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Observations
The various ARM observations used in the analysis of the SCM and/or GSM
forecasts are described below. At present, observations are limited to
only a few variables. This page will be updated as more observations
become available.
Temperature and Relative Humidity Profiles
Southern Great Plains
Vertical profiles of temperature and relative humidity are measured using
radiosondes that are a component of the
Balloon-Borne Sounding System (BBSS).
Normally, the radiosondes are launched from the Central Facility every
6 hours (00, 06, 12, and 18 GMT).
Downwelling Surface Shortwave Radiation
Southern Great Plains
The observations of DWSO at the ARM SGP site are from the Oklahoma Mesonet
system that consists of 116 different surface monitoring stations, of which
72 are within the SCM domain. The observed data shown in the figures and tables
is an average of the downwelling surface shortwave flux measured at these 72 stations.
Tropical West Pacific
The observations of DWSO at the ARM TWP site are from the
Multi-Filter Rotating Shadowband Radiometer (MFRSR) and the
ARCS Downwelling Radiation System (SKYRAD) instruments
located on Nauru Island near the center of the SCM domain. The observed
data shown in the figures and tables is an average of the downwelling surface shortwave
flux measured by these two instruments.
Note: There are only two surface measurements used to characterize the entire
SCM domain at the TWP site. Comparison to the model data which are
representative of an average over the entire domain should proceed with caution.
North Slope of Alaska
The observations of DWSO at the ARM NSA site are from the
Multi-Filter Rotating Shadowband Radiometer (MFRSR)
instrument located at Barrow, Alaska near the center of the SCM domain.
Note: There is only one surface measurement used to characterize the entire
SCM domain at the NSA site. Comparison to the model data which are
representative of an average over the entire domain should proceed with caution.
Precipitation
Southern Great Plains
The observations of precipitation at the ARM SGP site are from the Oklahoma Mesonet
system that consists of 116 different surface monitoring stations, of which
72 are within the SCM domain. The observed data shown on these figures
is an average of the precipitation measured at these 72 stations.
Overhead Cloud Amount and Outgoing Longwave Radiation (OLR)
Southern Great Plains
Observations of cloud amount and OLR at the ARM SGP site are obtained from GOES satellite
measurements using retrieval algorithms developed by
Pat Minnis's group at NASA Langley.
This data set generally has a time resolution of 30 minutes
and covers the entire SGP site.
Tropical West Pacific
Observations of OLR at the ARM TWP site are obtained from GMS satellite
measurements produced by the Meteorological Satellite Center, Japan Meteorology
Agency. The data are monthly means produced on a 2.5 x 2.5
degrees latitude-longitude grid.
Vertical Profiles of Cloud Fraction
Southern Great Plains, Tropical West Pacific and North Slope of Alaska
TheMillimeter Wavelength
Cloud Radar (MMCR) instrument located at each of the ARM sites
is designed to produce near-continuous radar reflectivities that can be used to
obtain information on clouds and cloud boundaries. The MMCR is a zenith oriented
radar and operates at a frequency of 35 GHz. An algorithm
(Clothiaux et al. 2000: J. Appl. Meteorol., 39, 645-665.)
is employed to produce the vertical boundaries (top and bottom heights) of clouds
using radar reflectivities from the MMCR along with co-located lidar measurements.
A profile of cloud frequency as a function of height is obtained by averaging over
time. Assuming there are no preferential regions of cloud formation within the
site and that the averaging period is long enough, this cloud frequency profile
can also be used as a surrogate for the cloud fraction over
the entire ARM site.
Sensible and Latent Heat Fluxes
Southern Great Plains
Measurements of the sensible and latent heat fluxes are obtained from a network of
Energy Balance Bowen Ratio (EBBR)
systems located at the ARM SGP site. There are 12 systems currently operating at the SGP
site. The observed data shown on these figures is an average of the fluxes measured
by these 12 systems.
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