Physical Sciences and Mathematics Commons^™

Nitrate Deposition To Surface Snow At Summit, Greenland, Following The 9 November 2000 Solar Proton Event, Katherine A. Duderstadt, Jack E. Dibb, Charles H. Jackman, Cora E. Randall, Stanley C. Solomon, Michael J. Mills, Nathan A. Schwadron, Harlan E. Spence

Earth Sciences

Abstract

This study considers whether spikes in nitrate in snow sampled at Summit, Greenland, from August 2000 to August 2002 are related to solar proton events. After identifying tropospheric sources of nitrate on the basis of correlations with sulfate, ammonium, sodium, and calcium, we use the three-dimensional global Whole Atmosphere Community Climate Model (WACCM) to examine unaccounted for nitrate spikes. Model calculations confirm that solar proton events significantly impact HO_x, NO_x, and O₃ levels in the mesosphere and stratosphere during the weeks and months following the major 9 November 2000 solar proton event. However, solar …

Effect Of Carex Rostrata On Seasonal And Interannual Variability In Peatland Methane Emissions, Genevieve L. Noyce, Ruth Varner, Jill L. Bubier, Steve Frolking

Earth Sciences

Peatlands are a large natural source of atmospheric methane (CH₄), and the sedge Carex rostrata plays a critical role in the production, oxidation, and transport of CH₄ in these systems. This 4 year clipping experiment examined the changes in CH₄ emissions from a temperate peatland after removing all aboveground C. rostrata biomass. Methane fluxes, dissolved CH₄, and environmental variables were measured during spring, summer, and fall from 2008 to 2011. Clipping and removing the C. rostrata leaves and stems caused an immediate decrease in CH₄ emissions that persisted over 4 years of this …

Dynamics Of Wind-Driven Upwelling And Relaxation Between Monterey Bay And Point Arena: Local-, Regional-, And Gyre-Scale Controls, James M. Pringle, Edward P. Dever

Earth Sciences

In north and central California, equatorward winds drive equatorward flows and the upwelling of cold dense water over the shelf during the midspring and summer upwelling season. When the winds temporarily weaken, the upwelling flows between Point Reyes and Point Arena "relax,'' becoming strongly poleward over the shelf. Analytical and numerical models are used to describe the effect of alongshore variability of winds, bathymetry, and basin-scale pressure gradients on the strength of upwelling and its relaxation. Alongshore winds weaken to the south of Point Reyes, and the shelf becomes narrower from Point Reyes to Monterey Bay. Both of these lead …

Global Irrigation Water Demand: Variability And Uncertainties Arising From Agricultural And Climate Data Sets, Dominik Wisser, Steve Frolking, Ellen M. Douglas, Balazs M. Fekete, Charles Vorosmarty, Andreas H. Schumann

Earth Sciences

Agricultural water use accounts for around 70% of the total water that is withdrawn from surface water and groundwater. We use a new, gridded, global-scale water balance model to estimate interannual variability in global irrigation water demand arising from climate data sets and uncertainties arising from agricultural and climate data sets. We used contemporary maps of irrigation and crop distribution, and so do not account for variability or trends in irrigation area or cropping. We used two different global maps of irrigation and two different reconstructions of daily weather 1963–2002. Simulated global irrigation water demand varied by ∼30%, depending on …

Geostatistical Analysis Of An Experimental Stratigraphy, Y Zhang, M Person, C Paola, C W. Gable, X H. Wen, J M. Davis

Earth Sciences

[1] A high-resolution stratigraphic image of a flume-generated deposit was scaled up to sedimentary basin dimensions where a natural log hydraulic conductivity (ln( K)) was assigned to each pixel on the basis of gray scale and conductivity end-members. The synthetic ln( K) map has mean, variance, and frequency distributions that are comparable to a natural alluvial fan deposit. A geostatistical analysis was conducted on selected regions of this map containing fluvial, fluvial/ floodplain, shoreline, turbidite, and deepwater sedimentary facies. Experimental ln(K) variograms were computed along the major and minor statistical axes and horizontal and vertical coordinate axes. Exponential and power …

