skip to main content

Title: The role of heating and cooling associated with ice processes on tropical cyclogenesis and intensification: Tropical Cyclogenesis
Author(s) / Creator(s):
 ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Quarterly Journal of the Royal Meteorological Society
Page Range / eLocation ID:
99 to 114
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Changes to the tropical eastern North Pacific Intraseasonal Oscillation (ISO) at the end of the 21st century and implications for tropical cyclone (TC) genesis are examined in the Shared Socioeconomic Pathways (SSP585) scenario of the Coupled Model Intercomparison Project phase 6 (CMIP6) data set. Multimodel mean composite low-level wind and precipitation anomalies associated with the leading intraseasonal mode indicate that precipitation amplitude increases while wind amplitude weakens under global warming, consistent with previous studies for the Indo-Pacific warm pool. The eastern North Pacific intraseasonal precipitation/wind pattern also tends to shift southwestward in a warmer climate, associated with weaker positive precipitation anomalies near the coast of Mexico and Central America during the enhanced convection/westerly wind phase. Implications for the modulation of TC genesis by the leading intraseasonal mode are then explored using an empirical genesis potential index (GPI). In the historical simulation, GPI shows positive anomalies in the eastern North Pacific in the convectively enhanced phase of the ISO. The ISO’s modulation of GPI weakens near the coast of Mexico and Central America with warming, associated with a southward shift of GPI anomalies. Further examination of the contribution from individual environmental variables that enter the GPI shows that relative humidity and vorticity changes during ISO events weaken positive GPI anomalies near the Mexican coast with warming and make genesis more favorable to the southwest. The impact of vertical shear anomaly changes is also to favor genesis away from the coast. These results suggest a weaker modulation of TCs near the Mexican Coast by the ISO in a warmer climate. 
    more » « less
  2. null (Ed.)
    Abstract Tropical cyclogenesis (TCG) is a multiscale process that involves interactions between large-scale circulation and small-scale convection. A near-global aquaplanet cloud-resolving model (NGAqua) with 4-km horizontal grid spacing that produces tropical cyclones (TCs) is used to investigate TCG and its predictability. This study analyzes an ensemble of three 20-day NGAqua simulations, with initial white-noise perturbations of low-level humidity. TCs develop spontaneously from the northern edge of the intertropical convergence zone (ITCZ), where large-scale flows and tropical convection provide necessary conditions for barotropic instability. Zonal bands of positive low-level absolute vorticity organize into cyclonic vortices, some of which develop into TCs. A new algorithm is developed to track the cyclonic vortices. A vortex-following framework analysis of the low-level vorticity budget shows that vertical stretching of absolute vorticity due to convective heating contributes positively to the vorticity spinup of the TCs. A case study and composite analyses suggest that sufficient humidity is key for convective development. TCG in these three NGAqua simulations undergoes the same series of interactions. The locations of cyclonic vortices are broadly predetermined by planetary-scale circulation and humidity patterns associated with ITCZ breakdown, which are predictable up to 10 days. Whether and when the cyclonic vortices become TCs depend on the somewhat more random feedback between convection and vorticity. 
    more » « less
  3. Abstract

    Tropical cyclogenesis (TCG) remains an elusive phenomenon partly due to the limited understanding of complex water vapor‐convection‐wave interactions. The Model for Prediction Across Scales‐Atmosphere (MPAS‐A) was used to study the TCG of the African easterly wave (AEW) that became Hurricane Helene (2006). The two main objectives were: (a) evaluate the capability of MPAS‐A to simulate TCG from an AEW by comparing MPAS‐A—initialized with the Integrated Forecasting System (IFS) and the Global Forecast System (GFS)—with observations together with reanalysis and, (b) use the hindcast to investigate the role of moisture in the mechanisms that led to Helene's TCG. The more intense GFS‐initialized pre‐Helene was slower propagating and was associated with a wetter and stronger monsoon when compared to both the IFS‐initialized simulation and observed. TCG occurred when net moisture flux within the boundary layer toward the center of the wave increased persistently. The reanalysis pre‐genesis top‐heavy vertical mass flux profile transitioned to a bottom‐heavy profile during TCG, whereas the simulations had top‐heavy and bottom‐heavy profiles simultaneously, resulting from a more‐intense and fast‐occurring TCG than in the reanalysis. Moisture‐vortex instability helped explain the vertical mass fluxes and the co‐location of convection, moisture and wave vortex demonstrating to be an applicable theoretical model for TCG. Moisture mode was tested as a diagnostic tool for AEW evolution and TCG. The case exhibited some moisture mode properties, and it is proposed that AEWs become more moisture‐mode like once reaching western Africa and during TCG. An AEW TCG pathway is proposed.

    more » « less