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Patrick Minnis, Edwin F. Harrison, and Patrick W. Heck

(1989b) describedabove. 2) CLOUD CENTER TEMPERATURE AND INFRARED EMITTANCE Neglecting scattering, the infrared radiation emanating from the top of the cloud is the combination ofabsorptions and emissions at the various levels andtemperatures within the cloud with the radiation thatenters the cloud's base and passes unattenuated throughthe cloud. The radiance observed by the satellite overthe cloud may be divided into two radiances: one thatpasses through the cloud and one that is emitted bythe

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Erika L. Duran, Emily B. Berndt, and Patrick Duran


Hyperspectral infrared satellite sounding retrievals are used to examine thermodynamic changes in the tropical cyclone (TC) environment associated with the diurnal cycle of radiation. Vertical profiles of temperature and moisture are retrieved from the Suomi National Polar–orbiting Partnership (S–NPP) satellite system, National Oceanic and Atmospheric Administration (NOAA)–20, and the Meteorological Operational (MetOp) A/B satellite system, leveraging both infrared and microwave sounding technologies. Vertical profiles are binned radially based on distance from the storm center and composited at 4–hr intervals to reveal the evolution of the diurnal cycle. For the three cases examined – Hurricane Dorian (2019), Hurricane Florence (2018) and Hurricane Irma (2017) – a marked diurnal signal is evident that extends through a deep layer of the troposphere. Statistically significant differences at the 95% level are observed in temperature, moisture, and lapse rate profiles, indicating a moistening and destabilization of the mid to upper troposphere that is more pronounced near the inner core of the TC at night. Observations support a favorable environment for the formation of deep convection caused by diurnal differences in radiative heating tendencies, which could partially explain why new diurnal pulses tend to form around sunset. These findings demonstrate that the diurnal cycle of radiation affects TC thermodynamics through a deep layer of the troposphere, and suggest that hyperspectral infrared satellite sounding retrievals are valuable assets in detecting thermodynamic variations in TCs.

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Steven M. Cavallo and Gregory J. Hakim

1. Introduction Radiation has been shown to play an important role in the intensification and maintenance of cyclonic tropopause polar vortices (TPVs) ( Cavallo and Hakim 2010 , hereafter CH10 ). Cyclonic TPVs are frequently observed, high-latitude, cold-core vortices based on the tropopause and play an important role in the formation of surface cyclones. The Arctic is particularly favorable for the maintenance and intensification of cyclonic TPVs ( Cavallo and Hakim 2009 ; CH10 ), and

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theatmosphere is absorbed by the snow surface which acts asa black-body for infrared radiation but not all of theupcoming radiation is absorbed by the atmosphere whichis not a black-bsody. Consequently there is a. net loss ofenergy in the atmosphere which cools and then sends lessback radiation to the surface, which then cools also, andso on.Shliakhov essent.ially attempt,s to calculate this effectand comes to the conclusion that. it could only change thetemperature of the lowest 3 km. by lo C. in 200 hours

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Frances C. Parmenter

MONTHLY WEATHER REVIEW VOLUMEI04PICTURES OF THE MONTHLow-Level Moisture Intrusion from Infrared Imagery Fa,A~CES C. P,AaM,v~r~ l~a~io~a~ Environmenlal Sa~lli~ 8erv~, NOAA, Washington, D. C. 20233 21 July 1975 Infrared sensors on the NOAA and SMS satellitesare designed to measure the longwave radiation emittedby clouds and terrestrial surfaces. CO2 and H20 vaporare strong absorbers of this emitted terrestrial

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figures 3 and 4. However, over aperiod of about 36 days the regions of day and nightcoverage would be almost completely reversed.Even though much small-scale detail has already beensmoothed out through use of the relatively large gridspacing and in some pIaces through the a.veraging of datain overlapping orbits, the radiation patterns in figures24 exhibit much detail. For the most part these radia-tion patterns are related t20 the fields of cloudiness overthe earth, since the overall outgoing infrared

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adiabaticcomponent of the vertical motion field, and equation (5),which represents the diabatic effect, will for conveniencebe designated the diabatic component of the verticalmotion field. In this study, only nonadiabatic heatingdue to the field of terrestrial radiation is considered. Understeady-state conditions and horizontal isotropy for thefield of infrared irradiance, the heat addition per unit massdue t.o infrared divergence isThus the diabatic component of vertical mot,ion due to thefield of infrared

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substantial portion of the %-hourperiod. At any given latitude (except north of about40' N.) the measurements are taken a t either one or twospecific local times during the day. Data on these chartsare limited by the basic maximum number of orbitalpasses that' can be interrogated by th.? two acquisition307FIGURE 1.-Composite chart of overall infrared radiation for a24-hour period derived from channel 4 data through use of pro-cedure given by Wark et al. [3]. At grid points with overlappirlgobservations

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algebraically reduceto the above-defined cloud emissivity.Having observa.tions of cloud emissivities one may cal-636MONTHLY WEATHER REVIEWcte the upward flus of infrared radiation at satellitelevel in the presence of clouds by means of one of thevarious forms of the transfer equation. A review ofobservations of TZROS infrared data has illustratedeffects of clouds and possible atmospheric particulates.The 7-30-1nicron broad response channel on TIROS, aswell the 8-12-1nicron "window" channel have shownlarge

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cloudswere clearly understood, one faces the monumental taskof defining cloud characteristics and structure beforeproceeding with model calculations.This paper describes infrared cooling radiation modelsof classical synoptic features constructed from directmeasurements of infrared radiation. Short-wave radia-tion models are produced by applying the techniques ofHanson et al. (1967) to composite maps of the matervapor distribution.In general, the symbols follow standard meteorologicalusage; however, the

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