Solar Cycle Variability of Nonmigrating Tides in the 5.3 and 15 μm Infrared Cooling of the Thermosphere (100–150 km) from SABER

This paper discusses the solar cycle variation of the DE3 and DE2 nonmigrating tides in the nitric oxide (NO) 5.3 μm and carbon dioxide (CO2) 15 μm infrared cooling between 100 and 150 km altitude and ±40° latitude. Tidal diagnostics of SABER NO and CO2 cooling rate data (2002–2013) indicate DE3 (DE2) amplitudes during solar maximum are on the order of 1 (0.5) nW/m3 in NO near 125 km, and on the order of 60 (30) nW/m3 in CO2 at 100 km, which translates into roughly 15–30% relative to the monthly zonal mean. The NO cooling shows a pronounced (factor of 10) solar cycle dependence (lower during solar minimum) while the CO2 cooling does not vary much from solar min to solar max. Photochemical modeling reproduces the observed solar cycle variability and allows one to delineate the physical reasons for the observed solar flux dependence of the tides in the infrared cooling, particularly in terms of warmer/colder background temperature versus smaller/larger tidal temperatures during solar max/min, in addition to cooling rate variations due to vertical tidal advection and tidal density variations. Our results suggest that (i) tides caused by tropospheric weather impose a substantial—and in the NO 5.3 μm case solar cycle dependent—modulation of the infrared cooling, mainly due to tidal temperature, and (ii) observed tides in the infrared cooling are a suitable proxy for tidal activity including its solar cycle dependence in a part of Earth's atmosphere where direct global temperature observations are lacking

On the relative roles of dynamics and chemistry governing the abundance and diurnal variation of low latitude thermospheric nitric oxide

We use data from two NASA satellites, the Thermosphere Ionosphere Energetics and Dynamics (TIMED) and the Aeronomy of Ice in the Mesosphere (AIM) satellites in conjunction with model simulations from the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) to elucidate the key dynamical and chemical factors governing the abundance and diurnal variation of nitric oxide (NO) at near solar minimum conditions and low latitudes. This analysis was enabled by the recent orbital precession of the AIM satellite which caused the solar occultation pattern measured by the Solar Occultation for Ice Experiment (SOFIE) to migrate down to low and mid latitudes for specific periods of time. We use a month of NO data collected in January 2017 to compare with two versions of the TIME-GCM, one driven solely by climatological tides and analysis-derived planetary waves at the lower boundary and free running at all other altitudes, while the other is constrained by a high-altitude analysis from the Navy Global Environmental Model (NAVGEM)up to the mesopause. We also compare SOFIE data with a NO climatology from the Nitric Oxide Empirical Model (NOEM). Both SOFIE and NOEM yield peak NO abundances of around 4×107cm−3; however, the SOFIE profile peaks about 6-8 km lower than NOEM. We show that this difference is likely a local time effect; SOFIE being a dawn measurement and NOEM representing late morning/near noon. The constrained version of TIME-GCM exhibits a low altitude dawn peak while the model that is forced solely at the lower boundary and free running above does not. We attribute this difference due to a phase change in the semi-diurnal tide in the NAVGEM-constrained model causing descent of high NO mixing ratio air near dawn. This phase difference between the two models arises due to differences in the mesospheric zonal mean zonal winds. Regarding the absolute NO abundance, all versions of the TIME-GCM overestimate this. Tuning the model to yield calculated atomic oxygen in agreement with TIMED data helps, but is insufficient. Further, the TIME-GCM underestimates the electron density [e-] as compared with the International Reference Ionosphere empirical model. This suggests a potential conflict with the requirements of NO modeling and [e-] modeling since one solution typically used to increase model [e-] is to increase the solar soft X ray flux which would, in this case, worsen the NO model/data discrepancy

Halfway to doubling of CO2 radiative forcing

The “double CO2” experiment has become a standard experiment in climate science, and a convenient way of comparing the sensitivity of different climate models. Double CO2 was first used by Arrhenius in the 19th century and in the classic paper by Manabe and Wetherald, published 50 years ago, which marked the start of the modern era of climate modeling. Doubling CO2 now has an iconic role in climate research. The equilibrium climate sensitivity (ECS) is defined as the global-mean surface temperature change resulting from a doubling of CO2, which is a headline result in Intergovernmental Panel on Climate Change (IPCC) assessments. In its most recent assessment IPCC concluded that the ECS “is likely in the range 1.5 to 4.5oC”. We show that we are now halfway to doubling of CO2 since pre-industrial times in terms of radiative forcing, but not in concentration

Temporal Variability of Atomic Hydrogen From the Mesopause to the Upper Thermosphere

