More Like this

1. Biomass burning nitrogen dioxide emissions derived from space with TROPOMI: methodology and validation

   https://doi.org/10.5194/amt-14-7929-2021  

   Griffin, Debora; McLinden, Chris A.; Dammers, Enrico; Adams, Cristen; Stockwell, Chelsea E.; Warneke, Carsten; Bourgeois, Ilann; Peischl, Jeff; Ryerson, Thomas B.; Zarzana, Kyle J.; et al (January 2021, Atmospheric Measurement Techniques)

   Abstract. Smoke from wildfires is a significant source of air pollution, which can adversely impact air quality and ecosystems downwind. With the recently increasing intensity and severity of wildfires, the threat to air quality is expected to increase. Satellite-derived biomass burning emissions can fill in gaps in the absence of aircraft or ground-based measurement campaigns and can help improve the online calculation of biomass burning emissions as well as the biomass burning emissions inventories that feed air quality models. This study focuses on satellite-derived NOx emissions using the high-spatial-resolution TROPOspheric Monitoring Instrument (TROPOMI) NO2 dataset. Advancements and improvements to the satellite-based determination of forest fire NOx emissions are discussed, including information on plume height and effects of aerosol scattering and absorption on the satellite-retrieved vertical column densities. Two common top-down emission estimation methods, (1) an exponentially modified Gaussian (EMG) and (2) a flux method, are applied to synthetic data to determine the accuracy and the sensitivity to different parameters, including wind fields, satellite sampling, noise, lifetime, and plume spread. These tests show that emissions can be accurately estimated from single TROPOMI overpasses.The effect of smoke aerosols on TROPOMI NO2 columns (via air mass factors, AMFs) is estimated, and these satellite columns and emission estimates are compared to aircraft observations from four different aircraft campaigns measuring biomass burning plumes in 2018 and 2019 in North America. Our results indicate that applying an explicit aerosol correction to the TROPOMI NO2 columns improves the agreement with the aircraft observations (by about 10 %–25 %). The aircraft- and satellite-derived emissions are in good agreement within the uncertainties. Both top-down emissions methods work well; however, the EMG method seems to output more consistent results and has better agreement with the aircraft-derived emissions. Assuming a Gaussian plume shape for various biomass burning plumes, we estimate an average NOx e-folding time of 2 ±1 h from TROPOMI observations. Based on chemistry transport model simulations and aircraft observations, the net emissions of NOx are 1.3 to 1.5 times greater than the satellite-derived NO2 emissions. A correction factor of 1.3 to 1.5 should thus be used to infer net NOx emissions from the satellite retrievals of NO2. 

   more » « less
2. How Identifying Circumgalactic Gas by Line-of-sight Velocity instead of the Location in 3D Space Affects O vi Measurements

   https://doi.org/10.3847/1538-4357/ac2c73  

   Ho, Stephanie H.; Martin, Crystal L.; Schaye, Joop (December 2021, The Astrophysical Journal)

   Abstract The high incidence rate of the O vi λλ 1032, 1038 absorption around low-redshift, ∼ L * star-forming galaxies has generated interest in studies of the circumgalactic medium. We use the high-resolution EAGLE cosmological simulation to analyze the circumgalactic O vi gas around z ≈ 0.3 star-forming galaxies. Motivated by the limitation that observations do not reveal where the gas lies along the line of sight, we compare the O vi measurements produced by gas within fixed distances around galaxies and by gas selected using line-of-sight velocity cuts commonly adopted by observers. We show that gas selected by a velocity cut of ±300 km s −1 or ±500 km s −1 produces a higher O vi column density, a flatter column density profile, and a higher covering fraction compared to gas within 1, 2, or 3 times the virial radius ( r vir ) of galaxies. The discrepancy increases with impact parameter and worsens for lower-mass galaxies. For example, compared to the gas within 2 r vir , identifying the gas using velocity cuts of 200–500 km s −1 increases the O vi column density by 0.2 dex (0.1 dex) at 1 r vir to over 0.75 dex (0.7 dex) at ≈ 2 r vir for galaxies with stellar masses of 10 9 –10 9.5 M ⊙ (10 10 –10 10.5 M ⊙ ). We furthermore estimate that excluding O vi outside r vir decreases the circumgalactic oxygen mass measured by Tumlinson et al. (2011) by over 50%. Our results demonstrate that gas at large line-of-sight separations but selected by conventional velocity windows has significant effects on the O vi measurements and may not be observationally distinguishable from gas near the galaxies. 

