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Christoph Senff, Jens Bösenberg, and Gerhard Peters

Abstract

A remote-sensing method to retrieve vertical profiles of water vapor flux in the convective boundary layer by using a differential absorption lidar and a radar-radio acoustic sounding system is described. The system's height range presently extends from 400 to 700 m above the surface, and flux data can be sampled with a height resolution of 75 m and a time resolution of 60 s. The results of a first measurement in July 1991 under predominantly convective conditions are presented. The resolution of the remote-sensing system apparently is sufficient to resolve the major contributions to the flux in the convective mixed layer. In addition, the advantages and limitations of this method are discussed.

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Donald H. Lenschow, Volker Wulfmeyer, and Christoph Senff

Abstract

The authors derive expressions for correcting second- through fourth-order moments of measured variables that are contaminated by random uncorrelated noise. These expressions are then tested by applying them to an artificially produced time series as well as measurements from two upward-pointing ground-based lidar systems:a differential absorption lidar that measures water vapor density and a high-resolution Doppler lidar that measures vertical wind velocity. Both sets of measurements were obtained in a convective boundary layer, and contain sufficient noise to significantly affect measurements of second- and fourth-order moments (as well as integral scale and skewness) throughout the boundary layer. It is shown that the corrections derived here can be used to obtain useful measurements of these moments from instruments such as lidars, which are inherently noisy. The authors also obtain information on higher-order moments of the noise as well as the correlation between noise and atmospheric measurements.

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Stephen A. Cohn, Shane D. Mayor, Christian J. Grund, Tammy M. Weckwerth, and Christoph Senff

The authors describe and present early results from the July–August 1996 Lidars in Flat Terrain (LIFT) experiment. LIFT was a boundary layer experiment that made use of recently developed Doppler, aerosol backscatter, and ozone lidars, along with radars and surface instrumentation, to study the structure and evolution of the convective boundary layer over the very flat terrain of central Illinois. Scientific goals include measurement of fluxes of heat, moisture, and momentum; vertical velocity statistics; study of entrainment and boundary layer height; and observation of organized coherent structures. The data collected will also be used to evaluate the performance of these new lidars and compare measurements of velocity and boundary layer height to those obtained from nearby radar wind profilers. LIFT was a companion to the Flatland96 experiment, described by Angevine et al.

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John W. Nielsen-Gammon, Christina L. Powell, M. J. Mahoney, Wayne M. Angevine, Christoph Senff, Allen White, Carl Berkowitz, Christopher Doran, and Kevin Knupp

Abstract

An airborne microwave temperature profiler (MTP) was deployed during the Texas 2000 Air Quality Study (TexAQS-2000) to make measurements of boundary layer thermal structure. An objective technique was developed and tested for estimating the mixed layer (ML) height from the MTP vertical temperature profiles. The technique identifies the ML height as a threshold increase of potential temperature from its minimum value within the boundary layer. To calibrate the technique and evaluate the usefulness of this approach, coincident estimates from radiosondes, radar wind profilers, an aerosol backscatter lidar, and in situ aircraft measurements were compared with each other and with the MTP. Relative biases among all instruments were generally less than 50 m, and the agreement between MTP ML height estimates and other estimates was at least as good as the agreement among the other estimates. The ML height estimates from the MTP and other instruments are utilized to determine the spatial and temporal evolution of ML height in the Houston, Texas, area on 1 September 2000. An elevated temperature inversion was present, so ML growth was inhibited until early afternoon. In the afternoon, large spatial variations in ML height developed across the Houston area. The highest ML heights, well over 2 km, were observed to the north of Houston, while downwind of Galveston Bay and within the late afternoon sea breeze ML heights were much lower. The spatial variations that were found away from the immediate influence of coastal circulations were unexpected, and multiple independent ML height estimates were essential for documenting this feature.

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Sara C. Tucker, Christoph J. Senff, Ann M. Weickmann, W. Alan Brewer, Robert M. Banta, Scott P. Sandberg, Daniel C. Law, and R. Michael Hardesty

Abstract

The concept of boundary layer mixing height for meteorology and air quality applications using lidar data is reviewed, and new algorithms for estimation of mixing heights from various types of lower-tropospheric coherent Doppler lidar measurements are presented. Velocity variance profiles derived from Doppler lidar data demonstrate direct application to mixing height estimation, while other types of lidar profiles demonstrate relationships to the variance profiles and thus may also be used in the mixing height estimate. The algorithms are applied to ship-based, high-resolution Doppler lidar (HRDL) velocity and backscattered-signal measurements acquired on the R/V Ronald H. Brown during Texas Air Quality Study (TexAQS) 2006 to demonstrate the method and to produce mixing height estimates for that experiment. These combinations of Doppler lidar–derived velocity measurements have not previously been applied to analysis of boundary layer mixing height—over the water or elsewhere. A comparison of the results to those derived from ship-launched, balloon-radiosonde potential temperature and relative humidity profiles is presented.

