IPASRC

A Second International Pyrgeometer and Absolute Skyscanning Radiometer Comparison (IPASRC II) was held at the North Slope of Alaska (NSA) site on March 5 - 16, 2001. IPASRC I took place at the Southern Great Plains (SGP), Cloud and Radiation Testbed (CART). The stated objective of IPASRC II was "to learn more about the accuracy of longwave measurements and calculations at low temperatures." It appeared that spring would be the best time to schedule the intensive operational period (IOP) because that is when low temperatures most overlap with clear skies at the NSA.

In addition, Alexander Makstas of the International Arctic Research Center at the University of Alaska in Fairbanks inquired about deploying the type of radiometric instrumentation that he and others used for decades at the former Russian "North Pole" stations on the drifting sea ice and at other Russian arctic research stations. The objective was to establish the degree to which this instrumentation produces data streams comparable to those produced by the instrumentation used by ARM and NOAA/CMDL. Since the Russian data is now largely available, demonstrated comparability would be of considerable value to the climate research community. Makstas has funding from NOAA to proceed with this effort. It has been suggested that it would be appropriate to deploy the instrumentation during IPASRC II. A separate IOP may also be scheduled.

Activity Summary

The second IPASRC II was successfully carried out at the NSA-CART site at Barrow from March 5 to March 15, 2001.

During most of the time, great weather and clear skies provided measurements of longwave downward irradiances between 130 and 170 Wm-2 and air temperatures between -25 and -35 degrees Celsius. All pyrgeometers were mounted in ventilators on trackers to shade them from the direct sun. The measurements of these pyrgeometers can directly be compared to several scans of the Absolute Sky-Scannning Radiometer (ASR) during 5 clear sky nights.

First preliminary analyses of data from the pyrgeometers, which already participated in IPASRC I, proved again that a field calibration improves the accuracy of pyrgeometers compared to a black body calibration. Furthermore, the use of the IPASRC I calibration coefficients on the IPASRC II data showed that pyrgeometers preferably have to be field calibrated in conditions they will be used in order to provide accurate measurements of longwave downward irradiance.

One regular Vaisala RS-80 sonde was launched twice a day (noon and midnight Universal Time Coordinates) during the whole IOP. During clear-sky nights, the same balloon was additionally loaded with a Snowwhite chilled mirror hygrometer, in order to get the best possible humidity measurements. Together with the data from the Microwave Radiometer (MWR), these data will serve as input for LBLRTMs. To compare such model calculations with the measured longwave irradiance and the extended range is another goal of IPASRC II.

Timeline

Campaign Data Sets