Operations Updates
ARM Climate Research Facility Operations Update - October 15, 2007
This bimonthly report provides a brief summary of significant accomplishments and activities in the operations area of the ARM Climate Research Facility (ACRF).
Enchanted Isle Selected as Site for 2009 ARM Mobile Facility Deployment
Graciosa Island, also known as White Island, covers an area of about 62 km2. Meaning "enchanting," Graciosa is the beneficiary of a mild tropical climate throughout most of the year.
In 2009, the ARM Mobile Facility will be deployed in the Azores to support the Clouds, Aerosol, and Precipitation in the Marine Boundary Layer (CLAP-MBL) field campaign. From April through December, the AMF will be located on Graciosa Island in the Azores, a Portuguese archipelago located about 3,900 km (2,400 mi) from the east coast of North America. The Azores are ideally located to sample the transition from the overcast stratocumulus regime in the spring to the broken trade cumulus regime in the summer. Led by principal investigator Robert Wood, scientists involved in the campaign will use the data from the AMF to study processes controlling the radiative properties and microphysics of marine boundary layer clouds over the remote subtropical Northeast Atlantic Ocean (NEA).
A previous study, the Atlantic Stratocumulus Transition Experiment in 1992, sampled clouds in the NEA and featured one of the first successful deployments of millimeter radars to study marine boundary layer clouds. The results of that study suggest that CLAP-MBL will sample a broad range of these cloud types and aerosol conditions. The campaign will address science questions about daily to seasonal lower tropospheric processes over the NEA, such as:
- synoptic-scale features that dominate the variability in subtropical low clouds, and
- variability in precipitation frequency and strength in the subtropical cloud-topped marine boundary layer, including how this variability may be correlated with variability in aerosol properties.
Synthesized long term data from this campaign will be used to initialize, constrain, and validate numerical models including large eddy simulation, single column, and regional and global atmospheric models.
Aerial Vehicles Program to Support "CLOWD" Statistical Analyses
Several instruments, such as this miniature cloud condensation nuclei counter, will be used on the RACORO aircraft payload to measure cloud microphysical properties.
In 2009, the ARM Aerial Vehicles Program (AVP) will support the Routine AVP Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations (RACORO) field campaign, led by principal investigator Andrew Vogelmann. During this long-term campaign, the AVP will conduct routine flights at the ACRF Southern Great Plains (SGP) site to sample low-altitude liquid-water clouds in the boundary layer. The purpose is to obtain representative statistics of cloud microphysical properties needed to validate retrieval algorithms and support process studies and model simulations of boundary layer clouds and, in particular, CLOWD-type clouds. The results will include extensive statistics on these clouds, given their high frequency of occurrence in mid-latitudes.
The objectives of the campaign are to:
- Obtain representative statistics of cloud optical and microphysical properties, and cloud radiative fluxes for cloud retrieval validations.
- Observe aerosol properties—such as aerosol amount, aerosol size distribution, and the number of cloud condensation nuclei—associated with cloud variability.
- Facilitate understanding of how meteorological factors influence cloud dynamics, microphysical properties, and aerosol-cloud interactions.
The knowledge gained through this effort will be used to evaluate and improve global climate models. Potential model improvements include the parameterization of continental boundary layer clouds, the representation of broken cloudiness in 3D radiative transfer, and inclusion of unresolved sub-grid dynamical processes, and aerosol-cloud interactions.
Second Phase of Far-Infrared Study To Take Place in Chile
Because of its altitude and arid conditions, Cerro Chajnantor in Chile is an ideal location for obtaining atmospheric measurements in the far-infrared. (Photo credit California Institute of Technology)
The Radiative Heating in Underexplored Bands Campaign (RHUBC II) was selected for support by ACRF as an off-site campaign in 2009. Led by principal investigators Dr. David Turner and Dr. Eli Mlawer, RHUBC-II will take place from August to October 2009 at a location near Cerro Chajnantor in Chile, at an altitude of more than 5,000 m. This effort is a follow-on to RHUBC-I, conducted from February 22 to March 14, 2007, at the ACRF North Slope of Alaska site in Barrow. RHUBC-I was the first experiment to make detailed observations of downwelling infrared radiation in the far-infrared (wavelengths greater than 15 μm). This spectral region has been underexplored to date and is normally opaque at the surface due to strong absorption by water vapor.
During RHUBC-II, the same spectral band will be explored; however, this absorption band is much more transparent in the dry, low pressure conditions at Chajnantor. Thus, useful measurements can be made to even longer wavelengths than was possible during RHUBC-I. RHUBC-II will also investigate the normally opaque water vapor bands in the near-infrared (wavelengths between 1 and 3 μm), which could not be investigated during RHUBC-I due to the low sun angles during the polar winter. In both spectral regions, the observed radiance will be compared against high-resolution calculations from advanced radiative transfer models, which should greatly reduce the uncertainties associated with modeling these spectral bands. RHUBC-II will provide scientific data to document the extent of upper tropospheric cooling as an effective regulator of global warming. The current uncertainty associated with water vapor absorption in these bands can lead to assumptions about their cooling effect in the upper troposphere, which is reflected in model simulations of global climate.
