We describe novel hybrid algorithms for inversion of electromagnetic geophysical data, combining the computational and storage efficiency of a conjugate gradient approach with an Occam scheme for regularization and step-length control. The basic algorithm is based on the observation that iterative solution of the symmetric (Gauss-Newton) normal equations with conjugate...
I derive probability densities for virtual geomagnetic pole( VGP) longitudes for a general statistical model of
local magnetic field variations. I show that even for very
simple statistically homogeneous models of secular variation,
the distribution of VGP longitudes is peaked 90° away
from the sampling longitude. Thus, when sites are...
Although satellite electromagnetic induction studies
have usually assumed a symmetric magnetospheric ring
current source, there is growing evidence for significant
source asymmetry. Here we apply empirical orthogonal
function methods to mid-latitude night-side hourly mean
geomagnetic observatory data to search for evidence of nonzonal
low-frequency source fields. The dominant spatial
mode...
We conducted a comparative hazard assessment for 325,000 ha in a fire-prone area of southwest Oregon, USA. The landscape contains a variety of land ownerships, fire regimes, and management strategies. Our comparative hazard assessment evaluated the effects of two management strategies on crown fire potential and northern spotted owl (Strix...
The objectives of this study were (i) to provide further evidence of a positive correlation of stand density with early growth of coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii); (ii) to determine when after planting the positive growth response occurs and how long it lasts; and (iii) to use...
Economic theory predicts that individual migration decisions for working-age adults will depend on area differences in wages, housing costs, and amenities. While the importance of wages and amenities is well-established from previous empirical studies, evidence regarding housing costs is far less conclusive. We develop and test a new method for...
Large-scale lateral advection of seawater within the oceanic crust is thought to be the cause of low heat flow in the Equatorial Pacific. Until now supportive evidence is limited to reversals of B and δ¹¹B, Ca, Mg, SO₄⁻², Sr and ⁸⁷Sr/⁸⁶Sr in sediment pore waters. Here we report new evidence...
The most accurate determinations of the global ocean tides are currently based on altimeter measurements made by the Topex/Poseidon satellite. The error spectrum corresponding to the M₂ tidal solution is here estimated, primarily by inverse methods and secondarily by simple differencing in flatter than tidal signal spectrum, and it exceeds...
In conjunction with the USArray component of
EarthScope, long period magnetotelluric (MT) data are
being acquired in a series of arrays across the continental US.
Initial deployments in 2006 and 2007 acquired data (10–
10,000 s) at 110 sites covering the US Pacific Northwest,
distributed with the same nominal spacing...
How and where the ocean tides dissipate
their energy are longstanding questions with both
oceanographic and astronomical implications. Two
decades ago, Doake suggested that flexing of Antarctic
ice shelves by the underlying ocean tide is an important
energy sink, perhaps accounting for over half the global
dissipation rate. Observational constraints...