The preliminary results of a research study that emphasizes the analysis and interpretation of data related to total precipitable water and nonprecipitating cloud liquid water obtained from NIMBUS-6 SCAMS are reported. Sixteen cyclonic storm situations in the northeastern Pacific Ocean that resulted in significant rainfall along the west coast of the United States during the winter season October 1975 through February 1976 are analyzed in terms of their distributions and amounts of total water vapor and liquid water, as obtained from SCAMS data. The water-substance analyses for each storm case are related to the distribution and amount of coastal precipitation observed during the subsequent time period when the storm system crosses the coastline. Concomitant precipitation predictions from the LFM are also incorporated. Techniques by which satellite microwave data over the ocean can be used to improve precipitation prediction for the Pacific West Coast are emphasized

Chang, A. T. C.

Shigeishi, H.

Viezee, W.

English

NASA Technical Reports Server

Paper No. 39
APPLICATION OF NIMBUS-6 MICROWAVE DATA TO PROBLEMS IN
PRECIPITATION PREDICTION FOR THE PACIFIC WEST COAST
W. Viezee and H. Shigeishi, SRI International, Menlo Park, California, and
A. T. C. Chang, Laboratory for Atmospheric Science, Goddard Space Flight
Center, Greenbelt, Maryland
1. INTRODUCTION
Reliable predictions of the rapid augmentation of mountain snowpack or of run-
off in the Pacific Northwest westward of the Cascades depend largely on the extent
to which pertinent percursor meteorological conditions can be diagnosed over the
northeastern Pacific Ocean, where little or no conventional weather data exist. Al-
though interpretations from satellite cloud-image data are increasingly used in weather
forecast preparation, it is difficult to identify in advance those storm systems that
produce surges of heavy precipitation over land, especially between October and April.
At present, the regional Limited-Area Fine-Mesh Model (LFM) of the National
Meteorological Center (NMC) predicts precipitation for the West Coast. However, as
pointed out by Fawcett (1977), the absence of observations over the eastern Pacific
and the failure to model correctly atmospheric convection and complicated terrain
effects on the atmosphere make the model less accurate over the western United States
than for other geographic areas. Weather forecasters, therefore, must still depend on
personal insight and experience in conjunction with numerical guidance when fore-
casting precipitation. The output of the numerical prediction models is currently
complemented by objective precipitation forecasts from the Model Output Statistics
(MOS) technique and the map-type PoPs (Klein and Glahn, 1974; Rasch and MacDon-
ald, 1975); however, precipitation in moderate and heavy amounts remains one of the
most difficult weather variables to predict.
Passive microwave sensors carried on satellite platforms provide measurements
inside extensive storm cloud systems that the visible and infrared radiometers cannot
obtain. For example, the electrically scanning microwave radiometer (ESMR) and
scanning microwave spectrometer (SCAMS) instruments on the NIMBUS 5 and 6 sat-
ellites have provided data directly related to precipitable water, cloud liquid water,
and rainfall over the ocean. This information should be exploited in research related
to the precipitation prediction problems and the hydrology of the Pacific West Coast
States, since conditions antecedent to significant precipitation and those with which
numerical prediction models must be initialized develop over the ocean.
This paper reports on the preliminary results of a research study that emphasizes
the analysis and interpretation of data related to total precipitable water and nonpre-
cipitating cloud liquid water obtained from NIMBUS-6 SCAMS.
Sixteen cyclonic storm situations in the northeastern Pacific Ocean that resulted
in significant rainfall along the west coast of the United States during the winter sea-
son October 1975 through February 1976 are analyzed in terms of their distributions
and amounts of total water vapor and liquid water, as obtained from SCAMS data.
The water-substance analyses for each storm case are related to the distribution and
amount of coastal precipitation observed during the subsequent time period when
the storm system crosses the coastline. Concomitant precipitation predictions from
the LFM are incorporated into the study also. The overall objective of the research
233
https://ntrs.nasa.gov/search.jsp?R=19790012501 2020-03-20T18:24:52+00:00Z
is to exploretechniquesbywhichsatellitemicrowavedataovertheoceancanbe
usedto improveprecipitationpredictionforthePacificWestCoaststates.
