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Department of Earth and Space Science and Engineering

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Collection consists of research, scholarship and publications produced by graduate students and faculty members of the Department of Earth and Space Science and Engineering.

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Now showing 1 - 6 of 6
  • ItemOpen Access
    Mechanism of Interannual Cross-Equatorial Overturning Anomalies in the Pacific Ocean
    (2021-10-01) Rao, Devanarayana R. M.; Tandon, Neil F.
    The meridional overturning circulation (MOC) transports heat and mass between the tropics and the extratropics. Recent research has shown that the variability of the Indo-Pacific MOC dominates the variability of the global MOC on interannual timescales, and this variability is characterized by a prominent cross-equatorial cell (CEC) spanning the tropics. This CEC is a potentially important influence on interannual climate variability, but the mechanism responsible for the CEC is not understood. This study seeks to elucidate the mechanism of the CEC using two observational estimates of the ocean. Our analysis shows that the CEC can be explained by the following mechanistic chain: (a) Anomalies in the atmospheric circulation and hydrological cycle produce equatorially antisymmetric density anomalies in the upper Pacific Ocean (above approximately 500 m); (b) these density anomalies generate equatorially antisymmetric anomalies of sea surface height (SSH); (c) these SSH anomalies generate a cross-equatorial flow above approximately 1,000 m; and (d) this anomalous cross-equatorial flow drives compensating flow below approximately 1,000 m. This mechanism contrasts with that responsible for anomalous cross-equatorial overturning on seasonal timescales, which is primarily the Ekman response to equatorially antisymmetric anomalies of zonal wind stress. On interannual timescales, the zonal wind stress anomalies associated with the CEC are equatorially symmetric, and steric SSH variations are the dominant driver of the CEC. These insights may lead to improved understanding and prediction of interannual climate variability.
  • ItemOpen Access
    The bifurcation of periodic orbits and equilibrium points in the linked restricted three-body problem with parameter ω
    (AIP Publishing, 2019-10-08) Shan, Jinjun; Liang, Yuying; Xu, Ming; Lin, Mingpei
    This paper is devoted to the bifurcation of periodic orbits and libration points in the linked restricted three-body problem (LR3BP). Inherited from the classic circular restricted three-body problem (CR3BP), it retains most of the dynamical structure of CR3BP, while its dynamical flow is dominated by angular velocity ω and Jacobi energy C. Thus, for the first time, the influence of the angular velocity in the three-body problem is discussed in this paper based on ω-motivated and C-motivated bifurcation. The existence and collision of equilibrium points in the LR3BP are investigated analytically. The dynamic bifurcation of the LR3BP under angular velocity variation is obtained based on three typical kinds of periodic orbits, i.e., planar and vertical Lyapunov orbits and Halo orbits. More bifurcation points are supplemented to Doedel's results in the CR3BP for a global sketch of bifurcation families. For the first time, a new bifurcation phenomenon is discovered that as ω approaches to 1.4, two period-doubling bifurcation points along the Halo family merge together. It suggests that the number and the topological type of bifurcation points themselves can be altered when the system parameter varies in LR3BP. Thus, it is named as “bifurcation of bifurcation” or “secondary bifurcation” in this paper. At selected values of ω, the phase space structures of equilibrium points L2 and L3 are revealed by Lie series method numerically, presenting the center manifolds on the Poincaré section and detecting three patterns of evolution for center manifolds in LR3BP. Holding the key to the origin of the universe, small bodies, e.g., asteroids are attracting more and more interest from academic and industrial fields. Current simulation on asteroid is implemented based on the regular spinning rate of an asteroid body. However, recently, the observation results on some asteroids show that their spinning velocity varies due to the solar radiation pressure, such as 2000 PH5, whose spinning velocity increases by (2.0 ± 0.2) × 10−4°/day2. The effect of the variable spinning velocity has not been fully understood. To cope with the orbital dynamics near a celestial object with varying angular velocity, a linked restricted three-body problem (LR3BP) is proposed in this paper given that the primary and the secondary are connected by a massless link. The bifurcations motivated by both angular velocity and Jacobi energy are detected to present the influence of the angular velocity. The expected results will provide new insights into orbital dynamics near asteroids, serving for future asteroid exploration mission. The LR3BP and the discovered bifurcation phenomena are important theoretical supplementation to the classic three-body problem theory.
