North Slope of Alaska Site Hosts Guest Instruments for Arctic Aerosol Study
In addition to airborne measurements obtained at the North Slope of Alaska for the Indirect and Semi-direct Aerosol Campaign (ISDAC) in April, the ACRF site in Barrow also hosted several guest instruments throughout the campaign. Measurements from these additional instruments will provide important supplementary data to the continuous data collected at Barrow for investigating the role of aerosol physics and chemistry in regulating cloud microphysical properties in the Arctic. In particular, they will enhance the ISDAC data set with specific information about cloud and aerosol properties, aerosol indirect effects, precipitation, visibility (extinction), particle spectra, and ice crystal processes.
![Researchers from Environment Canada filled the roof of the Guest Instrument Facility to capacity during ISDAC.](https://webarchive.library.unt.edu/eot2008/20080917153902im_/http://www.arm.gov/images/nsa_guest0408.jpg)
ACRF operations staff helped Environment Canada researchers install 18 instruments for measuring small ice crystal particles, aerosols, precipitation amount, cloud cover and radiative fluxes, and extinction (visibility) at the Guest Instrument Facility in Barrow. Measurements from this instrument suite will be used to study ice and freezing fog, ice nucleation, visible extinction, the fog/drizzle effect on the surface heat budget, precipitation rate versus temperature, and precipitation rate-radar reflectivity relationships, and for model precipitation at the surface. Results from this project will also lead to a completely new data set related to atmospheric boundary layer processes in the Arctic. These data will improve remote sensing analyses of condensation, extinction, and precipitation processes, leading to a better understanding of model simulations of these processes.
![Inlet tubes for the indoor instruments, including the HTDMA and CCN counter, are covered with insulated tape for protection from the cold. Heated coils inside the inlets keep the lines from plugging with ice.](https://webarchive.library.unt.edu/eot2008/20080917153902im_/http://www.arm.gov/images/nsa_inlettube.jpg)
Additional guest instruments included the hemispheric flux spectroradiometer (HFS) and a combined differential mobility analyzer (DMA) / humidified tandem differential mobility analyzer (HTDMA) with integrated cloud condensation nuclei (CCN) counter. These instruments were housed inside the facility with inlets mounted on the outside to obtain sample volumes. The HTDMA measures size-resolved aerosol hygroscopic properties, or how an aerosol responds to a change in relative humidity. Measurements from this instrument, operated by researchers from Texas A&M University, will be particularly valuable for quantifying the contribution of specific classes of particles to the total concentration of CCN. Size-resolved CCN activity was directly measured by operating the DMA and CCN counter in series. The HFS obtains retrievals of changing cloud optical and microphysical properties on short time scales, and directly measures the shortwave component (350-2200 nm) of the spectrum. Provided by the University of California-San Diego, this instrument is operating at the ACRF Barrow site through May with additional funding from the National Science Foundation.