Erdal Yiğit

Internal wave coupling processes in Earth’s atmosphere

Abstract This paper presents a contemporary review of vertical coupling in the atmosphere and ionosphere system induced by internal waves of lower atmospheric origin. Atmospheric waves are primarily generated by meteorological processes, possess a broad range of spatial and temporal scales, and can propagate to the upper atmosphere. A brief summary of internal wave theory is given, focusing on gravity waves, solar tides, planetary Rossby and Kelvin waves. Observations of wave signatures in the upper atmosphere, their relationship with the direct propagation of waves into the upper atmosphere, dynamical and thermal impacts as well as concepts, approaches, and numerical modeling techniques are outlined. Recent progress in studies of sudden stratospheric warming and upper atmospheric variability are discussed in the context of wave-induced vertical coupling between the lower and upper atmosphere.

Heating and cooling of the thermosphere by internal gravity waves

For the first time, estimates of heating and cooling in the upper thermosphere due to dissipating and breaking gravity waves ( GWs) of tropospheric origin have been obtained with a comprehensive general circulation model ( GCM). A GW parameterization specifically designed for thermospheric heights has been implemented in the CMAT2 GCM covering altitudes from the tropopause to the F-2 region, and simulations for the June solstice have been performed. They reveal that the net thermal effect of GWs above the turbopause is cooling. The largest ( up to -170 K d(-1) in a zonally and temporally averaged sense) cooling takes place in the high latitudes of both hemispheres near 210 km. The instantaneous values of heating and cooling rates are highly variable, and reach up to 500 and -3000 K d(-1) in the F-2 region, respectively. Inclusion of the GW thermal effects reduces the simulated model temperatures by up to 200 K over the summer pole and by 100 to 170 K at other latitudes near 210 km.

Internal gravity waves in the thermosphere during low and high solar activity: Simulation study

GW drag and wave‐induced heating/cooling are shown to be smaller below ∼170 km at high solar activity, and larger above. The maxima of GW momentum deposition occur much higher in the upper thermosphere, but their peaks are half as strong, 120 vs 240 m s −1 day −1 in the winter hemisphere when the insolation is large. Instead of strong net cooling in the upper thermosphere, GWs produce a weak heating at high solar activity created by fast harmonics less affected by dissipation. Molecular viscosity increases with solar activity at fixed pressure levels, but seen in Cartesian altitude grids it can either increase or decrease in the lower thermosphere, depending on the height. Therefore, in pressure coordinates, in which most GCMs operate, the influence of larger temperatures can be viewed as a competition between the enhanced dissipation and vertical expansion of the atmosphere.

Simulated variability of the high‐latitude thermosphere induced by small‐scale gravity waves during a sudden stratospheric warming

We present the results of the first investigation of the influence of small-scale gravity waves (GWs) originating in the lower atmosphere on the variability of the high-latitude thermosphere during a sudden stratospheric warming (SSW). We use a general circulation model that incorporates the spectral GW parameterization of Yigit et al. (2008). During the warming, the GW penetration into the thermosphere and resulting momentum deposition rates increase by up to a factor of 3–6 in the high-latitude thermosphere. The associated temporal variability of GW dynamical effects at ~250 km are enhanced by up to a factor of ~10, exhibiting complex geographical variations. The peak magnitude of the GW drag temporal variability locally exceeds the mean GW drag by more than a factor of 2. The small-scale thermospheric wind variability is larger when GW propagation into the thermosphere is allowed compared to the case when thermospheric GW effects are absent. These results suggest that GW-induced variations during SSWs constitute a significant source of high-latitude thermospheric variability.

Cooling of the Martian thermosphere by CO2 radiation and gravity waves: An intercomparison study with two general circulation models

Observations show that the lower thermosphere of Mars (∼100–140 km) is up to 40 K colder than the current general circulation models (GCMs) can reproduce. Possible candidates for physical processes missing in the models are larger abundances of atomic oxygen facilitating stronger CO2 radiative cooling and thermal effects of gravity waves. Using two state-of-the-art Martian GCMs, the Laboratoire de Meteorologie Dynamique and Max Planck Institute models that self-consistently cover the atmosphere from the surface to the thermosphere, these physical mechanisms are investigated. Simulations demonstrate that the CO2 radiative cooling with a sufficiently large atomic oxygen abundance and the gravity wave-induced cooling can alone result in up to 40 K colder temperature in the lower thermosphere. Accounting for both mechanisms produce stronger cooling at high latitudes. However, radiative cooling effects peak above the mesopause, while gravity wave cooling rates continuously increase with height. Although both mechanisms act simultaneously, these peculiarities could help to further quantify their relative contributions from future observations.

