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[en] During the first months of observations, the Magnetospheric Multiscale Fly's Eye Energetic Particle Spectrometer instrument has observed several instances of electron acceleration up to >100 keV while in the vicinity of the dayside reconnection region. While particle acceleration associated with magnetic reconnection has been seen to occur up to these energies in the tail region, it had not yet been reported at the magnetopause. This study reports on observations of electron acceleration up to hundreds of keV that were recorded on 19 September 2015 around 1000 UT, in the midst of an X-line crossing. In the region surrounding the X-line, whistler-mode and broadband electrostatic waves were observed simultaneously with the appearance of highly energetic electrons which exhibited significant energization in the perpendicular direction. The mechanisms by which particles may be accelerated via reconnection-related processes are intrinsic to understanding particle dynamics among a wide range of spatial scales and plasma environments.
[en] Atmospheric low-frequency sound, i.e., infra-sound, from underwater events has not been considered thus far, due to the high impedance contrast of the water-air interface making it almost fully reflective. Here we report for the first time on atmospheric infra-sound from a large underwater earthquake (Mw 8.1) near the Macquarie Ridge, which was recorded at 1325 km from the epicenter. Seismic waves coupled to hydro acoustic waves at the ocean floor, after which the energy entered the Sound Fixing and Ranging channel and was detected on a hydro-phone array. The energy was diffracted by a sea-mount and an oceanic ridge, which acted as a secondary source, into the water column followed by coupling into the atmosphere. The latter results from evanescent wave coupling and the attendant anomalous transparency of the sea surface for very low frequency acoustic waves. (authors)
[en] Here, we alleviate the bias in the tropospheric vertical distribution of black carbon aerosols (BC) in the Community Atmosphere Model (CAM4) using the Cloud-Aerosol and Infrared Pathfinder Satellite Observations (CALIPSO)-derived vertical profiles. A suite of sensitivity experiments are conducted with 1x, 5x, and 10x the present-day model estimated BC concentration climatology, with (corrected, CC) and without (uncorrected, UC) CALIPSO-corrected BC vertical distribution. The globally averaged top of the atmosphere radiative flux perturbation of CC experiments is ~8–50% smaller compared to uncorrected (UC) BC experiments largely due to an increase in low-level clouds. The global average surface temperature increases, the global average precipitation decreases, and the ITCZ moves northward with the increase in BC radiative forcing, irrespective of the vertical distribution of BC. Further, tropical expansion metrics for the poleward extent of the Northern Hemisphere Hadley cell (HC) indicate that simulated HC expansion is not sensitive to existing model biases in BC vertical distribution.
[en] Anthropogenic greenhouse gas emissions have modified the rate at which oceans have absorbed atmospheric CO2 over the last centuries through rising atmospheric CO2 and modifications in climate. However, there are still missing pieces in our understanding of the recent evolution of air-sea CO2 exchanges related to the magnitude of their response to anthropogenic forcing versus that controlled by the internal variability. Here, to detect and attribute anthropogenic influences on oceanic CO2 uptake between 1960 and 2005, we compare an ensemble of Coupled Model Intercomparison Project Phase 5 (CMIP5) climate model simulations forced by individual drivers to ocean-only model reconstructions. We demonstrate that the evolution of the global oceanic carbon sink over the last decades can be understood without invoking climate change, attributing rising atmospheric CO2 as prominent driver of the oceanic sink. Nonetheless, at regional scale, the influence of climate change on air-sea CO2 exchanges seems to emerge from the internal variability within the low-latitude oceans. (authors)
[en] In this paper we investigate a severe pollution episode that occurred in Beijing, Tianjin, and the Hebei province in January 2013. The episode was caused by the combination of anthropogenic emissions and a high-pressure system that trapped pollutants in the boundary layer. Using IASI (Infrared Atmospheric Sounding Interferometer) satellite measurements, high concentrations of key trace gases such as carbon monoxide (CO), sulfur dioxide (SO2), and ammonia (NH3) along with ammonium sulfate aerosol ((NH4)2SO4) are found. We show that IASI is able to detect boundary layer pollution in case of large negative thermal contrast combined with high levels of pollution. Our findings demonstrate that anthropogenic key pollutants, such as CO and SO2, can be monitored by IASI in the North China Plain during wintertime in support of air quality evaluation and management. (authors)
[en] Variations in terrestrial oxygen-isotope reconstructions from ice cores and speleothems have been primarily attributed to climatic changes of surface air temperature, precipitation amount, or atmospheric circulation. In this work, we demonstrate with the fully coupled isotope-enabled Community Earth System Model an additional process contributing to the oxygen-isotope variations during glacial meltwater events. This process, termed “the direct meltwater effect,” involves propagating large amounts of isotopically depleted meltwater throughout the hydrological cycle and is independent of climatic changes. We find that the direct meltwater effect can make up 15–35% of the δ18O signals in precipitation over Greenland and eastern Brazil for large freshwater forcings (0.25–0.50 sverdrup (106 m3/s)). Model simulations further demonstrate that the direct meltwater effect increases with the magnitude and duration of the freshwater forcing and is sensitive to both the location and shape of the meltwater. These new modeling results have important implications for past climate interpretations of δ18O.
