Allison Parker Remote Sensing of the Oceans and Atmosphere
Allison ParkerRemote Sensing of the Oceans and Atmosphere
AbstractThe milli-meter wavelength cloud radar (MMCR) is the
first fully operational, unattended radar for the sole purpose of remote sensing of clouds. The MMCR operates at wavelengths about ten times smaller than conventional radar systems, allowing for better remote sensing of non-precipitating clouds. There are several MMCRs currently in use by the Atmospheric Radiation Measurement (ARM) program in Oklahoma, Alaska, and the western south Pacific. These MMCRs provide statistical surveys of cloud location and frequency, information about cloud microphysical characteristics, and produce data for basic research into cloud microphysics. The data provided by the MMCRs is important for research into climate change and cloud radiative processes.
Atmospheric Radiation Measurement Program (ARM)
Created in 1989 with funding from the US DOE
Primary Objective: Improved scientific understand of physics related to interactions of clouds and radiative feedback processes in atmosphere
Main Sites: Oklahoma, Alaska, and Western Pacific
ARM Field Research SitesSouthern Great Plains - Oklahoma
Dedicated Nov. 1992Chosen because
homogenous geography, easy accessibility, variability of climate cloud type and surface flux properties, and variation of temperature and humidity
Source: www.arm.gov
ARM Field Research SitesHigh Latitudes – North Slope of AlaskaDedicated July 1997Data being used to
refine models and parameterizations as they related to the Arctic
Reasons to study climate change in high latitudes include ice & snow, dry climate, & major “pumps” for global ocean currents
Source: www.arm.gov
ARM Field Research SitesTropical Western Pacific
Located in Australia, Nauru Island, & Papua New Guinea
Region plays a large role in El Nino
Pacific “warm pool” supplies heat and moisture for deep convective cloud systems that produce high altitude cirrus clouds Source: www.arm.gov
Milli-Meter Wavelength Cloud Radar (MMCR)
Developed by the ARM Program for quantifying properties of radiatively important clouds
Main purpose is to determine cloud boundaries & radar reflectivity up to 20km
Doppler capability for measurement of cloud constituent vertical velocities
Primary Measurements: Horizontal Wind, Radar Doppler, Radar Reflectivity, Vertical Velocity Source: www.arm.gov
MMCR DesignVertically pointing,
single polarization, Doppler system operating at 35Ghz (λ = 8.7 mm) or 94 Ghz (λ = 3.1mm)
Low peak power transmitter for long term reliability
High-gain antenna and pulse-compressed wave forms to maximize sensitivity and resolution
Sources: Moran, et al. , www.arm.gov
Characteristic Values for Meteorological Radars
Examples of MMCR Data
Examples of MMCR DataMode 1 – Samples lowest kilometers only with high sensitivity
Mode 2 – Most sensitive above 3 km
Mode 3 – Good general mode, not as sensitive to thin clouds as Mode 2
Mode 4 – Less sensitive than modes 2 and 3 but does not saturate as easily in higher reflectivity regions
Contributions of the MMCR to the ARM ProgramStatistical Surveys of Cloud Location & Frequency
MMCR data is compared with climate simulations, weather forecast models, and cloud resolving models (1 km resolution)
Contributions of the MMCR to the ARM ProgramRetrievals of Cloud Microphysical Characteristics
Liquid water content vs. height / ice water
Cloud particle phaseCloud droplet size
distribution – number of particles per radius size
Contributions of the MMCR to the ARM ProgramBasic Research into Cloud Microphysics
How does the precipitation process actually work?
When do clouds begin to precipitate?
SourcesAtmospheric Radiation Measurement Program,
www.arm.gov , 4/23/08. Clothiaux, E., M. Miller, B. Albrecht, T.
Ackerman, J. Verlinde, D. Babb, R. Peters, and W. Syrett, 1995: An Evaluation of a 94-GHz Radar for Remote Sensing of Cloud Properties. J. Atmos. Oceanic Technol., 12, 201–229.
Moran, K.P., B.E. Martner, M.J. Post, R.A. Kropfli, D.C. Welsh, and K.B. Widener, 1998: An Unattended Cloud-Profiling Radar for Use in Climate Research. Bull. Amer. Meteor. Soc., 79, 443–455.