NASA Research Announcement NRA-01-OES-05

Nasa, Washington DC

Investigators

Abstract

This project will allow the National Aeronautics and Space Administration (NASA) to fund two proposals that utilize geomagnetic satellite data. The abstract of each proposal is listed below: Catherine Constable Multiple Satellite Induction Studies UCSD 22-8760 Variations in the magnetic field generated by the ring current will be used to study electromagnetic induction in the interior of the Earth, with the ultimate goal of determining three-dimensional electrical conductivity structure in Earth's mantle. Induction studies complement other geophysical approaches to understanding thermal, compositional, and rheological structures in the deep earth. Our work will involve data analysis as well as theoretical and algorithm developments. We will investigate modeling procedures that take advantage of more than one satellite simultaneously measuring the magnetic field. We believe this is key to the second part of our study, namely improved representation of the external source fields that induce magnetic fields in Earth's interior. This will allow us to use better-parameterized models for both primary and secondary fields. The third aspect will concern development of both theoretical and practical tools for studying 3-dimensional induction using satellite data. One-dimensional satellite electromagnetic response function estimates from single satellites have already been shown to be compatible with an average of responses derived from geomagnetic observatory data, and extend the global response function down to 104 s periods. Current long period satellite response estimates are rather poorly constrained and we will improve them through the use of longer time series and better estimation techniques involving multiple satellites measurements where feasible. Electrical conductivity estimates, obtained using modem external inversion techniques, will provide constraints on the rheological and thermal state of the upper mantle and address the issue of conductivity structure in the transition zone of Earth's mantle. Qualitative measures of lateral conductivity variations derived from satellite observations demonstrate the pre-dominant influence of the oceans and crust on near-surface electrical structure. Current algorithm developments will be used to generate forward models that predict these effects: this will allow an assessment of whether 3-dimensional conductivity structures can be detected below the crust. We plan to exploit Champ, Orsted, and SAC-C (Orsted-2) observations, using different orbital configurations and satellite altitudes to assess limitations in assumptions about external source field structures. Data used will be 0.1 Hz samples of orthogonal vector magnetic field components along individual satellite passes where they are available. When adequate attitude control is not available, and for long period estimates we expect to use scalar data. Anticipated duration of this investigation is three years, but once interpretation techniques and algorithms are in place continued addition of, data offers potential for ongoing improvement of Earth conductivity models and understanding of how events such as large storms modulate the structure of the external source field. ABSTRACT Geodynamo Modeling of Core Dynamics and its Applications to Surface Geodynamic Observables (pI: Weijia Kuang) The solid mantle, the fluid outer core, and the solid inner core interact with one another through various mechanisms and on various time scales. We propose to investigate the Earth's core dynamics and the response of the mantle using a numerical geodynamo model, and study its applications to surface geodynamic observables. The proposed work has three specific objectives: (1) We intend to study variation of core flow and geomagnetic field on decadal time scales, using our numerical geodynamo modeling in conjunction with the geomagnetic field secular variation (SV) observed at Earth's surface. In particular, we shall study the non-hydrostatic pressure at the core-mantle boundary (CMB), and large-scale mass redistribution arising from density anomalies in the outer core that drive core convection, as well as that from inner core rotation relative to the mantle.. (2) Based on our understandings from (1), we intend to examine the responses of the solid Earth to these core variations. In particular, we shall focus on the magnitude and time scales of the contributions of core on time-variable gravity field and on possible surface deformation, and their detectability in gravity field signals from past and future space missions (including satellite- laser-ranging, CHAMP, GRACE, GOCE, and possibly COSMIC and GRACE Follow-On). (3) Based on research in (1), and on previous knowledge about the core angular momentum variation that changes the decadallength-of-day, we intend to continue our research (supported by SENH and by NSF) on the core-mantle interactions and their effect on variation of the Earth's rotation, in particular the decadal polar motion (Markowitz wobble). The proposed work cuts across several topics listed in the (A. 1) of the NRA: magnetohydrodynamic modeling of core processes, its applications to analysis of spatial and temporal variations of internal component of the geomagnetic field, of core contributions to time-variable gravity field, surface deformation, and Earth's rotation variation. The proposed work is a classic example of multi-disciplinary studies of Earth's interior that makes use of NASA's mission observations and modeling capabilities in advancing our knowledge about Earth system changes.