2. DATAANALYSISANDINTERPRETATIONTECHNIQUE
Table1liststhe16three-dayperiodsforwhichstormcasesoverthenorth-
easternPacificOceanwereselectedforanalysis.In eachcase,theselectedstorm
system ovedeastwardtowardtheWestCoast.
TheNIMBUS-6SCAMSdigitaldatatapesofverticallyintegratedwatervapor
andnonprecipitatingcloudliquidwaterareusedin theanalyses.Twotimeperiods
of SCAMSdatacoverage(ascendinganddescendingode)atintervalsof 10to 13
hoursareavailableforeachstormday.
Dailyprecipitationrecordswereexaminedinconjunctionwithsequencesof
SMS-2cloudimagesto determinethetimeperiodduringwhicheachselectedstorm
systemaffectedrainfallalongtheWestCoast.Forthistimeperiod(usuallytwoto
threesuccessivedays),rainfallobservationsat 27coastalstationsextendingfrom
Washington(48°N)to centralCalifornia(34°N)wereanalyzedin termsof thelat-
itudevariationordistributionof coastalprecipitation.Thisobservedvariationwas
thenrelatedto antecedentconditionsof thestorm'sliquidwatercontentoverthe
ocean,asobtainedfromSCAMS.
Thecomputerprogramusedinanalysisof theNIMBUS-6SCAMSdigitaldata
andthecoastalrainfalldatahasthreemajorsubroutines.Onesubroutineprints
thesatellitescanspotvaluesforagiventimeperiodonaMercatormapextending
from30°Nto 54°Nlatitudeand120°Wto 168°Wlongitude.Thesecondsubrou-
tineaveragesthesedataona1° meshgrid-pointarray(25rows,27columns).For
eachtimeperiod,thethirdsubroutinecharacterizesthestorm(onthebasisofthe
SCAMSdata)in termsof thedistributionof watervaporandliquidwaterasa
functionoflatitudefromnorthto southacrossthestormarea.
Figures1and2illustratethetechnique.Figure1showstheconditionsof
cloudliquidwaterassociatedwithamajorstormsystemovertheoceanat 1045
GMT7 Oct.1975,andabout24hourslater,at0915GMT8Oct.1975.These
Table1
StormCasesinNortheasternPacific Ocean Selected for Analysis
Case No. Dates (PST) Case No. Dates (PST)
7- 9 Oct 75
15- 17 Oct 75
24-26 Oct 75
9
10
11
10- 12 Dec 75
19-21 Dec 75
23-25 Dec 75
27-29 Oct 75
3 - 5 Nov 75
12- 14 Nov 75
17- 19 Nov 75
3 - 5 Dec 75
12
13
14
15
16
6 - 8 Jan 76
12- 14 Jan 76
11 - 13 Feb 76
23-25 Feb 76
26-28Feb76
234
50"N
30""
r:_N
4O"
3O"
lr=o" 1_
1045 GMT, 70CTOEER 1975
160' 1=10" t30"
ODI S GMI",
130" I_V
120=W
TOTAL L)QUID H20--x 100 toni
LONGITUDE -- =W
-SS
============================= _' so
............................................... :=5
...................................................... -3O
0e34-1131 GMT, 7 OCTOBER 1975
LONGITUDE -- "W
:::::::::::::::::: : =
P _................ _ -,in";= .'::2:_._",,.,.._._= "i.. _ 22 < _
0850-1047 GMT. E OCTODER 1975
0.2 0.4 0.6 o.e _o 1.= 1.4
, , ,., , ,
0.2 0.4 0.6 o.e 1.0 1.2 1.4
Fig. 1-SMS--2 infrared cloud image (left frame) and analysis of Nimbus-6 SCAMS
cloud liquid water content (middle frame, units of mg/cm 2) for storm system at
1045GMT, 7 October 1975, and 24 hours later at 0915GMT, 8 October. Charac-
teristic profiles of liquid water (right frames) are used to extract information on
coastal rainfall distribution.