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Wayne M. Angevine, Christoph J. Senff, Allen B. White, Eric J. Williams, James Koermer, Samuel T. K. Miller, Robert Talbot, Paul E. Johnston, Stuart A. McKeen, and Tom Downs

Abstract

Air pollution episodes in northern New England often are caused by transport of pollutants over water. Two such episodes in the summer of 2002 are examined (22–23 July and 11–14 August). In both cases, the pollutants that affected coastal New Hampshire and coastal southwest Maine were transported over coastal waters in stable layers at the surface. These layers were at least intermittently turbulent but retained their chemical constituents. The lack of deposition or deep vertical mixing on the overwater trajectories allowed pollutant concentrations to remain strong. The polluted plumes came directly from the Boston, Massachusetts, area. In the 22–23 July case, the trajectories were relatively straight and dominated by synoptic-scale effects, transporting pollution to the Maine coast. On 11–14 August, sea breezes brought polluted air from the coastal waters inland into New Hampshire.

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Albert Ansmann, Jens Bösenberg, Gérard Brogniez, Salem Elouragini, Pierre H. Flamant, Karlheinz Klapheck, Holger Linn, Louis Menenger, Walfried Michaelis, Maren Riebesell, Christoph Senff, Pierre-Yves Thro, Ulla Wandinger, and Claus Weitkamp

Abstract

Four lidars located roughly 75 km from each other in the inner German Bight of the North Sea, were used to measure geometrical and optical properties of cirrus clouds during the International Cirrus Experiment 1989 (ICE '89). A complete cirrus life cycle was observed simultaneously with three lidan during a case study on 18 October 1989. Time series of particle backscatter, depolarization-ratio height profiles, cloud depth, optical thickness, and of the cirrus extinction-to-backscatter, or lidar, ratio describe the evolution of the cloud system. A two-wavelength lidar measurement was performed and indicates wavelength independence of ice-crystal scattering. The optical and geometrical depths of the cirrus were well correlated and varied between 0.01 and 0.5 and 100 m and 4.5 km, respectively. Although the evolution of the cloud deck was similar over the different observation sites, cirrus geometrical, scattering, and microphysical properties were found to vary considerably within the lidar network. A statistical analysis of ice-cloud properties is performed based on 38 different cirrus cases sampled during ICE '89. Cirrus formation was found to start at the tropopause in most cases. Ice clouds, measured at high midlatitudes (around 54°N), were thin with mean optical and geometrical depths mainly below 0.4 and 2 km, respectively. A good correlation between mean cloud optical and geometrical thickness, and a weak decrease of the mean optical depths with temperature was observed.

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Ian C. Faloona, Sen Chiao, Arthur J. Eiserloh, Raul J. Alvarez II, Guillaume Kirgis, Andrew O. Langford, Christoph J. Senff, Dani Caputi, Arthur Hu, Laura T. Iraci, Emma L. Yates, Josette E. Marrero, Ju-Mee Ryoo, Stephen Conley, Saffet Tanrikulu, Jin Xu, and Toshihiro Kuwayama

Abstract

Ozone is one of the six “criteria” pollutants identified by the U.S. Clean Air Act Amendment of 1970 as particularly harmful to human health. Concentrations have decreased markedly across the United States over the past 50 years in response to regulatory efforts, but continuing research on its deleterious effects have spurred further reductions in the legal threshold. The South Coast and San Joaquin Valley Air Basins of California remain the only two “extreme” ozone nonattainment areas in the United States. Further reductions of ozone in the West are complicated by significant background concentrations whose relative importance increases as domestic anthropogenic contributions decline and the national standards continue to be lowered. These background concentrations derive largely from uncontrollable sources including stratospheric intrusions, wildfires, and intercontinental transport. Taken together the exogenous sources complicate regulatory strategies and necessitate a much more precise understanding of the timing and magnitude of their contributions to regional air pollution. The California Baseline Ozone Transport Study was a field campaign coordinated across Northern and Central California during spring and summer 2016 aimed at observing daily variations in the ozone columns crossing the North American coastline, as well as the modification of the ozone layering downwind across the mountainous topography of California to better understand the impacts of background ozone on surface air quality in complex terrain.

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