Effects Of Uncertainty In Climate Inputs On Simulated Evapotranspiration And Runoff In The Western Arctic, Michael A. Rawlins, Steve Frolking, Richard B. Lammers, Charles Vorosmarty

Earth Sciences

Hydrological models require accurate precipitation and air temperature inputs in order to adequately depict water fluxes and storages across Arctic regions. Biases such as gauge undercatch, as well as uncertainties in numerical weather prediction reanalysis data that propagate through water budget models, limit the ability to accurately model the terrestrial arctic water cycle. A hydrological model forced with three climate datasets and three methods of estimating potential evapotranspiration (PET) was used to better understand the impact of these processes on simulated water fluxes across the Western Arctic Linkage Experiment (WALE) domain. Climate data were drawn from the NCEP–NCAR reanalysis (NNR) …

Statistical Uncertainty Of Eddy Flux–Based Estimates Of Gross Ecosystem Carbon Exchange At Howland Forest, Maine, Stephen Hagen, Rob Braswell, Ernst Linder, Steve Frolking, Andrew D. Richardson, David Y. Hollinger

Earth Sciences

We present an uncertainty analysis of gross ecosystem carbon exchange (GEE) estimates derived from 7 years of continuous eddy covariance measurements of forest-atmosphere CO₂fluxes at Howland Forest, Maine, USA. These data, which have high temporal resolution, can be used to validate process modeling analyses, remote sensing assessments, and field surveys. However, separation of tower-based net ecosystem exchange (NEE) into its components (respiration losses and photosynthetic uptake) requires at least one application of a model, which is usually a regression model fitted to nighttime data and extrapolated for all daytime intervals. In addition, the existence of a significant amount …

Remotely Forced Nearshore Upwelling In Southern California, James M. Pringle, K Riser

Earth Sciences

[1] Alongshore winds in Baja California strongly influence nearshore temperatures hundreds of kilometers to the north at Point Loma, San Diego, California, on timescales of a week to a year. The time lag between wind and temperature is consistent with first mode coastal trapped wave phase speed. The nearshore cross-shelf circulation forced by the coastal trapped waves is, at least much of the year, oppositely directed at the surface and bottom. No relation is found between the winds and temperature for periods greater than a year. It is argued that similar results may be found elsewhere in the Southern California …

Enhancement Of Wind-Driven Upwelling And Downwelling By Alongshore Bathymetric Variability, James M. Pringle

Earth Sciences

Steady wind-driven flow along a shelf of changing width is described with a frictional barotropic model valid in the limit of small Rossby and Burger number. In these limits, an alongshore wind drives enhanced onshelf transport in a coastal ocean if the shelf widens downwind, and the change in shelf width only affects the flow in the direction of Kelvin wave propagation ("downwave'') from the change in shelf width. There is enhanced onshore transport of cold, nutrient-laden bottom water if the winds favor upwelling and the shelf narrows in the direction of Kelvin wave propagation. This enhanced transport extends a …

Cross-Shelf Eddy Heat Transport In A Wind-Free Coastal Ocean Undergoing Winter Time Cooling, James M. Pringle

Earth Sciences

A steady state cross-shelf density gradient of a wind-free coastal ocean undergoing winter time cooling is found for cooling and geometries which do not vary in the along-shelf direction. The steady state cross-shelf density gradient exists even when the average density of the water continues to increase. The steady state density gradient dan be attained in less than a winter for parameters appropriate to the mid-Atlantic Eight. The cross-shelf eddy-driven buoyancy fluxes which cause this steady state gradient are found to depend critically on bottom friction and bottom slope, and the coastal polyna solutions of Chapman and Gawarkiewicz [1997] are …