ALBERT

Beschreibung: The TARFOX (Tropospheric Aerosol Radiative Forcing Observational Experiment) intensive field campaign was designed to reduce uncertainties in estimates of the effects of anthropogenic aerosols on climate by measuring direct radiative effects and the optical, physical, and chemical properties of aerosols [1]. TARFOX was conducted off the East Coast of the United States between July 10-31, 1996. Ground, aircraft, and satellite-based sensors measured the sensitivity of radiative fields at various atmospheric levels to aerosol optical properties (i.e., optical thickness, phase function, single-scattering albedo) and to the vertical profile of aerosols. The LASE (Lidar Atmospheric Sensing Experiment) instrument, which was flown on the NASA ER-2 aircraft, measured vertical profiles of total scattering ratio and water vapor during a series of 9 flights. These profiles were used in real-time to help direct the other aircraft to the appropriate altitudes for intensive sampling of aerosol layers. We have subsequently used the LASE aerosol data to derive aerosol backscattering and extinction profiles. Using these aerosol extinction profiles, we derived estimates of aerosol optical thickness (AOT) and compared these with measurements of AOT from both ground and airborne sun photometers and derived from the ATSR-2 (Along Track and Scanning Radiometer 2) sensor on ERS-2 (European Remote Sensing Satellite-2). We also used the water vapor mixing ratio profiles measured simultaneously by LASE to derive precipitable water vapor and compare these to ground based measurements.

Beschreibung: The instrumentation and the observations performed by four identically instrumented sounding rockets, designed to investigate the mesosphere and lower thermosphere, are reported. The four sounding rockets were launched from the Brazilian equatorial range Alcantara in August 1994. The instruments were capable of determining ion and electron densities. The results of data processing showed discrepancies hitherto unnoticed by other experiments.

Beschreibung: Progress, significant results, and future plans regarding the following project objectives are presented: (a) Develop techniques for optimizing structural analysis of basement trends in arid regions with extremely subdued topography and/or thin aeolian cover. b) Apply results of (a) to map the southern extension of the Hamisana Shear Zone and the western extension of Nakasib Suture. c) Apply results of (b) to constrain the roles of terrane accretion and strike-slip re-organization for late Precambrian crustal evolution in NE Africa.

Beschreibung: Progress and future plans for the following objectives are presented: (1) To develop a technique to obtain values of aeolian roughness for geologic surfaces from values of surface roughness determined from calibrated L- and C-band, like- and cross-polarized, multiple incidence angle radar data from SIR-C; (2) To define the optimal combination of radar parameters from which aeolian roughness can be derived; and (3) To gain an understanding of the physical processes behind the empirical relationship.

Beschreibung: In recent years, the role of PSCs in the ozone depletion process has become better understood. PSCs provide the surfaces upon which heterogeneous reactions take place that affect the gas phase partitioning between active and reservoir chlorine and nitrogen species. Present methods of PSC detection include in situ measurements by lidar and various satellite-borne instruments such as the Stratospheric Aerosol Measurement II (SAM II) on the Nimbus 7 spacecraft, which produced PSC measurements from 1978 to 1994 and several instruments onboard the Upper Atmospheric Research Satellite (UARS) such as the Cryogenic Limb Array Etalon Spectrometer (CLAES) which provided measurements for 1991-1993. All of the PSC-detection methods devised so far have been hampered by incomplete sampling of the places and times in which PSCs are likely to form. There is a need to understand the climatology of PSCS, in particular the timing of their onset and duration, their vertical distribution, geographic extent, annual variability and responses to volcanic aerosol forcing. Poole and Pitts [1994] assembled a PSC climatology based on SAM II data, but this climatology is incomplete, as it is limited to the edge of the polar night due to the limitations of the solar occultation scan geometry. The Advanced Very High Resolution Radiometer (AVHRR) five- channel sensors onboard the NOAA polar-orbiting satellites have been collecting data over the polar regions continuously since 1979. These operational satellites provide unmatched coverage in space and time of both polar regions, but were not designed for the detection of optically-thin PSCS. However, the AVHRR data archive would be an invaluable source for the construction of a long-term climatology of PSCs if techniques can be developed and tested to detect PSCs in AVHRR data. In the last few years, the members of our group at San Francisco State University and NASA Ames Research Center have been engaged in the development of various PSC detection methods using AVHRR data. There is strong evidence that a subset of PSCS, those that are optically thick, can be readily identified in the AVHRR data set. Our group has also made significant progress in the identification of optically thinner PSCs using a variety of techniques.

