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Alan Brammer, Chris D. Thorncroft, and Jason P. Dunion

1. Introduction Tropical cyclogenesis is known to be favored by several large-scale conditions, including a preexisting low-level disturbance, warm SSTs (≥26.5°C), increased low- and midlevel moisture around the disturbance, and relatively low environmental vertical wind shear ( Gray 1968 ). These conditions typically favor the maintenance of deep convection associated with the tropical cyclogenesis process. Over the eastern Atlantic, African easterly waves (AEWs) propagate from West Africa

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

) based on surface wind speed, soil moisture, and soil erodibility. Sea salt emissions were calculated by the parameterization based on Gong (2003) . The meteorological initial and lateral boundary conditions were derived from the 6-hourly European Centre for Medium-Range Weather Forecasts (ECMWF) interim reanalysis (ERA-Interim) global reanalysis data ( Dee et al. 2011 ). The chemical initial and lateral boundary conditions were obtained from global GOCART ( Chin et al. 2007 ) simulations that also

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Erin B. Munsell, Fuqing Zhang, Jason A. Sippel, Scott A. Braun, and Yonghui Weng

cycling was performed every 3 h until the dissipation of Edouard. As in all forecasts produced by the PSU WRF–EnKF system, ensemble initial and lateral boundary conditions were generated by adding perturbations derived from the background error covariance of the WRF variational data assimilation system ( Barker et al. 2004 ) to the pressure, temperature, moisture, and horizontal wind fields of the initial and boundary conditions. The EnKF analysis perturbations from 1200 UTC 11 September were used to

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Erin B. Munsell, Jason A. Sippel, Scott A. Braun, Yonghui Weng, and Fuqing Zhang

exceed 2 m s −1 . The relative humidity profiles of the composite groups at 3 and 6 h are similar to the observed profiles at these times, except in the upper troposphere where dropsondes used in HS3 are known to have a dry bias ( DeSlover et al. 2013 ). At 9 and 12 h, there is a bigger difference between the observed and simulated moisture profiles, particularly in the mid- to upper troposphere. Though it is possible that the increased midlevel moisture present in the simulations leads to later

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Scott A. Braun, Paul A. Newman, and Gerald M. Heymsfield

, and S. R. Guimond , 2015 : The coplane analysis technique for three-dimensional wind retrieval using the HIWRAP airborne Doppler radar . J. Appl. Meteor. Climatol. , 54 , 605 – 623 , doi: 10.1175/JAMC-D-14-0203.1 . Durran , D. R. , and J. B. Klemp , 1982 : On the effects of moisture on the Brunt-Väisälä frequency . J. Atmos. Sci. , 39 , 2152 – 2158 , doi: 10.1175/1520-0469(1982)039<2152:OTEOMO>2.0.CO;2 . Emanuel , K. A. , 1986 : An air–sea interaction theory for tropical

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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

Eastin 2012 ; Nguyen and Molinari 2012 ); moisture gradients in the environment of the TC and the penetration of dry air into the inner core (e.g., Dunion and Velden 2004 ; Shu and Wu 2009 ), particularly at weaker intensities ( Braun 2010 ; Sippel et al. 2011 ; Braun et al. 2012 ); lateral mixing of vorticity, heat, and moisture across gradients at the eye–eyewall interface (e.g., Schubert et al. 1999 ; Kossin and Schubert 2001 ; Kossin and Eastin 2001 ; Cram et al. 2007 ); and diabatic

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Hui Christophersen, Altug Aksoy, Jason Dunion, and Kathryn Sellwood

( Figs. 8a–c ). For relative humidity, both experiments greatly underestimate the moisture content in the upper levels of the vortex core, forecasting a much dryer upper vortex than actually observed. However, considering that the corresponding HEDAS analysis (verifying at the same time as the dropwindsonde composite) presents a very realistic humidity structure ( Fig. 8d ), we deduce that the upper-level dry bias in the forecasts is due to model error rather than data assimilation itself

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William A. Komaromi and James D. Doyle

2014. The number of dropsondes in each bin is labeled in magenta. A meaningful relationship between the θ of the maximum 100–500-km radially averaged V r and the present intensity was not observed ( Fig. 9c ). However, a notable positive relationship between the θ of the outflow layer and the θ e of the boundary layer inflow, which is a proxy for low-level moisture and SSTs, does occur ( Fig. 9d ). These values are obtained by first computing azimuthal-mean V r in radius– θ (radius θ e

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E. P. Nowottnick, P. R. Colarco, S. A. Braun, D. O. Barahona, A. da Silva, D. L. Hlavka, M. J. McGill, and J. R. Spackman

moisture condensation on the instrument window and telescope, as well as attenuation by clouds during the first four legs of the flight over Nadine and the SAL; therefore, only the components of the flight where dust was observed and CPL was not affected by lens condensation are shown. Despite these limitations, MODIS Terra observed a broad region of dust to the east of Nadine, which was also observed by CPL on the latter legs of the flight. Figure 1b shows the 550-nm total AOT from the GEOS-5 FP

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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

, R. H. , 1984 : Partitioning tropical heat and moisture budgets into cumulus and mesoscale components: Implications for cumulus parameterization . Mon. Wea. Rev. , 112 , 1590 – 1601 , doi: 10.1175/1520-0493(1984)112<1590:PTHAMB>2.0.CO;2 . Jones , S. C. , 1995 : The evolution of vortices in vertical shear. I: Initially barotropic vortices . Quart. J. Roy. Meteor. Soc. , 121 , 821 – 851 , doi: 10.1002/qj.49712152406 . Kelley , O. A. , J. Stout , and J. B. Halverson , 2004 : Tall

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