A41E-01 INVITED
Tropospheric layers and LASE measurements for atmospheric process studies
The Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) program has provided extensive data about the distribution of ozone and water vapor in the troposphere. Analyses of these data by researchers from the Massachusetts Institute of Technology have revealed the ubiquity of layers of ozone and water vapor in the troposphere. Measurements by other remote and in situ sensors have confirmed the frequent presence of many layers in the troposphere. Measurements of the location and composition of these layers can be used to study the origin and transport of the layers as well as the dynamical and chemical processes associated with these layers. Lidar systems are ideally suited to study structural information in the atmosphere. Differential absorption lidar (DIAL) systems are capable of providing simultaneous profiles of aerosol and atmospheric gas species for studying these processes. The Lidar Atmospheric Sensing Experiment (LASE) is an airborne DIAL system that is capable of providing high resolution profiles of water vapor and aerosols, and cloud distributions over the entire troposphere. LASE system has been used in 11 field experiments over the past 12 years to study atmospheric boundary layer development, convection, storm development, Saharan dust layers, anthropogenic pollution, cirrus clouds, stratosphere-troposphere exchange, and for comparing water vapor measurements from other remote and in situ sensors. Data obtained from these field experiments have been used to study boundary layer dynamics and derive entrainment fluxes; convection initiation; influences of water vapor distributions on hurricane development; optical properties of pollution and dust layers and their humidification; relative humidity associated with cirrus; and many transport and dynamical processes. Examples of some of these data will be presented in this talk along with a discussion of their association with the atmospheric processes.
A41E-02
Study of Global Cirrus Cloud Seasonal Distributions Using CALIPSO Data
We study the global and seasonal distribution of cirrus clouds using the measurements made by the Cloud- Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite mission. In addition, we present local ground-based lidar validation measurements during CALIPSO overpasses of Hampton University. Few satellite instruments can deduce the presence of cirrus clouds, especially subvisual clouds and those of low optical thickness. Cirrus clouds play a significant role in the energy budget of the earth atmosphere system by means of their effects on the transfer of radiant energy through the atmosphere. Satellite lidar has the ability to profile multi-layer cloud structures and it is particularly useful for the detection of subvisual cirrus. We investigate the latitude-longitude and vertical distributions of occurrence frequency and thickness of cirrus clouds measured by CALIPSO. The investigation of top-layer cirrus clouds shows maximum occurrence frequency of up to 70% near the tropics over the 100° - 180° E longitude band. The average thickness of cirrus clouds is generally between 1.5 and 1.9 km in the majority of latitude-longitude bins. We also analyze the seasonal behavior of the cirrus cloud frequency and geometric thickness. The results show large latitudinal movement of cirrus cloud cover with the changing seasons. The examination of the vertical distribution of cirrus clouds shows the maximum of cirrus top altitude occurrence frequency of ~13% at 16 km in the tropics. The maximum of cirrus cloud base altitude frequency in the tropics is about 10% at 13 km. Cirrus clouds with thickness of ~1 km have the highest occurrence frequency of approximately 15% in the 20° S - 20° N latitude band.