[en] On 15 February 2013, a large Earth-impacting fireball disintegrated over the Ural Mountains. This extraordinary event is, together with the 1908 Tunguska fireball, among the most energetic events ever instrumentally recorded. It generated infra-sound returns, after circling the globe, at distances up to ∼85,000 km, and was detected at 20 infrasonic stations of the global International Monitoring System (IMS). For the first time since the establishment of the IMS infra-sound network, multiple arrivals involving waves that traveled twice round the globe have been clearly identified. A preliminary estimate of the explosive energy using empirical period-yield scaling relations gives a value of 460 kt of TNT equivalent. In the context of the future verification of the Comprehensive Nuclear-Test-Ban Treaty, this event provides a prominent milestone for studying in detail infra-sound propagation around the globe for almost 3 days as well as for calibrating the performance of the IMS network. (authors)
[en] Gaseous carbon dioxide (CO_2) and radon-222 release from the ground was investigated along the Main Central Thrust zone in the Nepal Himalayas. From 2200 CO_2 and 900 radon-222 flux measurements near 13 hot springs from western to central Nepal, we obtained total CO_2 and radon discharges varying from 10"-"3 to 1.6 mol s"-"1 and 20 to 1600 Bq s"-"1, respectively. We observed a coherent organization at spatial scales of≅ 10 km in a given region: low CO_2 and radon discharges around Pokhara (midwestern Nepal) and in the Bhote Kosi Valley (east Nepal); low CO_2 but large radon discharges in Lower Dolpo (west Nepal); and large CO_2 and radon discharges in the upper Trisuli Valley (central Nepal). A 110 km long CO_2-producing segment, with high carbon isotopic ratios, suggesting metamorphic de-carbonation, is thus evidenced from 84.5 degrees E to 85.5 degrees E. This spatial organization could be controlled by geological heterogeneity or large Himalayan earthquakes. (authors)
[en] Here we report measurements of energized outflowing/bouncing ionospheric ions and heated electrons in the inner magnetosphere during a geomagnetic storm. The ions arrive in the equatorial plane with pitch angles that increase with energy over a range from tens of eV to>50 keV while the electrons are field aligned up to ~1 keV. These particle distributions are observed during intervals of broadband low-frequency electromagnetic field fluctuations consistent with a Doppler-shifted spectrum of kinetic Alfvén waves and kinetic field line resonances. The fluctuations extend from L≈3 out to the apogee of the Van Allen Probes spacecraft at L ≈ 6.5. They thereby span most of the L shell range occupied by the ring current. Lastly, these measurements suggest a model for ionospheric ion outflow and energization driven by dispersive Alfvén waves that may account for the large storm time contribution of ionospheric ions to magnetospheric energy density.
[en] We regret that a factor of (1/2)1/3 was mistakenly unaccounted for in converting the Debye sound velocities to km/s unit. The correct figure of the derived Vp, Vs, and G are presented here. The derived Vp, Vs, and G at ambient conditions are now lower than that of ultrasonic measurements. The difference may arise from the choice of the energy range for deriving the Debye sound velocities, in combination with the energy resolution of the partial phonon density of states in our study. Further analyses to resolve the difference are forthcoming and will be presented elsewhere. Other parts of this Letter, including the discussion, remain unchanged