Arthur Richmond, Ph.D. - US grants

The objective of this project is to improve estimates of the high latitude electrodynamic forcing of the thermosphere through quantification of variable electric fields and auroral precipitation, and through analysis of their influences on the thermosphere and on ionospheric currents. The PIs propose to construct an empirical model of high-latitude electric fields and auroral precipitation that includes both average and variable components, and that quantifies magnitudes, coherences, and the correlation between the field and the precipitation. Data will come from the Dynamics Explorer-2 (DE-2) spacecraft and from incoherent scatter radars. The PIs will validate this new model by using it as input to the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) and comparing their results with high-latitude observations of ground magnetic variations and neutral thermospheric winds and temperatures, including both mean values and standard deviations.

The Whole Atmosphere Community Climate Model (WACCM) is improved by extension of the upper boundary to 550 km, and by adaptation (from other models) of physical algorithms for thermosphere-ionosphere energetic, dynamic, and composition interactions. New parameterizations characterizing gravity-wave forcing and tidal coupling are also established in the new model, completing a comprehensive whole-atmosphere modeling approach. The resultant model, including source code, is made available to the entire community with application support from the National Center for Atmospheric Research. Model validation is accomplished by model and data comparisons performed by the research team, and by collaboration with independent outside investigators. Particular emphasis is placed on evaluating upper atmospheric response to secular changes in trace species, temperature, and dynamics in the lower atmosphere in the context of global climate change.

The scientific objective of this investigation is to evaluate the contribution of lower atmospheric dynamics to the variability of ionospheric electrodynamics and electron densities. The investigation addresses the two scientific questions:

1. How well can winds generated internally in a whole-atmosphere model explain observed quiet-day ionospheric electric fields and currents? What information can model-observation discrepancies give us about atmospheric processes?

2. How much of the observed quiet-day variability of ionospheric electric fields, currents, and electron densities can be attributed to variable winds from the lower atmosphere?

The Whole Atmosphere Community Climate Model (WACCM), a numerical simulation model of atmospheric dynamics, chemistry, energetics, and electrodynamics from the ground to about 500 km altitude, will be upgraded to simulate ionospheric dynamics and electrodynamics realistically, and to calculate geomagnetic perturbations produced by ionospheric electric currents. Comparisons between simulated and observed ionospheric electric fields and electron densities, as well as geomagnetic perturbations on the ground and at low-Earth-orbit satellite altitudes, will indicate how well WACCM can simulate winds in the ionospheric dynamo region. Additional simulations using adjustments to uncertain WACCM parameterizations, to achieve improved model-data agreement, will provide information about the parameterized processes, especially the effects of momentum transport by gravity waves. The WACCM results will then be analyzed to evaluate the variability of electric fields, currents, and ionospheric densities associated with variability in atmospheric tides and planetary waves produced in the lower and middle atmosphere. This variability will be assessed in relation to that caused by magnetospheric electrodynamic effects on the ionosphere, through additional simulations that vary the magnetospheric electric potential imposed at high latitudes.

The investigation will contribute to the development of WACCM, a community model for exploring and understanding effects of coupling between the lower and upper atmosphere. The WACCM documentation will be expanded to include the new model developments, and the enhanced version of WACCM will be made available to the scientific community for use in other studies. The developments of WACCM components in this investigation will also be used to improve other upper-atmosphere models on which the research team are collaborating.

Millions of lightning flashes occur per day over the Earth, transferring tremendous power from electrical clouds to Earth's surface in the form of electric current. Lightning discharges also occur between the clouds and the edge of space, producing luminous displays called sprites and elves. These events can occur because cosmic rays from other galaxies and x-rays from the Sun make the edge of space electrically-conducting. It is not well understood how lightning might modify ionospheric conditions that affect communications and navigation (e.g., GPS) systems, or how changes in the space environment might affect electrical processes in polar-region clouds relevant to weather and climate, or how society would be impacted in other ways through electrical connections within the Earth-atmosphere-geospace system. This Broad topic is the subject of the project "Electrical Connections and Consequences Within the Earth System".

It is the purpose of this 5-year multi-institutional basic research investigation to better understand the electrical processes that link together the atmosphere, solid earth and geospace components of the Earth system. The approach is to develop improved understanding of processes controlling the charge and discharge of electrified clouds, the electrical coupling between the atmosphere and ionosphere, and the flow of current throughout the system. The project will culminate in creation of a global model that is capable of replicating much of the experimental data accumulated to date, and that Interfaces with the rest of the atmosphere-ionosphere system within the Whole Atmosphere Community Climate Model (WACCM) at the National Center for Atmospheric Research (NCAR). Other key goals of this project are to educate the public about this field of study, and to motivate and educate a cadre of next-generation scientists on this global view of the Earth-atmosphere-geospace system.

