A system is described for time-lapse stereoscopic cloud photography using 16-mm cameras, for rectification of the photographs for camera tilt, and for analysing them to obtain cloud dimensions by superimposing the projected images of stereo-pairs on a gridded screen. A discussion of theoretical photogrammetry as applied to cloud photography, and an analysis of the system errors and measurement uncertainties are given. [...]

The Oort Cloud (OC) is a roughly spherical cloud of comets surrounding the solar system, stretching from well beyond the orbit of Neptune, half way to the nearest star. This body of comets is interesting because it contains a record of the gravitational perturbations suffered by the solar system over its lifetime. Here, we investigate the effects of a particular class of perturbing objects - enormous complexes of molecular gas called giant molecular clouds (GMCs). Recent evidence has shown that the classical picture of Oort Cloud formation is inadequate to describe certain properties of the OC. To re-investigate the dynamical evolution of the Oort Cloud, we simulate the Sun's emergence from its natal molecular cloud, and its subsequent encounters with GMCs. While the role of giant molecular clouds in OC formation has been explored before, they have been implemented in a general way, not explicitly taking into account the 3D structure of the cloud. In this research, we draw on an extensive body of evidence which suggests that GMCs are not uniform, diffuse objects, but are instead organized into high density clumps, connected by a very diffuse inter-clump medium. Recent research has shown that GMCs are likely to be fractal in nature, and so we have modeled them as fractal distributions with dimension 1.6. We then perform N-body simulations of the passage of the Sun and its Oort Cloud through such a molecular cloud. We find that the fractal structure of the GMC is, in fact, an important parameter in the magnitude of the cometary energy change. The significant energy changes occur as a result of interactions with the GMC substructure, not simply as a result of its overall density distribution. We find that interactions with GMCs can be quite destructive to the OC, but can also serve to move comets from tightly bound orbits to less tightly bound orbits, thus partially replacing those lost to stripping. Simulations of the Sun's relatively slow exit from its birth GMC paint a picture of a potentially very destructive era, in which a large portion of the OC's evolution may have occured. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-09-21 13:05:17.527

Surface downward far-infrared (far-IR) spectra were collected from NASA’s Far-Infrared Spectroscopy of the Troposphere (FIRST) instrument from August to October 2009 at an altitude of 5.4 km near the summit of Cerro Toco, Chile. This region is known for its dry, cold, and dominantly clear atmosphere, which is optimal for studying the effects, that water vapor and cirrus clouds have on the far-IR. Comparisons with Line-By-Line Discrete Ordinants Radiative Transfer model, LBLDIS, show that FIRST observes the very fine spectral structure in the far-IR with differences as small as +/- 0.7% for both clear-sky and cloudy-sky simulations. Clear sky model analysis demonstrated the greatest sensitivity to atmospheric conditions is between 300 and 500 cm-1. The cloudy-sky simulations demonstrated that the far-IR radiation has minimal sensitivity to cloud particle effective radius, yet is very sensitive to cloud optical thickness at wavenumbers between 400 - 600 cm-1. In fact, cirrus optical thickness found to be inferred from the brightness temperature differences at 250 and 559.5 cm-1. Aerosols proved to reduce downwelling radiance by half that a clear-sky would emit, but had little effect on the total far-IR radiative forcing. Furthermore, these far-IR measurements open a new window to understanding the radiative impacts of various atmospheric constituents such as water vapor and clouds, and to understanding and modeling the Earth’s climate and energy budget.