A41E-03
Global Distributions of Aerosol Types Determined Using CALIPSO Measurements and an Automated Aerosol Classification Scheme
One month of CALIPSO Level II data are analyzed to assess the veracity of the CALIPSO aerosol type identification algorithm and generate distributions of aerosol types and their respective optical characteristics. Aerosol classification has several purposes: attribution of aerosol radiative forcing to natural or anthropogenic emissions requires the determination of the source of the aerosol; aerosol radiative properties vary significantly by type; and, most directly, determination of aerosol type allows an estimate of extinction-to-backscatter ratio. In the CALIPSO classification scheme, each aerosol type is assumed to be a mixture of different species, where the mixing can be internal, external or both. The underlying paradigm is that the variety of emission sources and atmospheric processes will act to produce airmasses that can be characterized as consisting of a single, generic aerosol type. This is an idealization, but one that allows us to classify aerosols based on observations and location, and thus gain insight into the geographic distribution of aerosols and constrain the possible values of extinction-to- backscatter ratios for use in the CALIPSO aerosol extinction retrievals. The CALIPSO models define six aerosol types: desert dust, biomass burning, background, polluted continental, marine and polluted dust. While this set does not cover all possible aerosol mixing scenarios, it accounts for a majority of mesoscale aerosol layers. In essence the algorithm trades off complex transient multi-component mixtures for relatively stable layers with large horizontal extent (10-1000 km). For this initial assessment of algorithm performance, we produce global distributions of the CALIPSO aerosol types, along with the complementary distributions of integrated attenuated backscatter, backscatter color ratio, and volume depolarization ratio for each type. The aerosol type distributions are further partitioned according to various geophysical discriminators (e.g., geographic region, land vs. ocean, and day vs. night). For selected geographic regions, we compare the CALIPSO type distributions to distributions obtained from the MODIS aerosol products.
A41E-04
Flux measurements of atmospheric CO2 by Lidar: from the micro to the regional scale
A mechanistic understanding of the global carbon cycle requires quantification of terrestrial ecosystem CO2 fluxes at regional scales. In this paper, we analyze the potential of a Doppler DIAL system to make flux measurements of atmospheric CO2 using the eddy-covariance and boundary layer budget methods and present results from a ground based experiment. In June 2007, a field experiment combining a 2-µm Doppler Heterodyne Differential Absorption Lidar (HDIAL) and in-situ sensors of a 447-m tall tower (WLEF) took place in Wisconsin. The HDIAL measures simultaneously: 1) CO2 mixing ratio, 2) atmosphere structure via aerosol backscatter and 3) radial velocity. We demonstrate how to synthesize these data into regional flux estimates. Lidar-inferred fluxes are compared with eddy-covariance fluxes obtained in-situ at 396m AGL from the tower. In cases where the lidar was not yet able to measure the fluxes with acceptable precision, we discuss possible modifications to improve system performance.
A41E-05 INVITED
A Thermodynamically General Theory for Convective Circulations and Vortices
Convective circulations and vortices are common features of atmospheres that absorb low-entropy-energy at higher temperatures than they reject high-entropy-energy to space. These circulations range from small to planetary-scale and play an important role in the vertical transport of heat, momentum, and tracer species. Thus, the development of theoretical models for convective phenomena is important to our understanding of many basic features of planetary atmospheres. A thermodynamically general theory for convective circulations and vortices is proposed. The theory includes irreversible processes and quantifies the pressure drop between the environment and any point in a convective updraft. The article's main result is that the proposed theory provides an expression for the pressure drop along streamlines or streamtubes that is a generalization of Bernoulli's equation to convective circulations. We speculate that the proposed theory not only explains the intensity, but also shed light on other basic features of convective circulations and vortices.
