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.