ATMO 551a Fall Water Vapor

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Noreen Short
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1 Watr Vapor Introducton Th conttunt that mak Earth wathr and clmat o ntrtng and challngng to undrtand and modl watr. Watr xt on Earth n all thr pha: apor, lqud and old. Watr play many mportant rol many of whch ar brfly ummarzd hr: Watr th mot mportant of th grnhou ga that kp th Earth urfac rlatly warm at 288 K n comparon to t radat qulbrum tmpratur of 255 K. It concntraton wll chang a a complx fdback, gnrally thought to b pot orall that wll amplfy th ffct of ncrang CO 2 concntraton Watr ha a ry hgh latnt hat and a uch o rla much nrgy nto th atmophr whn t condn and o cool th ar and urfac whn t aporat. Th condnaton of watr prod th nrgy nput to th atmophr that dr much of r wathr, partcularly n th warm aon, uch a hurrcan and tornado. Mot of th rtcal nrgy tranport n th atmophr du to condnaton of watr. Ran fallng nto dry ar can cau r downdraft uch a mcroburt that can b qut damagng. Bob Maddox, formr mmbr of our dpartmnt and had of th Natonal Sr Storm Lab (NSSL), thnk our rgon ha th mot r downdraft n th world. In Sonora and Snaloa, Mxco, th daly cycl of mot concton dramatcally altr th durnal cycl of tmpratur rlat to th dry ummr, lowrng both th daytm maxmum tmpratur and th nghttm mnmum tmpratur a aporat coolng Th condnaton that crat cloud and prcptaton hat th ar n th cloud. Cloud altr th radat balanc by o rflctng mor hortwa radaton o aborbng and mttng mor long wa radaton. Hgh rlat humdty (>8%) can alo cau arool partcl to grow n z altrng thr cattrng proprt. Th typ and xtnt of th contnntal bophr controlld largly by th amount and tmng of prcptaton t rc. Watr ha a ry hgh hat capacty, partcularly n th lqud form, uch that th ocan tor a hug amount of hat. Th normou amount of nrgy rqurd to warm up hatng of th ocan g u tm to mak dcon. (Conrly, onc thy ar warm, t wll tak a long tm to cool thm) Th rultng land-a tmpratur contrat (bcau land tmpratur r fatr than ocan tmpratur for th am amount of nrgy nput) dr th monoon and play a trong rol n th aonal cycl. Frzng ran cau powr outag and traffc accdnt oftn n th Southatrn US. Incrang c ra th Earth albdo, coolng th Earth. Mltng c lowr th albdo, warmng th Earth. W ar gong to buld up ral nw tool to undrtand watr and t mpact on th atmophr. Th nclud Varabl w u to dcrb atmophrc watr 1 Kurnk 1/12/1

2 Th Clauu Clapyron quaton that dfn how much watr apor th ar can hold Th mot adabatc tmpratur lap rat that nclud th ffct of latnt hat. Vrtual tmpratur that nclud th ffct of watr apor bng lghtr than dry ar. Sral ky pont about th mpact of watr can b undrtood by xamnng th flow of mot ar or orography. Thr ar a multpl arabl that dcrb watr apor n th ar. Th raon for th multpl dcrpton non of thm nclud all rlant nformaton ndd. Varabl dcrbng atmophrc watr Total watr apor amount typ arabl Abolut humdty: ρ (g/m 3, kg/m 3 ): Th ma of watr (apor) pr cubc mtr of ar. Abolut humdty rang from gram pr cubc mtr n dry ar to 3 gram pr cubc mtr whn th ar aturatd at 3 C. Prcptabl watr apor: PWV (kg/m 2, mm, cm) Th rtcal ntgral of th abolut apor ma dnty whch yld th column watr pr m 2. Th can b conrtd to unt of prcptabl mm or cm by ddng by th dnty of lqud watr, 1 g/cc. PWV = ρ dz = qρ ar dz = q dp = g P q dp (1) g Prcptabl watr: PW (kg/m 2, mm, cm) Th rtcal ntgral of th humdty, both apor and condnd motur, whch yld th column watr pr m 2. Th can b conrtd to unt of prcptabl mm or cm by ddng by th dnty of lqud watr, 1 g/cc. Mxng rato typ arabl Mxng rato typ arabl dcrb th fracton of ar that mad of watr apor thr n trm of ma dnty or numbr dnty. Mxng rato arabl ha a ry mportant proprty: In th abnc of watr ourc and nk, th arabl ar conrd a ar mo around. Th tracr fatur ry uful for undrtandng how watr bha and dtrmnng how watr apor controlld n th atmophr. Spcfc humdty: q (kg/kg, g/kg) Spcfc humdty th rato of th ma of watr apor to th ma of ar (ncludng both watr apor and dry ar) n a partcular olum. Spcfc humdty rato xprd a a rato of klogram of watr apor, mw, pr klogram of mxtur, mt. It oftn wrttn n g/kg to aod th ladng zro. (Ma) mxng rato: r (kg/kg, g/kg) P 2 Kurnk 1/12/1

