Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996. / Includes bibliographical references. / by Eiichi Takazawa. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989. / Includes bibliographical references. / by Michael D. Prange. / Ph.D.

Thesis (S.M. in Earth and Planetary Sciences)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 67-71). / Records of ocean biogeochemistry in marine sediments show shifts across the Cretaceous-Paleogene boundary (K-Pg) that are simultaneous with the extinction event and onset of the boundary clay deposition. However, the timescale of these records is difficult to determine near the boundary because of fluctuating sedimentation rates and the short duration of the event. In this study, we have used extraterrestrial helium-3 as a constant flux proxy for instantaneous mass accumulation rates in four marine sections: Caravaca, Spain; El Kef, Tunisia; and Hojerup and Kulstirenden, Denmark. These sections are characterized by a thick boundary clay layer and, therefore, are more suitable than many other proxies for high-resolutions studies. In order to better understand the extent of the impact-related perturbations in different paleoenvironments, we performed a high-resolution analysis at Caravaca and lower-resolution analyses at the other three sections. We find that Hojerup and Kulstirenden are not suitable for this analysis due to the probable variation in the flux of extraterrestrial helium-3 as a result of lateral changes in sedimentation rate. Our results suggest that carbonate burial, and likely carbonate production, were more severely affected with increasing paleolatitude. However, the unique depositional environments are probably much more important than just paleolatitude alone. We calculate boundary clay durations of Caravaca and El Kef of 6.45 (h 0.86) kyr and 6.28 (± 1.03) kyr, respectively. These results are consistent with other studies and indicate a uniform, global deposition of the boundary clay and a rapid recovery of carbonate burial in the marine ecosystem after the Cretaceous-Paleogene extinction event. / by Marie Minh-Thu Giron. / S.M.in Earth and Planetary Sciences

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2017. / Cataloged from PDF version of thesis. "May 16, 2017." "This thesis was submitted to the Institute Archives without all the required signatures"--Disclaimer Notice page. / Includes bibliographical references (page 53). / Transit light curves of the exoplanet K2-25b were studied to examine the possibility of transit timing variations (TTVs) in the system, which could imply the presence of a perturbing planet. Observations of K2-25b transits were taken using 14-inch and 24-inch telescopes at Wallace Astrophysical Observatory. Two transit light curves were fit using an MCMC implementation to find the orbital period, planetary radius, and semi-major axis. A new period calculation yielded an orbital period of 3.48457 +/-0.00004, consistent with the period of 3.484552 +0.000044/-0.000036 from Mann et al. 2016. No significant variations were found in the midtimes of the new transit observations when comparing them to the midtime originally published in Mann et al. 2016. Future observations will require smaller uncertainties to meaningfully constrain the mass and period of potential perturbing planets. Signal-to-noise ratio calculations showed that telescopes over approximately 2.2 meters in diameter have better potential to detect small TTVs. / by Ishara Nisley. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2006. / Includes bibliographical references (p. 111-117). / The methods of analyzing stellar occultations by small bodies in the outer solar system are discussed with examples from Triton, Pluto, and Charon. Simulations were performed characterizing the analysis of multi-chord occultations including: the effects of the direction of residual minimization in figure fits, the complications in measuring the reliability of fitted figure parameters when there are few degrees of freedom, and the proper treatment of grazing chords in model fitting. The 2005 July 11 C313.2 stellar occultation by Charon was analyzed. Occultation timings from the three published data sets were combined to accurately determine the mean radius of Charon: 606.0 ± 1.5 km. The analysis indicates that a slight oblateness in the body (0.006 ± 0.003) best matches the data, with a confidence level of 86%. Charon's mean radius corresponds to a bulk density of 1.63 0.07 g/cm3, which is significantly less than Pluto's (1.92 ± 0.12 g/cm3), consistent with an impact formation scenario in which at least one of the impactors was differentiated. The 2002 August 21 P131.1 and the 1988 June 9 P8 stellar occultations by Pluto were analyzed. / (cont.) The ellipticity of Pluto's atmosphere as measured by the P131.1 event is 0.066 ± 0.040, with a Gaussian confidence level of 63%, and the ellipticity as measured by the P8 occultations is 0.091 ± 0.041, with a Gaussian confidence level of 70%. If this non-sphericity is confirmed, its size and variation could possibly be attributed to super-rotating winds driven by sources such as surface frost migration due to changing insolation patterns or albedo properties, gravity waves, and an asymmetric mass distribution in Pluto itself. The 2001 August 23 Tr231 stellar occultation by Triton was analyzed. The half-light radius of Triton's atmosphere was calculated from astrometrically calibrated model fits to the occultation light curve. The resulting half-light radius of 1479.01 km is larger than the value of 1456.3 km derived from the 1997 Trl80 occultation, with a confidence of 77% derived from the uncertainty in the astrometric calibration. If this increase were confirmed, it would indicate that the expansion of Triton's atmosphere detected between the 1989 Voyager 2 observations the 1995 and 1997 stellar occultations by Triton has continued through 2001. / by Michael James Person. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2008. / Cataloged from PDF version of thesis. "May 9, 2008." / Includes bibliographical references (pages 25-26). / A model was created to form synthetic plots of sea surface height (SSH) from monthly SSH statistics in the Gulf of Mexico generated from satellite laser altimetry data. SSH is a signal of the upper ocean mixed layer heat content and is an input for hurricane intensity models. A significant ocean feature in the Gulf of Mexico is the Loop Current (LC) which sheds warm eddies into the Gulf of Mexico at irregular intervals, which adds to the variability in monthly SSH readings beyond seasonal change. Satellite laser altimetry data was used from October 14th 1992 to May 23rd 2007. The SSH data included an area of the Gulf of Mexico (16°N-30°N latitude, 80°W-100°W longitude) with a resolution of 1/3° by 1/3° on a Mercator grid. Monthly SSH averages, variances, and covariances were created from a total of 763 samples, which allowed for approximately 65 samples per month. Once monthly SSH averages, variances, and covariances were made, synthetic plots were made by using a Karhunen-Loève transform, the Singular Variable Decomposition of the SSH monthly covariance, and random vector composed of random numbers in a Gaussian distribution. Differences in synthetic SSH plots compared to individual SSH observations could vary greatly; the average of all synthetic SSH plot nodes differed by no more than plus or minus 10 cm. The difference between observed and synthetic SSH variance was no more than 400 cm². The large differences occurred in the in the eddy shedding region of the LC. To assess the effectiveness of the model, the synthetic SSH model will need to be used in a hurricane intensity model. / by Adam C. Rigel. / S.B.

Thesis: Ph. D. in Climate Science, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Recognition of stratospheric ozone depletion as a significant global danger sparked the landmark international agreement of the Montreal Protocol to control the production of ozone depleting substances (ODSs). There are now signs of stratospheric ozone recovery, and it is essential to understand whether the observed historical changes, during both the depletion and recovery eras, are directly the result of secular changes in ODSs, or influenced by other anthropogenic and natural forcings such as greenhouse gases (GHGs) and solar variability. This thesis explores the climate impacts of stratospheric ozone depletion, and how we can attribute, with high confidence, the causes of observed changes in stratospheric ozone. First, the linkages between Antarctic ozone loss and midlatitude surface climate changes are investigated. Unusually hot summer extremes in Australia, South America and Africa were found to be associated with elevated levels of ozone the previous November, and that this link has only emerged in the era of the Antarctic ozone hole. This study provides motivation for understanding the causes of ozone changes, showing direct impacts to regions where humans live. Second, a formal detection and attribution study of stratospheric ozone change is presented. A multi-satellite observational dataset and simulations from a chemistry climate model are analyzed. An improvement to conventional fingerprint attribution methodology is presented that accounts for nonlinearities in the temporal evolution of anthropogenic forcings. High confidence in the detection of ODSs upon observed stratospheric ozone change is shown. Detection of a GHG signal, in stratospheric ozone, is projected to emerge in the mid-21st century. Third, the improved attribution methodology is applied to seasonal atmospheric circulation changes. Reanalysis products and simulations from a multimodel assessment are used. Positive detection of both ODS and GHG fingerprints is found during the months of December- May, with the ODS signal dominating in the Southern Hemisphere. Ultimately, the results of this thesis further our scientific understanding of the role of ODSs in climate change, and provide new steps for future detection and attribution studies of the climate system. / by Justin Bandoro. / Ph. D. in Climate Science

