Since the middle of the last decade, UCSD has incorporated magnetic field data in its Institute for Space‐Earth Environmental Research interplanetary scintillation tomographic analysis. These data are extrapolated upward from the solar surface using the Current Sheet Source Surface model (Zhao & Hoeksema, 1995,
Based on the C‐14 data of Druffel et al. (2021,
- NSF-PAR ID:
- 10360558
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 48
- Issue:
- 17
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract https://doi.org/10.1029/94JA02266 ) to provide predictions of the interplanetary field in RTN coordinates. Over the years this technique has become ever more sophisticated, and allows different types of magnetogram data (SOLIS, Global Oscillation Network Group, etc.,) to be incorporated in the field extrapolations. At Earth, these fields can be displayed in a variety of ways, including Geocentric Solar Magnetospheric (GSM) Bx, By, and Bzcoordinates. Displayed daily, the Current Sheet Source Surface model‐derived GSM Bzshows a significant positive correlation with the low‐resolution (few day variation) in situ measurements of the Bzfield. The nano‐Tesla variations of Bzmaximize in spring and fall as Russell and McPherron (1973,https://doi.org/10.1029/JA078i001p00092 ) have shown. More significantly, we find that the daily variations are correlated with geomagnetic Kp and Dst index variations, and that a decrease from positive to negative Bzhas a high correlation with minor‐to‐moderate geomagnetic storm activity, as defined by NOAA Space Weather Prediction Center planetary Kp values. Here we provide an 11‐year study of the predicted Bzfield, from the extrapolation of the Global Oscillation Network Group‐magnetograms. We provide a skill‐score analysis of the technique's geomagnetic storm prediction capability, which allows forecasts of moderate enhanced geomagnetic storm activity. UCSD and the Korean Space Weather Center currently operate a website that predicts this low‐resolution GSM Bzfield component variation several days in advance. -
more » « less
Abstract Atomic oxygen (O) in the mesosphere and lower thermosphere (MLT) results from a balance between production via photo‐dissociation in the lower thermosphere and chemical loss by recombination in the upper mesosphere. The transport of O downward from the lower thermosphere into the mesosphere is preferentially driven by the eddy diffusion process that results from dissipating gravity waves and instabilities. The motivation here is to probe the intra‐annual variability of the eddy diffusion coefficient (k
zz ) and eddy velocity in the MLT based on the climatology of the region, initially accomplished by Garcia and Solomon (1985,https://doi.org/10.1029/JD090iD02p03850 ). In the current study, the intra‐annual cycle was divided into 26 two‐week periods for each of three zones: the northern hemisphere (NH), southern hemisphere (SH), and equatorial (EQ). Both 16 years of SABER (2002–2018) and 10 years of SCIAMACHY (2002–2012) O density measurements, along with NRLMSIS®2.0 were used for calculation of atomic oxygen eddy diffusion velocities and fluxes. Our prominent findings include a dominant annual oscillation below 87 km in the NH and SH zones, with a factor of 3–4 variation between winter and summer at 83 km, and a dominant semiannual oscillation at all altitudes in the EQ zone. The measured global average kzz at 96 km lacks the intra‐annual variability of upper atmosphere density data deduced by Qian et al. (2009,https://doi.org/10.1029/2008JA013643 ). The very large seasonal (and hemispherical) variations in kzz and O densities are important to separate and isolate in satellite analysis and to incorporate in MLT models. -
more » « less
Abstract All else equal, if the ocean's “biological [carbon] pump” strengthens, the dissolved oxygen (O2) content of the ocean interior declines. Confidence is now high that the ocean interior as a whole contained less oxygen during the ice ages. This is strong evidence that the ocean's biological pump stored more carbon in the ocean interior during the ice ages, providing the core of an explanation for the lower atmospheric carbon dioxide (CO2) concentrations of the ice ages. Vollmer et al. (2022,
