Surface-subsurface hydrologic exchange and nutrient dynamics in the hyporheic zone of the Tanana River

Thesis (M.S.) University of Alaska Fairbanks, 2007The aquatic-terrestrial interface is an active site of biogeochemical transformation, regulating the flux of nutrients between ecosystems. I addressed the hydrologic controls on nitrogen biogeochemistry in the hyporheic zone of a glacially fed river. I measured hyporheic concentrations of solutes and gases along subsurface flowpaths on two islands. Denitrification was quantified using an in situ [delta]⁻¹⁵NO₃⁻ push-pull technique. Nitrate concentration was consistently greater in river than in hyporheic water. Denitrification ranged from 1.9 - 29.4 mgN kg sediment⁻¹ day⁻¹. Hotspots of methane partial pressure, averaging 50,000 ppmv, were found in densely vegetated areas with low oxygen concentration (<0.5 mgO₂ L⁻¹). Hyporheic flow was an important source of nitrogen to microbes and vegetation, transporting on average 0.41 gNO₃⁻-N m⁻² day⁻¹ through surface sediments. Results suggest that denitrification is a major sink for river nitrate in boreal forest floodplain soils, particularly at the river-sediment interface. The stability of the river hydro graph is a key factor regulating anaerobic metabolism in the hyporheic zone.1. Introduction -- The hyporheic zone -- Biogeochemical transformations along hyporheic flowpaths -- Nitrogen supply in riparian zones -- Hydrology and biogeochemistry of the Tanana River at Bonanza Creek LTER -- Literature cited -- 2. Surface-subsurface hydrologic exchange and nutrient dynamics in the hyporheic zone of the Tanana River in Interior Alaska -- Literature cited -- 2. Surface-subsurface hydrologic exchange and nutrient dynamics in the hyporheic zone of the Tanana River in Interior Alaska -- Abstract -- Introduction -- Methods -- Study site -- Study design -- Sampling and analytical techniques -- In situ denitrification -- Push-pull calculations -- Data analysis -- Analysis of subsurface hydrology and capillary rise -- Long term patterns in climate and river hydrology -- Results -- Climate and river hydrology -- Spatial patterns in hyporheic chemistry -- Subsurface hydrology and nitrogen losses -- Temporal variation in hyporheic chemistry -- Discussion -- Hyporheic zone hydrology and nitrogen transformation -- Subsurface methane and carbon dioxide -- Climate, river hydrology and hyporheic chemistry -- Acknowledgements -- Literature cited -- 3. Conclusions -- Literature cited

Effects of solar wind magnetosphere coupling recorded at different geomagnetic latitudes: Separation of directly-driven and storage/release systems

The effect on geomagnetic activity of solar wind speed, compared with that of the strength of the interplanetary magnetic field, differs with geomagnetic latitude. In this study we construct a new index based on monthly standard deviations in the H-component of the geomagnetic field for all geomagnetic latitudes. We demonstrate that for this index the response at auroral regions correlates best with interplanetary coupling functions which include the solar wind speed while mid- and low-latitude regions respond to variations in the interplanetary magnetic field strength. These results are used to isolate the responsible geomagnetic current systems

Corrigendum to "Geomagnetic activity related NOx enhancements and polar surface air temperature variability in a chemistry climate model: modulation of the NAM index" published in Atmos. Chem. Phys., 11, 4521–4531, 2011

No abstract available

Missing driver in the Sun–Earth connection from energetic electron precipitation impacts mesospheric ozone

Energetic electron precipitation (EEP) from the Earth’s outer radiation belt continuously affects the chemical composition of the polar mesosphere. EEP can contribute to catalytic ozone loss in the mesosphere through ionization and enhanced production of odd hydrogen. However, the long-term mesospheric ozone variability caused by EEP has not been quantified or confirmed to date. Here we show, using observations from three different satellite instruments, that EEP events strongly affect ozone at 60–80 km, leading to extremely large (up to 90%) short-term ozone depletion. This impact is comparable to that of large, but much less frequent, solar proton events. On solar cycle timescales, we find that EEP causes ozone variations of up to 34% at 70–80 km. With such a magnitude, it is reasonable to suspect that EEP could be an important part of solar influence on the atmosphere and climate syste

Lightning driven inner radiation belt energy deposition into the atmosphere: regional and global estimates

