Influence of varying time scale flows on tropical cyclone track changes

Abstract

It is often difficult to predict tropical cyclone (TC) tracks for the case of binary or even multiple TCs. To investigate this issue, two TCs over the western North Pacific basin in September 2016, Meranti and Malakas, were explored in this study. The two TCs formed close to each other, and their tracks were similar at an early stage but then deflected northward over different regions. The results indicate that the Meranti track change may be due to the asymmetric highfrequency flows induced by topography, while the Malakas track change is attributed to the formation and strengthening of low-frequency southerlies. It was found that the formation and evolution of low-frequency monsoon circulation is the main cause for the emergence of the low-frequency flows, and the process is accompanied by the enhancement and movement of low-frequency positive vorticity. Therefore, based on the diagnostic results using the lowfrequency vorticity budget equation, it is shown that the low-frequency vorticity advection and convergence induced by the low-frequency flows play varying roles in the development of low-frequency positive vorticity. More noteworthy is that the high-frequency positive vorticity of TCs can trigger the enhancement of low-frequency positive vorticity through nonlinear interactions, which have rarely been discussed in previous studies. It can be concluded that the interactions between high-and low-frequency flows and vorticity may affect the development and evolution of the TCs at different time scales, finally leading to TC track deflection. K E Y W O R D S different time scale steering flows, low-frequency vorticity, tropical cyclone track

Landfalling tropical cyclone characteristics and their multi‐timescale variability connected to monsoon and easterly formation environments over the western North Pacific

“…Figure 11 shows the difference in environmental steering flow between monsoon‐ and easterly‐TCs. The definition of steering flow shown in Figure 11 is consistent with Figure 4, but the steering flow is composited based on the disturbance centre and the TC circulation is first removed using a 10‐day low‐pass filter (Wu et al ., 2013b; Chen et al ., 2020). Easterly‐TCs have significantly stronger steering flow around the disturbance centre than monsoon‐TCs at the times of TCC formation and TC landfall and throughout the entire TC lifetime (the stronger steering flow for monsoon‐TCs is not significant).…”

Analysis of Diurnal Sea Surface Temperature Variability in the Tropical Indian Ocean

“…The years of El Niño and La Niña events were selected accordingly (Table 3). Figure 8 shows Previous studies indicate that the seasonal variation of DSST is influenced by factors such as solar radiation, wind speed, and precipitation [2,30,[39][40][41]. Therefore, this study analyzed the seasonal variations of solar radiation, sea surface wind speed, and precipitation in the tropical Indian Ocean.…”

“…However, the southern Indian Ocean region exhibits a completely different seasonal pattern, with maximum DSST during the southern hemisphere sum-mer, and minimum DSST during the southern hemisphere winter, showing a significant annual cycle. Previous studies indicate that the seasonal variation of DSST is influenced by factors such as solar radiation, wind speed, and precipitation [2,30,[39][40][41]. Therefore, this study analyzed the seasonal variations of solar radiation, sea surface wind speed, and precipitation in the tropical Indian Ocean.…”

“…This result passed the significance test at a 95% confidence level using the Student's t-test. Chen et al [40] used RAMA buoy data to analyze the impact of different ENSO phases on DSST in the equatorial eastern Indian Ocean, and also noted that DSST is slightly larger during El Niño years compared to La Niña years. Kawai et al [42] pointed out that there are differences in DSST in the same region under different ENSO phases.…”