One of the goals of the First ISCCP Regional Experiment (FIRE) is to relate the relatively small scale (spatial and temporal) Intensive Field Observations (IFO) to larger time and space domains embodied in the Extended Time Observations (ETO) phase of the experiment. The data analyzed as part of the ETO are to be used to determine some climatological features of the limited area which encompasses the Marine Stratocumulus IFO which took place between 29 June and 19 July 1987 off the coast of southern California

Harrison, Edwin F.

Minnis, Patrick

Young, David F.

English

NASA Technical Reports Server

 OB^ s 
Patrick Minnis and Edwin F. Harrison 
Hampton, Virginia 23665-5225 
and 
David F. Young 
Aerospace Technologies Division, Planning Research Corporation 
Hampton, Virginia 23666 
Atmospheric Sciences Division, NASA Langley Research Center 
1. Introduction 
One of the goals of the First ISCCP Regional Experiment (FIRE) is to 
relate the relatively small scale (spatial and temporal) Intensiv? Field 
Observations (IFO) to larger time and space domains embodied in the Extended 
Time Observations (ETO) phase of the experiment. The data analyzed here as 
part of the ET0 are to be used t o  determine some climatological features of 
the limited area which encompasses the Marine Stratocumulus IF0 which took 
place between 29 June and 19 July 1987 off the coast of southern California 
(Kloessel et al., 1988). 
2. D a t a  and methodology 
infrared (10.5 pm) radiances taken by the series of Geostationary 
Operational Environmental Satellites (GOES) which operated at various 
longitudinal positions bemeen 1983 and 1987. 
confined to the month of July during each year. 
satellite, subsatellite longitude, dates of analysis, and satellite viewing 
zenith angle, VZ, relative t8 the center of the stratocumuAus limitgd area. 
The latter is defined by 140 W and 115OW longitudes and 40 N and 25 N 
latitudes. 
would fall in the domain and that areas with stratocumulus presumably free 
from continental influences would bg included. 
threshold method described by Minnis et el. (1987). Resulting parameters 
include cloud amount, cloud-top temperature, cloud albedo, and clear-sky 
temperature and albedo for each region. All of the cloud parameters were 
derived for total, low (< 2 km), middle (2-6 Ian), and high (> 6 km) clouds. 
Because of the extremely high values (up to 79 ) of VZ, the 1987 cloud 
amounts were adjusted to the viewing angles found for the 1985 data using 
the technique outlined by Minnis (1988). This correction lowered the cloud 
amounts by 2-4% absolute cloud amount. 
(0.2 - 5.0 pm) albedo over clear or cloudy areas. The narrowband visible 
radiances are converted to broadband radiances using the same conversion 
formula and coefficients as Minnis et al. (1987) for 1983, 1985, and 1986. 
That calibration produced good estimates of clear-sky reflectance and 
eonsistent mean cloud albedos for all 3 years. 
the same throughout the period. 
A different approach wa 
instruments were different e previous years (see Tab1 
offset voltage was much low 
the square root of radiance 
model of Minnis arrison (1984) calibrated with the same formula used 
The primary data for this study are 3-hourly, 8-km visible (0.65 pm) and 
Analysis of the data was 
Table I lists the 
These bounds were selected to ensure that IF0 flight tracks 
The data were analyzed on a 2.5 grid with the hybrid bispectral 
Albedo here refers to the mean top-of-the-atmosphere broadband shortwave 
The offset voltage remained 
pplied for the 1987 GOES-East 
e clear-sky visible count (proportional to 
s @stimat@d using the ocean bidirectional 
201 
https://ntrs.nasa.gov/search.jsp?R=19910001175 2020-03-19T20:14:42+00:00Z
for the previous years. 
derived from the 1987 GOES-East data. 
calibrated model results and used to fit the GOES-East radiances by forcing 
