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NASA NTRS2012

Using Schumann Resonance Measurements for Constraining the Water Abundance on the Giant Planets - Implications for the Solar System Formation

The formation and evolution of the Solar System is closely related to the abundance of volatiles, namely water, ammonia, and methane in the protoplanetary disk. Accurate measurement of volatiles in the Solar System is therefore important to understand not only the nebular hypothesis and origin of life but also planetary cosmogony as a whole. In this work, we propose a new, remote sensing technique to infer the outer planets water content by measuring Tremendously and Extremely Low Frequency (TLF-ELF) electromagnetic wave characteristics (Schumann resonances) excited by lightning in their gaseous envelopes. Schumann resonance detection can be potentially used for constraining the uncertainty of volatiles of the giant planets, mainly Uranus and Neptune, because such TLF-ELF wave signatures are closely related to the electric conductivity profile and water content.

Simoes, Fernando↗

NASA NTRS2012

Detection of Ionospheric Alfven Resonator Signatures in the Equatorial Ionosphere

The ionosphere response resulting from minimum solar activity during cycle 23/24 was unusual and offered unique opportunities for investigating space weather in the near-Earth environment. We report ultra low frequency electric field signatures related to the ionospheric Alfven resonator detected by the Communications/Navigation Outage Forecasting System (C/NOFS) satellite in the equatorial region. These signatures are used to constrain ionospheric empirical models and offer a new approach for monitoring ionosphere dynamics and space weather phenomena, namely aeronomy processes, Alfven wave propagation, and troposphere24 ionosphere-magnetosphere coupling mechanisms.

Simoes, Fernando↗

NASA NTRS2012

Performance of the IRI-2007 Model for Equatorial Topside Ion Density in the African Sector for Low and Extremely Low Solar Activity

The recent availability of new data sets during the recent extreme solar minimum provides an opportunity for testing the performance of the International Reference Ionosphere in historically under-sampled regions. This study will present averages and variability of topside ionospheric densities over Africa as a function of season, local time, altitude, and magnetic dip latitude as measured by the Coupled Ion-Neutral Dynamics Investigation (CINDI) Mission of Opportunity on the C/NOFS satellite. The results will be compared to the three topside model options available in IRI-2007. Overall, the NeQuick model is found to have the best performance, though during the deepest part of the solar minimum all three options significantly overestimate density.

Klenzing, J.↗

NASA NTRS2012

A Review of Low Frequency Electromagnetic Wave Phenomena Related to Tropospheric-Ionospheric Coupling Mechanisms

Investigation of coupling mechanisms between the troposphere and the ionosphere requires a multidisciplinary approach involving several branches of atmospheric sciences, from meteorology, atmospheric chemistry, and fulminology to aeronomy, plasma physics, and space weather. In this work, we review low frequency electromagnetic wave propagation in the Earth-ionosphere cavity from a troposphere-ionosphere coupling perspective. We discuss electromagnetic wave generation, propagation, and resonance phenomena, considering atmospheric, ionospheric and magnetospheric sources, from lightning and transient luminous events at low altitude to Alfven waves and particle precipitation related to solar and magnetospheric processes. We review in situ ionospheric processes as well as surface and space weather phenomena that drive troposphere-ionosphere dynamics. Effects of aerosols, water vapor distribution, thermodynamic parameters, and cloud charge separation and electrification processes on atmospheric electricity and electromagnetic waves are reviewed. We also briefly revisit ionospheric irregularities such as spread-F and explosive spread-F, sporadic-E, traveling ionospheric disturbances, Trimpi effect, and hiss and plasma turbulence. Regarding the role of the lower boundary of the cavity, we review transient surface phenomena, including seismic activity, earthquakes, volcanic processes and dust electrification. The role of surface and atmospheric gravity waves in ionospheric dynamics is also briefly addressed. We summarize analytical and numerical tools and techniques to model low frequency electromagnetic wave propagation and solving inverse problems and summarize in a final section a few challenging subjects that are important for a better understanding of tropospheric-ionospheric coupling mechanisms.

