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NOAA Highly Reflective Clouds
Entry ID: noaa_cdc043

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Abstract: The data presented here are the record of subjectively identified
areas of large-scale organized convection over the global tropics on
the daily daytime Mercator projection mosaics for a 15-year period
from 1971 to 1988. These convection areas appear as highly reflective
clouds in the visible-range mosaics and as white areas in the infrared
(IR) range. Highly reflective cloud (HRC) is defined here as a deep,
organized tropical convection system extending at least 200 km
horizontally. HRCs are composed of many individual convective cells
embedded within a common cirrostratus canopy. These cloud systems,
commonly known as cloud clusters, have been extensively studied in
recent years (e.g., Houze, 1982); they are responsible for most
tropical rainfall and are important components in the general
circulation of the atmosphere. These data originally appeared in the
Atlas of Highly Reflective Clouds for the Global Tropics: 1971-1985.
Until now, the most widely used indicator of large-scale convection
over the global tropics has been the outgoing longwave radiation (OLR)
data set (Gruber and Krueger, 1984). OLR data for 9 years were
recently summarized in NOAA Atlas No. 6 (Janowiak et al., 1985). In
the tropics, low values of OLR are found over areas covered by high
clouds with low cloud-top temperatures. In most cases, such clouds are
convective. However, low OLR values are also associated with
nonconvective clouds such as cirrostratus plumes. In contrast to the
OLR data, the HRC data presented here deliberately exclude
nonconvective cold clouds. The original idea for the creation of the
HRC data set came from a study conducted at the University of Hawaii
by Kilonsky and Ramage (1976). The study was based on the assumption
that most tropical rainfall occurs in organized convective systems
(cloud clusters), which appear as HRC in the polar-orbiting satellite
picture mosaics. Kilonsky and Ramage (KR) obtained monthly rainfall
data for Pacific atoll stations assumed to be representative of open
ocean conditions. They correlated these data with the number of days
per month having HRC. The presence of HRC was noted in grid squares of
the satellite picture mosaics. KR assumed a linear relationship
between the number of days with HRC at a particular location and the
amount of rainfall recorded there; a linear regression equation was
thus derived, linking the number of days with HRC cover (the
independent variable) to the observed rainfall (the dependent
variable). The correlation coefficient between the two variables was
0.75. Both the regression relationship and the correlation between the
two variables were found to be significant at the 1% level.
Subsequent to the original work of Kilonsky and Ramage, Garcia (1981)
used HRC data and the KR technique to produce rainfall estimates for
the tropical Atlantic Ocean. The estimates proved to be reasonably
close to those obtained by using more sophisticated geostationary
satellite techniques and to those estimated from shipboard radar
data. These results provided the impetus for extending the HRC data
set to the entire tropical belt, including land areas, and for
updating the HRC data continually. Note that the validity of using
HRC data from the daytime visible and IR Mercator projection mosaics
as a means of estimating monthly rainfall amounts is greatly affected
by the mean diurnal cycle of convection over different regions of the
tropics. There is some evidence (e.g., Griffith et al., 1980) that
convection over land areas has a fairly pronounced maximum during the
late evening hours, whereas convection over oceans is more evenly
distributed throughout the 24-hour cycle. Thus, a rainfall estimation
scheme (such as the KR technique) that samples conditions only once a
day during daylight hours will tend to underestimate rainfall over
land areas. In addition, changes in the time of passage of
polar-orbiting satellites can significantly change cumulative amounts
of convection observed in a given area.

NOAAServer Codes: [POL 25 -25 180 -180] ; nodateline preview obtain

Purpose: Scientific research.

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Geographic Coverage
 N: 25.0 S: -25.0  E: 180.0  W: -180.0

Data Set Citation
Dataset Creator: NOAA-CIRES Climate Diagnostics Center
Dataset Title: NOAA Highly Reflective Clouds
Dataset Release Date: 1988-01-31
Dataset Release Place: Boulder, CO
Dataset Publisher: NOAA-CIRES Climate Diagnostics Center
Online Resource:

Temporal Coverage
Start Date: 1971-01-01
Stop Date: 1988-01-31

Location Keywords

Science Keywords

ISO Topic Category

DODS >Distributed Oceanographic Data System    [Information]
ESIP >Earth Science Information Partners Program    [Information]
OPENDAP >Open-source Project for a Network Data Access Protocol    [Information]

Access Constraints

Use Constraints
None. Acknowledgement of CDC would appreciated in products derived
from these data.

NOAA Highly Reflective Clouds [POL 25.00 -25.00 180 -180]

Data Set Progress

Data Center
Climate Analysis Branch, Physical Sciences Division, Earth System Research Laboratory, OAR, NOAA, U.S. Department of Commerce    [Information]
Data Center URL:
Dataset ID: CDC043

Data Center Personnel
Email: at

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Extended Metadata Properties
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Creation and Review Dates
DIF Creation Date: 2002-03-22
Last DIF Revision Date: 2017-08-24