We investigate atomic hydrogen (H) variability from the mesopause to the upper thermosphere, on time scales of solar cycle, seasonal, and diurnal, using measurements made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere Ionosphere Mesosphere Energetics Dynamics satellite, and simulations by the National Center for Atmospheric Research Whole Atmosphere Community Climate Model‐eXtended (WACCM‐X). In the mesopause region (85 to 95 km), the seasonal and solar cycle variations of H simulated by WACCM‐X are consistent with those from SABER observations: H density is higher in summer than in winter, and slightly higher at solar minimum than at solar maximum. However, mesopause region H density from the Mass‐Spectrometer‐Incoherent‐Scatter (National Research Laboratory Mass‐Spectrometer‐Incoherent‐Scatter 00 (NRLMSISE‐00)) empirical model has reversed seasonal variation compared to WACCM‐X and SABER. From the mesopause to the upper thermosphere, H density simulated by WACCM‐X switches its solar cycle variation twice, and seasonal dependence once, and these changes of solar cycle and seasonal variability occur in the lower thermosphere (~95 to 130 km), whereas H from NRLMSISE‐00 does not change solar cycle and seasonal dependence from the mesopause through the thermosphere. In the upper thermosphere (above 150 km), H density simulated by WACCM‐X is higher at solar minimum than at solar maximum, higher in winter than in summer, and also higher during nighttime than daytime. The amplitudes of these variations are on the order of factors of ~10, ~2, and ~2, respectively. This is consistent with NRLMSISE‐00

Impact of Space Weather on Climate and Habitability of Terrestrial Type Exoplanets

The current progress in the detection of terrestrial type exoplanets has opened a new avenue in the characterization of exoplanetary atmospheres and in the search for biosignatures of life with the upcoming ground-based and space missions. To specify the conditions favorable for the origin, development and sustainment of life as we know it in other worlds, we need to understand the nature of astrospheric, atmospheric and surface environments of exoplanets in habitable zones around G-K-M dwarfs including our young Sun. Global environment is formed by propagated disturbances from the planet-hosting stars in the form of stellar flares, coronal mass ejections, energetic particles, and winds collectively known as astrospheric space weather. Its characterization will help in understanding how an exoplanetary ecosystem interacts with its host star, as well as in the specification of the physical, chemical and biochemical conditions that can create favorable and/or detrimental conditions for planetary climate and habitability along with evolution of planetary internal dynamics over geological timescales. A key linkage of (astro) physical, chemical, and geological processes can only be understood in the framework of interdisciplinary studies with the incorporation of progress in heliophysics, astrophysics, planetary and Earth sciences. The assessment of the impacts of host stars on the climate and habitability of terrestrial (exo)planets will significantly expand the current definition of the habitable zone to the biogenic zone and provide new observational strategies for searching for signatures of life. The major goal of this paper is to describe and discuss the current status and recent progress in this interdisciplinary field and to provide a new roadmap for the future development of the emerging field of exoplanetary science and astrobiology.Comment: 206 pages, 24 figures, 1 table; Review paper. International Journal of Astrobiology (2019

Spaceborne mid‐ and far‐infrared observations improving nighttime ice cloud property retrievals

Two upcoming missions are scheduled to provide novel spaceborne observations of upwelling far‐infrared spectra. In this study, the accuracy of ice cloud property retrievals using spaceborne middle‐to‐far‐infrared (MIR‐FIR) measurements is examined toward a better understanding of retrieval biases and uncertainties. Theoretical sensitivity studies demonstrate that the MIR‐FIR spectra are sensitive to ice cloud properties, thereby providing a robust means for retrieving cloud properties under nighttime conditions. However, the temperature dependence of the ice refractive index and relevant ice particle shape models need to be incorporated into the retrieval procedure to avoid systematic biases in inferring cloud optical thickness and effective particle radius. Furthermore, prior information of subpixel cloud fractions is essential to mitigation of substantial systematic retrieval biases due to inconsistent subpixel cloud fractions

Interaction of gravity waves with the QBO: A satellite perspective

One of the most important dynamical processes in the tropical stratosphere is the quasi-biennial oscillation (QBO) of the zonal wind. Still, the QBO is not well represented in weather and climate models. To improve the representation of the QBO in the models, a better understanding of the driving of the QBO by atmospheric waves is required. In particular, the contribution of gravity waves is highly uncertain because of the small horizontal scales involved, and there is still no direct estimation based on global observations. We derive gravity wave momentum fluxes from temperature observations of the satellite instruments HIRDLS and SABER. Momentum flux spectra observed show that particularly gravity waves with intrinsic phase speeds <30m/s (vertical wavelengths <10km) interact with the QBO. Gravity wave drag is estimated from vertical gradients of observed momentum fluxes and compared to the missing drag in the tropical momentum budget of ERA-Interim. We find reasonably good agreement between their variations with time and in their approximate magnitudes. Absolute values of observed and ERA-Interim missing drag are about equal during QBO eastward wind shear. During westward wind shear, however, observations are about 2 times lower than ERA-Interim missing drag. This could hint at uncertainties in the advection terms in ERA-Interim. The strong intermittency of gravity waves we find in the tropics might play an important role for the formation of the QBO and may have important implications for the parameterization of gravity waves in global models. © 2014. American Geophysical Union. All Rights Reserved