A coupled surface boundary-layer-quasigeostrophic model

A three-dimensional model of the mesoscale surface boundary layer of the open ocean is developed through scale analysis of the primitive equations with mixing included. A set of surface boundary-layer equations appropriate for a broad range of oceanic and atmospheric scales is thereby derived. The essential basis of the model is a coupling between quasigeostrophic dynamics away from the boundary layer and arbitrary mixing models within the mixed layer. The coupling consists of advection of the boundary layer by the horizontal and vertical components of the interior quasigeostrophic flow and forcing of the interior by the boundary layer in the form of divergence within the boundary layer which leads to vortex stretching/compression in the interior. The divergence is generalized for mesoscale wind-driven flows and includes nonlinear interaction between the directly wind-driven boundary-layer flow and the interior flow in the form of interior relative vorticity advection by the wind-driven flow. The nature of the equations leads us to apply a numerical algorithm to their solution. This algorithm is calibrated through application to idealized problems to determine the temporal and spatial grid requirements. The model is initialized with a realistic ocean flow having the properties of the Gulf Stream.     

Emigration of juvenile Atlantic menhaden,Brevoortia tyrannus (Pisces: Clupeidae), from the York River estuary

The emigration of juvenile Atlantic menhaden,Brevoortia tyrannus (Latrobe), from the York River Estuary, Virginia, was studied during the years 1981 and 1982. Concurrent observations of menhaden catch, water temperature, and phytoplankton abundance suggested that the migration began in response to environmental events in the estuary. Juvenile menhaden appeared to begin their migration five days after the sustained onset of water temperatures below 24 °C. The temperature change was hypothesized as the proximate factor that initiates the migration. Coincident with the migrations, phytoplankton communities in the estuary bloomed, suggesting that the ultimate factor that initiates the migration may be the occurrence of sufficient food for the emigrating menhaden as they moved down and out of the estuary. Migration timing may have evolved as a mechanism to enhance the survival of migrating juvenile menhaden during a period of physiologic stress.     

Geochemical implications from Sr isotopes and K-Ar age determinations for the cook-austral islands chain

Sr isotopes and K-Ar ages were determined for volcanic rocks from three islands, Samoa, Rarotonga and Rurutu in the Austral-Gilbert-Marshall chain. We have established that Rurutu originated from the same “hot spot” as Tubuai and Raivavae in the Cook-Austral chain as indicated by its 11 m.y. K-Ar age and ( ) ratios. The ( ) ratios for Rurutu, Tubuai and Raivavae lie in the restricted range 0.7026–0.7035. K-Ar ages of all volcanic rocks from Samoa and Rarotonga are all less than 4 m.y. and their ( ) ratios are much higher than those in Rurutu, Tubuai and Raivavae. These findings suggest that Samoa and Rarotonga did not originate in a single hot spot for the Cook-Austral islands.     

Marine Layer Stratus Study

The intent of this study is to develop a better understanding of the behavior of late spring through early fall marine layer stratus and fog at Vandenberg Air Force Base, which accounts for a majority of aviation forecasting difficulties. The main objective was to use Leipper (1995) study as a starting point to evaluate synoptic and mesoscale processes involved, and identify specific meteorological parameters that affected the behavior of marine layer stratus and fog. After identifying those parameters, the study evaluates how well the various weather models forecast them. The main conclusion of this study is that weak upper-air dynamic features work with boundary layer motions to influence marine layer behavior. It highlights the importance of correctly forecasting the surface temperature by showing how it ties directly to the wind field. That wind field, modified by the local terrain, establishes the low-level convergence and divergence pattern and the resulting marine layer cloud thicknesses and visibilities.     

Application of a library based method to time domain electromagnetic data for the identification of unexploded ordnance

A simple library based algorithm for the identification of unexploded ordnance is tested on time domain electromagnetic data. A library of polarization tensors is generated from data acquired on a test stand over a collection of different UXO. The objective of the algorithm is to determine which target of the library is most likely to have produced an observed data anomaly. For each target in our library a non-linear inverse problem is solved for the position and orientation that minimizes the least-squares difference between the observed data anomaly and the data predicted from each target. This technique avoids direct inversion for polarization tensor, making it feasible for cases where sensor data quality may not be sufficient to support confident estimation of model parameters. For cases where the background soil response is significant, we also invert for the t⁻¹ decay characteristic of viscous remnant magnetic soil. We present results of preliminary tests of the library technique to Geonics EM63 time domain electromagnetic data collected on a test plot seeded with UXO. These tests demonstrate an excellent ability to accurately identify isolated targets. Misidentification of single targets occur when data anomalies have low signal to noise ratios or when targets within the library have similar polarization tensors.     

Clearing the Martian air: The troubled history of dust storms

This note is an attempt to resolve some misconceptions regarding the historical record of the Martian atmospheric phenomena referred to as “dust storms,” but often called yellow storms, yellow clouds, planetwide dust storms, global dust storms, great dust storms, etc. The known frequency of planet-encircling storms will be specifically addressed. Better knowledge of the sizes, frequencies, and locations of Martian dust storms is needed for atmospheric modeling and for future mission planning.     

Measuring channel planform change from image time series: A generalizable,spatially distributed,probabilistic method for quantifying uncertainty

Channels change in response to natural or anthropogenic fluctuations in streamflow and/or sediment supply and measurements of channel change are critical to many river management applications. Whereas repeated field surveys are costly and time-consuming, remote sensing can be used to detect channel change at multiple temporal and spatial scales. Repeat images have been widely used to measure long-term channel change, but these measurements are only significant if the magnitude of change exceeds the uncertainty. Existing methods for characterizing uncertainty have two important limitations. First, while the use of a spatially variable image co-registration error avoids the assumption that errors are spatially uniform, this type of error, as originally formulated, can only be applied to linear channel adjustments, which provide less information on channel change than polygons of erosion and deposition. Second, previous methods use a level-of-detection (LoD) threshold to remove non-significant measurements, which is problematic because real changes that occurred but were smaller than the LoD threshold would be removed. In this study, we present a new method of quantifying uncertainty associated with channel change based on probabilistic, spatially varying estimates of co-registration error and digitization uncertainty that obviates a LoD threshold. The spatially distributed probabilistic (SDP) method can be applied to both linear channel adjustments and polygons of erosion and deposition, making this the first uncertainty method generalizable to all metrics of channel change. Using a case study from the Yampa River, Colorado, we show that the SDP method reduced the magnitude of uncertainty and enabled us to detect smaller channel changes as significant. Additionally, the distributional information provided by the SDP method allowed us to report the magnitude of channel change with an appropriate level of confidence in cases where a simple LoD approach yielded an indeterminate result. © 2020 John Wiley & Sons, Ltd.