Sensitivity of Tropical Cyclone Feedback on the Intensity of the Western Pacific Subtropical High to Microphysics Schemes

Abstract

The Advanced Research version of Weather Research and Forecasting (WRF-ARW) Model is used to examine the sensitivity of a simulated tropical cyclone (TC) track and the associated intensity of the western Pacific subtropical high (WPSH) to microphysical parameterization (MP) schemes. It is found that the simulated WPSH is sensitive to MP schemes only when TCs are active over the western North Pacific. WRF fails to capture TC tracks because of errors in the simulation of the WPSH intensity. The failed simulation of WPSH intensity and TC track can be attributed to the overestimated convection in the TC eyewall region, which is caused by inappropriate MP schemes. In other words, the MP affects the simulation of the TC activity, which influences the simulation of WPSH intensity and, thus, TC track. The feedback of the TC to WPSH plays a critical role in the model behavior of the simulation. Further analysis suggests that the overestimated convection in the TC eyewall results in excessive anvil clouds and showers in the middle and upper troposphere. As the simulated TC approaches the WPSH, the excessive anvil clouds extend far away from the TC center and reach the area of the WPSH. Because of the condensation of the anvil clouds' outflows and showers, a huge amount of latent heat is released into the atmosphere and warms the air above the freezing level at about 500 hPa. Meanwhile, the evaporative (melting) process of hydrometers in the descending flow takes place below the freezing level and cools the air in the lower and middle troposphere. As a result, the simulated WPSH intensity is weakened, and the TC turns northward earlier than in observations.

Dependence of the relationship between the tropical cyclone track and western Pacific subtropical high intensity on initial storm size: A numerical investigation

“…Yet which influence plays a major role in the storm motion remains unknown. As discussed in Sun et al [] and Sun et al [], the anvil clouds could change the microphysical latent heating over the edge of the WPSH, which subsequently affects the WPSH and TC motion. Meanwhile, the TC movement often deviates from the large‐scale steering flow due to the beta‐effect propagation (BEP), which depends on the mean relative angular momentum and thus is highly sensitive to the outer wind structure of a TC [ Holland , ; Fiorino and Elsberry , ; Carr and Elsberry , ].…”

“…Previous studies have indicated that the storm size affects its motion not only by changing the large‐scale environmental flow but also by influencing the BEP [ Holland , ; Fiorino and Elsberry , ; Carr and Elsberry , ; Bu et al ., ; Sun et al ., , ]. Figure compares the storm track simulated in the sensitivity experiments with the JTWC best track of Songda.…”

“…The National Center for Environmental Prediction (NCEP) global final analysis data at 1° × 1° latitude‐longitude grids with 6 h interval are used to provide initial and lateral boundary conditions for the WRF‐ARW model. The model configuration for the simulation of TC Megi (2010) is identical to that in our previously study [ Sun et al ., ] except that the initial time is different, as follows in the next two paragraphs. A 20 km resolution domain with 36 vertical levels is set up for the simulations of both Songda and Megi.…”

“…For example, RCMs often do not perform well in simulating the East Asian monsoon system [ McGregor , ; Wang and Wang , ; Zhong , ; Zhou et al ., , ; Zou and Zhou , ]. Recent studies have suggested that large biases appear in East Asian monsoon simulation when tropical cyclones (TCs) are active over the western North Pacific (WNP), and the departure of the simulated TC track from its observed position may be one reason for RCMs' failure in simulating the WPSH and thus the large‐scale atmospheric circulation [ Zhong , ; Sun et al ., , , ].…”

“…Such a pattern of vertical heating profile causes a weakening of the WPSH, which in turn contributes to the early recurvature of the TC. Sun et al [] suggested that this is also the physical mechanism that explains different performances of some microphysical parameterization schemes in the simulation of TC and the WPSH.…”