Matthew A. Miller

Thin Liquid Water Clouds: Their Importance and Our Challenge

Abstract Many of the clouds important to the Earths energy balance, from the Tropics to the Arctic, contain small amounts of liquid water. Longwave and shortwave radiative fluxes are very sensitive to small perturbations of the cloud liquid water path (LWP), when the LWP is small (i.e., < 100 g m−2; clouds with LWP less than this threshold will be referred to as “thin”). Thus, the radiative properties of these thin liquid water clouds must be well understood to capture them correctly in climate models. We review the importance of these thin clouds to the Earths energy balance, and explain the difficulties in observing them. In particular, because these clouds are thin, potentially mixed phase, and often broken (i.e., have large 3D variability), it is challenging to retrieve their microphysical properties accurately. We describe a retrieval algorithm intercomparison that was conducted to evaluate the issues involved. The intercomparison used data collected at the Atmospheric Radiation Measurement (ARM) S...

Millimeter-Wavelength Radars: New Frontier in Atmospheric Cloud and Precipitation Research

During the past 20 yr there has been substantial progress on the development and application of millimeter-wavelength (3.2 and 8.6 mm, corresponding to frequencies of 94 and 35 GHz) radars in atmospheric cloud research, boosted by continuous advancements in radar technology and the need to better understand clouds and their role in the Earths climate. Applications of millimeter-wavelength radars range from detailed cloud and precipitation process studies to long-term monitoring activities that strive to improve our understanding of cloud processes over a wide range of spatial and temporal scales. These activities are the result of a long period of successful research, starting from the 1980s, in which research tools and sophisticated retrieval techniques were developed, tested, and evaluated in field experiments. This paper presents a cohesive, chronological overview of millimeter-wavelength radar advancements during this period and describes the potential of new applications of millimeter-wavelength rad...

Clouds, Aerosol, and Precipitation in the Marine Boundary Layer: An ARM Mobile Facility Deployment

© Copyright 2015 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act September 2010 Page 2 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at (https://www.ametsoc.org/) or from the AMS at 617-227-2425 or copyrights@ametsoc.org.

Lack of correlation between chlorophyll a and cloud droplet effective radius in shallow marine clouds

[1] The hypothesis that areas of high oceanic productivity affect the physical properties of shallow marine clouds via the production of secondary organic aerosols is evaluated using satellite data. The correlation between chlorophyll a concentrations, an indication of oceanic productivity, and low cloud droplet liquid phase effective radius (R e ) is examined for several ocean regions and time periods. While a strong correlation between chlorophyll a and low R e can occur for specific periods in some locations, the correlation is not reproducible in other regions and time periods. The intermittent correlation between high concentrations of chlorophyll a and low R e is a coincidence and is not representative of a dominant, monotonic, causative relation between secondary organic aerosols and marine shallow cloud properties.

Near-Surface Density Currents Observed in the Southeast Pacific Stratocumulus-Topped Marine Boundary Layer*

AbstractDensity currents (i.e., cold pools or outflows) beneath marine stratocumulus clouds are characterized using 30 days of ship-based observations obtained during the 2008 Variability of American Monsoon Systems (VAMOS) Ocean–Cloud–Atmosphere–Land Study Regional Experiment (VOCALS-REx) in the southeast Pacific. An air density increase criterion applied to the Improved Meteorological (IMET) sensor data identified 71 density current front, core (peak density), and tail (dissipating) zones. The similarity in speeds of the mean density current propagation speed (1.8 m s−1) and the mean cloud-level advection relative to the surface layer wind (1.9 m s−1) allowed drizzle cells to deposit elongated density currents in their wakes. Scanning Doppler lidar captured prefrontal updrafts with a mean intensity of 0.91 m s−1 and an average vertical extent of 800 m. Updrafts were often surmounted by low-lying shelf clouds not connected to the overlying stratocumulus cloud. The observed density currents were 5–10 time...

