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At least 1,027 records · Page 57
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NASA NTRS1990

A comparison of vertical velocity in cirrus obtained from aircraft and lidar divergence measurements during FIRE

Techniques are presented to obtain vertical velocity (w) in cirrus clouds from in situ aircraft lateral wind measurements and from ground-based remote Doppler lidar measurements. In general, direct measurements of w from aircraft are not feasible because of offsets in the air velocity sensors. An alternative is to calculate w from the integral of the divergence of the horizontal velocity around a closed path. This technique is applied to a cirrus cloud investigated during the FIRE Cirrus Intensive Field Observation Program. The results indicate that the error in w is about + or - 14 cm/sec from the aircraft technique; this can be reduced to about + or - 2-3 cm/sec with technical improvements in both ground-speed and lateral-velocity measurements. The error in w from Doppler lidar measurements, which is about + or - 8 cm/sec can be reduced to about + or - 5 cm/sec by improvements in the Doppler velocity measurements with technology that is currently available.

Gultepe, I.↗
NASA NTRS1990

AVHRR monitoring of U.S. crops during the 1988 drought

Effects of the 1988 drought on crops in the U.S. Corn Belt were assessed and monitored by the Foreign Crop Condition Assessment Division (FCCAD), U.S. Department of Agriculture. The primary data were vegetation index numbers (VINs), each of which was calculated as an average vegetation index of a geographically referenced cell of AVHRR pixels. Using VINs, the FCCAD was able to detect the existence of drought early in the season, monitor changing conditions, and provide objective assessments of the drought's extent and severity. Field observations confirmed the image analyses, and underlined the importance of the timing of extreme weather events with respect to crop stages for interpreting VINs. The analyses were conducted in an operational environment, providing a unique test of the AVHRR data for large area, near real-time crop monitoring. Because large area, operational remote sensing of crops is quite different from traditional, controlled, small plot research studies, more work is needed to link the two; this would improve crop assessment capabilities.

Teng, William L.↗
NASA NTRS1990

Remote sounding of the tropical cirrus cloud temperature and optical depth using 6.5 and 10.5-micron radiometers during STEP

A dual-channel retrieval technique involving the water vapor band at 6.5 microns and the window region at 10.5 microns has been developed to infer the temperature and emissivity of tropical anvils. This technique has been applied to data obtained from the ER-2 narrow field-of-view radiometers during two flights in the field observation of the Stratosphere-Troposphere Exchange Project near Darwin, Australia, January-February 1987. The retrieved cloud temperatures are between 190 and 240 K, while the cloud emissivities derived from the retrieval algorithm range from about 0.2 to 1. Moreover, the visible optical depths have been obtained from the cloud emissivity through a theoretical parameterization with values of 0.5-10. A significant portion of tropical cirrus clouds are found to have optical depths greater than about 6. Because of the parameterization, the present technique is unable to precisely determine the optical depth values for optically thick cirrus clouds.

Liou, K. N.↗
NASA NTRS1990

Extensional reactivation of an abandoned thrust - A bound on shallowing in the brittle regime

Shallow dip angles (not greater than 45 deg) suggested by field observations of continental extensional faults are not predicted by classical isotropic Mohr-Coulomb-Anderson theory. Earthquake data indicate that normal faults exist in the upper crust with dip angles commonly as shallow as 30 deg. One explanation of the apparent conflict between theory and structural/seismic observations is that intrinsically weak, shallow-dipping pre-existing faults are preferentially reactivated. An analytical treatment clarifies the roles of geometry, intact/preexisting fault strengths and fluid pore pressures. Frictional strength ratios of 3 or greater could account for extremely shallow normal faults (dips 10-20 deg) without consideration of pore pressures in excess of the least principal stress or of principal stress systems rotated away from the gravity vector. Moderate reduction in friction (3/4) with respect to wall rock can reduce the dip to 30 deg and can account for shallow normal-slip earthquakes.

Ivins, E. R.↗
NASA NTRS1990

Model-data comparisons of moments of nonbreaking shoaling surface gravity waves

The predictions of linear and nonlinear (Boussinesq) shoaling wave models for nonbreaking unidirectional surface gravity waves are compared to field observations, with particular emphasis on quantities that may be important for cross-shore sediment transport. The extensive data sets were obtained on two natural beaches, span water depths between 1 and 10 m, and include incident wave power spectra with narrow, broad, and bimodal shapes. Significant wave heights varied between approximately 30 and 100 cm, and peak periods between approximately 8 and 18 s. The evolution of total variances of sea surface elevation, cross-shore velocity, and horizontal acceleration is modeled at least qualitatively well by both linear and nonlinear theories. Only the nonlinear theory predicts the increasingly asymmetric sea surface elevations and horizontal velocities (pitched-forward wave shapes) and the weaker variation of skewness (difference between crest and trough profiles) which are observed to occur during shoaling. The nonlinear theory also models qualitatively well the large skewed accelerations which occur during the passage of asymmetric waves.

Elgar, Steve↗
NASA NTRS1990

FIRE Science Results 1988

FIRE (First ISCCP Regional Experiment) is a U.S. cloud-radiation program that seeks to address the issues of a basic understanding and parameterizations of cirrus and marine stratocumulus cloud systems and ISCCP data products. The papers describe research analysis of data collected at the 1986 Cirrus Intensive Field Observations (IFO), the 1987 Marine Stratocumulus IFO, and the Extended Time Observations. The papers are grouped into sessions on satellite studies, lidar/radiative properties/microphysical studies, radiative properties, thermodynamic and dynamic properties, case studies, and large scale environment and modeling studies.

Mcdougal, David S.↗
NASA NTRS1990

Comparison of NOAA-9 ERBE measurements with Cirrus IFO satellite and aircraft measurements

Earth Radiation Budget Experiment (ERBE) measurements onboard the NOAA-9 are compared for consistency with satellite and aircraft measurements made during the Cirrus Intensive Field Observation (IFO) of October 1986. ERBE scene identification is compared with NOAA-9 TIROS Operational Vertical Sounder (TOVS) cloud retrievals; results from the ERBE spectral inversion algorithms are compared with High resolution Interferometer Sounder (HIS) measurements; and ERBE radiant existance measurements are compared with aircraft radiative flux measurements.

Ackerman, Steven A.↗
NASA NTRS1990

Cloud parameters from GOES visible and infrared radiances during the FIRE Cirrus IFO, October 1986

Visible (VIS, 0.65 micron) and infrared (IR, 10.5 microns) channels on geostationary satellites are the key elements of the International Satellite Cloud Climatology Project (ISCCP). All daytime ISCCP cloud parameters are derived from a combination of VIS and IR data. Validation and improvement of the ISCCP and other cloud retrieval algorithms are important components of the First ISCCP Regional Experiment (FIRE) Intensive Field Observations (IFO). Data from the Cirrus IFO (October 19 to November 2, 1986) over Wisconsin are available for validating cirrus cloud retrievals from satellites. The Geostationary Operational Environmental Satellite (GOES) located over the Equator at approximately 100 deg W provided nearly continuous measurements of VIS and IR radiances over the IFO areas. The preliminary results of cloud parameters derived from the IFO GOES data are presented. Cloud attitudes are first derived using an algorithms without corrections for cloud emissivity. These same parameters will then be computed from the same data relying on an emissivity correction algorithm based on correlative data taken during the Cirrus IFO.

Heck, Patrick W.↗
NASA NTRS1990

Both sides now

On November 2, 1986 of the cirrus Intensive Field Observations, cirrus clouds were observed from both ground-based and aircraft lidar. The NASA ER2 aircraft carrying a lidar, crossed Madison three times and Wausau five times during its mission. Ground-based lidars from the University of Wisconsin in Madison and the University of Utah in Wausau were operating during the ER2 overpasses. This gave FIRE unique lidar observations of cirrus clouds from both sides. This lidar data are presented and analyzed.

Wylie, Donald P.↗
NASA NTRS1990

Diurnal variation of marine stratocumulus over San Nicolas Island during the FIRE IFO

Preliminary analysis was made of data collected at San Nicolas Island during the Intensive Field Observation (IFO) phase of the First International Satellite Cloud Climatology Program's Regional Experiment (FIRE). Of particular interest was an examination of a distinct diurnal variation in the cloud properties, despite an apparent absence of diurnal forcing from the surface. Direct or indirect radiative modulation of such clouds, as proposed by Fravalo at el. (1981) and Turton and Nicholls (1987) indeed seems likely. Preliminary observational evidence for diurnal change in the marine stratocumulus adjacent to San Nicolas Island is presented. A comparison is then made between the observed behavior and predictions from theoretical models of the interactive effect of radiation on boundary layer clouds.

Davies, R.↗
NASA NTRS1990

NRL tethered balloon measurements at San Nicolas Island during FIRE IFO 1987

An overview is given of the tethered balloon measurements made during the First ISCCP Regional Experiment (FIRE) marine stratocumulus intensive field observations (IFO) at San Nicolas Island in 1987. The instrument utilized on the balloon flights, the 17 flights over a 10 day period, the state of the data analysis, and some preliminary results are described. A goal of the measurements with the Naval Research Laboratory (NRL) balloon was to give a unique and greatly improved look at the microphysics of the clear and cloud-topped boundary layer. For this goal, collocated measurements were made of turbulence, aerosol, cloud particles, and meteorology. Two new instruments which were expected to make significant contributions to this effort were the saturation hygrometer, capable of measuring 95 percent less than RH 105 percent (with an accuracy of 0.05 percent near 100 percent) and used for the first time in clouds; and the forward scatter meter which gives in situ LWC measurements at more than 10 Hz. The data set, while unfortunately only partially simultaneous with the bulk of the FIRE stratocumulus observations, is unique and worthwhile in its own right. For the first time accurate RH measurements near 100 percent have been made in-cloud; although, the use of the saturation hygrometer reflected a learning experience which will result is substantially better performance the next time. These measurements were made in conjunction with other microphysical measurements such as aerosol and cloud droplet spectra, and perhaps most important of all, they were all collocated with bivane turbulence measurements thus permitting flux calculations. Thus the analysis of this data set, which consisted of about 50 percent stratocumulus cases including increasing and decreasing partial cloud cover, should lead to new insights on the physical mechanisms which drive the boundary-layer/cloud/turbulence system.

Gerber, Hermann↗
NASA NTRS1990

Cloud optical parameters as derived from the multispectral cloud radiometer

Here, researchers analyze the data taken in the marine stratocumulus intensive field observation component of the First ISCCP Regional Experiment (FIRE), conducted off the California coast in July, 1987 using the Multispectral Cloud Radiometer (MCR). Researchers installed an efficient retrieval scheme for deriving the cloud optical thickness and droplet mode radius, and have described the behavior of the retrieval error. Generally the scheme can retrieve the optical thickness and mode radius adequately unless they are too small; the use of the forward scattering region is more sound than the use of the backscattering portion. Applying the method to real data, researchers derived the two-dimensional distribution of optical thickness and mode radius for a portion of one of the FIRE marine stratocumulus missions. In this case study, the droplet size showed a more uniform distribution than optical thickness with some correlation between large droplet size and small optical thickness. Although researchers can find microphysical reasons for these tendencies, they suspect that the remotely sensed droplet size may be overestimated. As a future problem, they will compare results with in situ data of the droplet size distribution. Also it will be very important to check several reasons why the droplet radius might be overestimated, e.g., soot contamination, effect of escaping photons from the lateral sides of broken clouds, and so on.

Nakajima, Eruyuki↗
NASA NTRS1990

Horizontal variability of the marine boundary layer structure upwind of San Nicolas Island during FIRE, 1987

During the months of June and July 1987, the Marine Stratocumulus Intensive Field Observation Experiment of First ISCCP Regional Experiment (FIRE) was conducted in the Southern California offshore area in the vicinity of San Nicolas Island (SNI). The Naval Ocean Systems Center (NOSC) airborne platform was utilized during FIRE to investigate the upwind low level horizontal variability of the marine boundary layer structure to determine the representativeness of SNI-based measurements to upwind open ocean conditions. The NOSC airborne meteorological platform made three flights during FIRE, two during clear sky conditions (19 and 23 July), and one during two stratus conditions (15 July). The boundary layer structure variations associated with the stratus clouds of 15 July 1987 are discussed. Profiles of air temperature (AT) and relative humidity (RH) taken 'at' and 'upwind' of SNI do show differences between the so-called open ocean conditions and those taken near the island. However, the observed difference cannot be uniquely identified to island effects, especially since the upwind fluctuations of AT and RH bound the SNI measurements. Total optical depths measures at SNI do not appear to be greatly affected by any surface based aerosol effects created by the island and could therefore realistically represent open ocean conditions. However, if one were to use the SNI aerosol measurements to predict ship to ship EO propagation conditions, significant errors could be introduced due to the increased number of surface aerosols observed near SNI which may not be, and were not, characteristic of open ocean conditions. Sea surface temperature measurements taken at the island will not, in general, represent those upwind open ocean conditions. Also, since CTT's varied appreciably along the upwind radials, measurements of CTT over the island may not be representative of actual open ocean CTT's.

Jensen, Douglas R.↗
NASA NTRS1990

Plume mechanics and stratocumulus convection

The First ISCCP Regional Experiment (FIRE) marine stratocumulus Intensive Field Observation (IFO) held in July, 1987 produced a data set that is far more comprehensive than data sets from previous stratocumulus experiments. One exciting new development was the use of the 10.6 micron lidar system for cloud-top mapping that was available on the National Center for Atmospheric Research (NCAR) Electra. This system provided a unique look at the small scales of the turbulence in the clouds, images of the turbulent structures that are quantitatively revealed by conditional sampling (e.g., Khalsa and Greenhut, 1987). The behavior of these updrafts and downdrafts is central to the dynamics of the stratocumulus-topped marine boundary layer. FIRE's objectives of understanding cloud dynamics and how they affect the cloud optical depth - which, in turn, is the crucial factor in determining the clouds' albedo - therefore require the investigation of these drafts. Given here are initial results from a simple model capable of simulating moist, entraining plumes that are subject to water phase changes and radiative heating and cooling. These results correspond, therefore, to the 'dry cloud' case discussed by Lilly and Schubert (1980). The model's simplicity limits the realism of the results - the plumes are assumed not to interact, for example - but the role of radiative processes in influencing the plume dynamics is clear. Also revealed is the role the plumes play is maintaining the cloud-top inversion. The model equations and methodology used, and qualitative results are given.

Hanson, Howard P.↗
NASA NTRS1990

Aircraft/island/ship/satellite intercomparison: Preliminary results from July 16, 1987

The First ISCCP Regional Experiment (FIRE) objective of validating and improving satellite algorithms for inferring cloud properties from satellite radiances was one of the central motivating factors in the design of the specific field experimental strategies used in the July, 1987 marine stratocumulus intensive field observations (IFO). The in situ measuring platforms were deployed to take maximum advantage of redundant measurements (for intercomparison of the in situ sensors) and to provide optimal coverage within satellite images. One of the most ambitious of these strategies was the attempt to coordinate measurements from San Nicolas Island (SNI), the R/V Pt. Sur, the meteorological aircraft, and the satellites. For the most part, this attempt was frustrated by flight restrictions in the vicinity of SNI. The exception was the mission of July 16, 1987, which achieved remarkable success in the coordination of the platforms. This presentation concerns operations conducted by the National Center for Atmospheric Research (NCAR) Electra and how data from the Electra can be integrated with and compared to data from the Pt. Sur, SNI, and the satellites. The focus is on the large-scale, integrated picture of the conditions on July 16 from the perspective of the Electra's flight operations.

Hanson, Howard P.↗
NASA NTRS1991

The influence of the hydrologic cycle on the extent of sea ice with climatic implications

The role was analyzed of the hydrologic cycle on the distribution of sea ice, and its influence on forcings and fluxes between the marine environment and the atmosphere. River discharge plays a significant role in degrading the sea ice before any melting occurs elsewhere along the coast. The influence is considered of river discharge on the albedo, thermal balance, and distribution of sea ice. Quantitative atmospheric-hydrologic models are being developed to describe these processes in the coastal zone. Input for the models will come from satellite images, hydrologic data, and field observations. The resulting analysis provides a basis for the study of the significance of the hydrologic cycle throughout the Arctic Basin and its influence on the regional climate as a result of possible climatic scenarios. The area offshore from the Mackenzie River delta was selected as the study area.

Dean, Ken↗
NASA NTRS1989

Basic properties of developed wind waves and their influence on microwave remote sensing signatures

Error trends in wind speed measurements by satellite scatterometer altimeter and microwave radiometer are shown to be correlated with the degree of wave development. These errors are analyzed theoretically by studying the rms wave slope which, directly or indirectly, affects all microwave signatures. For equilibrium sea state, the influence of spectrum parameters on the wave slope is reviewed. In well-developed seas, the dominant wavelength is shown to have no effect on the slope. Temporal-spatial rates of steep and breaking waves are derived and compared with field observations. The inner scale that determines a rapid falloff of spectral density function at high frequencies is estimated. The dependence of the spectral parameters on wind speed and sea maturity is studied using NOAA buoy observations. It is concluded that the removal of environmental error trends from satellite measurements can be best accomplished by a joint processing of microwave returns from several independent instruments.

Glazman, Roman E.↗
NASA NTRS1990

The 27-28 October 1986 FIRE IFO cirrus case study - A five lidar overview of cloud structure and evolution

During the case study from the First ISCCP (International Satellite Cloud Climatology Program) Regional Experiment (FIRE) Intensive Field Observation (IFO), one airborne lidar system and four ground-based systems collected linear depolarization, intrinsically calibrated backscatter, and Doppler velocity information. Data presented describe the temporal evolution and spatial distribution of cirrus clouds over an area encompassing southern and central Wisconsin. Cirrus cloud types include dissipating subvisual and thin fibrous cirrus cloud bands, an isolated mesoscale uncinus complex, a large-scale, deep cloud that developed into an organized cirrus structure within the lidar array, and a series of intensifying mesoscale cirrus cloud masses. It is noted that the cirrus frequently developed in the vertical from particle fallstreaks emanating from generating regions at or near cloud tops; however, glaciating supercooled altocumulus clouds contributed to the production of ice mass at the base of the deep cirrus cloud.

Sassen, Kenneth↗