We study the response of the thermosphere and ionosphere to gravity waves (GWs) excited by 6 h of deep convection in Brazil on the evening of 01 October 2005 via the use of convective plume, ray ...trace, and global models. We find that primary GWs excited by convection having horizontal wavelengths of λH∼70–300 km, periods of 10–60 min, and phase speeds of cH∼50–225 m/s propagate well into the thermosphere. Their density perturbations are ρ′/ρ¯∼15– 25% at z∼150 km and are negligible at z>300 km. The dissipation of these GWs creates spatially and temporally localized body forces with amplitudes of 0.2– 1.0 m/s2at z∼120–230 km. These forces generate two counter‐rotating circulation cells with horizontal velocities of 50–350 m/s. They also excite secondary GWs; those resolved by our global model have λH∼4000–5000 km and cH∼500–600 m/s. These secondary GWs propagate globally and have ρ′/ρ¯∼10– 25% and 5–15% at z=250 and 375 km, respectively. These forces also create plasma perturbations of foF2′∼0.2–1.0 MHz, TEC′∼0.4– 1.5 TECU (total electron content unit, 1TECU =1016 elm−2), and hmF2′∼5–50 km. The large‐scale traveling ionospheric disturbances (LSTIDs) induced by the secondary GWs have amplitudes of foF2′∼0.2–0.5 MHz, TEC′∼0.2– 0.6 TECU, and hmF2′∼5–10 km. In a companion paper, we discuss changes to the prereversal enhancement and plasma drift from these forces.
Key PointsThe dissipation of GWs creates circulation cells, secondary GWs, LSTIDs
Optical frequency combs act as rulers in the frequency domain and have opened new avenues in many fields such as fundamental time metrology, spectroscopy and frequency synthesis. In particular, ...spectroscopy by means of optical frequency combs has surpassed the precision and speed of Fourier spectrometers. Such a spectroscopy technique is especially relevant for the mid-infrared range, where the fundamental rotational-vibrational bands of most light molecules are found. Most mid-infrared comb sources are based on down-conversion of near-infrared, mode-locked, ultrafast lasers using nonlinear crystals. Their use in frequency comb spectroscopy applications has resulted in an unequalled combination of spectral coverage, resolution and sensitivity. Another means of comb generation is pumping an ultrahigh-quality factor microresonator with a continuous-wave laser. However, these combs depend on a chain of optical components, which limits their use. Therefore, to widen the spectroscopic applications of such mid-infrared combs, a more direct and compact generation scheme, using electrical injection, is preferable. Here we present a compact, broadband, semiconductor frequency comb generator that operates in the mid-infrared. We demonstrate that the modes of a continuous-wave, free-running, broadband quantum cascade laser are phase-locked. Combining mode proliferation based on four-wave mixing with gain provided by the quantum cascade laser leads to a phase relation similar to that of a frequency-modulated laser. The comb centre carrier wavelength is 7 micrometres. We identify a narrow drive current range with intermode beat linewidths narrower than 10 hertz. We find comb bandwidths of 4.4 per cent with an intermode stability of less than or equal to 200 hertz. The intermode beat can be varied over a frequency range of 65 kilohertz by radio-frequency injection. The large gain bandwidth and independent control over the carrier frequency offset and the mode spacing open the way to broadband, compact, all-solid-state mid-infrared spectrometers.
