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e‐POP and Red Line Optical Observations of Alfvénic Auroras (2019)

Jun Liang, Y. Shen, D. Knudsen, E. Spanswick, J. Burchill, E. Donovan

Wiley

In: Journal of Geophysical Research: Space Physics

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Publikationsdatum: 2019

Beschreibung: Abstract Suprathermal electron bursts (STEBs), characterized by a board energy spectrum and a field‐aligned pitch angle distribution, have been well recognized to be associated with electron acceleration by inertial Alfvén waves and are thus conventionally termed as “Alfvénic aurora.” In this study, we report joint Enhanced‐Polar‐Outflow‐Probe (e‐POP) and ground‐based optical observations of Alfvénic auroras. In particular, we highlight the prominence of 630‐nm red line emissions under low‐energy Alfvénic auroral precipitation. During the event interval, e‐POP traverses two arcs. One bright arc dominated by green line emissions is clearly seen by all optical instruments; it is embedded in upward field‐aligned currents (FACs) yet leaves little imprint on the e‐POP suprathermal electron imager (SEI), likely due to that the precipitation is well above the upper energy limit of SEI. On the other hand, there is a red line arc that is pronounced only in 630‐nm images. Such a red‐line‐only arc is located in a transition from large‐scale upward FACs to downward FACs and is associated with a prominent STEB structure detected by e‐POP SEI. The STEB features an inverse energy time dispersion, namely, that lower‐energy electrons are seen earlier while higher‐energy electrons appear later. The red‐line‐only arc and its separation from the green line arc evolve in a repeatable fashion, each stemming from a poleward auroral intensification (PAI) propagated from higher latitudes. Following each poleward auroral intensification the green line arc progressively moved southward, while the red‐line‐only arc is quasi‐stationary and stayed relatively stable in latitude. We propose tentative interpretations of the above features based upon stationary inertial Alfvén waves.

Print ISSN: 2169-9380

Digitale ISSN: 2169-9402

Thema: Geologie und Paläontologie , Physik

Publiziert von Wiley im Namen von American Geophysical Union (AGU).

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CO2 uptake in the East China Sea relying on Changjiang runoff is prone to change (2011)

Chun-Mao Tseng, K.-K. Liu, G.-C. Gong, P.-Y. Shen and W.-J. Cai

Wiley

In: Geophysical Research Letters

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Publikationsdatum: 2011-12-31

Beschreibung: Limited knowledge exists concerning the unusually large CO2 uptake capacity in the East China Sea (ECS), which is the eminent continental shelf pump for efficient transfer of atmospheric CO2 to the deep ocean. Here we show evidence of strong control of river runoff on the CO2 uptake capacity of the ECS. From 8-years of observations in the productive ECS shelf, we present the first dataset to show the complete seasonal cycle of CO2 flux, which gives an annual flux of 2.3 ± 0.4 mol C m−2 y−1 as a net sink of atmospheric CO2. Further, we found biological sequestration of CO2 taking place in the highly productive Changjiang river plume in warm seasons due to the riverine nutrient enrichment. Consequently, changes in the plume area due to changes in the Changjiang River Discharge (referred to as the Discharge hereafter) strongly affect the CO2 uptake capacity. As the Discharge may decrease due to the Three Gorges Dam operation, the Changjiang plume will probably also decrease, resulting in reduction in CO2 uptake capacity and even a shift from a CO2 sink to a source.

Print ISSN: 0094-8276

Digitale ISSN: 1944-8007

Thema: Geologie und Paläontologie , Physik

Publiziert von Wiley im Namen von American Geophysical Union (AGU).

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Greenland Telescope Project --- Direct Confirmation of Black Hole with Sub-millimeter VLBI --- (2014)

M. Inoue, J.C. Algaba-Marcos, K. Asada, C.-C. Chang, M-T. Chen, J. Han, H. Hirashita, P.T.P. Ho, S.-N. Hsieh, T. Huang, H. Jiang, P.M. Koch, D.Y. Kubo, C.-Y. Kuo, B. Liu, P. Martin-Cocher, S. Matsushita, Z. Meyer-Zhao, M. Nakamura, H. Nishioka, G. Nystrom, N. Pradel, H.-Y. Pu, P.A. Raffin, H.-Y. Shen, W. Snow, R. Srinivasan, T.-S. Wei, R. Blundell, R. Burgos, P. Grimes, E. Keto, S. Paine, N. Patel, T.K. Sridharan, S.S. Doeleman, V. Fish, W. Brisken, P. Napier

