Hot Flow Anomalies (HFAs) are phenomena observed near the Earth's bow shock that are marked by strongly heated plasmas and substantial deflections in the plasma flow direction. The objective of the proposed research is to determine the characteristics of HFAs, understand how particle heating occurs inside HFAs, and determine their impact on the magnetosphere and ionosphere. The first year will be a systematic survey of hot flow anomaly events to determine the characteristics of HFAs observed upstream of the bow shock and in the magnetosheath. During the second year, the project will determine how the electrons and ions are heated and how the energetic particles (>25 keV) are accelerated inside HFAs. During the third year, the impact of HFAs on the magnetosphere and ionosphere will be determined. The project will use a variety of data sets including data from the THEMIS, Cluster and Geotail spacecraft when they were located near the bow shock.

The significance of the proposed work lies in the fundamental information it will provide about HFAs, which can significantly modify the solar wind-magnetosphere interaction, generate shocks, and energize particles efficiently. The study will advance our understanding of the structure and characteristics of HFAs, the physics underlying particle heating inside HFAs, and their impact on the magnetosphere and ionosphere. The interaction between the solar wind and the magnetosphere is a key element in space physics.

This study will form the core of the Ph.D. thesis for a graduate student from an underrepresented minority at the Center for Atmospheric Research, University of Massachusetts, Lowell. The scientific results will be highlighted on the THEMIS science nugget website which was developed for members of the public who are interested in THEMIS science results but may not have space physics backgrounds.

Project Report

Hot flow anomalies (HFAs), with remarkable flow deflections and plasma heating inside the structure, are often observed near the Earth’s bow shock. It is generally accepted that HFAs are generated as the result of the interaction between certain kinds of solar wind discontinuities and the Earth’s bow shock. It is now recognized that HFA is a universal phenomenon, which has been observed at the bow shock of the Earth, Mars , Saturn and Venus. The outcome of this project, we have found that HFAs can be formed under the condition of either a quasi-parallel or a quasi-perpendicular shock at HFA edges The large flow deflections in HFAs are location dependent and that the ions are near-specularly reflected at the bow shock. HFAs can be generated spontaneously (in the absence of any current sheets) at quasi-parallel bow shocks where the interplanetary magnetic field lies nearly parallel to the shock normal. Strong correlations between the thermal energy increase and the kinetic energy decrease indicate that the major part of the thermal energy of HFAs is converted from plasma’s kinetic energy inside HFAs. The particle spectra inside HFAs can serve as good indicators for a young or a mature HFA. The reflected ion population could be diffusive from all directions rather than the unidirectional beam when an HFA is forming.

Agency
National Science Foundation (NSF)
Institute
Division of Atmospheric and Geospace Sciences (AGS)
Type
Standard Grant (Standard)
Application #
0962815
Program Officer
Raymond J. Walker
Project Start
Project End
Budget Start
2010-09-01
Budget End
2013-08-31
Support Year
Fiscal Year
2009
Total Cost
$140,387
Indirect Cost
Name
University of Massachusetts Lowell
Department
Type
DUNS #
City
Lowell
State
MA
Country
United States
Zip Code
01854