of the environmental conditions is performed for two stages of storms: one is categorized as intensifying events (maximum wind speed increases by 15 kn over 48 h) and the other is categorized as weakening events (maximum wind speed decreases by 15 kn over 48 h). Comparison of the composite analysis of these two cases show that environmental conditions associated with the WNPSH play important roles in the intensity changes of TCs over the WNP. When a TC moves along the southern periphery of the WNPSH, the relatively weaker easterly environmental vertical wind shear helps bring warm moist air from the south and southeast to its southeast quadrant within 500 km, which is favorable for the TC to intensify. However, when a TC moves along the western edge of the WNPSH, under the combined influences of the WNPSH and an upper-level westerly trough, a strong westerly vertical shear promotes the intrusion of dry environmental air associated with the WNPSH from the north and northwest, which may lead to the inhibition of moisture supply and convection over the western half of the TC and thus its weakening. These composite results are consistent with those with additional geographic restrictions, suggesting that the dry air intrusion and the vertical wind shear (VWS) associated with the WNPSH, indeed affect the intensity changes of TCs over the WNP beyond the difference related solely to variations in geographical locations. The average sea surface temperature (SST) of 27.6 °C for the weakening events is also lower than an average of 28.9 °C for the strengthening events, but remains above the critical value of 27 °C for TC intensification, suggesting that the SST may be regarded as a less positive factor for the weakening events.
Highlights
For the past few decades, despite large improvement in the track forecast of tropical cyclones (TCs), there has been almost no improvement in the intensity forecast for all lead times (Cangialosi and Franklin, 2012)
The objective of this study is to investigate observationally whether and how the environmental conditions associated with the western North Pacific subtropical high (WNPSH) may influence the intensity changes of TCs over the western North Pacific (WNP), in an effort to provide further guid
The influence of environmental conditions on the intensity changes of TCs over the WNP are investigated observationally by using the satellite-derived data (AIRS–Advanced Microwave Sounding Unit (AMSU)), NCEP Global Forecasting System (GFS) analyses and National Oceanic and Atmospheric Administration (NOAA) Reynolds sea surface temperature (SST) reanalysis, and TC best-track estimates from JMA in this paper
Summary
For the past few decades, despite large improvement in the track forecast of tropical cyclones (TCs), there has been almost no improvement in the intensity forecast for all lead times (Cangialosi and Franklin, 2012). A new empirical MPI has been developed for TCs over the WNP in a recent study by Zeng et al (2007), which considers the positive contributions of SST and the effect of the thermodynamic efficiency and the combined negative effect of translational speed and environmental vertical shear They found that the new empirical MPI with consideration of negative effects provides a relatively accurate estimation of TC maximum intensity, a large portion of TCs still could not reach their MPIs even in favorable environmental conditions, which indicates that other factors like dry air intrusion and the direction of environmental vertical wind shear vector should be taken into account in developing MPIs for TCs over the WNP. The objective of this study is to investigate observationally whether and how the environmental conditions associated with the WNPSH may influence the intensity changes of TCs over the WNP, in an effort to provide further guid-
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
