Research Support for International Polar Year (IPY)
International Polar Year Begins at ACRF with 3-week campaign in Barrow
This chart shows the spectral and height dependence of the infrared cooling rates for a mid-latitude summer profile. Note that the majority of the infrared cooling in the middle and upper troposphere occurs in spectral regions that RHUBC will investigate. (Larger image.)
Radiative cooling and heating in the mid-to-upper troposphere contribute significantly to the dynamic processes and radiative balance that regulate Earth's climate. However, accurate radiance observations in the far-infrared to evaluate the adequacy of the radiative transfer models (and improve them) have been limited by two things. First, due to the strength of the absorption of water vapor in this region, the atmosphere is largely opaque at the surface for the majority of locations around the globe. Second, until recently, there has been a lack of well-characterized and accurate radiometers to measure spectral radiation in this band.
Beginning on February 26, 2007, and lasting three weeks at the NSA site in Barrow, an international research team will conduct the Radiative Heating in Underexplored Bands Campaign, or RHUBC (pronounced "roobik"), to obtain detailed observations in the 17-100 micron (100-600 cm-1) and 6-7 micron (1400-1700 cm-1) spectral regions. These spectral bands are largely underexplored because they are normally opaque from the surface due to the strong absorption by water vapor; however, these bands do become semi-transparent in very low water vapor conditions. In particular, the so-called "Arctic window" opens up during the very dry conditions that are experienced during winter in high latitudes.
Aerosol Affects on Clouds To Be Studied
In April 2008 at the NSA locale, a research team will use an intensive airborne cloud and aerosol observing system to address one of the dominant scientific uncertainties in present understanding of climate-the interaction of aerosols with radiation and clouds. Data from this study, the Indirect and Semidirect Aerosol Campaign (ISDAC), will be used to test whether the cloud models can simulate the aerosol influence on the clouds. By running the cloud models with and without solar absorption by the aerosols, scientists can determine the semi-direct effect of the aerosol on the clouds. During the ISDAC campaign, many ancillary observing systems will be collecting data that will be synergistic with IPY for interpreting ISDAC data.
Data obtained during this campaign will be compared with measurements from the Mixed-Phase Arctic Cloud Experiment that was conducted at NSA in October 2004. This comparison will allow scientists to contrast the arctic aerosol and cloud properties at different times of the year. Researchers will use the data to study the differences in the microphysical and macrophysical properties of clouds and the surface energy balance, and also evaluate the ability of surface measurements to provide accurate retrievals aerosol, cloud, precipitation, and radiative heating in the Arctic.
Yearlong Study to Improve Polar Measurements of Radiative Energy
At ACRF's North Slope of Alaska site in Barrow, collocated sky radiometers are being evaluated to refine the methodology that accounts for infrared loss in polar conditions.
In the far northern reaches of Alaska, extended periods of both darkness and daylight occur throughout the year. Additionally, extremely cold weather conditions contribute to a harsh operating environment for research equipment. Therefore, broadband radiometers at the ACRF North Slope of Alaska (NSA) site are equipped with electric heaters inside the ventilators to keep frost and snow from causing interference with the measurements. Unfortunately, both of these issues—heating elements and the lack or surplus of sunlight at certain times of the year—appear to have an effect on correction methods used for known infrared loss problems in broadband shortwave measurements.
In August 2006, researchers began a 1-year field campaign to obtain the observational data needed for investigating and refining the infrared loss correction methodology for surface broadband measurements acquired at the NSA site. This campaign will not only produce the best surface radiation measurements possible at Barrow for the IPY time period, but will likely influence future measurements for polar research.
