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Charles N. Helms and Lance F. Bosart

occurred during a period of persistent widespread deep convection, as indicated by the ongoing and widespread presence of tropical overshooting tops (TOTs; Monette et al. 2012 ) in Figs. 3a–c , which indicate the locations where deep convective updrafts overshoot the top of the anvil, and the increased coverage of cold cloud tops in the vicinity of the low-level center ( Fig. 2 ). Then, 24 h after being upgraded to a tropical depression, the disturbance was downgraded again, having lost a closed low

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Jainn J. Shi, Scott A. Braun, Zhining Tao, and Toshihisa Matsui

, and airborne data to conclude that the impact of the SAL on Hurricane Helene was confined to the earliest stages of development. Dry air observed to wrap around Helene was determined to be of non-Saharan origin and appeared to have little impact on storm intensity. Saharan dust can affect storms in a couple different ways. First, dust can modify cloud microphysical processes within the storm by providing cloud condensation and ice nuclei ( Khain et al. 2008 , 2010 ). Second, the dust can absorb

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Zhining Tao, Scott A. Braun, Jainn J. Shi, Mian Chin, Dongchul Kim, Toshihisa Matsui, and Christa D. Peters-Lidard

longwave absorption within the stratocumulus cloud deck at the top of the boundary layer that is enhanced by the AM effect (figures now shown). Above the SAL, cooling occurs between 500 and 300 hPa and is particularly pronounced near the upper ITCZ region north of 12°N. The AR effect ( Fig. 10c ) is the major driving force of the change in radiative heating profiles below 400 hPa, while both the AM ( Fig. 10a ) and AR effects are important to the changes in atmospheric heating above 400 hPa. Although

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Robert F. Rogers, Jun A. Zhang, Jonathan Zawislak, Haiyan Jiang, George R. Alvey III, Edward J. Zipser, and Stephanie N. Stevenson

Rogers et al. 2013b , 2015 ), consist primarily of TCs already undergoing intensification, after the intensifying secondary circulation has had time to develop deep convection, while the satellite studies have a large number of cases prior to the onset of intensification, when low-level forcing mechanisms are likely important in the development of shallow/moderate convection ( Tao and Jiang 2015 ). It may also result from differences in how the timing of the onset of intensification is defined

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Jonathan Zawislak, Haiyan Jiang, George R. Alvey III, Edward J. Zipser, Robert F. Rogers, Jun A. Zhang, and Stephanie N. Stevenson

predominant occurrence of deep convection (proxy is cold cloud and lightning) in the downshear quadrants. Although they do not identify a clear diurnal cycle, Kossin (2002) has previously identified a semidiurnal signal in IR data within 100 km of the center of tropical storms and hurricanes. Dunion et al. (2014) do not identify a similar semidiurnal signal, although their dataset is restricted to major hurricanes and low to moderate shear cases (<7.5 m s −1 ). The upshear quadrants exhibit more

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Anthony C. Didlake Jr., Gerald M. Heymsfield, Paul D. Reasor, and Stephen R. Guimond

centers. Additional data used in this analysis come from flight level observations collected by U.S. Air Force (USAF) C-130 reconnaissance aircraft, which flew in between the flight times of the WB-57 and P3. Vigh et al. (2016) recently developed the FLIGHT+ dataset, which gathers all NOAA and USAF flight-level data dating back to 1997. In this dataset, flight tracks are segmented into radial legs relative to the storm center determined by the method of Willoughby and Chelmow (1982) . The flight

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