Hamburg, Univ., Diss., 2001. / Computerdatei im Fernzugriff.

Hamburg, Univ., Diss., 2001. / Computerdatei im Fernzugriff.

Hamburg, Universiẗat, Diss., 2001.

Thesis (M.S.)--University of Wyoming, 2009. / Title from PDF title page (viewed on June 2, 2010). Includes bibliographical references (p. 72-80).

We present the development of the adjoint of a physically based cirrus formation parameterization that computes the sensitivity of formed crystal number concentration to numerous model variables (e.g., updraft velocity, soluble aerosol geometric mean diameter and number concentration, insoluble aerosol geometric mean diameter and number concentration, and ice deposition coefficient). The adjoint is demonstrated in the CESM Community Atmosphere Model Version 5.1, where sensitivity information is computed and used to quantify which variables are most responsible for modeled variability in formed crystal number concentration. The sensitivity of formed crystal number concentration to updraft velocity is positive and largest over the tropics where regions of deep convection are collocated with large sulfate number concentrations. Sensitivity to sulfate number concentration is largest over the tropics where updraft cooling is sufficient and sulfate number concentration is low, pointing to a sulfate limited regime. Outside of the tropics, crystal production is dominated by heterogeneous freezing; unexpectedly, sensitivities to insoluble aerosol number concentration for accumulation and coarse mode dust, black carbon, and organic carbon are negative in sign here. This is a result of infrequent, anomalously high updraft velocity events causing shifts in the dominant modes of freezing which act to bias sensitivity information when annually averaged. Updraft velocity is responsible for ~95% of the variability in formed crystal number concentration in the high latitudes of the Northern Hemisphere. In the tropics, sulfate number concentration controls variability in formed crystal number concentration since crystal production here is sulfate limited. Insoluble aerosol species play a secondary role in influencing the variability of crystal concentrations; coarse mode dust is the largest contributor to crystal number variability at nearly 60%, although the spatial extent of this influence is small and concentrated over highly localized dust events. When globally averaged, nearly 90% of the variability in crystal number concentration can be described by only updraft velocity, sulfate number, temperature, and coarse mode dust number concentration. Although these results depend on parameter assumptions, the robustness of the underlying physics of the cirrus formation parameterization used throughout this work suggests that this approach can be a powerful method for efficiently identifying the origin of microphysical dependencies within large scale atmospheric simulations.

The tropics is a very important region in terms of earth’s radiation budget because the net radiative heating is largest in the tropics and that surplus energy is redistributed by the circulations of oceans and atmospheres. Moreover, a large number of clouds are formed by deep convection and convergence of water vapor. Thus, it is very important to understand the radiative energy balance of the tropics and the effect of clouds on the radiation field. For mixed-phase clouds, error analyses pertaining to the inference of effective particle sizes and optical thicknesses are performed. Errors are calculated with respect to the assumption of a cloud containing solely liquid or ice phase particles. The analyses suggest that the effective particle size inferred for a mixed-phase cloud can be underestimated (or overestimated) if a pure liquid phase (or pure ice phase) is assumed for the cloud, whereas the corresponding cloud optical thickness can be overestimated (or underestimated). The analyses of optical depth and fraction of occurrence for thin cirrus clouds showed that about 40% of pixels flagged as clear-sky contain detectible thin cirrus clouds. The regions of high occurrence and large optical depth located around deep convection showed seasonal variations. The thin cirrus clouds occur more frequently with larger optical depth in the northern (southern) hemisphere during spring and summer (autumn and winter). The net cloud radiative forcing by thin cirrus clouds is positive at the top of atmosphere and is negative at the bottom of atmosphere. The difference in OLR between measurement and model is 4.2 Wm-2 for September 2005. The difference is smaller in moist regions and larger in drier regions. OLR increases with increasing surface temperatures up to 300 K but decreases at surface temperatures larger than 300 K due to the strong absorption of increased water vapor. In summary, if the surface temperature is lower than the threshold of convection (300 K), temperature is a dominant factor in OLR and if the surface temperature is larger than 300 K, OLR is strongly influenced by water vapor.

The research presented here retrieves the cloud optical thickness and particle effective size of cirrus clouds using surface radiation measurements obtained during the Atmospheric Radiation Measurement (ARM) field campaign. The algorithm used is based on a method proposed by Yang et al. (2005). The research examines single-layer ice clouds in the midlatitude and polar regions. The retrieved information in the midlatitudes is then verified using retrievals from the Moderate-resolution Imaging Spectroradiometer (MODIS) onboard the Terra and Aqua satellites.

Universiẗat, Diss., 2004--München.

Universiẗat, Diss., 2004--München.

Clouds have pivotal influence on the Earth's hydrological cycle and climate system because they are intricately involved in the dynamical, chemical, and radiative processes within the upper troposphere and lower stratosphere. Cirrus clouds occur at high altitude around the tropopause level and, despite their thin appearance and low optical thickness, they contribute to the radiative balance of the atmosphere. The processes in this region of the atmosphere have become increasingly important for a clear understanding of feedback mechanisms in the climate system. The Canadian designed and built Optical Spectrograph and Infrared Imaging System (OSIRIS) satellite instrument measures the spectrum of sunlight scattered from the Earth's atmosphere at wavelengths from the ultraviolet (280 nm) to the near infrared (810 nm). The limb scattering measurement technique allows OSIRIS to collect information on the vertical profile of atmospheric chemical and particle composition at a resolution of approximately 2km with nearly global daily coverage. In this work, a technique characterizing the distribution of cirrus cloud top occurrences from OSIRIS limb scattering radiance profiles is presented. The technique involves computing residual profiles by comparing normalized measured radiance and modelled molecular density profiles where mismatches between the two traces indicate the presence of clouds. Probability density functions of scattering residuals show the distribution is not a continuum measurement; there is a clear distinction between the cloudy and cloud-free conditions. Observations show high cloud top occurrences in the upper troposphere and lower stratosphere region above Indonesia and Central America. Results obtained using the high altitude cloud detection technique and OSIRIS measurements are compared to those by Sassen et al. (2008) who used CALIPSO nadir measurements and to those by Wang et al. (1996) who used SAGE II solar occultation measurements of cirrus clouds. The cloud detection technique is applied to three case studies. Cloud top detections are used to support results presented in Dessler (2009) who theorized the local relative humidity controls either dehydration or hydration of the lower stratosphere through the efficiency of evaporation of ice lofted by deep convection. The second study makes use of the cloud detection technique to eliminate cloud-containing scans as to identify an Asian Tropopause Aerosol Layer in support of Vernier et al. (2011). Finally, the technique is used to track the dispersion and evolution of the volcanic plume following the Sarychev eruption in June 2009 since monitoring volcanic plumes is an effective way to help mitigate aviation hazards.