skip to main content


Title: Stratospheric contribution to the summertime high surface ozone events over the western united states
Abstract

The stratospheric influence on summertime high surface ozone (O3) events is examined using a twenty-year simulation from the Whole Atmosphere Community Climate Model. We find thatO3transported from the stratosphere makes a significant contribution to the surfaceO3variability where background surfaceO3exceeds the 95thpercentile, especially over western U.S. Maximum covariance analysis is applied toO3anomalies paired with stratosphericO3tracer anomalies to identify the stratospheric intrusion and the underlying dynamical mechanism. The first leading mode corresponds to deep stratospheric intrusions in the western and northern tier of the U.S., and intensified northeasterlies in the mid-to-lower troposphere along the west coast, which also facilitate the transport to the eastern Pacific Ocean. The second leading mode corresponds to deep intrusions over the Intermountain Regions. Both modes are associated with eastward propagating baroclinic systems, which are amplified near the end of the North Pacific storm tracks, leading to strong descents over the western U.S.

 
more » « less
Award ID(s):
1802248
NSF-PAR ID:
10303683
Author(s) / Creator(s):
; ; ;
Publisher / Repository:
IOP Publishing
Date Published:
Journal Name:
Environmental Research Letters
Volume:
15
Issue:
10
ISSN:
1748-9326
Page Range / eLocation ID:
Article No. 1040a6
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    We present a Keck/MOSFIRE rest-optical composite spectrum of 16 typical gravitationally lensed star-forming dwarf galaxies at 1.7 ≲z≲ 2.6 (zmean= 2.30), all chosen independent of emission-line strength. These galaxies have a median stellar mass oflog(M*/M)med=8.290.43+0.51and a median star formation rate ofSFRHαmed=2.251.26+2.15Myr1. We measure the faint electron-temperature-sensitive [Oiii]λ4363 emission line at 2.5σ(4.1σ) significance when considering a bootstrapped (statistical-only) uncertainty spectrum. This yields a direct-method oxygen abundance of12+log(O/H)direct=7.880.22+0.25(0.150.06+0.12Z). We investigate the applicability at highzof locally calibrated oxygen-based strong-line metallicity relations, finding that the local reference calibrations of Bian et al. best reproduce (≲0.12 dex) our composite metallicity at fixed strong-line ratio. At fixedM*, our composite is well represented by thez∼ 2.3 direct-method stellar mass—gas-phase metallicity relation (MZR) of Sanders et al. When comparing to predicted MZRs from the IllustrisTNG and FIRE simulations, having recalculated our stellar masses with more realistic nonparametric star formation histories(log(M*/M)med=8.920.22+0.31), we find excellent agreement with the FIRE MZR. Our composite is consistent with no metallicity evolution, at fixedM*and SFR, of the locally defined fundamental metallicity relation. We measure the doublet ratio [Oii]λ3729/[Oii]λ3726 = 1.56 ± 0.32 (1.51 ± 0.12) and a corresponding electron density ofne=10+215cm3(ne=10+74cm3) when considering the bootstrapped (statistical-only) error spectrum. This result suggests that lower-mass galaxies have lower densities than higher-mass galaxies atz∼ 2.

     
    more » « less
  2. Abstract

    M dwarfs are common host stars to exoplanets but often lack atmospheric abundance measurements. Late-M dwarfs are also good analogs to the youngest substellar companions, which share similarTeff∼ 2300–2800 K. We present atmospheric analyses for the M7.5 companion HIP 55507 B and its K6V primary star with Keck/KPIC high-resolution (R∼ 35,000)K-band spectroscopy. First, by including KPIC relative radial velocities between the primary and secondary in the orbit fit, we improve the dynamical mass precision by 60% and findMB=88.03.2+3.4MJup, putting HIP 55507 B above the stellar–substellar boundary. We also find that HIP 55507 B orbits its K6V primary star witha=383+4au ande= 0.40 ± 0.04. From atmospheric retrievals of HIP 55507 B, we measure [C/H] = 0.24 ± 0.13, [O/H] = 0.15 ± 0.13, and C/O = 0.67 ± 0.04. Moreover, we strongly detect13CO (7.8σsignificance) and tentatively detectH218O(3.7σsignificance) in the companion’s atmosphere and measure12CO/13CO=9822+28andH216O/H218O=24080+145after accounting for systematic errors. From a simplified retrieval analysis of HIP 55507 A, we measure12CO/13CO=7916+21andC16O/C18O=28870+125for the primary star. These results demonstrate that HIP 55507 A and B have consistent12C/13C and16O/18O to the <1σlevel, as expected for a chemically homogeneous binary system. Given the similar flux ratios and separations between HIP 55507 AB and systems with young substellar companions, our results open the door to systematically measuring13CO andH218Oabundances in the atmospheres of substellar or even planetary-mass companions with similar spectral types.

