ARM Observations


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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