Aeronomy

Abstract: We present a model of the longwave atmospheric spectrum that improves in many respects widely used older models such as the microwave propagation model (MPM), since it is based on broadband measurements and calculations. According to our data, the model is fully applicable from 0 to 2 THz while including lines up to 10 THz. Its primary goal is to simulate the millimeter/submillimeter region accessible from the ground (frequencies up to /spl sim/2 THz at most, with a few windows between 1 and 2 THz accessible only under exceptional conditions at very dry sites). Line-by-line calculations of the absorption are performed using a line database generated from the latest available spectroscopic constants for all relevant atmospheric species. The collisional line widths are obtained from published laboratory data. The excess of absorption in the longwave range that cannot be explained by the line spectrum is modeled by introducing two different continuum-like terms based on FTS measurements between 170 and 1100 GHz: collision-induced absorption of the dry atmosphere due to transient dipoles in symmetric molecules (N/sub 2/ and O/sub 2/) and continuum-like water vapor opacity. All H/sub 2/O lines up to 10 THz are included in order to correctly account for the entire H/sub 2/O far-wing opacity below 2 THz for a given line-shape. Hence, this contribution does not need to be part of a pseudocontinuum term below that frequency cutoff (still necessary, as shown in this paper) in contrast to other models used to date. Phase delays near H/sub 2/O and O/sub 2/ resonances are also important for ground-based astronomy since they affect interferometric phase. The frequency-dependent dispersive phase delay function is formally related to the absorption line shape via the Kramers-Kronig dispersion theory, and this relation has been used for modeling those delays. Precise calculations of phase delays are essential for the future Atacama large millimeter array (ALMA) project. A software package called atmospheric transmission at microwaves (ATM) has been developed to provide the radioastronomy and aeronomy communities with an updated tool to compute the atmospheric spectrum in clear-sky conditions for various scientific applications. We use this model to provide detailed simulations of atmospheric transmission and phase dispersion for several sites suitable for submillimeter astronomy.

Abstract: A new Mars Global Ionosphere-Thermosphere Model (M-GITM) is presented that combines the terrestrial GITM framework with Mars fundamental physical parameters, ion-neutral chemistry, and key radiative processes in order to capture the basic observed features of the thermal, compositional, and dynamical structure of the Mars atmosphere from the ground to the exosphere (0–250 km). Lower, middle, and upper atmosphere processes are included, based in part upon formulations used in previous lower and upper atmosphere Mars GCMs. This enables the M-GITM code to be run for various seasonal, solar cycle, and dust conditions. M-GITM validation studies have focused upon simulations for a range of solar and seasonal conditions. Key upper atmosphere measurements are selected for comparison to corresponding M-GITM neutral temperatures and neutral-ion densities. In addition, simulated lower atmosphere temperatures are compared with observations in order to provide a first-order confirmation of a realistic lower atmosphere. M-GITM captures solar cycle and seasonal trends in the upper atmosphere that are consistent with observations, yielding significant periodic changes in the temperature structure, the species density distributions, and the large-scale global wind system. For instance, mid afternoon temperatures near ∼200 km are predicted to vary from ∼210 to 350 K (equinox) and ∼190 to 390 k (aphelion to perihelion) over the solar cycle. These simulations will serve as a benchmark against which to compare episodic variations (e.g., due to solar flares and dust storms) in future M-GITM studies. Additionally, M-GITM will be used to support MAVEN mission activities (2014–2016).

Abstract: A comprehensive theoretical model of both the auroral and nonauroral atmosphere and ionosphere of Jupiter is presented and used to study particle precipitation effects in the Jovian upper atmosphere, both at middle and high latitudes. The sources of energy in the model include extreme ultraviolet radiation and energetic electrons. The precipitation of monoenergetic beams of both one and ten keV electrons at high Jovian latitudes are treated in detail, and the effects of higher energy electrons and soft electrons at middle and low latitudes are considered. The effects of this precipitation, such as airglow excitation, ionization, dissociation, and heating are examined. Calculations of the densities of hydrogen, hydrocarbons, and the important ions as well as the temperatures of the neutral, electron, and ion species are included.