conditions are antecedent to the coastal rainfall shown in Figure 2, which indicates
the observed distribution of 24-hour coastal rainfall for 8-10 Oct., and the 72-hour
cumulative total for the three days. In Figure 1, the digital data of SCAMS liquid
water (middle frames) are analyzed on the 1° mesh grid-point array. Each printed
number represents the vertically integrated (columnar) liquid water, averaged over
the grid square, expressed in units of 10 -2 mm (mg/cm2). The characteristic pro-
files of total liquid water (1 ° zonal strips across the grid-point area), expressed in
units of 108 tons, are shown on the right side. Figure 1 shows that the SCAMS
data:
• Have adequate quality for further analysis and ;nIerpretation.
• Reproduce the characteristic shape of the SMS-2 storm-cloud system.
• Reveal meaningful information on the space and time variations of cloud
liquid water content not apparent in the image data.
Comparing the data of Figures 1 and 2 shows that the distribution of SCAMS cloud
liquid water at about 0915GMT 8 Oct. has a maximum (>0.9 x 108 tons for 1°
latitude intervals) between latitude 45°N and 37°N where coastal rainfall has a
maximum on 9 Oct. and also in the three-day cumulative total. Thus, in this par-
ticular case, the distribution of the cloud liquid water content obtained from the
NIMBUS-6 SCAMS contains information related to the distribution of coastal pre-
cipitation observed at a later time.
Analyses such as presented in Figures 1 and 2 were made for all 16 cases. Re-
sults of the research study are summarized below on the basis of representative
case studies.
235
00
o__,.
= tO
'_tu
_'aaJ
r
8 OCTOBER 1975 9 OCTOBER
i,o I
.J_:
_ T =.01-
<z
O0
{J_ ,_1-
:31--
OE ,,.o
•,_j r-
_rLU
a- 0.0 I-\
% , J , _ J
-Io -4e -4o ._ .lo
LATITUDE-degrees LATITU DE-degrees
lu3 i i,o, r i r ' _-
10 OCTOBER 8, 9, 10 OCTOBER
_, LrF
.j .¢
T Lot
OQ
O _- io[z_ "
% , , , .... ,= , - , - -
-oo ._ -4o ._ .3o -w -3o
Fig. 2-Observed coastal rainfall distribution from Washington (48°N) to central
California (34°N) during 3-day period in which storm system of Figure 1 affected
weather conditions.
j_u
<_
8o
rf_ I.S
3. PRELIMINARY RESULTS
3.1 Discussion of Case Studies for December 1975
Table 2 summarizes the results for Cases 8 through 11 of Table 1. Two con-
secutive days of SCAMS data coverage are listed for each case. During these two
days, the storm system moved eastward from about 145°W onto the West Coast.
On each day, the area chosen for analysis is covered by SCAMS data from two con-
secutive descending-node (near local midnight) and two consecutive ascending-node
(near local noon) NIMBUS--6 orbital passes. Each storm system is associated with
approximately three consecutive days of coastal rainfall. At each listed time period
t 0, the latitude (north to south) variation of SCAMS liquid water across the storm
area is correlated with the distribution of the three-day (72-hour) cumulative coast-
al rainfall. The highest positive linear correlation coefficients are boxed: For these
cases, the north-to-south distribution of storm-cloud liquid water at t o is quite sim-
ilar to the distribution of the three-day total precipitation observed along the coast
from Washington to central California at later time t o + At. The positive correla-
tion increases when the two stations in Washington (Quillayute and Hoquiam),
where rainfall is significantly affected by orography, are eliminated from the data
sample.
