Analysis of Ar(1s\u3csub\u3e5\u3c/sub\u3e) Metastable Populations in High Pressure Argon-Helium Gas Discharges

Simulations of an argon-helium plasma are performed for two high pressure discharge scenarios to find a uniform, large-volume plasma with Ar(1s5) metastable densities on the order of 1013 cm-3 for use as the ground state in an optically pumped rare gas laser. An analysis of a pulsed direct current discharge is performed for a 7% argon in helium mixture at a pressure of 270 Torr using both zero and one-dimensional models. Kinetics of species relevant to the operation of an optically pumped rare gas laser are analyzed throughout the pulse duration to identify key reaction pathways. Simulations are extended to an α-mode radio frequency dielectric barrier discharge with varying mixtures of argon and helium at pressures ranging from 200-500 Torr. Metastable densities are analyzed as a function of argon fraction and pressure to determine the optimal conditions maximizing metastable density. Finally, optically pumped rare gas laser performance is analyzed as a function of the Ar(2p)+M → Ar(1s)+M branching ratio. A sensitivity study is performed due to the uncertainty in the branching ratio

Ensemble Forecasting of Coronal Mass Ejections using the WSA-ENLIL with Coned Model

The combination of the Wang-Sheeley-Arge (WSA) coronal model, ENLIL heliospherical model version 2.7, and Coned Model version 1.3 (WSA-ENLIL with Coned Model) was employed to form ensemble forecasts for 15 halo coronal mass ejections (CME\u27s). The input parameter distributions were formed from 100 sets of CME cone parameters derived from the Coned Model. The Coned Model employed image processing along with the bootstrap approach to automatically calculate cone parameter distributions from SOHO-LASCO imagery based on techniques described by Pulkkinen et al. [2010]. The input parameter distributions were used as input to WSA-ENLIL to calculate the temporal evolution of the CME\u27s, which were analyzed to determine the propagation times to the L1 Lagrangian point and the maximum Kp indices due to the impact of the CME\u27s on the Earth\u27s magnetosphere. The Newell et al. [2007] maximum Kp index formula was employed to calculate the maximum Kp indices based on the solar wind parameters near Earth

Effect of Ar(3p\u3csup\u3e5\u3c/sup\u3e4p; 2p)+M -\u3e Ar(3p\u3csup\u3e5\u3c/sup\u3e4s; 1s)+M branching ratio on optically pumped rare gas laser performance

Optically pumped rare gas laser performance is analyzed as a function of the Ar(3p54p; 2p) + M → Ar(3p54s; 1s) + M branching ratios. Due to the uncertainty in the branching ratios, a sensitivity study is performed to determine the effect on output and absorbed pump laser intensities. The analysis is performed using a radio frequency dielectric barrier discharge as the source of metastable production for a variety of Argon in Helium mixtures over pressures ranging from 200 to 500 Torr. Peak output laser intensities show a factor of 7 increase as the branching ratio is increased from 0.25 to 1.00. The collection of Ar* in Ar(1s4) is inversely proportional to the branching ratio and decreases output laser intensity by reducing the density of species directly involved with lasing

Detection of Reconnection Signatures in Solar Flares

Solar flare forecasting is limited by the current understanding of mechanisms that govern magnetic reconnection, the main physical phenomenon associated with these events. As a result, forecasting relies mainly on climatological correlations to historical events rather than the underlying physics principles. Solar physics models place the neutral point of the reconnection event in the solar corona. Correspondingly, studies of photospheric magnetic fields indicate changes during solar flares—particularly in relation to the field helicity—on the solar surface as a result of the associated magnetic reconnection. This study utilizes data from the Solar Dynamics Observatory (SDO) Helioseismic and Magnetic Imager (HMI) and SpaceWeather HMI Active Region Patches (SHARPs) to analyze full vector-field component data of the photospheric magnetic field during solar flares within a large HMI dataset (May 2010 through September 2019). This analysis is then used to identify and compare trends in the different categories of flare strengths and determine indications of the physical phenomena taking place

Editorial: Observations and Simulations of Layering Phenomena in the Middle/upper Atmosphere and Ionosphere

The middle/upper atmosphere and ionosphere are the transition between neutral and ionized components of the Earth’s atmosphere, including stratosphere, mesosphere, thermosphere, ionospheric E region and ionospheric F region (Laštovička et al., 2006; Xu, et al., 2007; Smith, 2012). The atmospheric thermal structure and composition are significantly affected by dynamical processes through coupling. The layering phenomena such as mesospheric metal layers, sporadic E layers, and noctilucent clouds are important tracers to study mechanisms of the vertical coupling from the lower to the upper atmosphere (Dou et al., 2010; Plane, 2012; Xue et al., 2013)