This dissertation investigates three topics concerning high clouds: 1) convectively coupled equatorial wave (CCEW) signals derived from cloud top temperature (CTT) and cirrus optical thickness retrieved from satellite observations; 2) investigation of the physical mechanism governing the fixed anvil temperature (FAT) hypothesis and test of FAT hypothesis with CTT measurements; and 3) the intercomparison of cloud fraction and radiative effects between satellite-based observations and reanalysis product and simulations from general circulation models (GCMs). A wealth of information on CCEWs is derived from Aqua/MODIS cloud-top properties. We apply space-time spectral analysis on more than 6 years of CTT and isolate various modes of CCEWs including Kelvin, n = 1 equatorial Rossby, mixed Rossby-gravity, n = 0 eastward inertio-gravity waves, and the Madden-Julian oscillation. The successful application of the same method to cirrus cloud optical thickness confirms robust convective signals at upper troposphere. Consistent with the physical governing mechanism of the FAT hypothesis, the peak clear-sky diabatic subsidence, convergence and cloud fraction are located at roughly the same level (200 hPa), which is fundamentally determined by the rapid decrease of water vapor concentration above this level. The geographical maxima of cloud fraction agree well with that of water vapor, clear-sky cooling rates, diabatic subsidence and convergence at 200 hPa. An analysis of the response of the tropical mean CTT anomaly time series to sea surface temperature indicates that a possible negative relationship is present. In addition, we suggest interpreting the FAT hypothesis, and the more recent proportionately higher anvil temperature (PHAT) hypothesis, by using the temperature at the maximum cloud detrainment level instead of the CTT. Simulations of cloud fraction and radiative properties using two versions of the NCAR CAM models indicate that an overall improvement is observed in CAM5 compared to CAM3. However, an apparent bias in CAM5 shortwave (SW) cloud radiative forcing (CRF) simulation is shown in boreal winter southern mid latitude. This bias is primarily due to the underestimation of fraction-weighted SW CRF related to both high and middle top clouds. Additionally, apparent compensation errors are observed in models.

An analysis of 5 minute resolution Quadra data on day 261 of GATE (0953 - 1451 GMT) is made to yield statistics of maximum area, echo top, lifetime and maximum reflectivity factor in medium-sized convective cells. The procedure generates a unique data set which is used to compare with the results of a three-dimensional cloud model and to study cloud interactions and merging processes between convective echoes. The results, obtained by tracking 140 echoes throughout their lifetime, indicate that the maximum area is log-normally distributed, 90% of the echoes being smaller than 40 km('2) and living shorter than 60 min. The modes of the maximum echo top and maximum reflectivity factor distributions are around 2.5 km and 30 dBz, respectively. / A fully three-dimensional cloud model including precipitation processes is used to simulate convective clouds on this day. A number of single cloud experiments are carried out to verify the numerical results against the radar observations. In addition, several two-cloud developments are simulated to study cloud interactions and merging processes. / Comparison of the modelled echo parameters against the observed ones indicates a fair degree of realism in the simulations. The computed maximum reflectivity factor, however, is considerably higher than that of the observations because of the unrealistic drop-size distribution assumed in the model. / The two-cloud simulations suggest that both the alignment of the clouds in relation to the wind shear vector and the spacing between the cells are important factors in determining the type of cloud interactions. Merging takes place when the spacing between the two elements becomes small enough. The numerical simulations indicate that the perturbation pressure structure is crucial to trigger echo merging.

No description available.

The mechanism of the intraseasonal oscillation in the South Asian summer monsoon region (ISO) is examined with a zonally averaged, atmospheric model (2D model), a three dimensional, atmospheric intermediate model (3D model). In both models an ocean mixed layer model is added to examine the influence of air-sea interactions on the characteristics of the ISO. Without the ocean mixed layer, an interaction between the baroclinic and barotropic modes of atmosphere can produce the ISO in both 2D and 3D models. The propagation of precipitation is caused by the phase relationship between convection and the barotropic divergence in the atmosphere. Most importantly, in the northern hemisphere, the vertical advection of July-mean easterly wind shear in regions of convection induces barotropic divergence (convergence) to the north (south) of convection. The resulting moisture convergence in the boundary layer induces the northward propagation of precipitation. The initiation of convection is also produced by the barotropic divergence in the atmosphere. Especially, the strong July-mean vertical motion at IDS causes convergence in the boundary layer between IDS and the equator. The baroclinic mode, on the other hand, acts to enhance existing convection. The differences between the ISO simulated by the 2D model and 3D models are caused by the zonal variation of winds, and atmospheric waves in the 3D model. The zonal divergence of barotropic winds enhances the westward propagation of convection along 18N, and the barotropic mode of zonal advection drives the continuous northward movement of convection across the equator. The continuous northward propagation across the equator is also enhanced by the atmospheric waves, since the Rossby wave response to the heating source in both hemispheres creates a divergence in the baroclinic mode near the equator. The inclusion of air-sea interactions in the 2D and 3D models improves the continuity in the northward propagation of convection. The meridional variation of SST enhances the boundary layer moisture convergence in front of the convection, thereby facilitating the northward propagation of convection. In addition, the SST gradient induced by the dipole type of Rossby-wave-like convection in the Indian ocean may increase the development of convection near the equator. / Thesis (Ph. D.)--University of Hawaii at Manoa, 2002. / Mode of access: World Wide Web. / Includes bibliographical references (leaves 117-122). / Electronic reproduction. / Also available by subscription via World Wide Web / xxii, 240 leaves ill. 29 cm

