Orographic cloud is investigated in a global context using both observations and a global climate model. Climatological cloud amounts from the International Satellite Cloud Climatology Project (ISCCP) are used in conjunction with wind reanalyses to study orographic cirrus amounts over the globe. Significant increases in cirrus are seen over many land areas, with respect to any surrounding oceans. To aid in interpretation of this result special attention is given to the New Zealand region as a case study for orographic cloud formation. Cirrus is found be more prevalent over New Zealand when compared to the adjacent ocean to the west. ISCCP cloud amounts are also compared with a ten year simulation of the UK Meteorological Office's Unified Model. The model is found to be considerably lacking in both cirrus and total high cloud over major mountain ranges. The model is also found to lack trailing cirrus clouds in the lee of orography despite the inclusion of a prognostic ice variable capable of being advected by the model winds. To improve the simulations of orographic cirrus and high cloud in the Unified Model a linear hydrostatic gravity wave scheme that predicts both the amplitude and phase of subgrid orographic gravity waves is introduced. The temperature perturbation caused by these waves in the troposphere is used to modify the amount of both liquid and ice cloud. One important feature of the parameterisation is that the launch amplitude of the gravity waves is predicted by a directional variance function which accounts for anisotropy in the subgrid orography. The parameterisation is explored in the context of an off-line testbed before implementation in the Unified Model. In a ten year simulation the parameterisation is found to increase the high cloud amounts over a number of the world's major mountain ranges. However, this extra cloud is optically thick and unable to remove the deficiency in optically thin cirrus amounts. Suggestions, as part of future work, for improvements to the model and orographic cloud parameterisation are also made.

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How are stars formed? This is one of the most fundamental questions in astronomy. It is therefore ironic that to date, no object has been unambiguously identified as a true protostar; an object which derives the bulk of its luminosity from accretion. While this may be ironic, it is not surprising. Stars are believed to form as a result of the gravitational collapse of a portion of a molecular cloud. Theory predicts that the cloud core in which the star is formed will be cold, dense and possess hundreds of magnitudes of extinction, rendering it opaque at visible and near-infrared wavelengths. Continuum observations at far-infrared, submillimeter, and millimeter wavelengths can be used to identify candidate protostars, but spectroscopic observations are needed to detect infall. The difficulties arise when there are systematic velocity fields present in the cloud core which are not the result of infall, such as would be produced by either a molecular outflow or rotation. In this dissertation we use both observations and theoretical models to sort through these problems and develop a strategy which could be used to identify and study protostars.

We have conducted a CS survey of the 10 outflows and 30 IRAS sources identified by Margulis (1987) in the Mon OB1 dark cloud to study the relationship between outflows, YSOs, and dense cores in this cloud. We have found that the CS J = 2 → 1 transition traces a large portion of the dense, low-velocity components of the outflows in Mon OB1. We find the mass of this component to be nearly an order of magnitude greater than previous estimates of the outflow "core" component. We detected little CS gas around the quiescent sources in this cloud. CS 2 → 1 temperatures and integrated intensities are 2 to 7 and 2 to 14 times higher, respectively, in the vicinities of IRAS sources associated with outflow activity than about the quiescent sources. This implies CS abundances, temperatures and/or densities are enhanced in regions where outflows impact the ambient cloud. The CS 2 → 1 emission is concentrated in two regions encompassing 6 of the 10 previously identified outflows in this cloud. Four of these six outflows are identifiable in CS. Two, previously identified as monopolar outflows, exhibit bipolar structure in CS. We have detected the CS J = 5 → 4 transition in the vicinity of 4 of the 10 outflows in this cloud, and around none of the quiescent IRAS sources. The CS 5 → 4 emission is extended around two of the outflow sources and has been mapped in these regions. CS J = 7 → 6 emission has been mapped about the brightest outflow source in this cloud. The morphology of the 7 → 6 region suggests it may have been part of the collimating structure for the outflow associated with this sources. The velocity structure and binding energies of the 5 → 4 and 7 → 6 cores suggest the outflows are disrupting these cores. The addition of the low-velocity CS outflow component to previous estimates of outflow energetics implies multiple generations of outflows need not be required to support this cloud against collapse. Our results neither support nor rule out the existence of fossil outflows in this cloud. A full-cloud, unbiased survey is required to search for such outflows.

No description available.

No description available.

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.

