Assessing the Influence of Upper-Tropospheric Troughs on Tropical Cyclone Intensification Rates after Genesis

Abstract

The role of upper-tropospheric troughs on the intensification rate of newly formed tropical cyclones (TCs) is analyzed. This study focuses on TCs forming in the presence of upper-tropospheric troughs in the North Atlantic basin between 1980 and 2014. TCs were binned into three groups based upon the 24-h intensification rate starting at the time of genesis: rapid TC genesis (RTCG), slow TC genesis (STCG), and neutral TC genesis (NTCG). Composite analysis shows RTCG events are characterized by amplified upper-tropospheric flow with the largest upshear displacement between the TC and trough of the three groups. RTCG events are associated with greater quasigeostrophic (QG) ascent in upshear quadrants of the TC, forced by differential vorticity advection by the thermal wind, especially around the time of genesis. This pattern of QG ascent closely matches the RTCG composite of infrared brightness temperatures. Conversely, NTCG events are associated with an upper-tropospheric trough that is closest to the TC center. The distribution of QG ascent in NTCG events becomes increasingly asymmetric around the time of genesis, with a maximum that shifts downshear of the TC center, consistent with infrared brightness temperatures. It is hypothesized that the TC intensification rate after tropical cyclogenesis, in environments of upper-tropospheric troughs, is closely linked to the structure and temporal evolution of the upper-level trough. The TC–trough configurations that provide greater QG ascent to the left of, and upshear of, the TC center feature more symmetric convection and faster TC intensification rates.

The Tropical Transition in the Western North Pacific: The Case of Tropical Cyclone Peipah (2007)

“…Consistent with these previous studies, the role of upper tropospheric PV forcing and attendant deep convection on 28 and 30 October are explained by investigating the CAPE (Figure ), and QG vertical motion (Figure ). In order to evaluate the QG vertical motion, we employed the same method as in Fischer et al () that solves a modified version of the Sutcliffe‐Trenberth form of the QG omega equation (Trenberth, ) using successive overrelaxation.…”

“…Journal of Geophysical Research: Atmospheres ( Figure 6). In order to evaluate the QG vertical motion, we employed the same method as in Fischer et al (2017) that solves a modified version of the Sutcliffe-Trenberth form of the QG omega equation (Trenberth, 1978) using successive overrelaxation.…”

A Numerical Study on Rapid Intensification of Typhoon Vicente (2012) in the South China Sea. Part II: Roles of Inner-Core Processes

“…First, the confluence between the southwesterly monsoon flow and the northerly winds to the west of the TC center induces a narrow convergence zone to the south of the TC center. Second, as the TC circulation gradually intensifies during its westward movement into the SCS [i.e., as it upgraded to a tropical depression according to the best track dataset from Joint Typhoon Warning Center (JTWC)], the enhanced differential vorticity advection by the steady thermal wind 1 (i.e., environmental VWS, ~10.5 m s −1 ) forces stronger vertical motion and thus enhanced low-level convergence on the downshear side according to quasi-geostrophic theory (Bracken and Bosart 2000;Fischer et al 2017), numerical simulations (e.g., Jones 1995, Wang et al 1996, and observational studies (e.g., Reasor et al 2009Reasor et al , 2013DeHart et al 2014). By 0600 UTC July 21, the differential vorticity advection by thermal wind is as large as 8 × 10 −4 m s −2 .…”

Environmental control of tropical, subtropical, and extratropical cyclone development over the North Atlantic Ocean: Idealized numerical experiments

“…Cyclones can extract energy from favourable environmental fields such as high SST and large baroclinicity. They are sometimes affected by transient external forcing such as upper‐tropospheric troughs (Deveson and Browning, ; Jones et al , ; Fischer et al , ), and tropical waves (Ritchie and Holland, ; Frank and Roundy, ). The geographical distribution of cyclone development may also depend on the life cycles of cyclones including extratropical transitions (Jones et al , ; Evans et al , ) and tropical transitions.…”