https://doi.org/10.1029/2021PA004339 ) combine proxies for the oxygen and nutrient content of bottom waters to show that the ocean nutrient reservoir was more completely harnessed by the biological pump during the Last Glacial Maximum, with an increase in the proportion of dissolved nutrients in the ocean interior that were “regenerated” (transported as sinking organic matter from the ocean surface to the interior) rather than “preformed” (transported to the interior as dissolved nutrients by ocean circulation). This points to changes in the Southern Ocean, the dominant source of preformed nutrients in the modern ocean, with an apparent additional contribution from a decline in the preformed nutrient content of North Atlantic‐formed interior water. Vollmer et al. also find a lack of LGM‐to‐Holocene difference in the preformed13C/12C ratio of dissolved inorganic carbon. This finding may allow future studies to resolve which of the proposed Southern Ocean mechanisms was most responsible for enhanced ocean CO2storage during the ice ages: (a) coupled changes in ocean circulation and biological productivity, or (b) physical limitations on air‐sea gas exchange. -
more » « less
Abstract The Mackenzie Mountains (MMs) in the Yukon and Northwest Territories, Canada, are an enigmatic mountain range. They are currently uplifting (Leonard et al., 2008,
https//doi.org/10.1029/2007JB005456 ), yet are about 700 km from the nearest plate boundary. Their arcuate shape is distinct and extends over 100 km eastward from the general trend of the Northern Canadian Cordillera. To better assess the cause and conditions of the current uplift, we processed ambient seismic noise data from a linear array of broadband seismographs crossing the mountains, along with other regional seismic stations, to estimate Rayleigh wave phase velocities between 6 and 40 s periods. From this, we estimated phase velocity dispersion and performed a tomographic inversion to estimateV S . Tomography reveals a low‐velocity structure that extends upward from the base of the ∼50–66 km thick lithosphere to the upper crust, and we hypothesize that inferred low density and low rigidity associated with theV S anomaly localizes the ongoing uplift and thrust‐dominated seismicity of the MMs. Additionally, we find relatively low crustal velocities that extend to the west of the MMs, suggesting that strain transfer from the Gulf of Alaska plate boundary plays a driving role as the crust translates to the northeast and buckles up against the craton consistent with the orogenic float hypothesis of Mazzotti and Hyndman (2002,https//doi.org/10.1130/0091-7613(2002)030〈0495:YCASTA〉2.0.CO;2 ). Finally, we observe lithospheric azimuthal anisotropy with an NW‐SE fast direction. This is nearly orthogonal to teleseismic shear wave splitting measurements in the central MMs, and suggests that asthenosphere flow and lithospheric strain are not aligned in this region. -
more » « less
Abstract We provide an updated analysis of the gamma ray signature of a terrestrial gamma ray flash (TGF) detected by the Fermi Gamma ray Burst Monitor first reported by Pu et al. (2020,
https://doi.org/10.1029/2020GL089427 ). A TGF produced 3 ms prior to a negative cloud‐to‐ground return stroke was close to simultaneous with an isolated low‐frequency radio pulse during the leader’s propagation, with a polarity indicating downward moving negative charge. In previous observations, this “slow” low‐frequency signal has been strongly correlated with upward‐directed (opposite polarity) TGF events (Pu et al., 2019,https://doi.org/10.1029/2019GL082743 ; Cummer et al., 2011,https://doi.org/10.1029/2011GL048099 ), leading the authors to conclude that the Fermi gamma ray observation is actually the result of a reverse positron beam generating upward‐directed gamma rays. We investigate the feasibility of this scenario and determine a lower limit on the luminosity of the downward TGF from the perspective of gamma ray timing uncertainties, TGF Monte Carlo simulations, and meteorological analysis of a model storm cell and its possible charge structure altitudes. We determined that the most likely source altitude of the TGF reverse beam was 7.5 km ± 2.6 km, just below an estimated negative charge center at 8 km. At that altitude, the Monte Carlo simulations indicate a lower luminosity limit of 2 × 1018photons above 1 MeV for the main downward beam of the TGF, making the reverse beam detectable by the Fermi Gamma ray Burst Monitor.
