Abstract
Abstract. Multi-instrument, ground-based measurements provide unique and comprehensive data sets of the atmosphere for a specific location over long periods of time and resulting data compliment past and existing global satellite observations. This paper explores the effect of ice hydrometeors on ground-based, high-frequency passive microwave measurements and attempts to isolate an ice signature for summer seasons at Summit, Greenland, from 2010 to 2013. Data from a combination of passive microwave, cloud radar, radiosonde, and ceilometer were examined to isolate the ice signature at microwave wavelengths. By limiting the study to a cloud liquid water path of 40 g m−2 or less, the cloud radar can identify cases where the precipitation was dominated by ice. These cases were examined using liquid water and gas microwave absorption models, and brightness temperatures were calculated for the high-frequency microwave channels: 90, 150, and 225 GHz. By comparing the measured brightness temperatures from the microwave radiometers and the calculated brightness temperature using only gas and liquid contributions, any residual brightness temperature difference is due to emission and scattering of microwave radiation from the ice hydrometeors in the column. The ice signature in the 90, 150, and 225 GHz channels for the Summit Station summer months was isolated. This measured ice signature was then compared to an equivalent brightness temperature difference calculated with a radiative transfer model including microwave single-scattering properties for several ice habits. Initial model results compare well against the 4 years of summer season isolated ice signature in the high-frequency microwave channels.
Highlights
Better characterization of precipitation in the Arctic is fundamental to improve our understanding of the hydrological cycle and mass balance of the polar ice sheets
Summit Station was the site of the Greenland Ice Sheet Project 2 (GISP2) ice core project, and has been expanded to a continuously operational science facility dedicated to studying the atmosphere and ice sheet properties of the GIS (Dansgaard et al, 1993)
The lower-frequency channels are comparably insensitive to ice (Johnson et al, 2012), so we focus on the 23.84 and 31.40 GHz channels to derive a first-order estimate for the MWR retrieval (MWRRET) liquid water path (LWP) and PWV biases from the ice signature
Summary
Better characterization of precipitation in the Arctic is fundamental to improve our understanding of the hydrological cycle and mass balance of the polar ice sheets. We propose that the enhanced BT from the ice hydrometeors can be isolated and quantified by combining the observed data from instruments in the Integrated Characterization of Energy, Clouds, Atmospheric State, and Precipitation at Summit project (ICECAPS; Shupe et al, 2013) with radiative transfer models of the gas and liquid in the atmosphere. By doing this we are enhancing the K10 study by expanding it to multiple years of data in an Arctic environment with very low amounts of liquid water and precipitable water vapor, which present unique challenges. We demonstrate an initial scattering model of the ice and compare these results to the observed signature (Sect. 5)
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