Simoes, Fernando↗

NASA NTRS2011

Topside Equatorial Ionospheric Density and Composition During and After Extreme Solar Minimum

During the recent solar minimum, solar activity reached the lowest levels observed during the space age. This extremely low solar activity has accompanied a number of unexpected observations in the Earth s ionosphere-thermosphere system when compared to previous solar minima. Among these are the fact that the ionosphere is significantly contracted beyond expectations based on empirical models. Altitude profiles of ion density and composition measurements near the magnetic dip equator are constructed from the Communication/Navigation Outage Forecast System (C/NOFS) satellite to characterize the shape of the topside ionosphere during the recent solar minimum and into the new solar cycle. The variation of the profiles with respect to local time, season, and solar activity are compared to the IRI-2007 model. Building on initial results reported by Heelis et al. (2009), here we describe the extent of the contracted ionosphere, which is found to persist throughout 2009. The shape of the ionosphere during 2010 is found to be consistent with observations from previous solar minima.

Klenzing, J.↗

NASA NTRS2012

Analyzing the IAR with IRI During the Recent Solar Minimum

The 2008-2009 solar minimum was deeper than any within the past century. As such, the performance of the empirical International Reference Ionosphere (IRI) model was impacted. This impact manifested as a disagreement between predicted and measured characteristic separation in frequency for a wave resonating within an Ionospheric Alfven Resonator (IAR). The predicted value of the characteristic was a factor of three lower than what was measured by the Communication/Navigation Outage Forecast System (C/NOFS). Analyzing the model performance and comparing output with measured ionospheric values showed that more than half of the inaccuracy could be explained by inaccuracies in the output of the model. The 2008-2009 solar minimum was outside of the bounds of the effectiveness of the empirical IRI model. Incorporating recent data measurements and new indices would increase the accuracy of IRI during this period.

Ivanov, S.↗

NASA NTRS2011

Comment on "An Analysis of VLF Electric Field Spectra Measured in Titan's Atmosphere by The Huygens Probe" By J. A. Morente et al.

Morente et al. have recently revisited the VLF electric field measurements made with the Permittivity, Wave and Altimetry (PWA) instrument during the descent of the Huygens Probe through the atmosphere of Titan. They assert that they have identified several harmonics of the transverse resonance mode of the surface?]ionosphere cavity, which would prove the existence of an electrical activity in the atmosphere of the largest satellite of Saturn. We refute this finding on the basis that it results from an artifact due to an improper analysis of the data set. [2] The investigators of the Permittivity, Wave and Altimetry (PWA) experiment on the Huygens Probe have reported the extremely low frequency (ELF) and very low frequency (VLF) electric signals recorded during the descent through the atmosphere of Titan. The PWA data are archived in the Planetary Science Archive (PSA) of ESA, and an extensive description of the instrument is at the disposal of the scientific community. Morente and his coworkers have revisited this data set and reported the results of their investigations in two papers. In a first paper, they claim that they have detected in the ELF range (0.100 Hz) several harmonics of a global resonance allegedly generated by lightning activity in the spherical cavity guide formed by the surface of Titan and the inner boundary of the ionosphere, a phenomenon similar to the Schumann resonance observed at EartH In the second paper dedicated to the VLF electric signal recorded by PWA, in the range 0.10 kHz, they argue that they can also bring out the transverse resonance and its harmonics, a more local phenomenon that develops around the excitation source and whose frequency is controlled by the separation between Titan?fs surface and the inner ionospheric boundary. [3] The PWA investigators have analyzed the narrowband ELF signal at about 36 Hz effectively observed during the entire descent. They have not endorsed, however, the alternative approach of Morente et al. that discloses additional ELF narrow-band signals and numerous related harmonics. Hamelin et al. and Beghin et al. have questioned the work of Morente and his coworkers and demonstrated unambiguously that their findings are mere artifacts entirely due to a faulty procedure. Morente et al. refuted this critical analysis of their ELF paper in a rebuttal. The present comment draws a parallelism between the ELF and VLF papers and demonstrates that the VLF signal carries no evidence whatever of any transverse resonance. The analyses of the ELF and VLF signals by Morente and his coworkers are flawed, and their conclusions are shown here to be invalid. A more comprehensive and thorough assessment of the numerical approaches proposed by Morente et al. is given by Berthelin et al..

