Bruce Morley

Dynamics and chemistry of marine stratocumulus - DYCOMS II

The second Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II) field study is described. The field program consisted of nine flights in marine stratocumulus west-southwest of San Diego, California. The objective of the program was to better understand the physics a n d dynamics of marine stratocumulus. Toward this end special flight strategies, including predominantly nocturnal flights, were employed to optimize estimates of entrainment velocities at cloud-top, large-scale divergence within the boundary layer, drizzle processes in the cloud, cloud microstructure, and aerosol–cloud interactions. Cloud conditions during DYCOMS-II were excellent with almost every flight having uniformly overcast clouds topping a well-mixed boundary layer. Although the emphasis of the manuscript is on the goals and methodologies of DYCOMS-II, some preliminary findings are also presented—the most significant being that the cloud layers appear to entrain less and drizzle more than previous theoretical work led investigat...

Highlights of Coastal Waves 1996

Some of the highlights of an experiment designed to study coastal atmospheric phenomena along the California coast (Coastal Waves 1996 experiment) are described. This study was designed to address ...

Active and widespread halogen chemistry in the tropical and subtropical free troposphere

Significance Our measurements show that tropospheric halogen chemistry has a larger capacity to destroy O3 and oxidize atmospheric mercury than previously recognized. Halogen chemistry is currently missing in most global and climate models, and is effective at removing O3 at altitudes where intercontinental O3 transport occurs. It further helps explain the low O3 levels in preindustrial times. Public health concerns arise from bioaccumulation of the neurotoxin mercury in fish. Our results emphasize that bromine chemistry in the free troposphere oxidizes mercury at a faster rate, and makes water-soluble mercury available for scavenging by thunderstorms. Naturally occurring bromine in air aloft illustrates global interconnectedness between energy choices affecting mercury emissions in developing nations and mercury deposition in, e.g., Nevada, or the southeastern United States. Halogens in the troposphere are increasingly recognized as playing an important role for atmospheric chemistry, and possibly climate. Bromine and iodine react catalytically to destroy ozone (O3), oxidize mercury, and modify oxidative capacity that is relevant for the lifetime of greenhouse gases. Most of the tropospheric O3 and methane (CH4) loss occurs at tropical latitudes. Here we report simultaneous measurements of vertical profiles of bromine oxide (BrO) and iodine oxide (IO) in the tropical and subtropical free troposphere (10°N to 40°S), and show that these halogens are responsible for 34% of the column-integrated loss of tropospheric O3. The observed BrO concentrations increase strongly with altitude (∼3.4 pptv at 13.5 km), and are 2–4 times higher than predicted in the tropical free troposphere. BrO resembles model predictions more closely in stratospheric air. The largest model low bias is observed in the lower tropical transition layer (TTL) over the tropical eastern Pacific Ocean, and may reflect a missing inorganic bromine source supplying an additional 2.5–6.4 pptv total inorganic bromine (Bry), or model overestimated Bry wet scavenging. Our results highlight the importance of heterogeneous chemistry on ice clouds, and imply an additional Bry source from the debromination of sea salt residue in the lower TTL. The observed levels of bromine oxidize mercury up to 3.5 times faster than models predict, possibly increasing mercury deposition to the ocean. The halogen-catalyzed loss of tropospheric O3 needs to be considered when estimating past and future ozone radiative effects.

Polarization lidar at 1.54 m and observations of plumes from aerosol generators

The ability to detect relative changes in backscatter polariza- tion from a scanning high-pulse-energy lidar system at 1.54-m wave- length is demonstrated. The new capability was tested during the dis- semination of various biological aerosol simulants and other particulate emissions at the U.S. Armys Dugway Proving Ground. Results demon- strate that the lidar is sensitive to different types of aerosols, and depar- tures from the atmospheric background depolarization ratio are consis- tent with the limited amount of information available on the degree of particle sphericity. We conclude that the polarization-sensitive coatings of the beam-steering unit mirrors are presently the largest source of error and that this error is minimized when scanning with a near-zero elevation angle. This is an encouraging result for aerosol source surveillance ap- plications, where the depolarization information may be useful in deter- mining the aerosol generation mechanism or provide an additional scalar variable for use in delineating the plume from the background.

Polarization lidar operation for measuring backscatter phase matrices of oriented scatterers

We describe implementation and demonstration of a polarization technique adapted for lidar to measure all unique elements of the volume backscatter phase matrix. This capability allows for detection of preferential orientation within a scattering volume, and may improve scattering inversions on oriented ice crystals. The technique is enabled using a Mueller formalism commonly employed in polarimetry, which does not require the lidar instrument be polarization preserving. Instead, the accuracy of the polarization measurements are limited by the accuracy of the instrument characterization. A high spectral resolution lidar at the National Center for Atmospheric Research was modified to demonstrate this polarization technique. Two observations where the instrument is tilted off zenith are presented. In the first case, the lidar detects flattened large raindrops oriented along the same direction due to drag forces from falling. The second case is an ice cloud approximately 5 km above lidar base that contains preferentially oriented ice crystals in a narrow altitude band.