Wiley

In: Radio Science

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Publikationsdatum: 2014-07-13

Beschreibung: A 12-m diameter radio telescope will be deployed to the Summit Station in Greenland to provide direct confirmation of a Super Massive Black Hole (SMBH) by observing its shadow image in the active galaxy M87. The telescope (Greenland Telescope: GLT) is to become one of the Very Long Baseline Interferometry (VLBI) stations at sub-millimeter (submm) regime, providing the longest baseline 〉 9,000 km to achieve an exceptional angular resolution of 20 µas at 350 GHz, which will enable us to resolve the shadow size of ~40 µas. The triangle with the longest baselines formed by the GLT, the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, and the Submillimeter Array (SMA) in Hawaii will play a key role for the M87 observations. We have been working on the image simulations based on realistic conditions for a better understanding of the possible observed images. In parallel, retrofitting of the telescope and the site developments are in progress. Based on three years of opacity monitoring at 225 GHz, our measurements indicate that the site is excellent for submm observations, comparable to the ALMA site. The GLT is also expected to make single-dish observations up to 1.5 THz.

Print ISSN: 0048-6604

Digitale ISSN: 1944-799X

Thema: Geologie und Paläontologie , Physik

Publiziert von Wiley im Namen von American Geophysical Union (AGU).

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Upper Mantle Earth Structure in Africa From Full‐Wave Ambient Noise Tomography (2019)

E. L. Emry, Y. Shen, A. A. Nyblade, A. Flinders, X. Bao

Wiley

In: Geochemistry, Geophysics, Geosystems

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Publikationsdatum: 2019

Beschreibung: Abstract Our understanding of the tectonic development of the African continent and the interplay between its geological provinces is hindered by unevenly distributed seismic instrumentation. In order to better understand the continent, we used long‐period ambient noise full‐waveform tomography on data collected from 186 broadband seismic stations throughout Africa and surrounding regions to better image the upper mantle structure. We extracted empirical Green's functions from ambient seismic noise using a frequency‐time normalization method and retrieved coherent signal at periods of 7–340 s. We simulated wave propagation through a heterogeneous Earth using a spherical finite‐difference approach to obtain synthetic waveforms, measured the misfit as phase delay between the data and synthetics, calculated numerical sensitivity kernels using the scattering integral approach, and iteratively inverted for structure. The resulting images of isotropic, shear wave speed for the continent reveal segmented, low‐velocity upper mantle beneath the highly magmatic northern and eastern sections of the East African Rift System (EARS). In the southern and western sections, high‐velocity upper mantle dominates, and distinct, low‐velocity anomalies are restricted to regions of current volcanism. At deeper depths, the southern and western EARS transition to low velocities. In addition to the EARS, several low‐velocity anomalies are scattered through the shallow upper mantle beneath Angola and North Africa, and some of these low‐velocity anomalies may be connected to a deeper feature. Distinct upper mantle high‐velocity anomalies are imaged throughout the continent and suggest multiple cratonic roots within the Congo region and possible cratonic roots within the Sahara Metacraton.

Digitale ISSN: 1525-2027

Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik

Publiziert von Wiley im Namen von American Geophysical Union (AGU).

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Gas-Phase Hydrogenolysis of Glycerol Catalyzed by Cu/MOx Catalysts (2012)

Y. Feng, H. Yin, L. Shen, A. Wang, Y. Shen, T. Jiang

Wiley

In: Chemical Engineering and Technology

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Publikationsdatum: 2012-12-13

Beschreibung: The catalytic activities of Cu/MO x (MO x = Al 2 O 3 , TiO 2 , and ZnO) catalysts in the gas-phase hydrogenolysis of glycerol were studied at 180–300 °C under 0.1 MPa of H 2 . Cu/MO x (MO x = Al 2 O 3 , TiO 2 , and ZnO) catalysts were prepared by the incipient wetness impregnation method. After reduction, CuO species were converted to metallic copper (Cu 0 ). Cu/Al 2 O 3 catalysts with high acidity, high specific surface areas and small metallic copper size favored the formation of 1,2-propanediol with a maximum selectivity of 87.9 % at complete conversion of glycerol and a low reaction temperature of 180 °C, and favored the formation of ethylene glycol and monohydric alcohols at high reaction temperature of 300 °C. Cu/TiO 2 and Cu/ZnO catalysts exhibited high catalytic activity toward the formation of hydroxyacetone with a selectivity of approx. 90 % in a wide range of reaction temperature. In gas-phase hydrogenolysis of glycerol, Cu/Al 2 O 3 catalysts with high acid strength of weak and strong acid sites and small-sized metallic copper favored the formation of propanediols, ethylene glycol and monohydric alcohols. Cu/TiO 2 and Cu/ZnO catalysts with low acid strength of weak acid sites and large-sized metallic copper favored the rapid dehydration of glycerol to hydroxyacetone.