236
Table 2
Linear Correlation Between SCAMS Liquid Water Distribution Over the Ocean at
t o and Coastal 72-Hour Total Rainfall Distribution at to + At
SCAMS Liquid Water Dislxibution 72-Hour Coastal Rainfall Distribution
Correlation Coefficient
Time
Case Dates
Period, t o
No. (Dec 75) (PST)
8 3 01144)312
1130-1330
4 0033-0230
1047-1247
9 10 0139-0333
1201-1348
11" 0052-0250
1107-1305
10 20 0135-0332
1151-1348
21 0051-0249
1107-1305
11 24 0032-0228
1233-1429
25 2347-0146
1150-1200
At
(Hours)
96
84
72
60
96
84
72
60
72
60
48
36
96
84
72
60
With
Washington:
48 ° _ 34°N
+0.89
+0.90
+0.69
+0.28
+0.23
+0.39
+0.63
+0.47
-0.02
+0.34
+0.62
-0.54
+0.48
-0.41
-0.61
-0.10
*Boxed numbers indicate highest positive correlations, discussed in the texL
Without
Washington: *
46 ° _ 34°N
+0.88
+0.63
+0.17
+0.27
+0.45
+0.70
+0.15
+0.37
rrdsrl
-0.56
+0.03
-0.74
-0.62
Coastal
Rainfall
Dates
(Dec 75)
4,5,6
11,12,13
20,21,22
25,26,27
Figure 3 shows the information sets of the SCAMS cloud liquid water distribu-
tion over the ocean and the coastal precipitation distribution without the stations in
Washington (46°N to 34°N) that correspond to the boxed correlations of Table 2.
Table 2 shows that antecedent time periods (At) associated with the maximum (boxed)
data correlations differ for each case, being 84 hours for Case 8 and 48 hours for Case
10. The reason is the difference in atmospheric circulation and storm movement.
The results for the storm cases examined in October and November 1975 showed
that the distribution of the 72-hour cumulative coastal rainfall was highly correlated
(linear correlation coefficients > 0.75) with the distribution of storm liquid water con-
tent over the ocean at a time period exclusively 60 to 72 hours earlier. The January
and February cases showed results similar to those of Table 2, with variable antece-
dent time periods. The analyses results are straightforward when storms systems move
from west to east, and our grid area (25 ° latitude x 26 ° longitude) encloses only one
system at a time as was the case in October and November (see Figure 1). For Dec-
ember, January, and February, however, two frontal-wave systems were frequently
present within the area of analysis, and a certain degree of discrimination must be
exercised to separate the liquid water distributions.
3.2 Discussion of the LFM Data
We requested and received forecasts (printouts) of the amount of LFM precipi-
tation corresponding to Cases 1 and 3 (October 1975) and Cases 5 and 7 (November
1975). Forecast periods up to 36 hours are available. Forecasts for longer time periods
237
c2E _
-°! u
_-o_
LATITU DE -_Vm LATITU DE --_m LATITU DE--_e_
I
J ¢ CORRELATION ../"
.................
u _. 0.92 _.r'.
¢<
o_.
....... _u,%',;;o-";,°,,°.
iI.........iI
.... " :; :,i. _ _ , "" ," "'1"" "'" "1 i i i,., i'"" "" "l"" """ "' _',1
TOTAL C OU O 20 10 B TOTAL L QUID H_O 10
Fig. 3-Data sets of observed 72-hour coastal rainfall between 46°N and 34°N lati-
tude, and of antecedent distribution of SCAMS liquid water over the ocean, that
correspond to the _ positive correlation coefficients of Table 2.
would have been preferable for comparison with the results of our October and
November case studies, which showed high positive correlation between coastal
rainfall distributions and the 60- to 72-hour antecedent SCAMS liquid water distri-
butions over the ocean. From the available data, the LFM 24--ho. ur precipitation
predictions were selected for further analysis and interpretation in the following
manner:
• The case studies for which LFM data are available were re-examined for
high positive correlation between the distributions of observed coastal rain-
fall and of SCAMS data over the ocean at antecedent time periods less than
the 60 to 96 hours considered previously (see At values in Table 2).
• For these "short-term" periods, our computer program analyzed the corres-
ponding data sets of observed rainfall over land and antecedent total vapor
and liquid water abundance over the ocean in a similar fashion, as shown in
Figures 2 and 3. However, the coastal distributions of LFM 24-hour precip-
itation prediction closest in validation time to the time of observed precipi-
tation (2400 PST) were included in the correlation.
• Values of LFM rainfall prediction at each location of the 27 coastal stations
used in the study were obtained from the printouts by linear interpolation.
These values provided the input to our computer program for correlation
with the microwave sensor data.