Global GNSS-RO Electron Density in the Lower Ionosphere

Lack of instrument sensitivity to low electron density (Ne) concentration makes it difficult to measure sharp Ne vertical gradients (four orders of magnitude over 30 km) in the D/E-region. A robust algorithm is developed to retrieve global D/E-region Ne from the high-rate GNSS radio occultation (RO) data, to improve spatiotemporal coverage using recent SmallSat/CubeSat constellations. The new algorithm removes F-region contributions in the RO excess phase profile by fitting a linear function to the data below the D-region. The new GNSS-RO observations reveal many interesting features in the diurnal, seasonal, solar-cycle, and magnetic-field-dependent variations in the Ne morphology. While the D/E-region Ne is a function of solar zenith angle (χ), it exhibits strong latitudinal variations for the same χ with a distribution asymmetric about noon. In addition, large longitudinal variations are observed along the same magnetic field pitch angle. The summer midlatitude Ne and sporadic E (Es) show a distribution similar to each other. The distribution of auroral electron precipitation correlates better with the pitch angle from the magnetosphere than from one at 100 km. Finally, a new TEC retrieval technique is developed for the high-rate RO data with a top reaching at least 120 km. For better characterization of the E- to F-transition in Ne and more accurate TEC retrievals, it is recommended to have all GNSS-RO acquisition routinely up to 220 km

Comparison of Seasonal foEs and fbEs Occurrence Rates Derived from Global Digisonde Measurements

A global climatology of sporadic-E occurrence rates (ORs) based on ionosonde measurements is presented for the peak blanketing frequency, fbEs, and the ordinary mode peak frequency of the layer, foEs. ORs are calculated for a variety of sporadic-E frequency thresholds: no lower limit, 3, 5, and 7 MHz. Seasonal rates are calculated from 64 Digisonde sites during the period 2006–2020 using ionograms either manually or automatically scaled with ARTIST-5. Both foEs and fbEs ORs peak in the Northern Hemisphere during the boreal summer, with a decrease by roughly a factor of 2–3 in fbEs rates relative to foEs rates without a lower threshold on the sporadic-E intensity. This ratio of foEs to fbEs OR increases with increasing sporadic-E intensity, up to a factor of 5 for the 7 MHz threshold. An asymmetry is observed with the Southern Hemisphere peaks during the austral summer, with slightly lower rates compared with the Northern Hemisphere during the boreal summer. A drastic decrease in ORs is observed for the higher intensity thresholds, such that the fbEs occurrence rates for 7 MHz are nearly zero during most locations and seasons. These updated occurrence rates can be used for future statistical comparisons with GPS radio occultation-based sporadic-E occurrence rates

Impact of Hurricane Michael (2018) on Local Vertical Total Electron Content

An analysis of vertical total electron content (TEC) estimates from the MIT Madrigal database is performed for the regions surrounding the eye of Hurricane Michael (2018). Absolute and detrended TEC values show a noticeable increase during the tropical cyclone (TC) relative to fluctuations at the same locations prior to the storm. Direct comparisons of TEC perturbation magnitudes to the number of lightning flashes in latitude-longitude boxes surrounding the eye of Hurricane Michael for each 5 min period of 10 October 2018 showed no visible trends. A similar comparison of the vertical TEC fluctuations with respect to the rainfall rates showed a positive correlation as the rainfall rate increased from light to moderate. However, a decrease in TEC perturbations were observed for the most intense rainfall rates. Additionally, ionosonde measurements in the Gulf of Mexico Region reveal an increased production of waves with periods less than 90 min after TC formation. These results indicate that the measured TEC fluctuations are most likely caused by atmospheric gravity waves produced by Hurricane Michael, which supports previous research

Deletion of the RNA-binding proteins ZFP36L1 and ZFP36L2 leads to perturbed thymic development and T lymphoblastic leukemia.

ZFP36L1 and ZFP36L2 are RNA-binding proteins (RBPs) that interact with AU-rich elements in the 3' untranslated region of mRNA, which leads to mRNA degradation and translational repression. Here we show that mice that lacked ZFP36L1 and ZFP36L2 during thymopoiesis developed a T cell acute lymphoblastic leukemia (T-ALL) dependent on the oncogenic transcription factor Notch1. Before the onset of T-ALL, thymic development was perturbed, with accumulation of cells that had passed through the beta-selection checkpoint without first expressing the T cell antigen receptor beta-chain (TCRbeta). Notch1 expression was higher in untransformed thymocytes in the absence of ZFP36L1 and ZFP36L2. Both RBPs interacted with evolutionarily conserved AU-rich elements in the 3' untranslated region of Notch1 and suppressed its expression. Our data establish a role for ZFP36L1 and ZFP36L2 during thymocyte development and in the prevention of malignant transformation