NASA Technical Reports Server (NTRS) 19990014072: Impacts of Large-Scale Circulation on Convection: A 2-D Cloud Resolving Model Study

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by  NASA Technical Reports Server (NTRS)

8D.11
IMPACTS OF LARGE-SCALE CIRCLUATION ON CONVECTION:
A 2-D CLOUD RESOLVING MODEL STUDY
X. L1I* , C.-H. Sui 2, K.-M. Lau 2
1Space Application Corporation, Vienna, VA 22180
2 NASA/Goddard Space Flight Center, Greenbelt, MD 20771
1. MOTIVATION
-4-H.,=4-_IQ,-_I=4-_IQ-_RI. (la)
Stduies of impacts of large-scale
circulation on convection, and the roles of SH CH RH
convection in heat and water balances over The equation for vertically-integrated water
tropical region are fundamentally important vapor budget is
for understanding global climate changes.
Heat and water budgets over warm pool rw ]
(SST=29.5°C) and cold pool (SST=26°C)
a, L J
were analyzed based on simulations of the
two-dimensional cloud resolving model. TQ HAQ VAQ P E
Here the sensitivity of heat and water budgets
to different sizes of warm and cold pools is Here, <0>=[0]/[1], and [()]= _)()dz, where
examined.
0
zr is the height of top model level; Overbar is
2. EXPERIMENT DESIGNS AND BUDGET
the horizontal mean; T, 0, and q,, are
EQUATIONS
temperature, potential temperature, and
The model has 20480-km horizontal
specific humidity, respectively; V and w are
domain, and a horizontal grid mesh of 2.5
horizontal wind vector and vertical velocity
km, and 33 vertical levels. The model also
respectively; p is a horizontal-mean air
has a cyclic lateral boundary. Two
R
experiments were carried out in this study.
The ratio of the sizes of warm pool to cold density; n"= (P)'", R is the gas constant,
pool is 1:2 in Experiment C, whereas it is Po
1:11 in Experiment CS. Otherwise, two and Cp is the specific heat of dry air at
experiments are identical. The model
constant pressure p, and po=1000 mb; Q,,,,
physical parameterization schemes can be
referred to Sui et al. (1998) and Li et al. QR, H,, P, and E are condensational heating,
(1998). The initial temperature and moisture radiative heating, surface sensible heat, rain
conditions were taken from observations over rate, and surface evaporation, respectively.
the western Pacific warm pool during TOGA Local temperature change (TT) is determined
COARE. by horizontal (HAT) and vertical (VAT)
temperature advections, surface sensible heat
The equation for mass-weighted heat flux (SH), condenational heating (CH), and
budget is radiative heating (RH). Local water vapor
change (TQ) is determined by horizontal
(HAQ) and vertical (VAQ) moisture
advections, precipitation (P), and surface
\
evaporation (E).
TT HAT VAT
3. RESULTS
Corresponding author address: X. Li, SAC,
NASA/GSFC, Code 913, Greenbelt, MD
20771 ;e-maih xli @eos913g.gsfc.nasa.gov.
Overwarmpool,themass-weighted C1 thanthatin CS.Thesetwo differences
temperatureincreasesfasterin C (0.36°C causewarmingandcoolingtrendsinCSand
day-1) thanin CS(0.17°Cday-l), whereas C1,respectively.ThemagnitudeofVAQ is
muchlargerin CSthanthatin C1,whereas
thetotalwatervaporincreasesatthesimilar
the magnitudeof Pis slightly largerin CS
ratesinbothexperiments(1.01mmday-1in
thanC1.Thesedifferencescausemoistening
C and1.21mm day-1 in CS)within day7-
anddryinginCSandC1respectively.
11. The heat and water vapor budgets
averagedwithin the sameperiod(Table 1)
Table 1Mean heat(°C day-1) andwater
showthattwo largestterms,VAT andCH,
are almost canceledeach other in both vapor(mm day-1) budgetswithin day7-11
for experimentsC andCSover warm and
experimentsin theheatbudgets,thoughthe
coldpoolsand2-daymeanheatbudgetinC1
magnitudesof bothtermsaresmallerin C
from Li et al. (1998). See text for C1.
than in CS. The larger increase of
Definition of eachtermin thetablecanbe
temperaturein C is aresultof warmHAT.
seenin (1).
ThemagnitudesofVAQ arelargerthanthose
of P sothatwatervaporincreasesin both Exp. C CS C1 C CS
Pool warm warm warm cold cold
experiments.
TI" 0.36 0.17 -0.71 0.38 0.28
Overcold pool, the mass-weighted HAT 0.46 -0.2 -0.06 0.06 -0.02
temperaturesincrease(0.4°Cday-1inCand VAT -2.81 -6.84 -6.36 1.01 0.62
0.3°Cday-1in CS)andthetotalwatervapor SH 0.22 0.32 0.25 0.11 0.12
decreases(-0.5mmday-1in Cand-0.4mm CH 2.72 6.93 5.88 0.18 0.43
day-1 in CS) at the similar ratesin both RH -0.23 -0.04 -0.42 -0.98 -0.87
experiments.The budgets show that two
largestterms,VAT andRH, almostoffset. Exp. C CS C1 C CS
CH and SH explain a large part of Pool warm warm warm Cold Cold
temperatureincreasein both experiments. TQ 1.1 1.21 -2.06 -0.49 -0.4
ThemagnitudesofVAQarelargerthanthose
HAQ -4.78 -8.82 -5.48 1.09 1.18
of E sothatwatervapordecreasesin both
VAQ 11.92 31.0 19.91 -4.33 -3.06
experiments.
P -10.7 -27.2 -23.2 -0.69 -1.68
E 4.63 6.21 6.75 3.44 3.16
Theheatandwatervaporbudgetsin
CSarecomparedwith thosein C1thatwas
REFERENCES
carriedout by Li et al. (1998).In C1, the
modelis imposedby thelarge-scalevertical
Li, X., C.-H. Sui, and K.-M. Lau, 1998:
velocity, zonal wind aswell ashorizontal
Large-scale forcing and cloud-radiation
temperatureandmoistureadvectionstaken
interaction in the tropical deep
andderivedfromobservationsduringTOGA
convective regime. J. Atmos. Sci.,
COARE,andis integratedfor selectedsix
(revised).
dayswhenstrongconvectionoccurred.The
budgets averagedwithin day 3-4 of the
Sui, C.-H., X. Li, K.-M. Lau, 1998:
integrationareshowninTable1.Themajor
Radiative-convective processes in
difference betweenCS andC1 is that the
simulated diurnal variations of tropical
interactionbetweenlarge-scalecirculations oceanic convection. J. Atmos.Sci., 55,
andconvectionisfully guaranteedin CSbut 2345-2357.
itispartiallyallowedinC1.
The magnitude of VAT is about
0.5°C day-1 largerthanthatof CH in C1,
whereastheirmagnitudesaresimilar inCS.
AlsothemagnitudeofRHis muchlargerin