15 research outputs found
Plant structure predicts leaf litter capture in the tropical montane bromeliad Tillandsia turneri
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ARM Facilities Newsletter
The ARM Program studies clouds, sunlight, and their interactions to understand how they affect Earth's climate. One of the many instruments used to look at clouds at the SGP CART site is the micropulse lidar (MPL; ''lidar'' was coined from ''light distance and ranging''). The ARM Program operates five MPLs. One is at the SGP central facility; one is at the North Slope of Alaska CART site in Barrow, Alaska; and three are for use at the Tropical Western Pacific site on Nauru and Manus islands. The MPL is a remote sensing instrument used to measure the height of overhead clouds and particles. An eye-safe laser in the system directs a beam vertically. As short pulses of laser light travel through the sky, they may encounter water droplets or aerosol particles in the atmosphere. These particles intercept the laser light and scatter it in different directions. Some of the scattered light returns to Earth's surface. A receiver on the ground collects backscattered light that bounces off atmospheric particles and uses the information to determine the distance between the ground and the particles. The signals detected are collected and plotted. The greater the signal strength, the more scatterers are present in the atmosphere. A plot based on this relationship provides a ''snapshot'' of the cloud overhead and shows the structure inside the cloud. In addition, the information gathered from the MPL can be used to determine the height of the planetary boundary layer, the well-mixed layer of the atmosphere that develops during daytime hours as the sun heats Earth's surface and sets up vertical mixing. Small airborne particles that can also be detected include smoke or dust carried into the atmosphere. This information is valuable to climate researchers. Because the MPL uses an eye-safe laser, it is not a danger to pilots of planes flying overhead and can be run continuously. The availability of continuous data is a great benefit to researchers in their efforts to incorporate the interactions of clouds and solar radiation into climate models. Another strength of the MPL is long-range detection. The MPL can detect clouds at altitudes above six miles and stratospheric aerosols as high as nine miles
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ARM Facilities Newsletter
The February 1998 issue of this newsletter discussed the Measurement of Pollution in the Troposphere (MOPITT) instrument that was to be tested at the SGP CART site before being launched aboard a NASA satellite to make precise, detailed measurements of tropospheric carbon monoxide and methane from space. The instrument was successfully launched on NASA's Terra satellite on December 18, 1999, by an Atlas IIAS rocket from Vandenberg Air Force Base in California and began collecting data at the end of February 2000. The instrument was designed by Dr. Jim Drummond, a physicist at the University of Toronto. The MOPITT Validation Exercise (MOVE) Campaign is schedule to take place at the SGP site from April 30 to May 18, 2001. Researchers will measure carbon monoxide by using instruments onboard the DOE Cessna Citation aircraft and other instruments located at the SGP CART. The data gathered will be compared with those collected by the MOPITT instrument to validate its performance thus far. MOPITT, which is scheduled for a five-year mission, will provide the first long-term global measurements of carbon monoxide and methane gas levels in roughly the lowest 10 miles of the atmosphere. Carbon monoxide and methane and their roles as greenhouse gases in global warming are of great interest. Greenhouse gases can trap escaping heat from Earth's surface, potentially increasing atmospheric temperatures. Carbon monoxide is a by-product of combustion, resulting primarily from industrial processing or biomass burning. Carbon monoxide levels in the atmosphere have been rising, indicating a problem. Normally, carbon monoxide is removed from the atmosphere by the hydroxyl radical, which can react with and remove many pollutants from the air
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ARM Facilities Newsletter
This Monthly newsletter discusses the following topic: New Atmospheric Profiling Instrument Added to SGP CART Suite--A new atmospheric profiling instrument at the SGP CART site is giving researchers an additional useful data stream. The new instrument is a microwave radiometer profiler (MWRP) developed by Radiometrics Corporation
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A three-month comparison of hourly winds and temperatures from co-located 50-MHz and 915-MHz RASS profilers
The Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program has operated a 915-MHz and a 50-MHz radar wind profiler (boundary layer profiler (BLP) and tropospheric profiler (TP), respectively], each coupled with a Radio Acoustic Sounding System (RASS) since April 1994 at its Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) central facility in north central Oklahoma. The dual system is designed to provide continuous wind profiles from near the surface to 12 km or more and virtual temperature profiles from near the surface to 6 km. Because the BLP has a larger antenna than many other 915-MHz systems, the wind profiles sampled by the two systems overlap between 1.5 km and 5.5 km. The two systems are adjacent, so the wind profilers sample almost identical air masses in their overlap region during the averaging period. Nevertheless, the two RASS systems can be compared, and methods can be devised to estimate the temperature profile in the inaccessible region. Data used in all comparisons and calculations discussed below are consensus-averaged values supplied by the profiler software. Although the spectra and moments from the data are available, they were not accessed for this analysis
Estimating the Long-Term Hydrological Budget over Heterogeneous Surfaces
Estimates of the hydrological budget in the Walnut River Watershed (WRW; 5000 km2) of southern
Kansas were made with a parameterized subgrid-scale surface (PASS) model for the period 1996–2002.
With its subgrid-scale distribution scheme, the PASS model couples surface meteorological observations
with satellite remote sensing data to update root-zone available moisture and to simulate surface evapotranspiration
rates at high resolution over extended areas. The PASS model is observationally driven,
making use of extensive parameterizations of surface properties and processes. Heterogeneities in surface
conditions are spatially resolved to an extent determined primarily by the satellite data pixel size. The
purpose of modeling the spatial and interannual variability of water budget components at the regional scale
is to evaluate the PASS model’s ability to bridge a large grid cell of a climate model with its subgrid-scale
variation. Modeled results indicate that annual total evapotranspiration at the WRW is about 66%–88% of
annual precipitation—reasonable values for southeastern Kansas—and that it varies spatially and temporally.
Seasonal distribution of precipitation plays an important role in evapotranspiration estimates. Comparison
of modeled runoff with stream gauge measurements demonstrated close agreement and verified the
accuracy of modeled evapotranspiration at the regional scale. In situ measurements of energy fluxes compare
favorably with the modeled values for corresponding grid cells, and measured surface soil moisture
corresponds with modeled root-zone available moisture in terms of temporal variability despite very heterogeneous
surface conditions. With its ability to couple remote sensing data with surface meteorology data
and its computational efficiency, PASS is easily used for modeling surface hydrological components over an
extended region and in real time. Thus, it can fill a gap in evaluations of climate model output using limited
field observations