The interaction of clouds and radiation is a particularly difficult issue in the study of climate change. Clouds have a large impact on the earth's radiation budget but the range of spatial and temporal scales and the complexity of the physical processes associated with clouds made these interactions difficult to simulate. The Department of Energy's Atmospheric Radiation Measurement (ARM) program was established to improve the understanding of the interaction of radiation with the atmosphere with a particular emphasis on the effects of clouds. To continue its role of providing data for the study of these interactions, the ARM program deployed an Atmospheric Radiation and Cloud Station (ARCS) in the tropical western Pacific. This site began operation in October 1996. The tropical western Pacific is a very important climatic region. It is characterized by strong solar heating, high water vapor concentrations, and active convection. The ARCS is equipped with a comprehensive suite of instruments for measuring surface radiation fluxes and properties of the atmospheric state and is intended to operate for the next 10 years. The ARCS is an integrated unit that includes a data management system, a site monitor and control system, an external communications system, redundant electrical power systems, and containers that provide shelter for the equipment as well as work space for site operators, technicians, and visiting scientists. The dataset the ARCS produces will be invaluable in studying issues related to clouds and radiation in the Tropics. The site is located in Manus Province, Papua New Guinea, at 2.060°S, 147.425°E, 300 km north of the island of New Guinea. Two more ARCS are planned for deployment across the tropical Pacific.
To measure the AOD with a radiometer, there must be a cloud-free line of sight to the Sun. Since the handheld instruments (Microtops and Sirebad radiometer) are manually operated, the operator can select cloud-free periods to perform the measurements, visually avoiding cloud contamination. However, the need for an operator results in fewer measurements than is possible with an automated instrument. The FRSR takes measurements throughout the day automatically, thus any cloud-free periods during the day will be sampled. However, since there is no operator continually monitoring the measurements, algorithms must be developed to screen the processed data for cloudy periods (described in section 2.3). The calibrated Micropulse LIDAR (MPL) allows measurements of the boundary layer AOD even during periods of cirrus clouds. In addition, since this is an active measurement, the AOD can also be measured during the night, while all the other methods require the Sun. However, this method also requires an algorithm to avoid periods of lower-level clouds and requires a clean, aerosol-free layer be defined above the aerosol. The MPL also only supplies the AOD at one wavelength, thus there is no information on the spectral variation of the AOD.In this paper we will present an overview of the methods used to obtain the AOD with each of these instruments. In addition, we will look at how the AOD and the spectral vari-20,811
A one‐layer, primitive equation model is presented for the atmospheric boundary layer over the marginal ice zone (MIZ). The model simulates the slow rate of inversion growth and rate of warming of the boundary layer seaward of an ice edge for off‐ice winds observed on two cruises in the Bering Sea by the NOAA R/V Surveyor. The horizontal temperature gradient in the boundary layer, caused by the oceanic heat flux seaward of an ice edge, induced an increase in wind speed with a maximum increase of 8% at 50 km seaward of the edge. At 100 km off ice, a momentum balance is established between accelerative terms (boundary layer baroclinity, momentum entrainment, synoptic‐scale scale pressure gradient) and decelerative terms (surface drag and the local pressure force resulting from inversion rise). Wind velocity in the boundary later over the MIZ during off‐ice winds is sensitive to changes in surface roughness. When an MIZ is modeled as a smooth interior (CD = 2 × 10−3) and a 30‐km‐wide rough marginal ice zone (CD = 3.8 × 10−3) with an unstable surface layer over the ocean, the model shows a decrease in wind speed of 9% at the windward side of the MIZ and an 18% increase in wind speed from 5 km interior to the ice edge to 40 km seaward of the edge. These results suggest an atmospheric mechanism for rafting at the windward side of the marginal ice zone, divergence of the ice at the edge, and ice‐band formation seaward of the edge.
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