The goal of this project is to investigate how the lower atmosphere affects the ionosphere through dynamical and electrodynamical processes during stratospheric sudden warming (SSW) events, when profound changes have been observed from the lower to upper atmosphere. The project involves using the National Center for Atmospheric Research Thermosphere-Ionosphere-Mesosphere- Electrodynamics General Circulation Model (TIME-GCM) and the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X) to address a number of questions: What causes changes to atmospheric solar and lunar tides during a SSW? Are there significant changes of traveling planetary waves during a SSW? What is the impact of rapid wind change during a SSW on gravity wave generation? How does the ionosphere respond to the changes of tides, planetary waves, and gravity waves? How do these effects depend on solar activity? The result of this study will be a better understanding of the cross-region and cross-scale coupling of the lower and upper atmosphere responsible for the SSW effects.

Daily variations of Earth's magnetic field result primarily from electric currents flowing above us in the ionosphere, at heights of about 100-150 km, with a secondary component due to currents induced below us in the deep interior of the electrically conducting Earth. This is a collaborative project, bringing solid Earth and ionospheric scientists together in an effort to better understand and separate the two current sources. A primary motivation for this effort is to improve understanding of the smaller and subtler internal component, and thence improve the ability to image electrical conductivity variations deep (200-700 km) in the Earth. Conductivity of rocks at these depths is highly sensitive to even small amounts of water, so these images will ultimately allow estimates the amount and distribution of water in the deep Earth, and improve understanding of deep Earth water cycles. These results will have important implications to a number of scientific fields, including the dynamics and evolution of the Earth and evolution of the oceans. The crucial step in this study is to significantly improve models of the external ionospheric component of the magnetic field. Such magnetic field models have many potentially important applications to basic and applied scientific research in geomagnetism and space physics. Ultimately they will be useful in applications of direct societal relevance where the knowledge of an accurate magnetic field is required, including navigation, orientation of solar arrays, and geophysical exploration for natural resources.

In conjunction with recent laboratory results on electrical conductivity of mantle minerals, improved imaging of electrical conductivity in Earth's mantle will provide valuable new information about water in the mantle, with potentially profound implications for mantle rheology, and for the dynamics and geochemical evolution of the Earth. Information about deep Earth resistivity comes almost exclusively from observations of long-period geomagnetic variations observed on Earth's surface--the sum of external fields due to ionospheric and magnetospheric current systems, and internal fields due to currents induced in the conducting Earth. Frequencies of 0.5-10 cycles per day (cpd) are most relevant to imaging through the aesthenosphere and into the transition zone, and these variations mostly have their origin in the ionospheric dynamo region at 100-150 km height. These ionospheric currents depend on the spatial and temporal varying thermospheric neutral wind and the ionospheric conductivity distribution. To reliably interpret the relatively subtle induced signals indicative of Earth conductivity variations, these spatially complex ionospheric magnetic field signals must be properly accounted. This project attacks this challenging problem through collaboration between specialists in EM induction imaging and experts in ionospheric physics and modeling. Spatial structure of external source and internal conductivity variations will be estimated simultaneously, using a large collection of ground-based geomagnetic array data from both historical and modern eras. There are two novel components to the proposed approach. First, a robust Principal Components Analysis (PCA) scheme is used for initial data reduction. This PCA scheme massively reduces the number of data (and thus the number of independent source parameters required), and allows data from different eras to be merged, thus significantly increasing data coverage. Second, the source modeling is tightly constrained through the use of a mature physics based numerical model for ionospheric currents, the Thermosphere-Ionosphere-Mesosphere-Electrodynamics general Circulation Model (TIME-GCM). In addition to the team's immediate application to improved EM induction imaging, these efforts may provide significant benefits to the ionospheric and broader geomagnetic communities. For example, the project includes detailed comparison between TIME-GCM outputs and a large collection of ground geomagnetic data, providing insight into strengths and weaknesses of this numerical model. More broadly, approaches developed for incorporating ground-based data into time dependent models of ionospheric magnetic fields will benefit a range of basic and applied studies of Earth's magnetic field.