the line through the pair of known offset counts. This "calibration" is 
very uncertain for high radiances but it provides a reasonable estimate of 
clear-sky reflectance essential for derivation of the cloud parameters. 
approach to the calibrations taken here is necessitated by the lack of a 
consistent calibration source at the present time. 
Clear-sky counts over the limited area were also 
These data were plotted against the 
The 
3. Results 
All of the results presented here exclude the results for 1984 and 1987 
GOES-West since they were unavailable at the time of printing. 
shows the mean total and layer cloud amounp for the entire period. 
total cloudiness is less thano70% within 5 
min&mum occurging north of 35 N. 
125 W and 130 W south of 30 N before decreasing to the southwest. 
the clouds are found in the lowest layer (Fig. lb), especially in the 
southern half of the domain. Midlevel and high clouds constitute less than 
10% of the total over all marine areas except in the northwest corner (Figs. 
IC and Id). Total cloudiness over the adjacent land areas is less than 30%. 
The interannual standard deviations of the monthly mean total cloudiness for 
the period range from 3% in the southwest to nearly 12% over the areas of 
maximum cloudiness. 
The clear-sky temperatures (Fig. 2) over the ocean range from 285K in 
the north to 290K in the southeast corner of the region. The interannual 
standard deviations of these temperatures are less than 1K over most of the 
ocean areas. 
regions of the grid. Mean equivalent blackbody cloud-top temperatures in 
Fig. 3 also show a general north-south decrease. The cloud-top isotherms, 
however, are skewed to the north ridging near the coast while the clear 
isotherms are more parallel with latitude troughing near the coast. 
results in a 1K to 2K east-west gradient in the difference between the two 
quantities. This difference is about 6K on average indicating that the 
clouds are confined to the boundary layer as expected. 
deviations of mean cloud-top temperature range from 0.5K to 1.5K over areas 
with less than 5% midlevel cloud cover. 
Mean clear ocean albedos (Fig. 4) range between 0.10 and 0.12 with 
standard deviations generally < 0.01. Cloud albedos (Fig. 5) over the ocean 
regions are typically around 0.35. 
the coast and along a line southwestward from 3S0N, 122OW. 
albedo (0.32) is found over the southeastern corner of the region. 
Interannual standard deviations of cloud albedo vary from less than 0.01 
over the northwest corner to 0.06 over the southeastern regions. 
diurnal variations. 
between 0300 U T  and 0900 LST with a minimum during the afternoon. 
Epecial regions have been defiped to determine if any significant 
differences exist between the diurnal variations of the stratocumulus clogds 
near the coast a8d far frgm the coagt. The pachfic (PAC) region is a 7.5 
box between 3265 N and g5 N and 120 W and 122.5 W; the IF0 region is 
bordered by 35 N and 30 N and 125 Woand 120 W, gith an additional 2.5' 
region to the east centered at 31.3 N and 118.8 W. 
hourly means for the IF0 and PAC. The diurnal range over the PAC is 25% 
Figure 1 
Mean 
of the California coalst with the 
Cloud cover increases to a maximum between 
Most of 
Values greater than 1K are found over some of the western 
This 
Interannual standard 
Maximum marine cloud albedos occur near 
Minimum cloud 
Cloud cover over both the marine and land areas undergoes distinct 
Over all of the ocean regions, cloud amount peaks 
Two 
Figure 6 compares the 3- 
202 
greater than that near the shore. Minimum cloudiness appears to occur 
earlier over the PAC and remain longer than it does over the IF0 region. 
4. Discussion 
(1976). 
night and morning hours in the analysis. 
surface temperatures over the area (Reynolds, 1983) are between 2K and 4K 
