Erdal Yiğit - George Mason University - Physics and Astronomy

Selected Conferences

American Geophysical Union, 12-16 December, 2022, Chicago, USA.

I have an oral presentation, "Climatology of Thermospheric Mean Winds and Circulation based on ICON/MIGHTI Observations".

Session Number and Title: SA52B: Dynamics of the Thermosphere and Ionosphere System at Low and Middle Latitudes Due to the External and Internal Forcing I Oral

Abstract: Neutrals winds play an important dynamical and thermodynamical role in the energy and momentum budget of the whole atmosphere system. Using the horizontal neutral wind observations from the MIGHTI instrument onboard NASA's ICON (Ionospheric Connection Explorer) spacecraft with continuous coverage, we produce a climatology of the mean zonal and meridional winds and the associated mean horizontal circulation at low- to middle latitudes (10oS--45oN) for Northern Hemisphere solstice conditions between 90 km and 200 km altitudes, speciotemporal variability often exceeding ~150 m s-1 in magnitude. The daily averaged zonal mean winds demonstrate day-to-day variability, which could be due to a combination of orbital variations and as well as intrinsic variability of thermospheric winds. Eastward zonal winds and northward (winter-to-summer) meridional winds are prevalent in the lower thermosphere, which provides indirect observational evidence of the eastward momentum deposition by propagating gravity waves. The mean neutral winds and circulation exhibit smaller scale structures in the lower thermosphere (90-120 km), while they are more homogeneous in the upper thermosphere, indicating the increasingly dissipative nature of the thermosphere. Comparison of the ICON mean winds and circulation with previous observations and modeling demonstrates reasonable agreement. The mean wind and circulation patterns inferred from ICON/MIGHTI measurements serve as a valuable dataset and can be used to drive, constrain, and validate numerical models of the atmosphere.

I have a poster presentation, "Observation and Modeling of Gravity Waves in the Martian Whole Atmosphere under Varying Atmospheric Conditions and Implications for Atmospheric Loss".

Session Number and Title: P42F: Processes in the Present-Day Atmosphere of Mars V Poster

Abstract: Gravity waves play an important role in the dynamical and thermal structure of the Martian whole atmosphere system. They are primarily generated in the lower atmosphere and propagate upward to the mesosphere and thermosphere-ionosphere, where they dissipate owing largely to nonlinear wave-wave interactions and increased background viscosity, and deposit their energy and momentum to the mean ow. They are the primary contributor to long-range atmospheric vertical coupling on Mars. We present recent progress in the modeling and observation of upper atmospheric effects of gravity waves, focusing on observations by the NGIMS instrument onboard the MAVEN spacecraft and the Atmospheric Chemistry Suite (ACS) instrument on board the Trace Gas Orbiter (TGO) as well as three-dimensional time-dependent Martian general circulation modeling. High-resolution climate models as well as global models utilizing subgrid- scale gravity wave parameterization demonstrate a substantial amount of wave drag, i.e., acceleration/deceleration of the mean winds, in the mesosphere and thermosphere over a broad range of altitudes, which is overall in good agreement with the magnitude and spatial distribution of the wave drag deduced from TGO. Satellite observations provide evidence for gravity wave- induced density uctuations in the thermosphere in the order of 20%, depending on the season and location, and a doubling of thermospheric gravity wave activity during the 2018 global dust storm. GW propagation from the lower atmosphere to the exobase indicates that the waves not only contribute to the intensication of the dynamical transport but can also directly enhance the thermal escape of hydrogen into space. The combined analysis of models and observations suggests that the inuence of gravity waves on atmospheric escape is a multi-step process and Observation and Modeling of Gravity Waves in the Martian Whole Atmosphere under Varying Atmospheric Conditions and Implications for Atmospheric Loss that gravity waves can significantly modulate escape rates.

COSPAR 2021,

28 January - 4 February 2021, Sydney, Australia

I have a virtual oral presentation, "Climatology of Gravity Wave Activity in the Middle and Upper Atmosphere as Simulated by a Whole Atmosphere Gravity Wave Parameterization and Comparison with SABER/TIMED Observations".
The presentation can be found on You Tube

https://www.youtube.com/watch?v=D4JboPyRKHk

European Geophysical Union, 8-12 April, 2019, Vienna, Austria

I have an invited talk, "Modeling and Observation of Gravity Waves in the Thermosphere-Ionosphere System".

Session: ST3.3/EMRP2.6/G4.5 - Dynamics and interaction of processes in Earth, atmosphere and space environment: global observations and modeling, room L1 on Thursday, 11 Apr 2019, 11:45.

Abstract: The lower atmosphere is the primary source of a broad spectrum of internal gravity waves. A significant portion of these waves survive wave filtering and dissipation processes in the lower and middle atmosphere, and thus reach the thermosphere-ionosphere system, where they appreciably contribute to the energy and momentum budget of the upper atmosphere. This process manifests an important form of vertical coupling mechanism between the lower and the upper atmospheres. Here I present a review of observation and modeling of the impact of gravity waves of lower atmospheric origin on the the thermosphere-ionosphere system. Dependence of the gravity wave processes on the background atmosphere, wave dissipation, magnetic field configuration, minor and major sudden stratospheric warmings, and tidal activity leads to a complex picture of gravity wave effects in the upper atmosphere. A whole atmosphere approach is required for a better understanding of gravity wave processes.

27th IUGG General Assembly, 8-18 July 2019, Montreal, Canada

A03 - COUPLING PROCESSES IN THE ATMOSPHERE-IONOSPHERE (DIVII-C/ICMA/SCOSTEP/ICDC)

Convener: Petra Knizova (Czech Republic)

Co-Conveners: Erdal Yiğit (USA), Subramanian Gurubaran (India), Christina Arras (Germany)

Description: The objective of this symposium is to bring new insights into the understanding of the coupling processes in the atmosphere-ionosphere system. The symposium will address fundamental physical processes covering whole atmosphere system. It covers various dynamical, chemical, and electrodynamical processes. The coupled effects can be expressed in terms of the modulation of waves from the lower to the upper atmosphere as well as from low- to high-latitudes, electrodynamic and compositional changes, plasma drifts, electric fields and plasma irregularities at different latitudinal regions of the globe due to the varying energy inputs. Middle atmospheric dynamics, and particularly atmospheric waves, play a leading role in determining the variability of the atmosphere-ionosphere system. The MLT region is a critical region in the coupling between the lower/middle atmosphere and the upper atmosphere/ionosphere. It represents a physical filter and shape the flux of waves ascending through the mesosphere into the overlying thermosphere. The manner in which the couplings take place due to varying energy inputs from the Sun and from the lower atmosphere is a question that is yet to be understood. This symposium solicits papers dealing with experiments, observations, modeling and data analysis that describe the effects of atmospheric coupling processes within the whole atmosphere-ionosphere system. The symposium will be particularly focused on the dependence of coupling processes on the solar and geomagnetic activity, the downward control effects transferring from the strongly solar dependent structure to the lower atmospheric levels and upward propagating structures induced in the lower atmosphere by changing solar activity. Theoretical and empirical results concerning the coupling mechanisms are invited. Symposium proposed in cooperation of International Commission on the Middle Atmosphere (ICMA) of the International Association of Meteorology and Atmospheric Science (IAMAS), the Scientific Committee on Solar Terrestrial Physics (SCOSTEP) and Interdivisional Commission on Developing Countries (ICDC).

For details: http://iugg2019montreal.com/a.html

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