Krista K. Laursen

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...

Bidirectional mixing in an ACE 1 marine boundary layer overlain by a second turbulent layer

In the Lagrangian B flights of the First Aerosol Characterization Experiment (ACE 1), the chemistry and dynamics of the postfrontal air mass were characterized by tracking a constant-level balloon launched into the air mass for three consecutive 8-hour flights of the instrumented National Center for Atmospheric Research C-130 aircraft during a 33-hour period. The boundary layer extended to a height of 400 to 700 m during this period, with its top defined by changes in the amount of turbulent mixing measured rather than by an inversion. Above the planetary boundary layer to a height of 1400 to 1900 m, a second layer was capped with a more pronounced temperature inversion and contained only intermittent turbulence. Since this layer served as a reservoir and mixing zone for boundary layer and free tropospheric air, we have called it a buffer layer to emphasize its differences from previous concepts of a residual or intermediate layer. Estimates of the entrainment rate of dimethyl sulfide (DMS) and aerosol particles between the boundary layer and the buffer layer demonstrated that exchange occurred across the interface between these two layers in both upward and downward directions. In situ measurements of aerosol particles revealed highly concentrated, nucleation-mode aerosol particles between 10 and 30 nm diameter at the beginning of the first Lagrangian B flight in the buffer layer, while few were present in the boundary layer. Observations during the second and third flights indicate that aerosol particles of this size were mixing downward into the boundary layer from the buffer layer while DMS was transported upward. This fortuitous enhancement of aerosol particles in the buffer layer allowed simultaneous use of DMS and aerosol particle budgets to track the bidirectional entrainment rates. These estimates were compared to those from measurements of mean vertical motion and boundary layer growth rate, and from estimates of the fluxes and changes in concentration across the layer interface. In addition, three different techniques were used to estimate DMS emission rates from the ocean surface and showed good agreement: (1) evalulation of the DMS and aerosol mean concentration budgets, (2) seawater DMS concentrations and an air-sea exchange velocity, and (3) the mixed-layer gradient technique.

Chemical composition of emissions from the Kuwait oil fires

Airborne measurements in the smoke from the Kuwait oil fires in May and June 1991 indicate that the combined oil and gas emissions were equivalent to the consumption of about 4.6 million barrels of oil per day. The combustion was relatively efficient, with about 96% of the fuel carbon burned emitted as CO{sub 2}. Particulate smoke emissions averaged 2% of the fuel burned, of which about 20% was soot. About two-thirds of the mass of the smoke was accounted for by salt, soot, and sulfate. The salt most likely originated from oil field brines, which were ejected from the wells along with the oil. The salt accounts for the fact that many of the plumes were white. SO{sub 2} and NO{sub x} were removed from the smoke at rates of about 6 and 22% per hour, respectively. The high salt and sulfate contents explain why a large fraction of the particles in the smoke were efficient cloud condensation nuclei. 14 refs., 3 figs., 1 tab.

Emission factors for particles, elemental carbon, and trace gases from the Kuwait oil fires

Emission factors are presented for particles, elemental carbon (i.e., soot), total organic carbon in particles and vapor, and for various trace gases from the 1991 Kuwait oil fires. Particle emissions accounted for ∼2% of the fuel burned. In general, soot emission factors were substantially lower than those used in recent “nuclear winter” calculations. Differences in the emissions and appearances of some of the individual fires are discussed. Carbon budget data for the composite plumes from the Kuwait fires are summarized; most of the burned carbon in the plumes was in the form of CO2. Fluxes are presented for several combustion products.

HIAPER: THE NEXT GENERATION NSF/NCAR RESEARCH AIRCRAFT

Abstract The development of the High-Performance Instrumented Airborne Platform for Environmental Research (HIAPER) will make possible a wealth of new geophysical research opportunities in the areas of atmospheric chemistry, climate forcing, weather system structure and evolution, the carbon and water vapor cycles, and ecosystem processes. In this paper, we present a brief background on the history of the HIAPER project and discuss the modifications made to the basic aircraft [a Gulfstream V (GV) business jet] and the infrastructure systems installed to transform it into an environmental research platform. General aircraft performance capabilities that make the GV uniquely suited for high-altitude, long-range studies of geophysical phenomena are also discussed. The conduct of research with HIAPER will require that suitable instrumentation payloads are available for use on the aircraft, and the processes followed by the National Science Foundation (NSF) and the National Center for Atmospheric Research (NCA...

Characteristics of the marine boundary layers during two Lagrangian measurement periods: 2. Turbulence structure

Characteristics of turbulence mixing in remote marine boundary layers are analyzed using aircraft measurements from six flights during the two intensive Lagrangian measurement periods of ACE1 (the southern hemisphere Aerosol Characterization Experiment). The six cases studied here represent a variety of boundary layer conditions in the region south of Tasmania, Australia. Our study indicated that (1) Lagrangian A (LA) had stronger turbulence mixing and entrainment compared to Lagrangian B (LB) due to greater shear generation of turbulence kinetic energy (TKE), (2) strong mesoscale variation in boundary layer turbulence and thus turbulence mixing existed in the ACE1 region during LB due to variations in sea surface temperature (SST), (3) stable thermal stratification in the boundary layer was found during the last flight of each Lagrangian, consequently, TKE decreased rapidly with height resulting in small or near-zero entrainment rate in spite of strong shear forcing at the surface and in the boundary layer; and (4) the buffer layer, which lies above the boundary layer and below the main inversion, had weak and intermittent turbulence mostly associated with cloud bands and cumulus. Evidence of entrainment was found in the buffer layer. However, it is difficult to quantify by flux measurements due to the weak and intermittent nature of the turbulence field.

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.

New environmental research platform begins to take shape

Work is underway at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, to develop the High-performance Instrumented Airborne Platform for Environmental Research (HIAPER). This advanced research platform is actually a modified Gulfstream V (G-V) business jet that is being built to serve the environmental research needs of the U.S. National Science Foundation (NSF) for the next several decades. HIAPER will be maintained and operated for the NSF by NCARs Atmospheric Technology Division. The first research deployment of the aircraft is planned for June 2005.