International audienceIn this study we examine energetic electron precipitation fluxes driven by lightning, in order to determine the global distribution of energy deposited into the middle atmosphere. Previous studies using lightning-driven precipitation burst rates have estimated losses from the inner radiation belts. In order to confirm the reliability of those rates and the validity of the conclusions drawn from those studies, we have analyzed New Zealand data to test our global understanding of troposphere to magnetosphere coupling. We examine about 10000h of AbsPAL recordings made from 17 April 2003 through to 26 June 2004, and analyze subionospheric very-low frequency (VLF) perturbations observed on transmissions from VLF transmitters in Hawaii (NPM) and western Australia (NWC). These observations are compared with those previously reported from the Antarctic Peninsula. The perturbation rates observed in the New Zealand data are consistent with those predicted from the global distribution of the lightning sources, once the different experimental configurations are taken into account. Using lightning current distributions rather than VLF perturbation observations we revise previous estimates of typical precipitation bursts at L~2.3 to a mean precipitation energy flux of ~1×10-3 ergs cm-2s-1. The precipitation of energetic electrons by these bursts in the range L=1.9-3.5 will lead to a mean rate of energy deposited into the atmosphere of 3×10-4 ergs cm-2min-1, spatially varying from a low of zero above some ocean regions to highs of ~3-6×10-3 ergs cm-2min-1 above North America and its conjugate region

Simultaneous observation of chorus and hiss near the plasmapause

On 4 August 2010 a moderate geomagnetic storm occurred with minimum Dst of −65 nT and maximum Kp of 7−. Shortly after the onset of this storm, VLF chorus was observed at Marion Island (L= 2.6). Over time the spectral structure of the chorus transformed into a hiss band spanning the same frequency range. The observation of overlapping chorus and hiss suggests that Marion Island was close to the plasmapause at the time of this event, and provides ground-based observational confirmation of the generation mechanism of plasmaspheric hiss from chorus waves outside of the plasmasphere. Chorus observations at Marion Island were not common during this period of the solar cycle and so this event was investigated in detail. The geomagnetic conditions are discussed and geosynchronous particle data and broadband data from two other stations are presented. Empirical models are employed to predict the location of the plasmapause, and its location is inferred from a knee whistler recorded at Dunedin, New Zealand. These show that Marion Island is in the vicinity of the plasmapause during the event. The event is also compared to chorus observed at similarL after the Halloween storms of 2003. The rarity of the chorus observation is quantified using DEMETER VLF data. The DEMETER data, along with the various ground based VLF measurements, allows us to infer temporal and spatial variations in the chorus source region

What Fraction of the Outer Radiation Belt Relativistic Electron Flux at L approximate to 3-4.5 Was Lost to the Atmosphere During the Dropout Event of the St. Patrick's Day Storm of 2015?

Observations of relativistic energetic electron fluxes in the outer radiation belt can show dropouts, that is, sudden electron flux depletions during the main phase of a geomagnetic storm. Many recent studies show that these dropouts typically involve a true loss of particles, that is, nonadiabatic losses in nature. Precipitation into the atmosphere of relativistic electrons driven into the bounce loss cone, through wave-particle interactions, is envisaged as one of the primary loss mechanisms. Such precipitation can be studied using ground-based observations such as VLF narrowband radio waves, due to the deposition of energy into the lower ionospheric D-region, thereby modifying the subionospheric waveguide. The present study focuses on the dropout event observed during the St. Patrick's Day storm of March 2015. Perturbations lasting several hours were observed in the received VLF amplitude and phase of the NAA transmitter signal measured at Seattle and Edmonton and the NML transmitter signal received at St. John's and Edmonton. All these L approximate to 3-4.5 paths were located on the nightside of the Earth during dropout phase of the storm. Observations of relativistic electron characteristics from Van Allen Probes, and ionospheric perturbation characterization from VLF radio waves, are used to calculate that during the time interval of the dropout event

A multi-instrument approach to determining the source‐region extent of EEP-driving EMIC Waves

Recent years have seen debate regarding the ability of electromagnetic ion cyclotron (EMIC) waves to drive EEP (energetic electron precipitation) into the Earth's atmosphere. Questions still remain regarding the energies and rates at which these waves are able to interact with electrons. Many studies have attempted to characterize these interactions using simulations; however, these are limited by a lack of precise information regarding the spatial scale size of EMIC activity regions. In this study we examine a fortuitous simultaneous observation of EMIC wave activity by the RBSP‐B and Arase satellites in conjunction with ground‐based observations of EEP by a subionospheric VLF network. We describe a simple method for determining the longitudinal extent of the EMIC source region based on these observations, calculating a width of 0.75 hr MLT and a drift rate of 0.67 MLT/hr. We describe how this may be applied to other similar EMIC wave events