Thesis: Ph. D. in Geophysics, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 133-143). / This dissertation presents improvements made on position estimation techniques applied to seismology, airborne gravimetry and planetary gravity recovery. In Chapters 2 and 3, a smoothed ionospheric model computed using GPS phase observations was applied to seismology and airborne gravimetry. The seismic investigation observed the 2010 El Mayor-Cucapah earthquake near Baja, California. The application of the ionospheric model resulted in an overall 4 mm RMS reduction in the measurements of GPS heights. The same ionospheric technique was applied to GPS data collected during an airborne gravity survey. In this study the model improved the RMS spread of four repeat gravity profiles by 0.6 mGal. Chapters 4 and 5 focus on the Dawn mission to the asteroid 4 Vesta. Chapter 4 details the use of spacecraft image constraints in the orbit determination software GEODYN, which is used by NASA/GSFC for trajectory reconstruction and geophysical analyses of planets. Image constraints are shown to converge an orbit solution that differs from that computed by the Dawn Science Team at JPL by less than 13 m. Chapter 5 describes the application of the new technique in the estimation of the orientation parameters and low-degree gravity field of Vesta. The pole orientation and low-degree gravity field estimated agree with that presented by the Dawn Science Team through the use of an independent software and estimation algorithm. / by Frank Joseph Centinello, III. / Ph. D. in Geophysics

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, February 1999. / Includes bibliographical references (p. 221-225). / The purpose of adaptive observations is to use information about individual atmospheric situations to identify regions where additional observations are likely to improve weather forecasts of interest. The observation network could be adapted for a wide range of forecasting goals, and it could be adapted either by allocating existing observations differently or by adding observations from programmable platforms to the existing network. In this study, we explore observation strategies in a simulated idealized system with a three-dimensional quasi-geostrophic model and a realistic data assimilation scheme. Several issues are addressed, including whether adapting observations has potential to improve forecasts, how observational resources can be optimally allocated in space and time, how effectively ensemble forecasts can estimate errors in initial conditions, and how much the data assimilation system affects the influence of the observations. Using simple error norms, we compare idealized non-adaptive observations with adaptive observations for a variety of observation densities. The adaptive strategies implemented incorporate information only about errors in the initial conditions. We test both an idealized adaptive strategy, which selects observation locations based on perfect knowledge of the true atmospheric state, and a more realizable adaptive strategy, which uses an ensemble to estimate errors in the initial conditions. We find that the influence of the observations, both adaptive and non-adaptive, depends strongly on the observation density. In this simulated system, observations on synoptic scales dominate the average error reduction; above a certain observation density, adding any observations, adaptive or non-adaptive, has a much smaller effect. Results presented show that for non-dense observation networks, the adaptive strategies tested can, on average in this simulated system, reduce analysis and forecast errors by a given amount using fewer observational resources than the non-adaptive strategies. In contrast, however, our results suggest that it is much more difficult to benefit from modifying the observation network for dense observation networks, for adaptive observations taken infrequently, or for additional observations taken to improve forecasts in individual cases. The interactions between the observations, the data assimilation system, the errors in the initial conditions, and the forecast model are complex and depend on the specific forecast situation. This leads to a non-negligible risk that forecasts will be degraded when observations are adapted in an individual situation. Further study is needed both to understand these interactions better and to learn to what extent the results from this idealized study apply to more complex, more realistic systems. / by Rebecca Elisabeth Morss. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2001. / Includes bibliographical references (p. 183-193). / The focus of this thesis is the sensitivity of the strength of the meridional overturning circulation to surface forcing and mixing on climatological time scales. An adjoint model is used to gain new insights into the spatial characteristics of the sensitivity patterns. Adjoint models provide the sensitivity of a diagnostic, often called cost function, to all model parameters in a single integration. In contrast, traditional sensitivity analyses are performed by repeated integrations of the so-called "forward" model, perturbing slightly the value of a single parameter at each integration. The results of the adjoint model allows us to calculate global maps of sensitivity. These maps provide a geographic picture of where on the ocean heat and freshwater flux, wind stress and diapycnal mixing perturbations in the North Atlantic are likely to have the greatest impact on the meridional overturning and its heat transport. The adjoint model provides clear identification of the physical mechanisms which can influence the meridional overturning on times scales of years to decades. Boundary and equatorial Kelvin waves and equatorially trapped Rossby waves carry information around the boundaries of the basin and across the equator in less than a decade for a basin of the size of the Atlantic. Advection of buoyancy perturbations