Stratus 9/VOCALS ninth setting of the Stratus Ocean Reference Station & VOCALS Regional Experiment

Abstract : The Woods Hole Oceanographic Institution (WHOI) Hawaii Ocean Timeseries (HOT) Site (WHOTS), 100 km north of Oahu, Hawaii, is intended to provide long-term, high-quality air-sea fluxes as a part of the NOAA Climate Observation Program. The WHOTS mooring also serves as a coordinated part of the HOT program, contributing to the goals of observing heat, fresh water and chemical fluxes at a site representative of the oligotrophic North Pacific Ocean. The approach is to maintain a surface mooring outfitted for meteorological and oceanographic measurements by successive mooring turnarounds. These observations will be used to investigate air-sea interaction processes related to climate variability. This report documents recovery of the WHOTS-4 mooring and deployment of the fifth mooring (WHOTS-5). Both moorings used Surlyn foam buoys as the surface element and were outfitted with two Air-Sea Interaction Meteorology (ASIMET) systems. Each ASIMET system measures, records, and transmits via Argos satellite the surface meteorological variables necessary to compute air-sea fluxes of heat, moisture and momentum. The upper 155 m of the moorings were outfitted with oceanographic sensors for the measurement of temperature, conductivity and velocity. A pCO2 system was installed on the WHOTS-5 buoy. The WHOTS mooring turnaround was done between 3 and 11 June 2008. Operations began with deployment of the WHOTS-5 mooring. This was followed by meteorological intercomparisons and CTDs at the WHOTS-4 site. A period of calmer weather was taken advantage of to recover WHOTS-4 on 6 June 2008. The Kilo Moana then returned to the WHOTS-5 mooring for CTD operations and meteorological intercomparisons. This report describes these cruise operations, as well as some of the in-port operations and pre-cruise buoy preparations.

Abrupt cloud clearing of marine stratocumulus in the subtropical southeast Atlantic

A shrinking marine refrigerator Low subtropical marine clouds scatter solar radiation back to space and thereby cool the climate system. Most work on understanding changes in the coverage of these types of clouds has focused on the effects of sea surface temperatures or on aerosols. Yuter et al. show that dynamic effects due to atmospheric gravity waves are responsible for the rapid clearing of large areas of these clouds. This phenomenon also has implications for marine ecology and biogeochemistry. Science, this issue p. 697 Atmospheric gravity waves can rapidly erode subtropical marine low cloud fronts. We document rapid and abrupt clearings of large portions of the subtropical marine low cloud deck that have implications for the global radiation balance and climate sensitivity. Over the southeast Atlantic, large areas of stratocumulus are quickly eroded, yielding partial or complete clearing along sharp transitions hundreds to thousands of kilometers in length that move westward at 8 to 12 meters per second and travel as far as 1000+ kilometers from the African coast. The westward-moving cloudiness reductions have an annual peak in occurrence in the period from April through June. The cloud erosion boundaries reduce cloud at ≈10-kilometer scale in less than 15 minutes, move approximately perpendicular to the mean flow, and are often accompanied by small-scale wave features. Observations suggest that the cloud erosion is caused by atmospheric gravity waves.

Joint synoptic and cloud variability over the Northeast Atlantic near the Azores

AbstractMarine boundary layer clouds are modified by processes at different spatial and temporal scales. To isolate the processes governing aerosol–cloud–precipitation interactions, multiday synoptic variability of the environment must be accounted for. Information on the location of low clouds relative to the ridge–trough pattern gives insight into how cloud properties vary as a function of environmental subsidence and stability. The technique of self-organizing maps (SOMs) is employed to objectively classify the 500-hPa geopotential height patterns for 33 years of reanalysis fields (ERA-Interim) into pretrough, trough, posttrough, ridge, and zonal-flow categories. The SOM technique is applied to a region of prevalent marine low cloudiness over the eastern North Atlantic Ocean that is centered on the Azores island chain, the location of a long-term U.S. Department of Energy observation site. The Azores consistently lie in an area of substantial variability in synoptic configuration, thermodynamic environ...