A41E-06
First comparison of products from the NCAR Raman-shifted Eye-safe Aerosol Lidar (REAL) and the NCAR Integrated Surface Flux Facility (ISFF) during the Canopy Horizontal Array Turbulence Study (CHATS)
The NCAR Raman-shifted Eye-safe Aerosol Lidar (REAL) and the Integrated Surface Flux Facility (ISFF) operated from 15 March to 11 June, 2007, for the Canopy Horizontal Array Turbulence Study (CHATS). Lidar aerosol backscatter data at 1.5 microns wavelength were recorded at 1.5 meter intervals to ranges of 5.8 kilometers. Scanning resulted in almost half a million vertical cross-sections and near horizontal slices. The horizontal scans ranged in altitude from meters to tens of meters above the surface and covered approximately 10-square kilometer areas. Scans were repeated at approximately 15 second intervals in order to create time-lapse animations of the flow. The ISFF 30-meter tall tower was located 1.6 km from the REAL. The tower intersected all of the horizontal scans and the vertical scan planes were approximately 10 meters or less from the tower. Time- series of in situ measurements and fluxes from the tower will be compared with the lidar backscatter at that range. Ultimately, by combining the spatial imaging and time-lapse visualization capability of the lidar with the precision of the in situ measurements, we hope to improve understanding of near-surface fluxes and their impact on the larger scales. http://www.lidar.ucar.edu
A41E-07
Microscale Analysis of Surface Wind Variability by Resolving Small-Scale Terrain Features in High-Resolution Simulations
The temporal and spatial variability of surface winds is a critical information in predicting the transport of atmospheric tracers and pollutants, operating wind energy power plants, and evaluating atmospheric environment in urban areas where deteriorating factors such as heat island phenomenta are significant. These surface wind analyses are required especially in areas with complex terrain and land-use characteristics. Although general meterological conditons can be evaluated by the current regional-scale simulations with a grid spacing of O(1 km) to O(10 km), the evaluation of surface winds that are sensitively affected by small-scale features of terrain and land use is relatively poor. In this study, we investigate the temporal and spatial variability of surface winds in the microscale by conducting high-resolution simulations with small-scale terrain features being well-resolved. A mesoscale meteorological model MM5 is used for the simulations in multi-nested mesoscale domains with a minimum grid spacing of 111 m in the finest-mesh domain. The area of interest is a Japanese peninsula whose size is about 30 km by 10 km projecting into the Pacific Ocean. A variety of simulations are conducted for a one-year period and the six-months periods of summer (JJA) and winter (DJF). In coarse-mesh (i.e., 1 km) runs examining the effects of boundary-layer mixing parameterizations, the sensitivity to stability is examined in different seasons and in different meteorological settings. With a best choice of the parameterization, 111-m mesh simulations are conducted and compared with the coarse-mesh results. Small-scale and short-term variabilities of surface winds are reproduced with the fine-mesh simulations. As the spatial variability of terrain elevations increases, the variability of wind speeds increases especially under weak-wind conditions. Resolving representative scales of terrain is important in predicting microscale features of surface winds.
A41E-08
A Coupled 1-Dimensional Atmosphere/Ocean/Microphysical Model to Probe Sea Spray Heat and Moisture Fluxes During a North Atlantic Summer Gale
Underway meteorological and oceanographic data recorded from the RRS Discovery (as part of the Atmospheric Chemistry Studies in the Ocean Environment, or ACSOE, experiment) during a summer gale south of Iceland in June, 1997 showed dramatic perturbations of air temperature and relative humidity, and near surface ocean temperature and salinity. The underwater ocean temperature decreased by about 1K and the salinity increased by 0.03 psu during the highest winds before decreasing by 0.1 psu. The atmospheric temperature decreased by 4K during the highest winds, and the relative humidity increased from 75 to 95 percent. The measured perturbations in both the oceanic and atmospheric boundary layers was due a combination of vertical advection and phase change effects associated with the production and evaporation of sea spray/aerosols, in addition to the conventional interfacial fluxes of heat and water vapor. The perturbations in the geophysical parameters are explored with a coupled 1-dimensional atmosphere/ocean/microphysical model. The oceanic boundary layer model is based on the PWP bulk mixed layer, and the atmospheric/microphysical model is based on MISTRA model with important modifications to take account of sea spray production during high winds. The oceanic model is initialized with measured profiles of temperature and salinity that were recorded from the RRS Discovery before the storm, and the atmospheric model is initialized with NCEP-NCAR re-analysis data. Known problems of temperature and humidity drift in the atmospheric model, associated with unbalanced surface heat and moisture fluxes, were overcome by relaxing the model predictions to the NCEP-NCAR data. The results from the forward model suggest that sea spray production and evaporation may have a profound impact on the temperature and moisture structure of the atmospheric boundary layer and may also have a measurable impact on upper ocean salinity. The coupled model may be used in an inverse mode to better constrain the sea spray volume production function, which is currently known only to within an order of magnitude. The spray fluxes derived from the inverse model indicate that the present estimates of the sea spray volume production function may have to be revised upward.