     
    more » « less
  3. Abstract

    Polyatomic molecules have been identified as sensitive probes of charge-parity violating and parity violating physics beyond the Standard Model (BSM). For example, many linear triatomic molecules are both laser-coolable and have parity doublets in the ground electronicX˜2Σ+(010)state arising from the bending vibration, both features that can greatly aid BSM searches. Understanding theX˜2Σ+(010)state is a crucial prerequisite to precision measurements with linear polyatomic molecules. Here, we characterize the fundamental bending vibration of174YbOH using high-resolution optical spectroscopy on the nominally forbiddenX˜2Σ+(010)A˜2Π1/2(000)transition at 588 nm. We assign 39 transitions originating from the lowest rotational levels of theX˜2Σ+(010)state, and accurately model the state’s structure with an effective Hamiltonian using best-fit parameters. Additionally, we perform Stark and Zeeman spectroscopy on theX˜2Σ+(010)state and fit the molecule-frame dipole moment toDmol=2.16(1)Dand the effective electrong-factor togS=2.07(2). Further, we use an empirical model to explain observed anomalous line intensities in terms of interference from spin–orbit and vibronic perturbations in the excitedA˜2Π1/2(000)state. Our work is an essential step toward searches for BSM physics in YbOH and other linear polyatomic molecules.

     
    more » « less
  4. Abstract

    We perform particle-in-cell simulations to elucidate the microphysics of relativistic weakly magnetized shocks loaded with electron-positron pairs. Various external magnetizationsσ≲ 10−4and pair-loading factorsZ±≲ 10 are studied, whereZ±is the number of loaded electrons and positrons per ion. We find the following: (1) The shock becomes mediated by the ion Larmor gyration in the mean field whenσexceeds a critical valueσLthat decreases withZ±. AtσσLthe shock is mediated by particle scattering in the self-generated microturbulent fields, the strength and scale of which decrease withZ±, leading to lowerσL. (2) The energy fraction carried by the post-shock pairs is robustly in the range between 20% and 50% of the upstream ion energy. The mean energy per post-shock electron scales asE¯eZ±+11. (3) Pair loading suppresses nonthermal ion acceleration at magnetizations as low asσ≈ 5 × 10−6. The ions then become essentially thermal with mean energyE¯i, while electrons form a nonthermal tail, extending fromEZ±+11E¯itoE¯i. Whenσ= 0, particle acceleration is enhanced by the formation of intense magnetic cavities that populate the precursor during the late stages of shock evolution. Here, the maximum energy of the nonthermal ions and electrons keeps growing over the duration of the simulation. Alongside the simulations, we develop theoretical estimates consistent with the numerical results. Our findings have important implications for models of early gamma-ray burst afterglows.

     
    more » « less
  5. Abstract

    The repeating fast radio burst FRB 20190520B is an anomaly of the FRB population thanks to its high dispersion measure (DM = 1205 pc cm−3) despite its low redshift ofzfrb= 0.241. This excess has been attributed to a large host contribution of DMhost≈ 900 pc cm−3, far larger than any other known FRB. In this paper, we describe spectroscopic observations of the FRB 20190520B field obtained as part of the FLIMFLAM survey, which yielded 701 galaxy redshifts in the field. We find multiple foreground galaxy groups and clusters, for which we then estimated halo masses by comparing their richness with numerical simulations. We discover two separateMhalo> 1014Mgalaxy clusters atz= 0.1867 and 0.2170 that are directly intersected by the FRB sight line within their characteristic halo radiusr200. Subtracting off their estimated DM contributions, as well that of the diffuse intergalactic medium, we estimate a host contribution ofDMhost=430220+140or280170+140pccm3(observed frame), depending on whether we assume that the halo gas extends tor200or 2 ×r200. This significantly smaller DMhost—no longer the largest known value—is now consistent with Hαemission measures of the host galaxy without invoking unusually high gas temperatures. Combined with the observed FRB scattering timescale, we estimate the turbulent fluctuation and geometric amplification factor of the scattering layer to beF˜G4.511(pc2km)1/3, suggesting that most of the gas is close to the FRB host. This result illustrates the importance of incorporating foreground data for FRB analyses both for understanding the nature of FRBs and to realize their potential as a cosmological probe.

     
    more » « less