Grard, Rejean↗

NASA NTRS2012

Performance of the IRI-2007 and SAMI2 Models during Extreme Solar Minimum

Klenzing, J.↗

NASA NTRS2012

Rb-Sr Isotopic Systematics of Alkali-Rich Fragments in the Yamato-74442 LL-Chondritic Breccia

Alkali-rich igneous fragments were identified in the brecciated LL-chondrites, Kr henberg (LL5)], Bhola (LL3-6) and Yamato (Y)-74442 (LL4), and show characteristic fractionation patterns of alkaline elements. The K-Rb-Cs-rich fragments in Kr henberg, Bhola, and Y-74442 are very similar in mineralogy and petrography (olivine + pyroxene + glass), suggesting that they could have come from related precursor materials. We have undertaken Rb-Sr isotopic studies on alkali-rich fragments in Y-74442 to precisely determine their crystallization ages and the isotopic signatures of their precursor material(s).

Yokoyama, T.↗

NASA NTRS2013

Dynamic Sampling of Trace Contaminants During the Mission Operations Test of the Deep Space Habitat

The atmospheric composition inside spacecraft during long duration space missions is dynamic due to changes in the living and working environment of crew members, crew metabolism and payload operations. A portable FTIR gas analyzer was used to monitor the atmospheric composition within the Deep Space Habitat (DSH) during the Mission Operations Test (MOT) conducted at the Johnson Space Center (JSC). The FTIR monitored up to 20 gases in near- real time. The procedures developed for operating the FTIR were successful and data was collected with the FTIR at 5 minute intervals. Not all the 20 gases sampled were detected in all the modules and it was possible to measure dynamic changes in trace contaminant concentrations that were related to crew activities involving exercise and meal preparation.

Monje, Oscar↗

NASA NTRS2013

Analytic Theory of Titans Schumann Resonance: Constraints on Ionospheric Conductivity and Buried Water Ocean

This study presents an approximate model for the atypical Schumann resonance in Titan's atmosphere that accounts for the observations of electromagnetic waves and the measurements of atmospheric conductivity performed with the Huygens Atmospheric Structure and Permittivity, Wave and Altimetry (HASI-PWA) instrumentation during the descent of the Huygens Probe through Titan's atmosphere in January 2005. After many years of thorough analyses of the collected data, several arguments enable us to claim that the Extremely Low Frequency (ELF) wave observed at around 36 Hz displays all the characteristics of the second harmonic of a Schumann resonance. On Earth, this phenomenon is well known to be triggered by lightning activity. Given the lack of evidence of any thunderstorm activity on Titan, we proposed in early works a model based on an alternative powering mechanism involving the electric current sheets induced in Titan's ionosphere by the Saturn's magnetospheric plasma flow. The present study is a further step in improving the initial model and corroborating our preliminary assessments. We first develop an analytic theory of the guided modes that appear to be the most suitable for sustaining Schumann resonances in Titan's atmosphere. We then introduce the characteristics of the Huygens electric field measurements in the equations, in order to constrain the physical parameters of the resonating cavity. The latter is assumed to be made of different structures distributed between an upper boundary, presumably made of a succession of thin ionized layers of stratospheric aerosols spread up to 150 km and a lower quasi-perfect conductive surface hidden beneath the non-conductive ground. The inner reflecting boundary is proposed to be a buried water-ammonia ocean lying at a likely depth of 55-80 km below a dielectric icy crust. Such estimate is found to comply with models suggesting that the internal heat could be transferred upwards by thermal conduction of the crust, while convective processes cannot be ruled out.

TITAN↗

NASA NTRS2012

Diagnostic modeling of dimethylsulfide production in coastal water west of the Antarctic Peninsula