For the first time a mesoscale‐resolving whole atmosphere general circulation model has been developed, using the National Center for Atmospheric Research Whole Atmosphere Community Climate Model ...with ∼0.25° horizontal resolution and 0.1 scale height vertical resolution above the middle stratosphere (higher resolution below). This is made possible by the high accuracy and high scalability of the spectral element dynamical core from the High‐Order Method Modeling Environment. For the simulated January–February period, the latitude‐height structure and the magnitudes of the temperature variance compare well with those deduced from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) observations. The simulation reveals the increasing dominance of gravity waves (GWs) at higher altitudes through both the height dependence of the kinetic energy spectra, which display a steeper slope (∼−3) in the stratosphere and an increasingly shallower slope above, and the increasing spatial extent of GWs (including a planetary‐scale extent of a concentric GW excited by a tropical cyclone) at higher altitudes. GW impacts on the large‐scale flow are evaluated in terms of zonal mean zonal wind and tides: with no GW drag parameterized in the simulations, forcing by resolved GWs does reverse the summer mesospheric wind, albeit at an altitude higher than climatology, and only slows down the winter mesospheric wind without closing it. The hemispheric structures and magnitudes of diurnal and semidiurnal migrating tides compare favorably with observations.
Key PointsFirst mesoscale‐resolving whole atmosphere general circulation modelSimulation reveals the growing dominance of gravity waves with altitudeGravity waves and their large‐scale impacts evaluated
Ionospheric day‐to‐day variability is a ubiquitous feature, even in the absence of appreciable geomagnetic activities. Although meteorological perturbations have been recognized as an important ...source of the variability, it is not well represented in previous modeling studies and the mechanism is not well understood. This study demonstrates that the thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model (TIME‐GCM) constrained in the stratosphere and mesosphere by the hourly whole atmosphere community climate model (WACCM) simulations is capable of reproducing observed features of day‐to‐day variability in the thermosphere‐ionosphere. Realistic weather patterns in the lower atmosphere in WACCM were specified by Modern Era Retrospective Reanalysis for Research and Application (MERRA). The day‐to‐day variations in mean zonal wind, migrating and nonmigrating tides in the thermosphere, vertical and zonal E × B drifts, and ionosphere F2 layer peak electron density (NmF2) are examined. The standard deviations of the drifts and NmF2 show local time and longitudinal dependence that compare favorably with observations. Their magnitudes are 50% or more of those from observations. The day‐to‐day thermosphere and ionosphere variability in the model is primarily caused by the perturbations originated in lower atmosphere, since the model simulation is under constant solar minimum and low geomagnetic conditions.
Key Points
Novel model capable of producing large day‐to‐day ionosphere variability
Short‐term wave variability leads to day‐to‐day ionosphere variability
Predictability of ionosphere/thermosphere affected by lower atmosphere waves
Unlike other variants of transition-metal-catalyzed cross-coupling reactions, those based on organosilicon donors have not been used extensively in natural product synthesis. However, recent advances ...such as: 1) the development of mild reaction conditions, 2) the expansion of substrate scope, 3) the development of methods to stereoselectively and efficiently introduce the silicon-containing moiety, 4) the development of a large number of sequential processes, and 5) the advent of bifunctional bis(silyl) linchpin reagents, signify the coming of age of silicon-based cross-coupling reactions. The following case studies illustrate how silicon-based cross-coupling reactions play a strategic role in constructing carbon-carbon bonds in selected target molecules.
A key assumption of optogenetics is that light only affects opsin-expressing neurons. However, illumination invariably heats tissue, and many physiological processes are temperature-sensitive. ...Commonly used illumination protocols increased the temperature by 0.2-2 °C and suppressed spiking in multiple brain regions. In the striatum, light delivery activated an inwardly rectifying potassium conductance and biased rotational behavior. Thus, careful consideration of light-delivery parameters is required, as even modest intracranial heating can confound interpretation of optogenetic experiments.
The high‐resolution Whole Atmosphere Community Climate Model with thermosphere/ionosphere extension (WACCM‐X) is used to study the impacts of gravity waves (GWs) on the thermospheric circulation and ...composition. The resolved GWs are found to propagate anisotropically with stronger eastward components at most altitudes. The dissipation of these waves in the thermosphere produces a net eastward forcing that reaches peak values between 200 and 250 km at mid‐high latitudes in both hemispheres. Consequently, the mean circulation is weakened in the winter hemisphere and enhanced in the summer, which in turn impacts the thermospheric composition. Most notably, the column integrated O/N2 in both hemispheres is reduced and agrees better with observations. The mean thermospheric GW forcing in the meridional direction has comparable amplitude and acts to modify the gradient‐wind relationship.
