Another critical science question to be addressed by HS3 is: What role does deep convection in the inner core of storms play in the intensification process? Intense convection occupies only a small fraction of the area of the hurricane eyewall, as little as 5-10%. Early studies viewed the eyewall as an axisymmetric ring of weak to moderate rising motion that contributed to the in-up-and-out secondary circulation, with the details of the convection not being particularly important (Shapiro and Willoughby 1982; Emanuel 1986; Rotunno and Emanuel 1987). The main role of convection was to achieve and maintain a state of near moist neutrality along angular momentum surfaces (Emanuel 1989). More recently, convective-scale processes have been identified as contributing more directly to the dynamics of tropical cyclone intensity change. Observational studies have linked genesis and intensity change to the intermittent occurrence of deep, strong convection (sometimes referred to as convective bursts) within the inner core (e.g., Gentry et al. 1970; Rodgers et al. 1998; Heymsfield et al. 2001; Kelley et al. 2004; Hendricks et al. 2004; Reasor et al. 2005, 2009; Montgomery et al. 2006; Braun et al. 2009; Rogers 2009). The relationship between convective bursts and intensification has been linked to enhanced latent heat release and subsidence in the storm core (e.g., Heymsfield et al. 2001). Recent modeling and observational studies have emphasized the importance of cyclonic rotation collocated with vigorous updrafts as being key (Hendricks et al. 2004; Montgomery et al. 2006; Braun et al. 2009; Houze et al. 2009). These rotating updrafts, termed vortical hot towers, are suggested to be important in tropical cyclogenesis and their importance has been recently extended to the intensity problem (Nguyen et al. 2008).

Addressing this topic requires a very frequent, high-resolution mapping of the inner-core wind and precipitation fields and the formation of the warm core in the developing eye. HS3’s over-storm payload will provide these measurements. The GH’s long flight duration (~30 h) will allow for on-station times far greater than conventional aircraft, providing the opportunity to capture evolutionary cycles on time scales of hours to up to one day within a single flight.

Schematic diagram showing the role of deep convective bursts in hurricane intensification. The concept portrayed in this figure is that the deep towers contribute to subsidence in the eye of the developing storm.

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