This thesis presents the initiation of a multi-site photometric programme to examine the extraordinary behaviour displayed by 18 R Coronae Borealis (RCB) stars in the Magellanic Clouds (MCs). RCB stars exhibit a unique variability whereby they undergo rapid declines of up to several magnitudes. The decline may take several weeks, whereas the recovery to maximum light may take months or even years. The accepted wisdom for the cause of these enigmatic declines is a phenomenon whereby dust formed in the stellar environment reduces the brightness by as much as eight magnitudes (Clayton 1996). This is followed by the recovery phase during which the dust becomes homogeneously distributed in the stellar environment. The monitoring programme comprised the collection of UBVRI photometric data using five telescopes located at three different southern hemisphere longitudes (Las Campanas Observatory in Chile, Mount John University Observatory (MJUO) in New Zealand and the Southern African Large Telescope (SALT) in South Africa). The Optical Gravitational Lensing Experiment (OGLE), that operates at Las Campanas Observatory, provided the longest extent of data (December 1994 to February 2008). This was supplemented by data collected with telescopes at MJUO (September 2007 to January 2008) and SALTICAM on SALT (October 2007 to February 2008). Data calibration across the five instruments was a key element of the analysis, and entailed the use of F116 (an F region standard star) and other tertiary standards. Two important RCB characteristics, the enigmatic declines and the pulsational variability, form the bulk of the analysis presented in this thesis. Examination of the data acquired in the V and I filters resulted in the identification of a total of 18 RCB declines occurring in four stars (three stars in the Large Magellanic Cloud (LMC) and one in the Small Magellanic Cloud (SMC)). Construction of colour-magnitude diagrams (V −I vs V ), during the recovery to maximum light were undertaken in order to study the unique colour behaviour associated with the RCB declines. The combined recovery slope for the four stars was determined to be [(delta V)/(delta(V −I))] = 3.37 ± 0.24, which is similar to the value of [(delta V)/(delta(V −I))] = 3.1 ± 0.1 calculated for galactic RCB stars (Skuljan et al. 2003). In addition, the slopes calculated for the stars in the LMC ([(delta V)/(delta(V −I))]LMC = 3.34 ± 0.21) and SMC ([(delta V)/(delta((V −I))]SMC = 3.21 ± 0.22) alone, also agree to within their uncertainty. These results may imply that the nature of the dust (i.e. the particle size) is similar in both our Galaxy and the MCs. The pulsation analysis focused on the identification of pulsation periods in nine RCB stars in the MCs. Two different methods, Fourier analysis and dominant period subtraction, were employed for this purpose. Periodic variations are apparent in these stars, and for the majority, a period of around 40 days (common in RCB stars, Lawson et al. 1990, 1994) was detected using the second identification method. In the future, frequent data collection over several years, and more sophisticated pulsation identification techniques, will increase the probability of extracting individual periods from the complex RCB light curves.

Thesis (Ph. D.)--McMaster University, 1999. / Includes bibliographical references (leaves 247-252). Also available via World Wide Web.

Thesis (Ph.D.) -- McMaster University, 1997. / Includes bibliographical references (p. 218-233). Also available via World Wide Web.