Repository logo

Browsing by Author "Heald, Colette L., committee member"

Now showing 1 - 3 of 3
  • Thumbnail Image
    ItemOpen Access
    A new look at the Earth's radiation balance from an A-train observational perspective
    (Colorado State University. Libraries, 2010) Henderson, David Scott, author; Stephens, Graeme L., 1952-, advisor; Heald, Colette L., committee member; Chandrasekar, V., committee member
    The weather and climate of the Earth are driven by interactions of the longwave and shortwave radiation between the Earth's atmosphere and surface. Past studies have tried to derive the Earth radiative budget through the use of models and passive satellite sensors. These past efforts did not have information about the vertical distribution of cloud or aerosols within the atmosphere that significantly influence radiative transfer within the atmosphere. This problem was improved upon with the launch of CloudSat and CALIPSO in 2006. These satellites provide the information on the vertical distribution of clouds. From CloudSat, a fluxes and heating rates product was produced to study the radiative budget, but this was limited to some degree because of undetected clouds and aerosol that have non-negligible effects on the radiative balance. This study addresses these issues by combining CALIPSO and MODIS data with CloudSat to detect and obtain the properties of cloud and aerosol undetected by the CloudSat CPR. The combined data were used to create a cloud and aerosol mask that identified distributions of undetected cloud and aerosol globally and quantified their radiative effects both seasonally and annually. Low clouds were found to have the highest impacts of nearly -6 Wm-2. High clouds globally have little effect, trapping 1 Wm-2, with the majority of the impact in the tropics. Four case studies are presented to show how heating rates change in the vertical due low cloud, cirrus, precipitation, and aerosol. The cloud and aerosol mask was used to create seasonal global distributions of cloud radiative effect using all clouds detected by CloudSat and CALIPSO, and the direct effect of aerosols estimated at the TOA. Using fluxes at the top and bottom of the atmosphere global distributions of outgoing and incoming radiation are shown, and an annual radiation budget of the Earth is derived. Clouds globally are found to have a radiative forcing of -20 Wm-2 at the TOA. The radiative budget of the Earth is calculated in two ways; using normalized shortwave fluxes by the average solar daily insolation, and by changing the solar zenith angle to simulate the diurnal cycle. Finally, the product is validated by comparing the outgoing and surface fluxes with CERES and ISCPP flux products.
  • Thumbnail Image
    ItemOpen Access
    Evaluating satellite-based cloud persistence and displacement nowcasting techniques over complex terrain
    (Colorado State University. Libraries, 2010) Guillot, Eric Michael, author; Vonder Haar, Thomas H., advisor; Heald, Colette L., committee member; Reising, Steven C., committee member
    Cloud nowcasting (0-6 hour forecasts) is an important area of study for weather forecasting, solar energy estimation, and Department of Defense (DoD) applications. The DoD is developing data assimilation methods to predict cloud movement. However these systems require valuable time to run and are not always accurate. Because many military operations are of a time-sensitive nature, fast-processing cloud nowcasting techniques are required. Satellite imagery has shown that clouds move at varying speeds and in different directions, while some tend not to move at all. We test the hypothesis that clouds forced by complex terrain do not displace with the wind, but instead persist along the barrier on which they were formed. Thus, a combination of persistence and displacement techniques in regions of complex terrain are expected to yield a better forecast than either of them alone. The Moderate Resolution Imaging Spectroradiometer (MODIS) sensor aboard both the Terra and Aqua satellites allows for the same region of Earth to be sampled twice by each satellite in a roughly 2-4 hour timeframe. This allows a 2-4 hour cloud nowcast to be created and tested. Using the MODIS Cloud Mask algorithm at 5 km resolution (interpolated to 1 km) and wind data from local weather balloon soundings, a cloud climatology nowcast, a cloud persistence nowcast, a cloud 700mb wind nowcast, a cloud various wind speed nowcast, and a cloud terrain-influenced nowcast were developed from December 2008 through November 2009 over Utah and southwestern Wyoming. Persistence/displacement forecasts were also conducted based on the phase of the cloud, as determined by the MODIS Cloud Phase algorithm. A new forecast skill evaluation scheme was also introduced, designed to equally appreciate correct cloudy areas and correct clear areas. Contrary to our hypothesis, the persistence nowcasting method demonstrated the best skill, especially in the winter months, by as much as 10% critical success index (CSI) over the other methods. The Persistence Method, 700mb Method, and Various Winds Method performed similarly during the summer months (~65% CSI for all three). Use of cloud phase information revealed that ice cloud persistence, while displacing either liquid-water clouds or mixed-phase clouds yielded the highest CSI scores, but the resulting scores were still lower than the Persistence Method. We conclude that cloud analysis at high resolution over complex terrain in Utah, using no model wind or moisture data, cannot improve upon a persistence nowcast over Utah. However, because these basic nowcasting methods can be run and their skill evaluated in less than two minutes, educated decisions can be made nearly instantaneously.
  • Thumbnail Image
    ItemOpen Access
    Wetland extent from a topographic index, wetland's impact on land surface fluxes and a model of CH4 exchange
    (Colorado State University. Libraries, 2011) Kraus, Parker Mayo, author; Denning, A. Scott, advisor; von Fischer, Joe, committee member; Heald, Colette L., committee member
    A method of estimating wetland extent is developed for use in the land surface components of climate/atmospheric models. The approach is developed within the Simple Biosphere Model, SiB, but is intended as a flexible framework applicable to other models. It uses the topographic index, ln(a/tanĪ²), to calculate wetland area as a function of regional hydrologic characteristics and model water content. The calculation of the index is discussed, alternatives to the formally required depression-less DEM are investigated and an approach utilizing a smoothed DEM is adopted. Modeled water content is used to establish a point of saturation on the histogram of topographic index, which varies as modeled water content varies, providing estimates of the wetland fraction over time. This relationship is parameterized for the WLEF-TV tower in northern Wisconsin, and tested at locations in Florida and Louisiana. The method of parameterization is found to be acceptable, but site specific parameterization is desirable. Applications of the model are developed. Sensible and latent heat fluxes and net ecosystem exchange modeled with SiB2.5 at the WLEF site are reevaluated with SiB3 and compared to observations. The wetland area model is used to scale SiB3 estimates of these fluxes using a saturated, "wetland," version of the model. Scaling improves estimates, but is overshadowed by errors introduced to the model by changes in the method by which water stress is calculated in SiB. A simple model of methanogenesis and methanotrophy employing predictions of wetland area is proposed and incorporated in SiB. The dynamics of this model are explored in relation to the temperature dependence, Q10, of methanogenic respiration and conditions of equilibrium. Inspection of the model suggests a seasonal cycle of methane flux with summertime emission and fall and springtime consumption. Estimates from the model are compared with Modified Bowen Ratio, MBR, estimates of methane flux based on observations at WLEF site. Observed fluxes offer some empirical constraint on methanogenic Q10, but uncertainties in the methane flux preclude assessment of the variability of wetland area. Methane consumption is overrepresented in the predicted seasonal cycle of methane flux due to the simplified representation of methanotrophy in the model, but the essential expected behavior is confirmed. Verification of model parameters beyond the WLEF is necessary, though the feasibility of modeling variable wetland extent using the topographic index is demonstrated. Applications of the calculation for representing sub-grid scale soil moisture variability and saturated zone biogeochemistry appear promising for use in atmosphere-coupled regional or global model runs.