Interactions between dry air and Hurricane Nadine (2012)

This study uses high-altitude airborne observations from the Hurricane and Severe Storm Sentinel Experiment (HS3), in conjunction with satellite observations and model analyses, to document the ability of sources of dry air such as the Saharan Air Layer (SAL) and upper-level subsidence to enter and impact the development of Hurricane Nadine (2012). Data from dropsondes and the Scanning High-resolution Interferometer Sounder (S-HIS) aboard the NASA Global Hawk, as well as satellite observations from MODIS and AIRS instruments aboard the Aqua and Terra platforms, indicate that Hurricane Nadine interacted with a distinct SAL air mass during the first four days of being a tropical cyclone. This low-level dry, dusty air wrapped around the storm's eastern and northern sides, while a separate very dry but dust-free upper-level air mass interacted with Nadine's western and southern regions. Despite the presence of both dry air masses, Nadine continued to intensify from 11-15 September.

Preliminary results indicate that during this period, the lower-level dry SAL air had a potentially limited amount of penetration into the storm's inner core. The nose of the SAL only reached the NW quadrant of the storm, with the low level winds mostly favoring transport away from the inner regions. However, high vertical wind shear later in this period likely allowed for westerly ventilation of dry upper-level air across the top of the storm, corresponding with the end of Nadine's intensification. This study will use reanalyses and high-resolution model output to further examine the interactions between these two dry air masses and Hurricane Nadine, and their potential pathways into the storm's circulation.