We present maps of the Large and Small Magellanic Clouds from combined South Pole Telescope (SPT) and Planck data. The Planck satellite observes in nine bands, while the SPT data used in this work were taken with the three-band SPT-SZ camera, The SPT-SZ bands correspond closely to three of the nine Planck bands, namely those centered at 1.4, 2.1, and 3.0 mm. The angular resolution of the Planck data ranges from 5 to 10 arcmin, while the SPT resolution ranges from 1.0 to 1.7 arcmin. The combined maps take advantage of the high resolution of the SPT data and the long-timescale stability of the space-based Planck observations to deliver robust brightness measurements on scales from the size of the maps down to similar to 1 arcmin. In each band, we first calibrate and color-correct the SPT data to match the Planck data, then we use noise estimates from each instrument and knowledge of each instrument's beam to make the inverse-variance-weighted combination of the two instruments' data as a function of angular scale. We create maps assuming a range of underlying emission spectra and at a range of final resolutions. We perform several consistency tests on the combined maps and estimate the expected noise in measurements of features in them. We compare maps from this work to those from the Herschel HERITAGE survey, finding general consistency between the data sets. All data products described in this paper are available for download from the NASA Legacy Archive for Microwave Background Data Analysis server.

A multispectral retrieval method is developed on the 100 km regional scale to extract the temperature, particle size, fractional cover and 11-μm emissivity of clouds which may be semitransparent in the infrared based on emitted radiances. The scheme utilizes the nonlinear relationship between emitted radiances when clouds are semitransparent and form a single-layered system. The retrieval method has the limitation that the particle size must be sufficiently small that the extinction and absorption cross sections at the different wavelengths are significantly different. For combinations of emission at 11 and 12 μm, the droplets must have radii less than 20 μm for both ice and water; for 3.7 and 12 μm the droplets must have radii less than 60 μm for ice and less than 100 μm for water; for 3.7 and 8 μm the droplets must have radii less than l50 μm for both ice and water. The retrieval scheme together with the spatial coherence method is applied to the analysis of NOAA-11 4-km Advanced Very High Resolution Radiometer 3.7, 11 and 12-μm observations obtained during the First ISCCP Regional Experiment Intensive Field Observations, Kansas, 1991. The results indicate that clear skies, single-layered and multi-layered cloud systems constitute equal proportions of 100-km scale regions. For the upper-level, single-layered clouds, 100-km scale emissivity and fractional cloud cover are correlated and the average effective radius of ice particles in semitransparent clouds is about 10 μm. Numerical simulations are performed to determine the sensitivity of the retrieved results to errors in observations and model assumptions and to compare the results of the current algorithm to those obtained with a threshold algorithm like that used by ISCCP. For effective radii less than 15 μm, errors in the retrieved effective radius are less than 1.5 μm and errors in cloud temperature are less than 5 K. The fractional cloud cover may be underestimated by 0.15. The 11-μm emissivity may be overestimated by 0.30. For upper-level, semitransparent/broken clouds, the current algorithm is superior to the threshold algorithm in the determination of cloud temperature and effective radius. / Graduation date: 1996

Realistic assessment of the vertical distribution of clouds, particularly the occurrence of multi-layered systems, is critical for accurate calculations of radiative transfer in general circulation models. Such information is also useful in the design and improvement of satellite retrieval techniques. Current methods for retrieving cloud properties from satellite data assume that the clouds reside in single-layered systems. These methods are not expected to be successful for multi-layered systems. Attempts to specifically address the question of cloud layering have thus far been limited, due in part to the difficulties of inferring vertical cloud structure from either surface or satellite data. In situ observations, such as those provided by aircraft, are available only for localized regions and are limited in time. This study uses data from a lidar instrument flown onboard the space shuttle and satellite imagery data to identify the frequencies of occurrence of layered cloud systems at different spatial scales over various regions of the globe. The Lidar In-Space Technology Experiment (L1TE) was flown on Space Shuttle Discovery in September 1994 and provided global-scale, high vertical resolution profiles of the earth's troposphere and lower stratosphere. Analysis of the LITE observations requires distinguishing clouds residing in organized, well-defined layers from clouds that are distributed in altitude throughout the troposphere. The analysis employs a histogram technique in which peaks having some critical number of observations are considered to correspond to observations belonging to well-defined cloud layers. Advanced Very High Resolution Radiometer (AVHRR) data for the 11-day duration of the LITE mission are analyzed using the spatial coherence method. This method identifies regions of locally uniform emission which are associated either with cloud-free pixels or with overcast pixels corresponding to clouds in a single layer at a well-defined altitude. The number of layers present is determined by the number of overcast radiances associated with pixel arrays exhibiting locally uniform emission within the region. Layer statistics are compiled for the Pacific, Atlantic, and Indian Oceans and the North and South American, African, European, Asian, and Australian continents using horizontal scales of 60 and 250 km. The results indicate a strong dependence on the spatial scale chosen for the analysis, with two- and three-layered systems more prevalent at the 250-km scale. Analysis of cloud-top altitudes from LITE and AVHRR show that low-level cloud systems comprise the majority of the observations over both ocean and land. / Graduation date: 1998