An analysis sample is summarized in Figure 4 for Case 3 (25-27 Oct. 75).
Available LFM 24-hour precipitation predictions, valid 1545 PST 25 Oct. and 0345
PST 26 Oct., are related to observed rainfall based on a midnight (2400 PST) ob-
servation time. In general, the distributions of SCAMS liquid water show a more
238
OO
b-
LATITU DE--degrm
SCAIVl$ f
, ,,z • 25 OCTOBER 1975
_o : -- :
7"°_
-_ o.*
_ o.o
_ o.z
25 OCTOBER 1975 ,_J L_ I
.I , ,m
LATITU DE --¢le_ee6
W
j8 u
u_o
_¢¢o.s
i.0 . , . , . ,
LFM 24-HR PREDICTION FOR
S z.l_ .25 OCTOBER 1975
.J _ 15:45 PST
<_ R4v) - -O.0e
T R(w) - +0.83
<z
°°
=,_ ,.o
.. , . , ,. , -
i.o
8 M
.J=
<_
_T "_
<Z
DO
O_.
LFM 24-HR PREDICTION FOR
.28 OCTOBER 1975
0_1:45 PST
Rlv) - +0.79
- R(w) - +0.__ l-_
LATITU DE--dqr_
)0
LATI TU DIE --deFm
OBSERVED
24:00p_.928_25OCTOBER 1975
.%
LATITU DE --dellre_
Fig. 4-Comparison between latitude variation of SCAMS-analyzed total
vapor and liquid water abundance over the ocean, and the observed and
LFM-predicted 24-hour cumulative coastal rainfall about 24 hours later.
Degree of linear correlation of the latitude variation between the pre-
cipitation data sets and the SCAMS data is indicated by R(v) and R(w)
for total vapor and liquid water, respectively (data refer to Case 3).
obvious relation than do the distributions of total vapor to observed and LFM-pre-
dicted rainfall at a later time. Most likely, total vapor would relate better if a
background component of atmospheric water vapor, which results from the gen-
eral increase in atmospheric temperature with decreasing latitude, were subtracted.
In Figure 4, the SCAMS liquid water distributions of 0047-0243 PST 25 Oct.
1975, shows a high positive correlation [R(w) = +0.92] with the distribution of
coastal rainfall observed 24 hours later, and a somewhat lower positive correlation
with the distributions of LFM-predicted rainfall about 15 hours later [ R(w) =
+0.83] and 27 hours later [R(w) = +0.69].
Analyses similar to those of Figure 4 were made for Cases 1, 5, and 7, and
will be continued for other cases to explore the input of passive microwave remote
sensor measurements of cloud liquid water to numerical prediction models.
4. CONCLUSIONS
Comparison and interpretation of information sets obtained from NIMBUS--6
passive microwave sensor data over the ocean and from precipitation records over
239
land indicate that rainfall along the coast of Oregon and California is related to
antecedent conditions of remotely sensed storm-cloud liquid water content over
the northeastern Pacific Ocean. Specifically, for each case examined, the distribu-
tion of SCAMS cloud liquid water across the storm system over the ocean fore-
shadows the relative distribution of coastal rainfall at a later time. Also, the ante-
cedent SCAMS liquid water distributions over the ocean generally show a somewhat
higher positive correlation with the observed coastal rainfall distributions than with
the LFM-predicted distributions. This may indicate that the passive microwave re-
mote sensor measurements contain information that can enhance the LFM predic-
tions of coastal rainfall distribution.
REFERENCES
Fawcett, E. B., "Current Capabilities in Prediction at the National Weather Service's
National Meteorological Center," Bull. Am. Met. Soc., 5_88,143-149 (1977).
Klein, W. H., and H. R. Glahn, "Forecasting Local Weather by Means of Model
Output Statistics," Bull. Am. Met. Soc., 55, 1217-1227 (1974).
Rasch, Glenn E., and Alexander E. MacDonald, "Map Type Precipitation Proba-
bilities for the Western Region," NOAA Technical Memorandum, WR-96
(February 1975).
240


Application of Nimbus-6 microwave data to problems in precipitation prediction for the Pacific west coast

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