Beschreibung: Lidar backscattering profiles available from the LITE data set have been used to estimate the optical depths of the Saharan dust layer over West Africa and E. Atlantic regions, in the context of validating the 3-D conceptual model of the Saharan dust plume proposed by Karyampudi and Carlson. The aerosol extinction profiles and optical depths were retrieved from LITE using the Fernald et al. (1972) method. An extinction-to-backscattering ratio, S(sub a), of 25 was selected for optical depth calculations. The spatial analysis of total column and Saharan dust layer optical depths show higher optical depths over W. Africa that decrease westward over E. Atlantic. The higher optical depths over W. Africa, in general, are associated with heavy dust being raised from the surface in dust source regions. Rapid depletion of these heavy dust particles, perhaps due to sedimentation, appear to decrease the dust loading within the dust layer as the plume leaves the west African continent. Higher optical depths are generally confined to the southern edge of the dust layer, where the middle level jet appears to transport the heavy dust concentrations that tend to mix downward from vertical mixing associated with the strong vertical shears underneath the middle jet. Thus, LITE measurements although, in general, validate the Saharan dust plume conceptual model, show maximum values of optical depths near the southern edge of the dust plume over the E. Atlantic region instead of near the center of the dust plume as described in the conceptual model.

Beschreibung: The purpose of the balloon flights performed in March 1993 from Aire-sur-Adour (France) was to measure trace gases in the polar vortex during a dynamically active period. These balloon flights revealed coincident layering in long-lived tropospheric source gases. A layer of mid-latitude air, enriched in trace gases, was detected at sampled levels near 15 mbar. High resolution advection models, fine scale distributions of ozone, nitrous oxide, methane, and halocarbons were constructed. The calculations showed how air enriched in trace gases is sampled near 15 mbar when a filament of such air is drawn into the outer portion of the vortex.

Beschreibung: Water vapor plays an important role in the energetics of the boundary layer processes which in turn play a key role in regulating regional and global climate. It plays a primary role in Earth's hydrological cycle, in radiation balance as a direct absorber of infrared radiation, and in atmospheric circulation as a latent heat energy source, as well as in determining cloud development and atmospheric stability. Water vapor concentration, expressed as a mass mixing ratio (g kg(exp -l)), is conserved in all meteorological processes except condensation and evaporation. This property makes it an ideal choice for studying many of the atmosphere's dynamic features. Raman scattering measurements from lidar also allow retrieval of water vapor mixing ratio profiles at high temporal and vertical resolution. Raman lidars sense water vapor to altitudes not achievable with towers and surface systems, sample the atmosphere at much higher temporal resolution than radiosondes or satellites, and do not require strong vertical gradients or turbulent fluctuations in temperature that is required by acoustic sounders and radars. Analysis of highly-resolved water vapor profiles are used here to characterize two important mesoscale flows: thunderstorm outflows and a cold front passage. The data were obtained at the Atmospheric Radiation Measurement Site (CART) by the groundbased Department of Energy/Sandia National Laboratories lidar (CART Raman lidar or CARL) and Goddard Space Flight Center Scanning Raman Lidar (SRL). A detailed discussion of the SRL and CARL performance during the IOPs is given by others in this meeting.

Beschreibung: The NASA Langley Research Center's airborne UV Differential Absorption Lidar (DIAL) system participated in the Subsonic Assessment, Ozone and Nitrogen Oxide Experiment (SONEX) mission from October 13 to November 12, 1997. The purpose of the mission was to study the upper troposphere/lower stratosphere in and near the North Atlantic flight corridor to better understand this region of the atmosphere and how civilian air travel in the corridor might be affecting the atmospheric chemistry. Bases of operations included NASA Ames, California (37.4 deg N, 122.1 deg W); Bangor, Maine (44.8 deg N, 68.8 deg W); Shannon, Ireland (52.7 deg N, 8.9 deg W); and Lajes, Terceira Island, Azores (38.8 deg N, 27.1 deg W). Since the UV DIAL system observes in the nadir as well as the zenith, aerosol and ozone data were obtained from near the Earth's surface to the lower stratosphere. A number of interesting features were noted relating to both chemistry and dynamics of the troposphere, which are reported here.

Beschreibung: Worldwide, about ten Differential Absorption Lidars are used for long-term monitoring of stratospheric ozone. These systems are an important component of the Network for the Detection of Stratospheric Change. Although DIALs are self-calibrating in principle, regular intercomparisons with other ozone-lidars, microwave radiometers or ozone-sondes are highly desirable to ensure high data quality at a well known level. The Network for the Detection of Stratospheric Change (NDSC) validation policy suggests that such intercomparisons be "blind", meaning all participants submit their data to an impartial referee, without seeing results from the other participants. Here we report on the "blind" intercomparison taking place from January 20th to February 10th 1998 at Ny-Alesund, Spitsbergen (78.92 deg N, 11.95 deg E). Participating groups were from the Alfred Wegener Institute, Potsdam, operating the NDSC DIAL system at Ny-Alesund, from the University of Bremen operating the NDSC microwave radiometer for ozone profiling at Ny-Alesund, and the NASA Goddard Space Flight Center group with the "NDSC travelling standard" STROZ-LITE. The first author acted as the impartial referee. Also used for the intercomparison were data from ECC-6A/Vaisala RS80 ozone sondes routinely launched at Ny-Alesund by the AWI group. A 1% KI solution (3 ml) and the 1986 ECC pump correction (1.092 at 5 hPa) are used. The ECC-data were available to all participants during the campaign and thus were not "blind". Table 1 summarizes the expected performance of the instruments participating in the ozone intercomparison reported in this paper.