Satellite Retrieval of Atmospheric Water Budget Over Gulf of Mexico-Caribbean Sea Basin Pablo Santos...
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Transcript of Satellite Retrieval of Atmospheric Water Budget Over Gulf of Mexico-Caribbean Sea Basin Pablo Santos...
Satellite Retrieval ofAtmospheric Water Budget Over
Gulf of Mexico-Caribbean Sea Basin
Pablo Santos 1 & Eric A. Smith 2
1 National Weather Service, Miami, FL[Florida State Univ. Dept. of Meteorology Graduate Student Program]
2 NASA/Goddard Space Flight Center, Greenbelt, MDPresented at 81st AMS Annual Meeting
Conference on Global Change & Climate Variations[January 14-18, 2001; Albuquerque, NM]
Motivation and Objectives
interest in understanding all terms of atmospheric branch of hydrological cycle within enclosed ocean basin
interest in quantifying water budget components from satellite measurements only
interest in extending past research which has been restricted largely to requiring balance between divergence of WV transport & E - P
develop remote sensing-based & portable retrieval methodology, using measurements from SSM/I & GOES satellites for calculating atmospheric water budget, verifying divergence residue with radiosonde-based estimates
quantify mean & variance properties of Gulf of Mexico-Caribbean Sea Basin atmospheric water budget in time-space
understand drawbacks within convectively active region under assumption that local rate of change of PW and cloud LWP are negligible in context of regionally & seasonally based atmospheric water balance
Study Area
Data Research utilizes data from three sources:
• DMSP (SSM/I)– used to retrieve precipitable water (W), cloud
liquid water path (Wc), precipitation (P), surface air temperature (Ta), surface specific humidity (qa), & surface wind speed (U)
• GOES (Imager)– used to retrieve sea surface temperature (SST)
& surface air temperatue (Ta) -- plus W, Wc, P, & qa with adjustments by SSM/I
• Upper Air T-q-V profiles
Methodology development of algorithms for water budget variables calculation & validation of water budget analysis of water budget atmospheric water budget equation for vertically
integrated total water in atmosphere where: W = precipitable water; Wc = cloud liquid water path; Q = vertically integrated water vapor transport; E = evaporation; & P = precipitation:
€
∂( W +Wc )
∂t[ ] + ∇ • Q[ ] = E−P[ ]
€
W +Wc
= [q(p )+ ql
(p )] dp / gop
o∫
€
Q = [q(p)r V (p)] dp /go
po∫
Surface Specific Humiditycalculated from GOESas function of SST &
adjusted by SSM/I qavia Schlüssel (1996)
SSM/I∑ NESDIS SSM/I alg (Ferraro et al. , 1998) cross-validated against 4 other SSM/I algs∑ SSM/I retrievals within expected uncertainty of ground truth (Smith et al. , 1998)
SSM/IGreenwald et al. (1995),
Lojou (1994),Petty (1994),Wentz (1995)
GOESSplit Window Technique
Chesters (1980), Crosson et al. (1993)
Combined SSM/I-GOESGOES W estimateadjusted by SSM/I
SSM/I Alishouse (1990), Greenwald et al. (1995), Lojou (1994), Weng and Grody (1994)
Combined SSM/I-GOES∑ GOES detects cloud area∑ GOES LWP estimate equals closest SSM/I retrieved mean cloud LWP in time∑ data from two SSM/Is are used to increase data sampling
Sea Surface Temp (GOES)Legeckis (1997)
Surface Wind Speed (SSM/I)Bates (1991),
Clayson & Curry (1996),Schlüssel (1996)
GOES E estimate usesclosest in time SSM/I
mean U retrieval fromtwo SSM/Is
Surface Air Temperature (SSM/I-GOES) Clayson and Curry (1996)SSM/I - cld classificationGOES - cld top temp & SSTTa func of cld type & SST
Combined SSM/I-GOES∑ GOES retrievals based on probability matching (PM) between SSM/I retrieved rainrates & GOES EBBTs∑ PM technique based on work of Turk et al. (2000) & Grose et al. (2000)
Rain ScreeningFerraro et al. (1998)
Cloud detectionbased on NESDIS & NAVY operational
screening techniquesLegeckis (1997) &
May (1998)
Water Budget Calculation
€
(∇ • Q )i, j = Ei, j − Pi, j −(Wi, j + Wci, j )t+1 − (Wi, j + Wci, j )t−1
2Δt
⎡ ⎣ ⎢
⎤ ⎦ ⎥
Once precipitable water (W), cloud liquid water path (Wc), precipitation (P), & evaporation (E) are retrieved at each grid point, divergence of vertically integrated water vapor transport (—∑Q) for time t at grid coordinate (i,j) is calculated using centered difference form of water balance equation, as follows:
Validation of Water Budget Divergence of water vapor transport obtained as
residue in water balance equation. Residue term compared to direct measure of divergence
obtained from ring of operational radiosonde stations surrounding basins in study area.
Direct measure obtained from line-integral technique (application of Greens’ theorem) in conjunction with sounding ring:
€
∇• Q[ ] =1A
(qu)dp/g0
po
∫ ⎧ ⎨ ⎪
⎩ ⎪
⎫ ⎬ ⎪
⎭ ⎪dy − (qv)dp/g
0
p o
∫ ⎧ ⎨ ⎪
⎩ ⎪
⎫ ⎬ ⎪
⎭ ⎪dx∫∫
⎡
⎣
⎢ ⎢ ⎢
⎤
⎦
⎥ ⎥ ⎥
Analysis Algorithm sensitivity analyses and multiple-algorithm
intercomparisons are being used to define retrieval system uncertainties.
