On the relationship between intensity changes and rainfall distribution in tropical cyclones over the North Indian Ocean

Abstract

Using Tropical Rainfall Measuring Mission rain estimates the relationship between rainfall and intensity changes in tropical cyclones (TCs) over the North Indian Ocean (NIO) based on 71 TCs during 1997–2017 is investigated. The axisymmetric analyses revealed that climatologically the Bay of Bengal (BoB) TCs produce extremely heavy rainfall (~9–10 mm⋅hr−1) and Arabian Sea TCs produce very heavy rainfall (~7–8 mm⋅hr−1) in the storm inner core region (0–100 km). The inner‐core region receives three times higher rainfall than the outer region (100–300 km). The left‐forward sector experiences the maximum rainfall for any TC intensity over the NIO basin. A significant increase (decrease) in the rain rate is seen during normal to rapid intensification (weakening) phase. A notable decrease in rainfall of ~4.3 mm⋅hr−1 is observed for the rapidly weakening TCs. Slow‐moving TCs are generally stronger and produce heavy rainfall (2–4 mm⋅hr−1) up to ~300 km storm radius. As the translation speed increases, rainfall gradually shifts from rear to the forward sector of the TC. The asymmetry (wavenumber‐1) in TC rainfall structures revealed that rainfall maximum is located in the left‐forward sector for almost all intensity stages. The amplitude of wave number‐1 asymmetry in TC rainfall shows cyclonic shift as the TC intensity increases and is particularly prevalent in the BoB region. These analyses would be helpful as a baseline for evaluating the performance of numerical models and to identify the vulnerable areas for TC heavy rainfall.

Observed Shear-Relative Rainfall Asymmetries Associated with Landfalling Tropical Cyclones

“…is result is similar to the recent satellite composites by Ankur et al [10]. e peak azimuthal mean rain rates for six basins experience a slight enhancement during the course of TCs approaching the coast and making landfall with the rain rate of ∼ 5.0-5.8 mm•hr −1 (Figure 1(b)).…”

“…However, the TC rainfall distribution can vary significantly from nearly axisymmetric to asymmetric under the influences of the storm dynamics and its environment over the open ocean. Asymmetries in TC circulations can be mainly induced by the effects of the storm motion [8][9][10], environmental deep-layer vertical wind shear (VWS) [11][12][13][14][15][16][17][18][19], and environmental flows interactions with the storm [20][21][22][23][24]. e rainfall maximum within the inner core region is generally located in down-motion flanks, which results from the friction-induced asymmetric boundary layer convergence, particularly to the right of motion [8,11].…”

“…e rainfall maximum within the inner core region is generally located in down-motion flanks, which results from the friction-induced asymmetric boundary layer convergence, particularly to the right of motion [8,11]. e rainfall front maxima shifted to the front-right as the storm translation speed increased in North Atlantic or North Indian basin TCs composite by using satellite-based observations [10,25]. With satellite data from the Tropical Rainfall Measuring Mission (TRMM), the TC rainfall was depicted as the sum of an azimuthal mean (or a wavenumber 0) component and a significant spatial asymmetric variability (or a series of lower-wavenumber components) [16].…”

Simulations of Bay of Bengal tropical cyclones in a regional convection-permitting atmosphere–ocean coupled model

“…Both models produce reasonable predictions of the location of rainfall associated with 665 landfalling TCs. Maximum rain rates are generally observed to the left of the cyclone track before landfall, typical for Bay of Bengal TCs (Ankur et al, 2020) and monsoon depressions (Hunt et al, 2016); this is well captured in the models. The simulations predict more spiral rainbands than IMERG.…”

Moisture Sources for Tropical Cyclones Genesis in the Coast of West Africa through a Lagrangian Approach

“…Tropical cyclones (TCs) are the atmospheric phenomena most likely to cause natural disasters [1]. These systems form over warm regions in tropical oceans and strengthen when environmental conditions are favorable [2].…”