The rate of gross biological dimethylsulfide (DMS) production at two coastal sites west of the Antarctic Peninsula, off Anvers Island, near Palmer Station, was estimated using a diagnostic approach that combined field measurements from 1 January 2006 through 1 March 2006 and a one-dimensional physical model of ocean mixing. The average DMS production rate in the upper water column (0-60 m) was estimated to be 3.1 +/- 0.6 nM/d at station B (closer to shore) and 2.7 +/- 0.6 nM/d1 at station E (further from shore). The estimated DMS replacement time was on the order of 1 d at both stations. DMS production was greater in the mixed layer than it was below the mixed layer. The average DMS production normalized to chlorophyll was 0.5 +/- nM/d)/(mg cubic m) at station B and 0.7 +/- 0.2 (nM/d)/(mg/cubic m3) at station E. When the diagnosed production rates were normalized to the observed concentrations of total dimethylsulfoniopropionate (DMSPt, the biogenic precursor of DMS), we found a remarkable similarity between our estimates at stations B and E (0.06 +/- 0.02 and 0.04 +/- 0.01 (nM DMS / d1)/(nM DMSP), respectively) and the results obtained in a previous study from a contrasting biogeochemical environment in the North Atlantic subtropical gyre (0.047 =/- 0.006 and 0.087 +/- 0.014 (nM DMS d1)/(nM DMSP) in a cyclonic and anticyclonic eddy, respectively).We propose that gross biological DMS production normalized to DMSPt might be relatively independent of the biogeochemical environment, and place our average estimate at 0.06 +/- 0.01 (nM DMS / d)/(nM DMSPt). The significance of this finding is that it can provide a means to use DMSPt measurements to extrapolate gross biological DMS production, which is extremely difficult to measure experimentally under realistic in situ conditions.

Dimethylsulfide↗

NASA NTRS2016

Observations and Simulations of the Na I D-1 Line profiles in an M-Class Solar Flare

We study the temporal evolution of the Na I D1 line profiles in the M3.9 flare SOL2014-06-11T21:03UT, using observations at high spectral resolution obtained with the Interferometric Bidimensional Spectrometer instrumentation the Dunn Solar Telescope combined with radiative hydrodynamic simulations. Our results show a significant increase in the intensities of the line core and wings during the flare. The analysis of the line profiles from the flare ribbons reveals that the Na I D1 line has a central reversal with excess emission in the blue wing (blue asymmetry).We combine RADYN and RH simulations to synthesize Na I D1 line profiles of the flaring atmosphere and find good agreement with the observations. Heating with a beam of electrons modifies the radiation field in the flaring atmosphere and excites electrons from the ground state 3s 2S to the first excited state 3p 2P, which in turn modifies the relative population of the two states. The change in temperature and the population density of the energy states make the sodium line profile revert from absorption into emission. Furthermore, the rapid changes in temperature break the pressure balance between the different layers of the lower atmosphere, generating upflow/downflow patterns. Analysis of the simulated spectra reveals that the asymmetries of the Na I D1 flare profile are produced by the velocity gradients in the lower solar atmosphere.

methods: numerical↗

NASA NTRS2021

Habitability Models for Astrobiology

Habitability has been generally defined as the capability of an environment to support life. Ecologists have beenusing Habitat Suitability Models (HSMs) for more than four decades to study the habitability of Earth fromlocal to global scales. Astrobiologists have been proposing different habitability models for some time, with lit-tle integration and consistency among them, being different in function to those used by ecologists. Habitabilitymodels are not only used to determine whether environments are habitable, but they also are used to charac-terize what key factors are responsible for the gradual transition from low to high habitability states. Here wereview and compare some of the different models used by ecologists and astrobiologists and suggest how theycould be integrated into new habitability standards. Such standards will help improve the comparison and charac-terization of potentially habitable environments, prioritize target selections, and study correlations between habit-ability and biosignatures. Habitability models are the foundation of planetary habitability science, and the synergybetween ecologists and astrobiologists is necessary to expand our understanding of the habitability of Earth,the Solar System, and extrasolar planets.

Habitability↗

NASA NTRS2023

The F-CHROMA Grid of 1D RADYN Flare Models

Context. Solar flares are the result of the sudden release of magnetic energy in the corona. Much of this energy goes into accelerating charged particles to high velocity. These particles travel along the magnetic field and the energy is dissipated when the density gets high enough, primarily in the solar chromosphere. Modelling this region is difficult because the radiation energy balance is dominated by strong, optically thick spectral lines. Aims. Our aim is to provide the community with realistic simulations of a flaring loop with an emphasis on the detailed treatment of the chromospheric energy balance. This will enable a detailed comparison of existing and upcoming observations with synthetic observables from the simulations, thereby elucidating the complex interactions in a flaring chromosphere. Methods. We used the 1D radiation hydrodynamics code RADYN to perform simulations of the effect of a beam of electrons injected at the apex of a solar coronal loop. A grid of models was produced, varying the total energy input, the steepness, and low-energy cutoff of the beam energy spectrum. Results. The full simulation results for a grid of models are made available online. Some general properties of the simulations are discussed.

hydrodynamics↗