Print ISSN: 0930-7516

Digitale ISSN: 1521-4125

Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung

Publiziert von Wiley

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Sheng Chen, Y. Hong, Qing Cao, J. J. Gourley, P-E. Kirstetter, B. Yong, Y. Tian, Z. Zhang, Y. Shen, J. Hu, J. Hardy

Wiley

In: Journal of Geophysical Research JGR - Atmospheres

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Publikationsdatum: 2013-11-15

Beschreibung: ABSTRACT [1] Similarities and differences of spatial error structures of surface precipitation estimated with successive version-6 (V6) and version-7 (V7) Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) algorithms are systematically analyzed through comparison with the China Meteorological Administration's national daily precipitation analysis from June 2008 to May 2011. The TMPA products include V6 and V7 real-time products 3B42RTV6 and 3B42RTV7 and research products 3B42V6 and 3B42V7. Both versions of research products outperform their respective real-time counterparts. 3B42V7 clearly improves upon 3B42V6 over China in terms of daily mean precipitation; the correlation coefficient (CC) increases from 0.89 to 0.93, the relative bias (RB) improves from -4.91% to -0.05%, and the root mean square error (RMSE) improves from 0.69 mm to 0.54 mm. When considering 3-year mean precipitation, 3B42V7 shows similar spatial patterns and statistical performance to 3B42V6. Both 3B42RTV7 and 3B42RTV6 demonstrate similar bias patterns in most regions of China with overestimation by 20% in arid regions (i.e., the north and west of China) and slight underestimation in humid regions (e.g., -5.82% in southern China). However, 3B42RTV7 overestimates precipitation more than 3B42RTV6 in the cold Qinghai-Tibetan plateau, resulting in a much higher RB of 139.95% (128.69%, 136.09%, and 121.11%) in terms of 3-year annual (spring, summer, and autumn) daily mean precipitation and an even worse performance during winter. In this region, 3B42RTV7 shows an overall slightly degraded performance than 3B42RTV6 with CC decreasing from 0.81 to 0.73 and RB (RMSE) increasing from 21.22% (0.95 mm) to 35.84% (1.27 mm) in terms of daily precipitation.

Print ISSN: 0148-0227

Thema: Geologie und Paläontologie , Physik

Publiziert von Wiley im Namen von American Geophysical Union (AGU).

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A comparison of small-scale magnetic fluctuations in the region 1 and 2 field-aligned current systems (2017)

J. Wu, M. S. Bryant, C. G. Ridley, Y. Shen, L. Yang, L. B. N. Clausen, K. A. McWilliams, K. R. Murphy, I. R. Mann, L. G. Ozeke, H. Korth, B. J. Anderson, C. L. Waters

Wiley

In: Journal of Geophysical Research JGR - Space Physics

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Publikationsdatum: 2017-02-22

Beschreibung: By determining the location and size of the Region 1 (R1) and Region 2 (R2) large-scale field-aligned currents (FACs) from Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) data, we are able to study the small-scale magnetic fluctuations observed by the Swarm satellites embedded within the large-scale FACs. A statistical comparison of R1 and R2 high-frequency fluctuations is presented in terms of different solar wind conditions and geomagnetic activities. We find that: (1) the amplitude of high-frequency fluctuations in both R1 and R2 increases as the large-scale R1 and R2 FACs intensify; (2) high-frequency fluctuations in R1 peak near dayside dawn and dusk, while those in R2 peak around noon; (3) the location of the largest high-frequency fluctuations in R1 shifts in local time in response to IMF By, indicating a connection between the R1 fluctuation and the driving solar wind most likely explained by magnetic reconnection; (4) high-frequency fluctuations in R2 are enhanced in a small region near local noon and respond clearly to nightside drivers, as characterized by the auroral electrojet index. Our analysis shows that the intensity of R1 and R2 high-frequency magnetic fluctuations is directly connected to the intensity of FACs, which implies that the magnetic fluctuations are closely related to the magnetospheric processes that drive them.

Print ISSN: 0148-0227

Thema: Geologie und Paläontologie , Physik

Publiziert von Wiley im Namen von American Geophysical Union (AGU).

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