  • ItemOpen Access
    WINDII Observations and WACCM‐X Simulations of High‐Latitude Winds Under Different Solar Radio Flux and Geomagnetic Disturbance Conditions
    (American Geophysical Union, 2019-07-04) Liu, Shushi; Shepherd, Gordon; Chen, Yongsheng; Shepherd, Marianna; Bhutia, Sangay
    Thermospheric zonal winds at altitudes of 140 to 250 km are shown to reverse from eastward to strong westward between 100° and 200° in geographic longitude and 60°S to 70°S latitude in the Southern Hemisphere. The reversal also occurs at the same latitude in the Northern Hemisphere, but from 200° to 340° longitude. The phenomenon has been previously described as a “wind wall.” Observations by the Wind Imaging Interferometer (WINDII) on the National Aeronautics and Space Administration's Upper Atmosphere Research Satellite (UARS) and simulations by the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X) are utilized to explore the characteristics of what has been called a wind wall. In order to study the dependence on solar radio flux and geomagnetic activity, the relationships of the maximum zonal wind and F10.7 (the solar radio flux at 10.7 cm) and ap indices are investigated. The results show that WINDII observations and WACCM‐X simulations agree well in describing this wind signature. Moreover, the appearance of the wind wall is found to have a strong dependence on the solar radio flux and geomagnetic activity. In addition, WINDII winds have a stronger response to geomagnetic activity than WACCM‐X winds.
  • ItemOpen Access
    Feasibility of 20 km free-standing inflatable space tower
    (British Interplanetary Society, May-10) Seth, R.K.; Quine, Brendan; Zhu, Z.H.
    This paper describes the theory and analysis for the construction of a thin walled inflatable space tower of 20 km vertical extent in an equatorial location on Earth using gas pressure. The suborbital tower of 20 km height would provide an ideal surface mounting point where the geosynchronous orbital space tether could be attached without experiencing the atmospheric turbulence and weathering in the lower atmosphere. Kevlar is chosen as an example material in most of the computations due to its compatibility in the space environment. The Euler beam theory is employed to the inflatable cylindrical beam structure. The critical wrinkling moment of the inflated beam and the lateral wind load moments are taken into account as the key factors for design guidelines. A comparison between single inflatable cylindrical beam and inflatable multiple-beam structures is also presented in order to consider the problems involving control, repair and stability of the inflated space tower. For enhancing load bearing capacity of the tower and for availability of more surface area at the top, the non-tapered inflatable structure design is chosen for the basic analysis, however further analysis can be performed with tapered structures.
  • ItemOpen Access
    A free-standing space elevator structure: a practical alternative to the space tether
    (Elsevier, 2009-04-19) Quine, Brendan; Seth, R. K.; Zhu, Z. H.
    Space tethers have been investigated widely as a means to provide easy access to space. However, the design and construction of such a device presents significant unsolved technological challenges. We propose an alternative approach to the construction of a space elevator that utilizes a free-standing core structure to provide access to near space regions and to reduce the cost of space launch. The structure is comprised of pneumatically inflated sections that are actively controlled and stabilized to balance external disturbances and support the structure. Such an approach avoids problems associated with a space tether including material strength constraints, the need for in-space construction, the fabrication of a cable at least 50,000 km in length, and the ageing and meteorite-damage effects associated with a thin tether or cable in Low Earth Orbit. An example structure constructed at 5 km altitude and extending to 20 km above sea level is described. The stability and control of the structure, methods for construction and its utility for space launch and other applications are discussed.