Events
SEAS Colloquium in Climate Science (SCiCS)
Thursday, February 23, 2012 - 2:45pm - 3:45pm
Columbia University
Morningside Campus
S.W. Mudd, Room 214
Mark Zondlo
Department of Civil and Environmental Engineering, Princeton University
"Ice Supersaturated Regions from Global Aircraft Observations: New Insights into Cirrus Cloud Formation"
Cirrus clouds have large but highly uncertain impacts on Earth's climate. Cirrus cloud formation requires supersaturation of the relative humidity with respect to ice (RHi), and in that regard, ice supersaturated regions are the birthplaces of cirrus clouds. However, relatively little is known about the scales, magnitudes, and mechanisms of the precursor ice supersaturated regions that form cirrus clouds. Sampling in the upper troposphere by itself is challenging, water vapor measurements may be biased by sampling and calibration artifacts, and clouds form at scales much smaller than model grid boxes or remote sensing measurements. We have developed a fast (25 Hz), accurate (6%), and precise (<1%) open-path vertical cavity laser hygrometer that flies routinely on the NSF Gulfstream-V research aircraft. Here we use the first global yet high-resolution aircraft-based observations to show that ice supersaturated regions are very small (km), nearly two orders of magnitude smaller than previous measurements. In addition, RHi spatial variability is dominated by water vapor inhomogeneities, as opposed to temperature anomalies, on scales from 200 m to 100 km. These results are in sharp contrast to the frequent assumption that temperature variability drives RHi variability at cloud scales. By examining tracer/tracer correlations and other microphysical parameters, we show that while adiabatic lift and cooling is important on the synoptic scale, it is the highly variable water vapor field that is most important to cirrus cloud formation at cloud scales.
Host: V. Faye McNeill
Department of Civil and Environmental Engineering, Princeton University
"Ice Supersaturated Regions from Global Aircraft Observations: New Insights into Cirrus Cloud Formation"
Cirrus clouds have large but highly uncertain impacts on Earth's climate. Cirrus cloud formation requires supersaturation of the relative humidity with respect to ice (RHi), and in that regard, ice supersaturated regions are the birthplaces of cirrus clouds. However, relatively little is known about the scales, magnitudes, and mechanisms of the precursor ice supersaturated regions that form cirrus clouds. Sampling in the upper troposphere by itself is challenging, water vapor measurements may be biased by sampling and calibration artifacts, and clouds form at scales much smaller than model grid boxes or remote sensing measurements. We have developed a fast (25 Hz), accurate (6%), and precise (<1%) open-path vertical cavity laser hygrometer that flies routinely on the NSF Gulfstream-V research aircraft. Here we use the first global yet high-resolution aircraft-based observations to show that ice supersaturated regions are very small (km), nearly two orders of magnitude smaller than previous measurements. In addition, RHi spatial variability is dominated by water vapor inhomogeneities, as opposed to temperature anomalies, on scales from 200 m to 100 km. These results are in sharp contrast to the frequent assumption that temperature variability drives RHi variability at cloud scales. By examining tracer/tracer correlations and other microphysical parameters, we show that while adiabatic lift and cooling is important on the synoptic scale, it is the highly variable water vapor field that is most important to cirrus cloud formation at cloud scales.
Host: V. Faye McNeill
Categories: