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Open Access
A cloud free vault
(Colorado State University. Libraries, 1975) Weaver, John F., author
A severe squall line, with several isolated storms near its southernmost end, was observed near Grover, Colorado, on the afternoon of 22 July 73 by the NHRE storm monitoring system. The northern segment of the squall line was oriented parallel to cloud level winds (i.e., northeast-southwest), while the southern segment was aligned north-south. The northern segment developed an extensive cloud free vault intruding into the cloud base above the lifting condensation level (LCL) between the precipitation and the updraft pedestal. No downdraft or gust front was observed from the northern segment. Downdrafts and a gust front characterized by a pressure jump of +3 mb and peak winds of 60 knots were produced by both the southern segment and the isolated storms.
Open Access
CIRA: a synopsis of activity, September 1980 - December 1981
(Colorado State University. Libraries, 1982-02) Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
This first "mid-year" report from the Cooperative Institute for in the Atmosphere (CIRA) is intended to communicate scientific results and information about current activities to NOAA and CSU scientists, students and staff as well as other interested parties. Falling as it does at a report time after the first full year of CIRA operations, it thus becomes the first CIRA summary report to carry scientific information.
Open Access
The genesis and development of deep convective storms
(Colorado State University. Libraries, 1983-01) Sinclair, P. C., author; Purdom, J. F. W., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
During the summer of 1980, NESS sponsored a research aircraft field program that combined research aircraft flights with rapid scan GOES imagery. The purpose of the research program was to provide a better understanding of the natural mechanisms that lead to the development of deep convective storms through integration and analysis of those special data sets. Data were taken during the field program with the goal of providing an in-depth understanding of the fundamental mechanism - arc cloud line interactions - that lead to the development of deep convection. The experiment provided a unique data base from which the convective storm's mesoscale flow field (dynamic and thermodynamic properties) could be documented by in-situ measurements and near simultaneous GOES visible and infrared data. Several arc clouds were penetrated on three separate GOES rapid scan imaging days, and representative results from those penetrations are given in the text. It is hoped that the improvement in knowledge gained from this experiment will lead to a better understanding of mesoscale dynamics, which is of great importance for the development of improved short-range forecasting techniques.
Open Access
CIRA: a synopsis of activity, January 1 - December 31, 1982
(Colorado State University. Libraries, 1983-03) Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
This second "mid-year" report from the Cooperative Institute for in the Atmosphere (CIRA) is intended to communicate scientific results and information about current activities to NOAA and CSU scientists, students and staff as well as other interested parties.
Open Access
An observational study of summer surface wind flow over northeast Colorado
(Colorado State University. Libraries, 1983-11) Toth, James J., author; Johnson, Richard H., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
Analysis of summer surface winds over northeast Colorado, using data from the Program for Regional Observing and Forecasting Services (PROFS), has been carried out to investigate the diurnal wind flow pattern over the broad drainage area of the South Platte River. The pattern, similar to the classic descriptions of valley wind flows, appears in monthly averages as well as on most individual days. Unique features of the flow are documented, in particular the upslope/downslope transitions which begin near the foothills of the Front Range of the Rocky Mountains and propagate eastward. Previous conceptual models of the afternoon and evening wind flow over northeast Colorado are verified. The afternoon upslope flow is often responsible for enhanced convective cloud cover in preferred locations during the summer. It is suggested that the development of moist convection modifies the diurnal flow and contributes to the late afternoon and early and evening transition to downslope flow. This study has pointed out the need for further investigations of this problem.
Open Access
CIRA: a synopsis of activity, January 1 - December 31, 1983
(Colorado State University. Libraries, 1984-03) Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
This third "mid-year" report from the Cooperative Institute for in the Atmosphere (CIRA) is intended to communicate scientific results and information about current activities to NOAA and CSU scientists, students and staff as well as other interested parties.
Open Access
Summary report: Pingree Park research retreat
(Colorado State University. Libraries, 1985) Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
On June 19-21, 1985 a retreat was held at the CSU Mountain Campus of Pingree Park for students and faculty involved with current research projects. The following is a compilation of attendees, presentations, and summary reports of the small group sessions.
Open Access
Satellite data support to the PRE-STORM operations center, May-June 1985
(Colorado State University. Libraries, 1985-09) Purdom, J. F. W., author; Green, R. N., author; Weaver, J. F., author; Zehr, R. M., author; Lubich, D. A., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
The activities of CIRA are described with regard to satellite support of the field phase of the Oklahoma-Kansas PRE-STORM experiment, and to the ongoing research projects which make use of PRE-STORM data sets. Routine GOES imagery and VAS products were displayed on a personal computer (PC) workstation located in the PRE-STORM operations support facility. Half-hourly visible and infrared imagery, two-hourly water vapor imagery, and a number of derived VAS sounding products were available in real-time. The impact of the PC workstation on PRESTORM operations is discussed. The image display and analysis products, and VAS data products for use on the PC workstation are described in detail. Finally, PC data archival procedures and preliminary plans for future research are presented.
Open Access
Acid deposition in Colorado: a potential or current problem; local versus long-distance transport into the state
(Colorado State University. Libraries, 1986) Pielke, Roger A., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
A compendium of papers presented at a workshop sponsored by the Cooperative Institute for Research in the Atmosphere, Colorado State University in Fort Collins, Colorado on August 13-15, 1986.
Open Access
A modeling study of visibility in the Grand Canyon
(Colorado State University. Libraries, 1986-08) Weissbluth, Michael Jeffrey, author; Cox, Stephen K., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
Using a backward version of the Monte Carlo Radiative Transfer model, radiance values in the Grand Canyon were simulated to within the precision of ten percent. The contiguous spectral contrast was introduced to distinguish between adjacent areas of the same target and compared to the apparent spectral contrast. The contiguous spectral contrast is a valuable tool in evaluating visibility because in some cases, the target became more distinguishable when viewed against the sky while the target features became less distinguishable. Average equilibrium radiance values were calculated and incorporated into the Koschmieder estimate; the Koschmieder estimate was deemed to be of limited value in the Grand Canyon because of the violation of the assumptions used to derive the estimate. It was shown that first order scattering results alone could be used to estimate apparent spectral contrast to within a 10% accuracy; higher order scattering must be considered when radiance values are calculated for the Grand Canyon scene.
Open Access
Interaction of shallow cold surges with topography on scales of 100-1000 kilometers
(Colorado State University. Libraries, 1987-12) Toth, James J., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
A shallow cold air mass is defined as one not extending to the top of the mountain ridge with which it interacts. The structure of such an airmass is examined using both observational data and a hydrostatic version of the Colorado State University Regional Atmospheric Modeling System. The prime constraint on a shallow cold surge is that the flow must ultimately be parallel to the mountain ridge. It is found that the effects of this constraint are altered significantly by surface sensible heat flux. Cold surges are slowed during the daylight hours, a result consistent with previous observational studies in Colorado east of the Continental Divide. Two case studies are described in detail, and several other events are cited. Since observations alone do not provide a complete description of diversion of the cold air by the mountain range, numerical model simulations provide additional insight into import ant mechanisms. A case study on 14 June 1985 is described using observational and model data. The model development of a deep boundary layer within the frontal baroclinic zone is consistent with the observations for this and other cases. This development is due to strong surface heating. Turning off the model shortwave radiation is seen to produce a rapid southward acceleration of the surface front, with very shallow cold air behind the front. Model simulations with specified surface temperature differences confirm the importance of upward heat flux from the surface in slowing the southward movement of the cold surge. It is concluded that the slowing is not due simply to the thermal wind developing in response to the heating of higher terrain to the west. Since surface heating is distributed over a deeper layer on the warm side of the temperature discontinuity, there is frontolysis at the surface. But this modification would develop even over flat terrain. Sloping terrain introduces additional effects. Heating at the western, upslope side of the cold surge inhibits the development of pressure gradients favorable to northerly flow. A second contribution comes from westerly winds at ridgetop level. These winds are heated over the higher terrain and flow downslope, further retarding the progression of the cold air at the surface.
Open Access
The sea-land breeze as local wind, the numerical and analytical approach to its modeling
(Colorado State University. Libraries, 1988) Dalu, Giovanni A., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
Lecture by Giovanni A. Dalu held at the International Center for Theoretical Physics-Trieste on 16-20 May 1988 during the workshop on Modeling of the Atmospheric Flow Field.
Open Access
Monitoring climate for the effects of increasing greenhouse gas concentrations
(Colorado State University. Libraries, 1988) Pielke, Roger A., editor; Kittel, Timothy G. F., editor; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
A compendium of papers presented at a workshop sponsored on August 26-28, 1987 by the Cooperative Institute for Research in the Atmosphere.
Open Access
1988 CIRA satellite research workshop
(Colorado State University. Libraries, 1988) Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
This document reports on a Satellite Research Workshop sponsored by the Cooperative Institute for Research in the Atmosphere (CIRA) that was held at the Colorado State University's Pingree Park campus from September 21-23, 1988. The workshop was designed to investigate research and applications opportunities using data from the next generation GOES and TIROS satellites.
Open Access
Annual report for 1987 from the Cooperative Institute for Research in the Atmosphere, Colorado State University, to Marine Meteorology Section, Ocean Sciences Division of the Office of Naval Research on studies of space/time variability of marine atmospheric boundary layer characteristics
(Colorado State University. Libraries, 1988-03) Vonder Haar, Thomas H., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
Open Access
Mesoscale analysis by numerical modeling coupled with satellite-based sounding
(Colorado State University. Libraries, 1988-11) Lipton, Alan E., author; Vonder Haar, Thomas H., author; Purdom, J. F. W., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
This dissertation deals with the development of a system for time-continuous mesoscale analysis and its use in studying the mesoscale distribution of summertime convective cloud development in the Northeastern Colorado region. There were two basic components of the system — a version of the CSU Regional Atmospheric Modeling System (RAMS) and an algorithm for retrieving temperatures and water vapor concentrations from VISSR Atmospheric Sounder (VAS) data. The system was designed to avoid some of the problems that researchers have encountered when satellite-retrieved parameters have been input to models. The primary distinguishing feature of the new method is that there is an intimate coupling of the retrieval and modeling processes. Water vapor concentrations and ground surface temperatures were the foci of the analyses. In preparation for analysis experiments we tested the sensitivity of a two-dimensional version of the model to various controls on the behavior of water vapor concentrations and surface temperatures. For water vapor mixing ratios, variations that might be caused by analysis errors had very little impact on the dynamics of circulations in the pre-convective stage. In contrast, ground surface temperature variations were shown to have a large impact on circulations, so analysis errors are very relevant to pre-convective dynamics. The first comparisons of the coupled analysis method with other, related, methods was by means of two-dimensional simulations. Analyses in which surface temperatures were derived from satellite-retrievals were compared with the alternative of relying on energy balance computations. The energy balance computations were so sensitive to soil characteristics, which were simulated as unknown, that the satellite retrieval method gave better results even with cloud contamination. In water vapor analysis comparisons no single method was superior in every respect, but the coupled method performed relatively well. Vertical gradients and horizontal gradients were well represented, and the method was relatively insensitive to a common problem in pre-convective analysis — contamination of satellite data by increasing amounts of small convective clouds. Analysis methods were further compared in a three-dimensional case study for 21 August 1983. The horizontal and time variations of satellite-retrieved surface temperatures closely corresponded to the conventional shelter temperature observations, but had much greater detail. In contrast, the energy balance-based temperatures tended to increase too quickly during the morning and lacked some of the observed gradients. According to the retrievals, there can be very large mesoscale gradients in temperatures at the ground surface even on the relatively flat plains. In the case study water vapor analyses there were substantial differences among the results of the several methods that were intercompared. The study demonstrated that, when the first set of satellite data is less reliable than the later sets, some of the contamination lingers throughout the time-continuous coupled analysis results. However, the coupled method generally appeared to be the most valuable of the methods considered in this study because it exploited the major strengths of the numerical model and the satellite data while making it relatively easy to recognize any impacts of their weaknesses. The results of this dissertation support the hypothesis that both ground surface temperatures and terrain variations can play important roles in pre-convective water vapor kinematics through their influences on vertical and horizontal winds. The development of convective clouds corresponded largely, but not exclusively, with convergence and deepening of low-level water vapor. The analysis system proved to be valuable for forecasting through the close correspondence between derived stability indices and later convective development. The new method is a step in the expanding capability of meteorologists to combine tools and sources of data for understanding and forecasting mesoscale phenomena.
Open Access
Microwave remote sensing of cloud liquid water and surface emittance over land regions
(Colorado State University. Libraries, 1989-01) Jones, Andrew S., author; Vonder Haar, Thomas H., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
Microwave remote sensing of cloud liquid water has largely been limited to areas over ocean surfaces. This study uses data from a new microwave instrument, the SSM/I on a polar-orbiting DMSP satellite, and infrared and visible data from the VISSR instrument on the GOES satellite in geostationary orbit. The region selected for the study was an area of 500 km x 500 km centered on northeast Colorado during the first week of August 1987. The SSM/I instrument has new high frequency channels (85.5 GHz) which are more strongly attenuated by cloud liquid water than channels on previous instruments. This allows for the estimation of integrated cloud liquid water based on the microwave brightness temperature depression caused by attenuation and emission of microwave radiation at the colder cloud levels. Atmospheric attenuation due to oxygen and water vapor is determined using a millimeter-wave propagation model (MPM). The Rayleigh approximation is used for the calculation of cloud liquid water attenuation. Surface emittance measurements at the SSM/I frequencies were made with the aid of co-located GOES infrared data during clear sky conditions. Images produced of the retrieved surface emittances suggest a strong influence by wet surfaces caused by precipitation and irrigation. Error analysis results indicate absolute errors of ±0.012 for surface emittance retrievals for the 85.5 GHz channels. Integrated cloud liquid water retrievals show good qualitative agreement with other available data sources. Numerical error sensitivity analysis and comparison of integrated cloud liquid water retrievals for the vertical and horizontal polarizations show error estimates of 0.15 kg•m-2 including instrument noise. A bias between the horizontal and vertical polarizations of the 85.5 GHz channels was noticed in the retrieved integrated cloud liquid water amounts. The bias appears to be due to a relative instrument error between channels of approximately 1.5 K. Absolute error estimates of the integrated cloud liquid water retrievals are unavailable but calibration of the method should be possible if quantitative integrated cloud liquid water amounts are known.
Open Access
Cloud and convection frequencies relative to small-scale geographic features
(Colorado State University. Libraries, 1990-01) Gibson, Harold M., author; Vonder Haar, Thomas H., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
Visible and infrared data of GOES West were collected for nine hours each day during the summer of 1986. Cloud frequency charts were computed for the area from Mississippi east to Georgia and the Gulf of Mexico north to Tennessee for each of the nine hours as well as convection frequency charts to four convection intensities as defined by the temperature of the cloud top. Strong diurnal tendencies were noted. As was expected, these charts show that over the land areas cloudiness is at a maximum during the early afternoon hours with convection at a maximum in the late afternoon and evening. Cloudiness and convection are at a maximum during the nocturnal hours over the Gulf of Mexico. Cloud frequency shows a strong relationship to small terrain features. Small fresh water bodies have cloud minima in the afternoon hours relative to the surrounding terrain while higher terrain, especially if there is a sharp slope, have cloud maxima. The adjacent lower terrain exhibits afternoon cloud minima due to divergence caused by the valley to mountain breeze. The sea breeze-induced convergence causes relative cloud maxima over near-shore land areas with the stronger maxima over peninsulas. It is shown that the sea breeze results in convergent low level flow regardless of the weather over a peninsula or over land adjacent to a bay or inlet. Cloud frequencies tend to be larger both in magnitude and areal extent over peninsulas. Small scale geographical features show no relationship to convection, but larger peninsulas and extensive higher terrain show late afternoon convection maxima.
Open Access
A physical/optical model for atmospheric aerosols with application to visibility problems
(Colorado State University. Libraries, 1990-01) Tsay, Si-Chee, author; Stephens, Graeme L., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
The objectives of this report are to describe a conceptually simple but accurate model for efficiently computing the optical properties of atmospheric aerosols. Aerosol characteristics such as size distribution, solubility, mixture and the atmospheric moisture effect are taken into account when computing its optical properties. The dependence of the latter on aerosol microstructure is also discussed. The optical properties of aerosols are computed by employing numerically stable algorithms for obtaining Mie solutions to coated spheres. Resulting bulk quantities such as the extinction/backscatter coefficient, the probability of scattering, and the scattering phase matrix can be incorporated into multiple scattering schemes of radiative transfer for visibility investigations and other types of studies.
Open Access
The wind's response to transient mesoscale pressure fields associated with squall lines
(Colorado State University. Libraries, 1990-05) Vescio, Michael D., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisher
A simple one-dimensional slab model has been developed to examine the wind's response to transient mesoscale pressure fields that frequently accompany mature midlatitude squall lines. The model numerically solves a form of the momentum equation that includes the pressure gradient force, advection, and the frictional force. The Coriolis force is neglected since attention is focused on time periods of 1-2 hrs. The pressure field is specified by a sine wave with a constant phase speed. The amplitude of this wave is initially zero, but then increases linearly with every timestep until t = 2 hrs. At this time, the wave reaches its predetermined maximum amplitude. This pressure wave represents a mesohigh and wake low that have the same amplitude and phase speed. Since these features are transient, the air lacks sufficient time to achieve a balanced state. Therefore, winds are directed forward through the mesohigh, and rearward through the wake low, at right angles to the isobars. This airflow pattern produces an axis of divergence to the rear of the mesohigh, with convergence occurring near the back edge of the wake low. The model is able to accurately simulate the airflow near these pressure features. Pressure waves with various maximum amplitudes and phase speeds are used in the model for the purpose of comparison. Model results vary slightly as the phase speed and maximum amplitude of the pressure wave is changed. Air parcel trajectories are used to help explain these variations. Model results are compared to the observed airflow near the mesohigh and wake low associated with an intense squall line that moved through Oklahoma and Kansas on 10-11 June 1985. The time period of interest is 0100–0400 UTC on the 11th of June, during which the squall line, as well as the mesoscale pressure fields, reached their maximum intensity. Cross sections through the center of the mesohigh and wake low indicate that the pressure field were roughly sinusoidal with an amplitude of approximately 2.5 mb. Therefore, model results obtained using a 2.5 mb maximum amplitude pressure wave are used for the comparison. The model derived wind field is similar to the observed wind field in many respects. Differences can be attributed to several factors, one of which is the fact that the pressure field, specified in the model, is only an approximation to the observed pressure field. Finally, a discussion of the frictional force is presented. To assess the relative importance of the surface friction term, a scale analysis of the momentum equation is performed. This analysis shows that this term is only one order of magnitude smaller than the next smallest term in the momentum equation. Therefore, surface friction cannot be neglected. Slight variations in model results occur as the magnitude of the term varies. The effects of momentum transport from above on the surface wind field are also discussed. It appears that such transport is only important near the leading convective line where convective scale updrafts and downdrafts are occurring. Behind the convective line, the rain cooled air is much too stable, and the convective scale motion is too weak, for significant momentum transport into the boundary layer.