An Investigation of Composite Dropsonde Profiles for Developing and Nondeveloping Tropical Waves during the 2010 PREDICT Field Campaign

Abstract

Composite dropsonde profiles are analyzed for developing and nondeveloping tropical waves in an attempt to improve the understanding of tropical cyclogenesis. These tropical waves were sampled by 25 reconnaissance missions during the 2010 Pre-Depression Investigation of Cloud-Systems in the Tropics (PREDICT) field campaign. Comparisons are made between mean profiles of temperature, mixing ratio, relative humidity, radial and tangential winds, relative vorticity, and virtual convective available potential energy (CAPE) for genesis and nongenesis cases. Genesis soundings are further analyzed in temporal progression to investigate whether significant changes in the thermodynamic or wind fields occur during the transition from tropical wave to tropical cyclone. Significant results include the development of positive temperature anomalies from 500 to 200 hPa 2 days prior to genesis in developing waves. This is not observed in the nongenesis mean. Progressive mesoscale moistening of the column is observed within 150 km of the center of circulation prior to genesis. The genesis composite is found to be significantly moister than the nongenesis composite at the middle levels, while comparatively drier at low levels, suggesting that dry air is more detrimental to genesis when located at the middle levels. Time-varying tangential wind profiles reveal an initial delay in intensification, followed by an increase in organization 24 h pregenesis. The vertical evolution of relative vorticity, in addition to a warm-over-cold thermal structure, is more consistent with a top-down than a bottom-up genesis mechanism. Last, CAPE values are much greater for nongenesis than genesis profiles, indicating that greater instability does not necessarily favor genesis.

Development of North Atlantic Tropical Disturbances near Upper-Level Potential Vorticity Streamers

“…It is known, however, that TCs also develop in environments with moderate to strong deep-layer vertical wind shear (e.g., Bracken and Bosart 2000;Davis and Bosart 2001, 2002, 2003 and over relatively cool SSTs (e.g., McTaggart-Cowan et al 2006). In fact, previous research has demonstrated that half of all TC developments over the North Atlantic occur in environments with moderate to strong baroclinicity and attendant vertical wind shear (e.g., McTaggart-Cowan et al 2008, 2013Hess et al 1995;Elsner et al 1996). These baroclinically influenced TC developments encompass subtropical cyclones that undergo tropical transition (TT; e.g., Bosart 2003, 2004;Evans and Guishard 2009;Guishard et al 2009;Hulme and Martin 2009a,b) and precursor low-level cyclonic vorticity centers that interact with upper-tropospheric troughs (e.g., Sadler 1976Sadler , 1978Lander 1994;Molinari et al 1995;Chen et al 2008).…”

Variability of Tropical Cyclone Track Density in the North Atlantic: Observations and High-Resolution Simulations

“…In addition, smaller-scale thermodynamics and TC internal dynamics also play an important role in TC genesis (e.g., Simpson et al 1997;Raymond and Sessions 2007;Wang 2012;Smith and Montgomery 2012;Komaromi 2013) and thus modulate TC counts. On the other hand, TC tracks are primarily determined by environmental steering flows with a relatively smaller contribution from the interaction between TC dynamics and the steering flow (e.g., George and Gray 1976;Holland 1983).…”

Observations of a Nondeveloping Tropical Disturbance in the Western North Pacific during TCS-08 (2008)

“…A trajectory analysis (not shown) indicates that the majority of the midlevel low-u e air to the north of TCS025 during IOP-2 originated from the TUTT cell that was originally to the east of TCS025. According to Komaromi (2013), the impact of midlevel low-u e air on storm development may be greater than low-u e air in the lower troposphere. Therefore, although vertical wind shear weakened when the TUTT cell was north of TCS025, the presence of low-u e air in the surrounding environment appears to have offset the positive impact of reduced vertical wind shear.…”

“…Komaromi (2013) found that nondeveloping systems were on average 10%-20% drier between 500 and 700 hPa than the mean, but were actually moister in the low levels. Komaromi (2013) suggested that midlevel dry air may have a larger negative impact on storm formation (through convective entrainment) compared to dry air in the low levels.…”

“…Komaromi (2013) found that nondeveloping systems were on average 10%-20% drier between 500 and 700 hPa than the mean, but were actually moister in the low levels. Komaromi (2013) suggested that midlevel dry air may have a larger negative impact on storm formation (through convective entrainment) compared to dry air in the low levels. Davis and Ahijevych (2012) found that the midtropospheric moist static energy increased over time for the developing systems analyzed, while the nondeveloping system (Gaston) exhibited a decrease in moist static energy and an increase in downdraft convective available potential energy (DCAPE).…”