The Convective Evolution and Rapid Intensification of Hurricane Earl (2010)

Abstract

The relationship between an inner-core (r , 100 km) lightning outbreak and the subsequent rapid intensification (RI) of Hurricane Earl (2010) is examined using lightning strikes recorded by the World Wide Lightning Location Network (WWLLN) and in situ observations from various aircraft missions. Moderate (8.4 m s 21 ) northeasterly deep-layer (850-200 hPa) vertical wind shear, caused by outflow from Hurricane Danielle, existed over Earl at the beginning of a prolonged period of RI. Over 70% of the lightning strikes within a 500-km radius occurred downshear, with a preference toward downshear right in the outer rainbands, in agreement with previous studies.The location of inner-core strikes in Earl differed markedly from previous studies. The inner-core lightning activity precessed from left of shear to upshear, an extremely rare event, beginning just prior to the onset of RI. Diagnosis of the vortex tilt midway through the lightning precession showed this convection was occurring downtilt in the upshear-left quadrant; however, limited observations could not confirm if the vortex tilt was precessing with the lightning. Elevated values of low-level relative humidity and CAPE were also found upshear and supported the inner-core convection, which was found to occur within the radius of maximum wind (RMW). Previous studies have shown that convection located inside the RMW promotes intensification. It is hypothesized that intensification may have occurred in part because the vertical wind shear acted to reduce the upshear tilt, and the occurrence of convection inside the RMW helped to enhance the warm core.

Climatology of overshootings in tropical cyclones and their roles in tropical cyclone intensity changes using TRMM data

“…However, this is inconsistent with previous observational case studies (e.g., Reasor et al 2009;Guimond et al 2010;Molinari and Vollaro 2010;Nguyen and Molinari 2012;Reasor and Eastin 2012;Stevenson et al 2014;Rogers et al 2015;Susca-Lopata et al 2015), which emphasized the role of asymmetric very deep convection in RI. As mentioned in section 3.7, most of these observational case studies are biased toward the ending period of RI, while the three studies about Hurricane Earl (2010) focused on deep convection before RI while the storm was in the slowly intensifying stage.…”

“…A vortical hot tower was observed 7 h before the RI event of Tropical Storm Gabrielle (2001) ended (Molinari and Vollaro 2010). There are several recent studies about Hurricane Earl (2010) (Stevenson et al 2014;Rogers et al 2015;Susca-Lopata et al 2015) showing asymmetric deep convection around 6-9h be-fore the onset of RI (Fig. 3.13).…”

“…The convective evolution in RI storms is examined extensively in recent case studies (e.g., Stevenson et al 2014, Susca-Lopata et al 2015. Stevenson et al (2014) The dataset for this study is derived from the TRMM Tropical Cyclone Precipitation Feature (TCPF) database (Jiang et al 2011), which includes the overpasses of all global TCs viewed by the TRMM satellite.…”

“…At this time, isolated very deep convection is often observed ( Fig. 3.3c; Stevenson et al 2014;Rogers et al 2015;Susca-Lopata et al 2015), which is possibly due to high wind shear ( axisymmetrization (Kieper and Jiang 2012;Susca-Lopata et al 2015), and more latent heat release. As RI continues, increased moderate to very deep precipitation is observed, producing much higher total volumetric rain and latent heating release (Figs.…”

“…While these satellite-based statistical studies implied that the symmetry of widespread precipitation containing a much lower percentage of asymmetric deep convection is important in initiating RI in the following 24 h, observational case studies mentioned above (Reasor et al 2009;Guimond et al 2010;Molinari and Vollaro 2010;Nguyen and Molinari 2012;Reasor and Eastin 2012;Stevenson et al 2014;Rogers et al 2015) emphasized the role of asymmetric very deep convection in RI. An important question raised from this is, what is the relative importance of precipitation-convection of different depths-intensities to RI?…”