Gravity waves and high‐altitude CO2 ice cloud formation in the Martian atmosphere

We present the first general circulation model simulations that quantify and reproduce patches of extremely cold air required for CO2 condensation and cloud formation in the Martian mesosphere. They are created by subgrid-scale gravity waves (GWs) accounted for in the model with the interactively implemented spectral parameterization. Distributions of GW-induced temperature fluctuations and occurrences of supersaturation conditions are in a good agreement with observations of high-altitude CO2 ice clouds. Our study confirms the key role of GWs in facilitating CO2 cloud formation, discusses their tidal modulation, and predicts clouds at altitudes higher than have been observed to date.

Introduction to Plasma

A plasma is an electrically conducting quasi-neutral gas mainly composed of charged particles that exhibit collective motion. The vast majority of observable universe consists of plasma. Closer to Earth, i.e., in the solar-terrestrial environment, the solar wind, the magnetosphere, and the ionosphere are the most studied plasma environments. Plasma processes are greatly influenced by ambient electromagnetic fields and, in analogy with neutral planetary atmospheres, waves are continuously generated in plasmas and their propagation and interaction influence the structure and the evolution of plasma. A naturally occurring magnetic field environment is the geomagnetic field, which has already been detected four centuries ago. In this introductory chapter, a conceptual discussion of plasma is first presented. Then, various space plasma environments are discussed along with a brief introduction to the history of space research. Finally, some key plasma parameters such as density, gyrofrequency, and temperature, and characteristics (collective motion, quasi-neutrality) are discussed concisely.

Simultaneous observations of atmospheric tides from combined in situ and remote observations at Mars from the MAVEN spacecraft

We report the observations of longitudinal variations in the Martian thermosphere associated with nonmigrating tides. Using the Neutral Gas Ion Mass Spectrometer (NGIMS) and the Imaging Ultraviolet Spectrograph (IUVS) on NASAs Mars Atmosphere and Volatile EvolutioN Mission (MAVEN) spacecraft, this study presents the first combined analysis of in situ and remote observations of atmospheric tides at Mars for overlapping volumes, local times, and overlapping date ranges. From the IUVS observations, we determine the altitude and latitudinal variation of the amplitude of the nonmigrating tidal signatures, which is combined with the NGIMS, providing information on the compositional impact of these waves. Both the observations of airglow from IUVS and the CO2 density observations from NGIMS reveal a strong wave number 2 signature in a fixed local time frame. The IUVS observations reveal a strong latitudinal dependence in the amplitude of the wave number 2 signature. Combining this with the accurate CO2 density observations from NGIMS, this would suggest that the CO2 density variation is as high as 27% at 0–10° latitude. The IUVS observations reveal little altitudinal dependence in the amplitude of the wave number 2 signature, varying by only 20% from 160 to 200 km. Observations of five different species with NGIMS show that the amplitude of the wave number 2 signature varies in proportion to the inverse of the species scale height, giving rise to variation in composition as a function of longitude. The analysis and discussion here provide a roadmap for further analysis as additional coincident data from these two instruments become available.

Comparison of the Martian thermospheric density and temperature from IUVS/MAVEN data and general circulation modeling

IUVS/MAVEN data are archived in the Planetary Atmospheres Node of the Planetary Data System (http://pds-atmospheres.nmsu.edu). Modeling data supporting the figures are available upon request from A.S.M. (medvedev@mps.mpg.de). The work was partially supported by German Science Foundation (DFG) grant ME2752/3-1. E.Y. was partially supported by NASA grant NNX13AO36G.

Importance of capturing heliospheric variability for studies of thermospheric vertical winds

[1] Using the Global Ionosphere Thermosphere Model with observed real-time heliospheric input data, the magnitude and variability of thermospheric neutral vertical winds are investigated. In order to determine the role of variability in the Interplanetary Magnetic Field (IMF) and solar wind density on the neutral wind variability, the heliospheric input data are smoothed. The effects of smoothing the IMF and solar wind and density on the vertical winds are simulated for the cases of no smoothing, 5-minute, and 12-minute smoothing. Various vertical wind acceleration terms, such as the nonhydrostatic acceleration, are quantified. Polar stereographic projections of the variabilities of vertical wind and ion flows are compared to highlight existing correlations. Overall, the smoother, that is, the less variable the IMF and solar wind parameters are, the weaker are the magnitude and the variability of the thermospheric vertical winds. Weaker IMF variability leads to smaller variability in ion flows, which in turn negatively impacts the variability and the magnitude of Joule heating. Small-scale temporal variation of the vertical wind acceleration, and thus the variability of the vertical wind, is dominated by the nonhydrostatic term that is controlled primarily by the temporal variation of the Joule heating, which in turn is related to ion flow variations that are shaped by the IMF in the high-latitude thermosphere. Wavelet analysis of the vertical wind data shows that gravity waves of � 5 and � 10-minute periods are more prominent when the model is run with high-resolution real-time IMF and solar wind data. Better capturing of the temporal variation of the IMF and solar wind parameters is crucial for modeling the variability and magnitude of thermospheric vertical winds.