| 31. |
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| 32. |
- Basu, N. B., et al.
(author)
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Nutrient loads exported from managed catchments reveal emergent biogeochemical stationarity
- 2010
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 37:L23404
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Journal article (peer-reviewed)abstract
- Complexity of heterogeneous catchments poses challenges in predicting biogeochemical responses to human alterations and stochastic hydro‐climatic drivers. Human interferences and climate change may have contributed to the demise of hydrologic stationarity, but our synthesis of a large body of observational data suggests that anthropogenic impacts have also resulted in the emergence of effective biogeochemical stationarity in managed catchments. Long‐term monitoring data from the Mississippi‐Atchafalaya River Basin (MARB) and the Baltic Sea Drainage Basin (BSDB) reveal that inter‐annual variations in loads (LT) for total‐N (TN) and total‐P (TP), exported from a catchment are dominantly controlled by discharge (QT) leading inevitably to temporal invariance of the annual, flow‐weighted concentration, = (LT/QT). Emergence of this consistent pattern across diverse managed catchments is attributed to the anthropogenic legacy of accumulated nutrient sources generating memory, similar to ubiquitously present sources for geogenic constituents that also exhibit a linear LT‐QT relationship. These responses are characteristic of transport‐limited systems. In contrast, in the absence of legacy sources in less‐managed catchments, values were highly variable and supply limited. We offer a theoretical explanation for the observed patterns at the event scale, and extend it to consider the stochastic nature of rainfall/flow patterns at annual scales. Our analysis suggests that: (1) expected inter‐annual variations in LT can be robustly predicted given discharge variations arising from hydro‐climatic or anthropogenic forcing, and (2) water‐quality problems in receiving inland and coastal waters would persist until the accumulated storages of nutrients have been substantially depleted. The finding has notable implications on catchment management to mitigate adverse water‐quality impacts, and on acceleration of global biogeochemical cycles.
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| 33. |
- Becerra Garcia, Marley, et al.
(author)
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On the velocity of positive connecting leaders associated with negative downward lightning leaders
- 2008
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 35:2
-
Journal article (peer-reviewed)abstract
- A self-consistent leader propagation model is used to estimate the velocity of upward connecting positive leaders initiated from a tall tower under the influence of downward negative lightning leaders. The propagation of upward connecting leaders has been found to be influenced not only by the average velocity of the downward leader but also by the prospective return stroke current, the lateral position of the downward leader channel as well as by the ambient electric field. This result show that the velocity and propagation time of upward connecting positive leaders change from flash to flash due to the variations in these parameters.
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| 34. |
- Beck, Lisa J., et al.
(author)
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Differing Mechanisms of New Particle Formation at Two Arctic Sites
- 2021
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 48:4
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Journal article (peer-reviewed)abstract
- New particle formation in the Arctic atmosphere is an important source of aerosol particles. Understanding the processes of Arctic secondary aerosol formation is crucial due to their significant impact on cloud properties and therefore Arctic amplification. We observed the molecular formation of new particles from low-volatility vapors at two Arctic sites with differing surroundings. In Svalbard, sulfuric acid (SA) and methane sulfonic acid (MSA) contribute to the formation of secondary aerosol and to some extent to cloud condensation nuclei (CCN). This occurs via ion-induced nucleation of SA and NH3 and subsequent growth by mainly SA and MSA condensation during springtime and highly oxygenated organic molecules during summertime. By contrast, in an ice-covered region around Villum, we observed new particle formation driven by iodic acid but its concentration was insufficient to grow nucleated particles to CCN sizes. Our results provide new insight about sources and precursors of Arctic secondary aerosol particles.
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| 35. |
- Behar, Etienne, et al.
(author)
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Mass loading at 67P/Churyumov-Gerasimenko : A case study
- 2016
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 43:4, s. 1411-1418
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Journal article (peer-reviewed)abstract
- We study the dynamics of the interaction between the solar wind ions and a partially ionized atmosphere around a comet, at a distance of 2.88 AU from the Sun during a period of low nucleus activity. Comparing particle data and magnetic field data for a case study, we highlight the prime role of the solar wind electric field in the cometary ion dynamics. Cometary ion and solar wind proton flow directions evolve in a correlated manner, as expected from the theory of mass loading. We find that the main component of the accelerated cometary ion flow direction is along the antisunward direction and not along the convective electric field direction. This is interpreted as the effect of an antisunward polarization electric field adding up to the solar wind convective electric field.
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| 36. |
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| 37. |
- Behlke, Rico, et al.