THE PENTAGON SHIELD FIELD PROGRAM Toward Critical Infrastructure Protection

The Pentagon, and its 25,000+ occupants, represents a likely target for a future terrorist attack using chemical, biological, or radiological material released into the atmosphere. Motivated by this, a building-protection system, called Pentagon Shield, is being developed and deployed by a number of government, academic, and private organizations. The system consists of a variety of data-assimilation and forecast models that resolve processes from the mesoscale to the city scale to the building scale, and assimilate meteorological and contaminant data that are measured by remote and in situ sensors. This paper reports on a field program that took place in 2004 in the area of the Pentagon, where the aim was to provide meteorological data and concentration data from tracer releases, and to support the development and evaluation of the system. In particular, the results of the field program are being used to improve our understanding of urban meteorological processes, verify the overall effectiveness of the ...

Polarization lidar observations of backscatter phase matrices from oriented ice crystals and rain

Oriented particles can exhibit different polarization properties than randomly oriented particles. These properties cannot be resolved by conventional polarization lidar systems and are capable of corrupting the interpretation of depolarization ratio measurements. Additionally, the typical characteristics of backscatter phase matrices from atmospheric oriented particles are not well established. The National Center for Atmospheric Research High Spectral Resolution Lidar was outfitted in spring of 2012 to measure the backscatter phase matrix, allowing it to fully characterize the polarization properties of oriented particles. The lidar data analyzed here considers operation at 4°, 22° and 32° off zenith in Boulder, CO, USA (40.0°N,105.2°W). The HSRL has primarily observed oriented ice crystal signatures at lidar tilt angles near 32° off zenith which corresponds to an expected peak in backscatter from horizontally oriented plates. The maximum occurrence frequency of oriented ice crystals is measured at 5 km, where 2% of clouds produced significant oriented ice signatures by exhibiting diattenuation in their scattering matrices. The HSRL also observed oriented particle characteristics of rain at all three tilt angles. Oriented signatures in rain are common at all three tilt angles. As many as 70% of all rain observations made at 22° off zenith exhibited oriented signatures. The oriented rain signatures exhibit significant linear diattenuation and retardance.

Scanning eye-safe depolarization lidar at 1.54 microns and potential usefulness in bioaerosol plume detection

Effective monitoring of the atmosphere for potentially hazardous aerosol plumes in urban areas requires a lidar that produces high signal-to-noise backscatter returns, fine spatial resolution, rapid updates, eye-safety at all ranges, and long-range operation. A scanning elastic backscatter lidar with high pulse energy that meets these requirements was recently developed at NCAR. The latest upgrades to the lidar system include the use of a new Raman cell for wavelength conversion and a two-channel receiver for backscatter depolarization ratio measurements. Highlights from recent field tests of the system are presented and plans to improve the prototype, as well as construct an unattended and continuously operating version, are discussed.

Airborne Lidar Tracking of Fluorescent Tracers for Atmospheric Transport and Diffusion Studies

Development and validation of transport models for the study of regional acid deposition require improved observations of pollutant transport and dispersion processes. No suitable method for air-parcel tracking along nonconstant density surfaces is available. The feasibility of using an airborne lidar system to observe atmospheric transport and dispersion of fluorescent-dye-particle (FDP) tracers was demonstrated for various meteorological conditions and FDP-release scenarios in the general area of the Cross-Appalachian Tracer Experiment (CAPTEX) during October 1983. This paper presents some of the results obtained on six case studies, each of which illustrates a unique application of the technique.

Optical properties of the Kuwait oil fires smoke plume as determined using an airborne lidar system: Preliminary results from 28 and 29 May 1991 case studies

An inversion algorithm is used to derive extinction coefficient profiles and total optical depth values from lidar data collected during a study of the Kuwait oil fires smoke plume. Extinction coefficients derived from infrared (IR) wavelength lidar data and green wavelength lidar data are found to be in the range 0.06–1.30 km−1 and 0.06–1.60 km−1 respectively, for a plume cross section study flown on 28 May 1991. Corresponding total optical depth values are determined to be ∼0.05–1.00 for the IR wavelength and ∼0.05–1.20 for the green. The lidar-derived extinction coefficient and total optical depth results are found to be in agreement with previously published data on the optical properties of the smoke plume. Finally, total optical depth results derived from both lidar and optical particle counter (OPC) data are compared for a plume study flown on 29 May 1991, and agreement is found to be within expected uncertainty limits.