has an important influence on the meridional overturning on the decadal time scale. Diffusion is important in determining the final equilibrated state of the meridional overturning on the centennial scale. The role of diapycnal mixing in determining the overturning's strength is confined to regions near the lateral boundaries in the Northern hemisphere and to the tropical region in both hemispheres. The important role played by the tropics in setting the overturning's strength seems to confirm the thermodynamic principles outlined by Sandstrom (1908), Jeffreys (1925) and Munk and Wunsch (1998): upward advection of heat is balanced by downward diffusion. The strength of the meridional overturning is then determined by the power available to return the fluid to the surface across the ocean's stratification. Because the ocean is most strongly stratified in the tropics, the mixing process is most efficient in that region. Along the eastern boundary in the extratropics, the importance of diapycnal mixing is confined to a shallow layer at the base of the thermocline. The large vertical temperature contrast between the western and deep western boundary currents induces efficient mixing in that region. Surface wind stress has two effects on the ocean's stratification which concentrate the sensitivity in the eastern equatorial region. Ekman suction increases the stratification along the equator while Ekman pumping decreases it in the rest of the tropics. The equatorial easterlies lift the thermocline on the eastern side of the basin, further increasing the stratification and the efficiency of the vertical mixing process in that region. These processes are similar in the results from a coupled model. Atmospheric feedbacks do, however, allow vertical mixing in the Pacific to play a role as important as mixing in the Atlantic in determining the overturning's strength. The large uncertainties in the global value of the diapycnal mixing in the ocean, estimated here at , KV = 3.10- 5 ± 2.10-5 m2s-1, translate into an uncertainty of approximately 6 Sv in the maximum value of the meridional overturning streamfunction. The role of surface buoyancy forcing on the overturning's strength depends on the formulation of the surface boundary conditions. The sensitivities are confined to high latitudes and the vicinity of convection sites when the surface forcing is prescribed as restoring the sea surface salinity or temperature towards observations. When the forcing is prescribed as have the greatest impact on the meridional overturning. On climatological time scales, it is the uncertainty in the precipitation and evaporation fields in the tropics which have the greatest impact on the uncertainty in the streamfunction, the latter can be estimated at: 'MAX = 29 ± 4 Sv. Over the intermediate time scale of climate change, the overturning is likely to weaken at first because of warming and freshening in high latitudes. It will, however, eventually recover as positive salinity anomalies are advected northwards from the tropics. The sensitivity of the overturning to the wind stress forcing is also dependent on the surface boundary conditions. Under restoring boundary conditions, large positive sensitivities are observed in the Antarctic Circumpolar Channel in a pattern reminiscent of the so-called Drake Passage effect. According to that hypothesis, upwelling of North Atlantic Deep Water takes place predominantly in a branch of the Deacon cell in the Drake Passage region. The importance of wind in the Drake Passage vanishes when the surface buoyancy fields are less tightly constrained, for example in the model forced by mixed boundary conditions or in the coupled model. The Agulhas Plateau, the Chilean coastline and the Indonesian throughflow play an important role in setting the overturning's strength in the ocean model forced by mixed boundary conditions. These "gateways" act as a regulator of the salinity of the Atlantic basin. The wind stress determines the balance between the inflow of relatively salty Indian Ocean water through the Agulhas current, the inflow of fresher Benguela current water southwest of Africa and the flow of very cold and fresh water through the Drake Passage. A wind stress perturbation of ±0.03 N m 2 over the Agulhas Plateau would have a significant impact on the meridional streamfunction's maximum, estimated at MAX = 29t ± 0.5 Sv. Both Drake Passage and gateway effects disappear almost completely in the coupled version of the model, which shows the strongest positive sensitivities to wind stress in the region of equatorial Ekman upwelling. Our study shows that, in a climatological ocean model, the choice of air-sea boundary conditions is crucial in determining the sensitivity of the meridional overturning circulation. The climatology of the forward ocean model is credible and quite similar in all scenarios. However, including interactive atmospheric transports of heat and moisture changes the manner in which the ocean model state adjusts to changes in wind stress, heat flux and diapycnal mixing. Considering the role of both the atmosphere and the ocean when studying the climatological behavior of the MOC is, therefore, clearly important. Models which keep one of the components fixed can lead to very different conclusions from models in which both components are represented. / by Véronique Bugnion. / Ph.D.