(author)
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Solitary structures associated with short large-amplitude magnetic structures (SLAMS) upstream of the Earth's quasi-parallel bow shock
- 2004
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 31:16
-
Journal article (peer-reviewed)abstract
- [1] For the first time, solitary waves (SWs) have been observed within short large-amplitude magnetic structures (SLAMS) upstream of the Earth's quasi-parallel bow shock. The SWs often occur as bipolar pulses in the electric field data and move parallel to the background magnetic field at velocities of v = 400–1200 km/s. They have peak-to-peak amplitudes in the parallel electric field of up to E′∥ = 65 mV/m and parallel scale sizes of L∥ ∼ 10 λD. The bipolar solitary waves exhibit negative potential structures of ∣Φ∥∣ = 0.4–2.2 V, i.e., eΦ∥/kTe ∼ 0.1. None of the theories commonly used to describe SWs adequately address these negative potential structures moving at velocities above the ion thermal speed in a weakly magnetized plasma.
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| 38. |
- Belcher, Stephen E., et al.
(author)
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A global perspective on Langmuir turbulence in the ocean surface boundary layer
- 2012
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 39, s. L18605-
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Journal article (peer-reviewed)abstract
- The turbulent mixing in thin ocean surface boundary layers (OSBL), which occupy the upper 100 m or so of the ocean, control the exchange of heat and trace gases between the atmosphere and ocean. Here we show that current parameterizations of this turbulent mixing lead to systematic and substantial errors in the depth of the OSBL in global climate models, which then leads to biases in sea surface temperature. One reason, we argue, is that current parameterizations are missing key surface-wave processes that force Langmuir turbulence that deepens the OSBL more rapidly than steady wind forcing. Scaling arguments are presented to identify two dimensionless parameters that measure the importance of wave forcing against wind forcing, and against buoyancy forcing. A global perspective on the occurrence of wave-forced turbulence is developed using re-analysis data to compute these parameters globally. The diagnostic study developed here suggests that turbulent energy available for mixing the OSBL is under-estimated without forcing by surface waves. Wave-forcing and hence Langmuir turbulence could be important over wide areas of the ocean and in all seasons in the Southern Ocean. We conclude that surface-wave-forced Langmuir turbulence is an important process in the OSBL that requires parameterization. Citation: Belcher, S. E., et al. (2012), A global perspective on Langmuir turbulence in the ocean surface boundary layer, Geophys. Res. Lett., 39, L18605, doi: 10.1029/2012GL052932.
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| 39. |
- Bergbauer, S., et al.
(author)
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Thermal stress evolution in cooling pluton environments of different geometries
- 1998
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 25:5, s. 707-71-
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Journal article (peer-reviewed)abstract
- Thermoelastic displacement potentials and fast Fourier transforms can be combined to rapidly calculate the thermal stresses in 2-D for plutons that cool by conduction. First, temperature distributions over time are computed by solving the diffusion equation. Thermal stresses are then obtained using thermoelastic stress potentials. This method can be applied to a broad range of pluton geometries and initial conditions, and requires far less computation time than finite difference or finite element analyses. Results of 2-D analyses show that pluton geometry strongly influences the thermal stresses that occur in a cooling pluton. Thermal stresses of several tens of MPa arise during cooling and are highest at the corners or where the intrusion is thin. The most tensile stress is greater inside a pluton than in the host rock. Moreover, the orientation of the most tensile stress in a cooling pluton generally changes over time. This could result in multiple fracture sets, which would significantly affect the mechanical and hydraulic behavior of a pluton.
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| 40. |
- Berggren, Ann-Marie, 1969-, et al.
(author)
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A 600-year annual 10Be record from the NGRIP ice core, Greenland
- 2009
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 36, s. L11801-
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Journal article (peer-reviewed)abstract
- Despite the extensive use of 10Be as the most significant information source on past solar activity, there has been only one record (Dye-3, Greenland) providing annual resolution over several centuries. Here we report a new annual resolution 10Be record spanning the period 1389-1994 AD, measured in an ice core from the NGRIP site in Greenland. NGRIP and Dye-3 10Be exhibits similar long-term variability, although occasional short term differences between the two sites indicate that at least two high resolution 10Be records are needed to assess local variations and to confidently reconstruct past solar activity. A comparison with sunspot and neutron records confirms that ice core 10Be reflects solar Schwabe cycle variations, and continued 10Be variability suggests cyclic solar activity throughout the Maunder and Spörer grand solar activity minima. Recent 10Be values are low; however, they do not indicate unusually high recent solar activity compared to the last 600 years.
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