lower than the clear-sky results shown here. 
from the coast toward the southwest are primarily due to water vapor 
attenuation and some cloud contamination. 
are probably responsible for the difference gradient. 
between clear-sky and cloud-top temperatures may be related to the strength' 
of the inversion over the marine boundary layer. 
maximum albedo extending from the coast, cloud albedos are within'l - 2% of 
those found in previous studies (e.g., Hinnis et al.. 1987) over areas of 
stratocumulus over the open ocean. The cloud albedo maximum could result 
from an infusion of continental aerosols near the coast. Diurnal variations 
of cloudiness are also similar to those found over other parts of the 
Pacific (e.g., Hinnis et al., 1987). Coastal-open ocean differences in the 
diurnal range may be tied to variations in the strength of the inversion and 
liquid water content. 
5. ConclWng reimarka 
The preliminary results described in this paper provide a long-term 
perspective of the large-scale cloudiness over the stratocumulus IF0 region. 
Inclusion of data from GOES-West taken during 1984 and 1987 will complete 
this .S-year climatology of July marine stratocumulus over the IF0 limited 
area. Measurements taken during the IF0 will improve our understanding of 
the behavior of the various parameters observed in this study and over 
larger time and space scales. 
provide the link between the IF0 and stratocumulus over the rest of the 
globe and other seasons. 
6. References 
Kloessel, K. A., B. A. Albrecht, and D. P. Wylie, 1988: FIRE Harine 
Stratocumulus Observations - -  Summary of Operations and Synoptic 
Conditions. FIRE TR No. 1, 171 pp. 
Minnis, P., 1988: Viewing Zenith Angle Dependence of Cloudiness Determined 
from Coincident GOES-East and GOES-West Data. Submitted to 3 .  Geovhvs, 
Hinnis, P. and E. F. Harrison, 1984: Diurnal Variability of Regional Cloud 
Cloud amount patterns are similar to those compiled by S8dler et al. 
The slightly higher values here may be the result of Including 
Climatological values of sea 
The differences which increase 
Atmospheric moisture variations 
The differences 
Except for the prea of 
This analysis and similar ET0 results will 
Res. 
and Clear-Sky Radiative Parameters Derived from GOES Data. Part 111: 
November 1978 Radiative Parameters. J .  Cl im.  ADD^. M etL, 23, 1033-1051. 
Minds, P., E .  F. Harrison, and G. G. Gibson, 1987: Cloud Cover Over the 
Equatorial Eastern Pacific Derived from July 1983 ISCCP Data Using a 
Hybrid Bispectral Threshold Method. J .  Geovhvs. R esL, 92, 4051-4073. 
Reynolds, R. W., 1983: A Comparison of Sea Surface Climatologies. J. A D D L  
Sadler. J. D., L. Oda, and B. J. Kilonsky, 1976: Pacific Ocean Cloudiness 
w, 22, 447-459. 
from Satellite Observations. UHMET 76-01, Univ. of Hawaii, Honolulu, 
137 pp. 
,’ 
135.0 
135.0 
1 m.7 
108.7 
75.0 
135.0 
Dotes I VZ (dog) 
Jury 17-31. 1983 
JJV 1-31, 1984 
Julr 1-31, 1WS 
.klu 1-31, lob6 
2-31,1#87 
&& 1-31, 1987 
Table 1. S d e l f i  Batcl chamcterbtlca. (Note that GOES-6 ond GOES-7 
~ l r b  01- ta G O E S - W d  ad GOES-EOS~.) 
14# 1 as 130 12s 110 I 
WEST UNCtTUDE WEST I D K l T U D E  
(c) Middle 
I 
WEST LDNGlTUDE 
Fig\rre 1. Mua cloud fa July (1983 - 1987). 
204 
Figure 2. Mean ckar-sky tmpcmmx fa Figure 4. Mua cleu-sky .IbeQs fa July 
July (1983 * 1987). (1983 - 1987). 
or . 
I I I I I 
fro f 35 #30 I I S  f m  t t l  
.EST LONlctTUDE 
Fig~re 3. bkancl~ud- Figure 5. Mean cloud albedos fa July (1983 
July (1983 - 7 1 87). - 1987). 
- .'7 BO 
c 
7 IF0 REGION 
--- PAC REGION 
0 
w1 I I I I 
0 8 12 in  24 
LOCAL TIME (HR) 
Figure 6. D i d  variation of cloud mer for 
July (1983 - 1987). 
205 


Extended time observations of California marine stratocumulus clouds from GOES for July 1983-1987

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