3 Th (ma) mxng rato th rato of th ma of watr apor to th ma of DRY ar only n a partcular olum. mxng rato xprd a a rato of klogram of watr apor, mw, pr klogram of dry ar. Volum mxng rato (%, ppm) Ud to dcrb watr apor n th tratophr. Spcfc humdty rlatd to mxng rato (and c ra) by: M q = w = r M d + M w 1+ r r = q 1 q Th two arabl ar ry mlar n magntud. (2) (3) Prur typ arabl Partal prur: (mb) Th prur of watr apor alon by tlf. Not that th dal ga law tat that P = n R* T (4) For a ga n thrmodynamc qulbrum, th ga ha a wll dfnd tmpratur. Thrfor, all conttunt of th ga ha th am, wll dfnd tmpratur. Th molar numbr dnty of th ga th um of th molar dnt of ach conttunt n th ga n = n (5) whr n th molar numbr dnty of th th conttunt of th ga. Pluggng th n yld P = n R *T = R *T n (6) from whch w can wrt P = n R *T = R *T n = P (7) whr P known a th partal prur of th th conttunt of th ga. Not that th partal prur concpt work undr th dal ga law whch a ry good approxmaton. Watr actually th lat dal of th major ga that mak up Earth atmophr. Saturaton apor prur: (mb) Th partal prur of watr apor at whch th watr apor bgn condnng out. Th prur a functon of tmpratur and dfnd by th (ntgral of th) Clauu Clapyron quaton. 3 Kurnk 1/12/1

4 ( ) ( ) T d = Aumng L contant, th ntgral lad to d ( ) = d ln = ln ( ) ( T ) = ln ( ) = ( T ) ( T ) Takng xp() of both d yld ( ) = T L dt T T = L dt (8) 2 T L dt = L = L 1 T 2 T T T 1 = L T T T ( )xp L T (9) T Th how that ndd th aturaton apor prur dpnd xponntally of tmpratur. For a tmpratur of 25 K, L /( T 2 ) =.87 uch that for ry 1K chang n tmpratur nar 25 K th watr aturaton apor prur or lqud watr about 9%. For a tmpratur of 288 K, L /( T 2 ) =.87 uch that for ry 1K chang n tmpratur nar 25 K th watr aturaton apor prur or lqud watr about 7%. NOTE: dcu Gab Vcch talk on xpctd lowng of th crculaton. A flaw n th abo draton t aum th latnt hat of aporzaton ndpndnt of tmpratur. Thr ar a lot of dffrnt formulaton that account for th tmpratur dpndnc. S for a ummary of th. A jut drd, th Clauu Clapyron uggt a mplr form for th (T) quaton rlat to th mor complcatd form or tmpratur rang or whch th latnt hat, L, do not ary much wth tmpratur. Rlat humdty (%) Th rato of th actual watr apor n th atmophr rlat to th amount th ar could hold whch calld aturaton. If rlat humdty dfnd n trm of partal prur thn On can alo wrt RH n trm of q uch that RH = 1 x / (n %) (1) RH = 1 x q/q (n %) (11) whr q th pcfc humdty whn th watr apor n th ar aturatd. q = µ = µ (12) P µ a ( P )µ d + µ NOTE: Thr an mportant ubtlty whn tmpratur ar ubfrzng. Th aturaton apor prur can b thr aturaton apor prur or lqud or or c. Th dffr bcau th latnt hat of aporaton mallr than th latnt hat of ublmaton. Thrfor watr molcul n th c pha ar mor tghtly bound than watr molcul n th (uprcoold) lqud pha. Thrfor th aturaton apor prur lowr or c. It turn out that tandard capact humdty nor ud n radoond maur rlat humdty or lqud, n at ubfrzng tmpratur. 4 Kurnk 1/12/1

Tmpratur form Dw pont ( o C, o F) Th tmpratur at whch th watr apor n th ar would qual th aturaton watr apor prur or a lqud urfac. It th tmpratur at whch th watr apor wll bgn to condn out nto dw.

5 Tmpratur form Dw pont ( o C, o F) Th tmpratur at whch th watr apor n th ar would qual th aturaton watr apor prur or a lqud urfac. It th tmpratur at whch th watr apor wll bgn to condn out nto dw. It a maur of th abolut amount of watr apor n th ar. Frot pont ( o C, o F) Th tmpratur at whch th watr apor n th ar would qual th aturaton watr apor prur or a watr c urfac. It th tmpratur at whch th watr apor wll bgn to condn out nto frot. It a maur of th abolut amount of watr apor n th ar. Saturaton apor prur or lqud (lft) and or lqud and c (rght) 5 Kurnk 1/12/1

Relate p and T at equilibrium between two phases. An open system where a new phase may form or a new component can be added

Relate p and T at equilibrium between two phases. An open system where a new phase may form or a new component can be added 4.3, 4.4 Phas Equlbrum Dtrmn th slops of th f lns Rlat p and at qulbrum btwn two phass ts consdr th Gbbs functon dg η + V Appls to a homognous systm An opn systm whr a nw phas may form or a nw componnt