   more » « less
3. Polarimetric and Electrical Structure of the 19 May 2013 Edmond–Carney, Oklahoma, Tornadic Supercell

   https://doi.org/10.1175/MWR-D-20-0280.1  

   Sharma, Milind; Tanamachi, Robin_L; Bruning, Eric_C; Calhoun, Kristin_M (July 2021, Monthly Weather Review)

   Abstract We demonstrate the utility of transient polarimetric signatures (Z_DRandK_DPcolumns, a proxy for surges in a thunderstorm updraft) to explain variability in lightning flash rates in a tornadic supercell. Observational data from a WSR-88D and the Oklahoma lightning mapping array are used to map the temporal variance of polarimetric signatures and VHF sources from lightning channels. It is shown, via three-dimensional and cross-sectional analyses, that the storm was of inverted polarity resulting from anomalous electrification. Statistical analysis confirms that mean flash area in theZ_DRcolumn region was 10 times smaller than elsewhere in the storm. On an average, 5 times more flash initiations occurred withinZ_DRcolumn regions, thereby supporting existing theory of an inverse relationship between flash initiation rates and lightning channel extent. Segmentation and object identification algorithms are applied to gridded radar data to calculate metrics such as height, width, and volume ofZ_DRandK_DPcolumns. Variability in lightning flash rates is best explained by the fluctuations inZ_DRcolumn volume with a Spearman’s rank correlation coefficient value of 0.72. The highest flash rates occur in conjunction with the deepestZ_DRcolumns (up to 5 km above environmental melting level) and largest volumes ofZ_DRcolumns extending up to the −20°C level (3 km above the melting level). Reduced flash rates toward the end of the analysis are indicative of weaker updrafts manifested as lowZ_DRcolumn volumes at and above the −10°C level. These findings are consistent with recent studies linking lightning to the interplay between storm dynamics, kinematics, thermodynamics, and precipitation microphysics. 

   more » « less
4. The Solar Minimum Eclipse of 2019 July 2. II. The First Absolute Brightness Measurements and MHD Model Predictions of Fe x, xi, and xiv out to 3.4 R _⊙

   https://doi.org/10.3847/1538-4357/ac8101  

   Boe, Benjamin; Habbal, Shadia; Downs, Cooper; Druckmüller, Miloslav (August 2022, The Astrophysical Journal)

   Abstract We present the spatially resolved absolute brightness of the Fex, Fexi, and Fexivvisible coronal emission lines from 1.08 to 3.4R_⊙, observed during the 2019 July 2 total solar eclipse (TSE). The morphology of the corona was typical of solar minimum, with a dipole field dominance showcased by large polar coronal holes and a broad equatorial streamer belt. The Fexiline is found to be the brightest, followed by Fexand Fexiv(in diskB_⊙units). All lines had brightness variations between streamers and coronal holes, where Fexivexhibited the largest variation. However, Fexremained surprisingly uniform with latitude. The Fe line brightnesses are used to infer the relative ionic abundances and line-of-sight-averaged electron temperature (T_e) throughout the corona, yielding values from 1.25 to 1.4 MK in coronal holes and up to 1.65 MK in the core of streamers. The line brightnesses and inferredT_evalues are then quantitatively compared to the Predictive Science Inc. magnetohydrodynamic model prediction for this TSE. The MHD model predicted the Fe lines rather well in general, while the forward-modeled line ratios slightly underestimated the observationally inferredT_ewithin 5%–10% averaged over the entire corona. Larger discrepancies in the polar coronal holes may point to insufficient heating and/or other limitations in the approach. These comparisons highlight the importance of TSE observations for constraining models of the corona and solar wind formation. 

   more » « less
5. Multi‐Frequency SuperDARN HF Radar Observations of the Ionospheric Response to the October 2023 Annular Solar Eclipse

   https://doi.org/10.1029/2024GL112450  

   Thomas, E_G; Shepherd, S_G; Kunduri, B_S_R; Themens, D_R (December 2024, Geophysical Research Letters)

   Abstract An annular solar eclipse was visible on 14 October 2023 from 15:00–21:00 UT as its path traveled across North, Central, and South America. In this letter, we present the first multi‐frequency Super Dual Auroral Radar Network (SuperDARN) observations of the bottomside ionospheric response to a solar eclipse using a novel experimental mode designed for the October 2023 annular eclipse. We compare our results from the mid‐latitude Christmas Valley East radar with measurements of the vertical electron density profile from the nearby Boulder Digisonde, finding the changes in 1‐ and 2‐hop ground scatter skip distance are well correlated with the ‐layer density response, which lags the peak obscuration by 30 min. Changes in the line‐of‐sight Doppler shifts are better aligned with the time derivative of eclipse obscuration. 

   more » « less