Budget calculations are being performed on 2 x 4 km grid mesh with hourly mean composites generated on 0.25 x 0.25 degree grid mesh for 6 one-month periods (Oct 1997; Jan, Apr, Jul, Oct 1998; Jan 1999).
Analyses are aimed at quantifying regional water budget variability of Gulf of Mexico-Caribbean Sea Basin to enable pursuit of key scientific objectives.
Final conclusions are to be based on analyses of filtered daily time series of sub-regional averages & gridded monthly/diurnal-composites with respect to individual terms of water budget equation.
Algorithm Intercomparison Results - Jan 98
Precipitable Water (W)
intercomparison results
(Jan/Jul 98)
SSM/I-GOES W algorithm
(Santos Adj-GOES)used for final budget
calculations
Cloud Liquid Water Path (Wc)intercomparison
results(Jan 98)
Alishouse SSM/I algorithm used as
control for GOES-8 retrievals
SSM/I-GOES Wc algorithm used for
final budget calculations
Precipitation (P) intercomparison
results(Jan 98)
NESDIS SSM/I algorithm used as
control for developing
probability matching lookup tables
between SSM/I rainfall & GOES-8
EBBTs (these tables used for GOES-8 rain
retrievals)
SSM/I-GOES P algorithm used for
final budget calculations
Sea Surface Temperature
(SST)intercomparison
results(Jan/Jul 98)
SST is input parameter for
Clayson & Curry (1996)
Evaporation algorithm
Legeckis GOES algorithm used for final SST
retrievals
Surface Air Temperature (Ta)
intercomparison results(Jan/Jul 98)
Ta is input parameter for Clayson & Curry (1996) Evaporation
algorithm
SSM/I-GOES algorithm
(modified Clayson & Curry where GOES
used in deriving cloud type) used for
final Ta retrievals
Surface Specific Humidity (qa)
intercomparison results
(Jan/Jul 98)
qa is input parameter for
Clayson & Curry (1996)
Evaporation algorithm
SSM/I-GOES algorithm used for final qa retrievals
Surface Wind Speed (U)
intercomparison results
(Jan/Jul 98)
U is input parameter for
Clayson & Curry (1996)
Evaporation algorithm
Schlüssel SSM/I algorithm used for final U retrievals
Ocean surface latent heat flux from
Clayson & Curry (1996) Evaporation
algorithm(based on surface renewal theory)
Comparisons to vertical q gradient over surface layer
[qs(SST) - qa]& to surface wind
speed (U)[Jan 98]
Ocean surface latent heat flux from Clayson &
Curry (1996) Evaporation algorithm
(based on surface renewal theory)
Comparisons to vertical q gradient over surface layer
[qs(SST) - qa]& to surface wind
speed (U)[Jul 98]
Jan 98 Hourly Composites of Rate of Change of
Precipitable Water (W)
Jan 98 Hourly Composites of Rate of Change of
Cloud Liquid Water Path (Wc)
Jan 98 Hourly Composites of Input Parameters for
Clayson (1996)Evaporation Algorithm:
Sea Surface Temperature (SST), Surface Air Temperature (Ta), Surface Specific Humidity (qa)
Jan 98 Hourly Composites of Surface Evaporation (E)
Jan 98 Hourly Composites of Divergence of
Water Vapor Transport (—∑Q)
Time Series Comparisons of Retrieved versus Sounding-Based
—∑Q
20-day time series of —∑Q retrieved
from satellite (green lines) compared to value calculated
using line integral technique applied to sounding data (red
lines)
series extends from day 6 - 25 for Jan 98
at 00Z with value for each day
corresponding to 10-day average centered on
respective day
20-day time series of —∑Q retrieved
from satellite (green lines) compared to value calculated
using line integral technique applied to sounding data (red
lines)
series extends from day 6 - 25 for Jan 98
at 12Z with value for each day
corresponding to 10-day average centered on
respective day
Summary A portable satellite-based retrieval system for obtaining
the atmospheric water budget has been developed for applications with combination of SSM/I & GOES data.
Preliminary single layer (troposphere) calculations have been generated for January-1998 over Gulf-Caribbean Basin (3-layer calculations will be made).
A verification analysis is underway to determine the validity of retrieving the (E - P) and ∂(W+Wc)/∂t terms of the atmospheric water budget while obtaining —∑Q as a residue term, thus circumventing the need for measurements of the wind velocity profile.
Analysis is underway to determine the uncertainty imposed on a regional-seasonal atmospheric water budget in a highly convective tropical basin, by ignoring the W and Wc storage terms.
Preliminary Conclusions Preliminary results for January-1998 indicate that the
algorithm system captures the main features of the regional budget on both daily and monthly/diurnal-composite time scales. Budgets for Oct-97, Apr-98, Jul-98, Oct-98, and Jan-99 are also being calculated to understand how well the methodology represents seasonal variability over an annual cycle.
Although validation checks are limited by the lack of continuous upper air data over the southern half of the Gulf of Mexico & parts of the Caribbean Sea basins and given that there are episodes of poor sounding data, preliminary —∑Q intercomparisons are within sufficient agreement to justify pursuing technique development and the underlying budget estimates.