The winter helium bulge revisited

“…X. Liu et al (2014b) studied the helium bulge using a newly implemented helium module in TIE-GCM. In contrast to the inter-hemispheric transport mechanism of Mayr and Volland (1972), they found that vertical advection (driven by horizontal wind divergence) and molecular diffusion are the dominant processes.…”

Section: Seasonal-latitudinal Variationsmentioning

confidence: 99%

Thermospheric mass density: A review

Emmert

2015

Advances in Space Research

210

217

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“…Hays et al [] stated unequivocally that “it is not divergences that cause compositional changes, but the vertical motions resulting from divergence in the wind field that cause the major changes in composition.” Likewise, Burns et al [], comparing the strength of individual terms in the differential composition equation, found that the vertical advection term dominated and that the horizontal advection term was of the incorrect sign to sustain such seasonal distributions. Further tests by Liu et al [] simulated a light minor species in a general circulation model, with various transport terms “switched” on and off. Significant seasonal accumulations were only seen during simulations in which the vertical advection term was turned on, while the effects of horizontal advection on the seasonal distribution were much less significant.…”

Section: Introductionmentioning

confidence: 99%

“…We find that a seasonal interhemispheric transport of light constituents does in fact occur and is directly responsible for the observed winter‐time thermospheric enhancements. Many of the conclusions drawn by Burns et al [], Liu et al [], and Burns et al [] still hold true, with vertical advection being the most crucial term in the composition equation. However, we elucidate the principal role of an interhemispheric transport of light species in determining the strength of this vertical advection term, and thus, the global distribution of light species.…”

Section: Introductionmentioning

confidence: 99%

Interhemispheric transport of light neutral species in the thermosphere

Sutton

2016

Geophysical Research Letters

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A mechanistic description of neutral species transport is presented, reconciling two long‐standing yet ostensibly incompatible interpretations of the “wind‐induced diffusion” of thermospheric constituents. Regarding the creation and sustainment of anomalous winter distributions of light species (e.g., atomic oxygen or helium), the theory of Reber and Hays (1973) cites vertical advection as the main cause while Mayr et al. (1978) cite horizontal transport—both in the presence of a diffusively separated atmosphere. We demonstrate that these theories are not at odds with each other. Instead, they describe two coherent aspects of a single process: convergent (divergent) horizontal motion increases downwelling (upwelling), thereby transporting light constituents both horizontally and vertically simultaneously. Such a connection between horizontal and vertical transport is straightforward and well established for the mass‐averaged circulation. Yet this connection has remained obscure for a single minor species entrained within the flow, in part due to the appearance of the composition equation when expressed in a Eulerian frame of reference. Concrete evidence is presented in terms of model equations and diagnostics, establishing a direct link between the horizontal and vertical transport of an atmospheric constituent. Consequently, we are able to show that winter accumulations of light species arise from an interhemispheric migration operating on seasonal timescales, rather than from their redistribution within the vertical column. This new understanding has implications for the timescales at play in both the F region ionosphere and lower exosphere, two regions profoundly impacted by light neutral species.

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“…It is straightforward to show that the effect of these terms is small when the mass mixing ratio of the minor species in question is also small. Helium as a minor species in the TIE-GCM was recently implemented by Liu et al [35]. While this approach demonstrated the model's ability to accumulate helium in the winter hemisphere, it required the ad hoc inclusion of helium into the scale height calculation in order to avoid unrealistically high values during long simulations.…”

Section: Implementing Helium As a Major Speciesmentioning

confidence: 99%

Semi-Empirical, First-Principles, and Hybrid Modeling of the Thermosphere to Enhance Data Assimilation

Sutton¹

2015

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Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY)27-10-2015 (From -To) REPORT TYPE Final Report DATES COVERED AFRL-RV-PS-TR-2015-0168 SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S)AFRL/RVBXI SPONSOR/MONITOR'S REPORT NUMBER(S) DISTRIBUTION / AVAILABILITY STATEMENTApproved for public release; distribution is unlimited. (OPS-15-9186 dtd 17 Nov 2015) SUPPLEMENTARY NOTES ABSTRACTDuring this task, we established a method for extracting the most significant basis functions from a physics-based model of the thermosphere and ionosphere. A new model was then constructed by replacing the spherical harmonic functions used in an existing semiempirical thermosphere model with these basis functions. The resulting hybrid model, published in the Space Weather Journal, demonstrated the ability to represent sparse thermospheric data in a more accurate and efficient way. In addition, we chose Jacchia 1970 as our underlying semi-empirical model so that the new hybrid model functions as a direct replacement for the High Accuracy Satellite Drag Model used by AFSPC and the JSpOC. We also worked to improve the hybrid model by investigating the limitations of and possible improvements to the underlying assumptions imposed by the chosen models. In particular, we realized that there was a large and potentially significant component missing from all general circulation models, that being the appropriate treatment of helium in the upper thermosphere. To rectify this situation, we undertook the project of adding helium to the solution of a first-principles community model of the thermosphere and ionosphere. In doing this, we discovered that this could only be done self-consistently by solving for helium as a major species, as opposed to as a minor species. The product of this work was the first physics-based model to accurately simulate the seasonal and latitudinal behavior of the helium distribution. This work was published in the Journal of Geophysical Research. 64This page is intentionally left blank.Approved for public release; distribution is unlimited.

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The winter helium bulge revisited

Cited by 26 publications

References 24 publications

Thermospheric mass density: A review

Thermospheric mass density: A review

Interhemispheric transport of light neutral species in the thermosphere

Semi-Empirical, First-Principles, and Hybrid Modeling of the Thermosphere to Enhance Data Assimilation

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