Plain Language Summary
Small‐scale waves originate from the lower atmosphere have been shown to propagate into the thermosphere. To study their effects a high‐resolution whole atmosphere model has been employed. Using this high‐resolution model, which can partially resolve the small‐scale waves, we can directly quantify the force exerted by these waves on the general circulation in the thermosphere. We found that such force is strong, and affects the thermospheric circulation in both winter and summer hemisphere. This consequently changes the distribution of important thermospheric species. One measure of the thermospheric composition is the ratio of atomic oxygen and molecular nitrogen, which is an indicator of the relative abundance of atomic and molecular species. This ratio has been grossly over‐estimated in previous modeling studies. It is reduced as a result of the circulation change, and is much better agreement with observations.
Key Points
Gravity waves (GWs) resolved by high‐resolution WACCM‐X displays anisotropic propagation
GW forcing alters thermospheric circulation
The circulation change leads to a much improved thermospheric O/N2
We show that atmospheric gravity waves can generate plasma ducts and irregularities in the plasmasphere using the coupled SAMI3/WACCM‐X model. We find the equatorial electron density is irregular as ...a function of longitude which is consistent with CRRES measurements (Clilverd et al., 2007, https://doi.org/10.1029/2007ja012416). We also find that plasma ducts can be generated for L‐shells in the range 1.5–3.0 with lifetimes of ∼ 0.5 hr; this is in line with observations of ducted VLF wave propagation with lifetimes of 0.5–2.0 hr (Clilverd et al., 2008, https://doi.org/10.1029/2007ja012602; Singh et al., 1998, https://doi.org/10.1016/s1364-6826(98)00001-7).
Plain Language Summary
Electromagnetic plasma waves, known as whistler waves, are observed to propagate in the ionosphere/plasmasphere system where the ionosphere is nominally defined as the partially ionized gas surrounding the earth in the altitude range 90–1,000 km and the plasmasphere is essentially the extension of the ionosphere 1,000s of km into space along closed geomagnetic field lines. Whistler wave propagation has been characterized as ducted and non‐ducted. Ducted propagation is guided along the magnetic field by density tubes in which the plasma density is lower or higher than the background plasma. However, the physical processes that generate these ducts has remained unclear. We show that these plasma ducts can be generated by atmospheric gravity waves that perturb the ionosphere and plasmasphere electron density using the coupled SAMI3/WACCM‐X model.
Key Points
Atmospheric gravity waves can generate plasma ducts and irregularities in the plasmasphere using the coupled SAMI3/WACCM‐X model
The electron density in the equatorial plasmasphere is irregular as a function of longitude
Plasma ducts can be generated for L‐shells in the range 1.5–3.0 with lifetimes of 0.5–2.0 hr
Anti-Asian discrimination and assaults have increased significantly during the Coronavirus disease 2019 (COVID-19) pandemic, contributing to a "secondary contagion" of racism. The United States has a ...long and well-documented history of both interpersonal and structural anti-Asian discrimination, and the current pandemic reinforces longstanding negative stereotypes of this rapidly growing minority group as the "Yellow Peril."We provide a general overview of the history of anti-Asian discrimination in the United States, review theoretical and empirical associations between discrimination and health, and describe the associated public health implications of the COVID-19 pandemic, citing relevant evidence from previous disasters in US history that became racialized.Although the literature suggests that COVID-19 will likely have significant negative effects on the health of Asian Americans and other vulnerable groups, there are reasons for optimism as well. These include the emergence of mechanisms for reporting and tracking incidents of racial bias, increased awareness of racism's insidious harms and subsequent civic and political engagement by the Asian American community, and further research into resilience-promoting factors that can reduce the negative health effects of racism.
PDF
