Wendell A. Nuss

Highlights of Coastal Waves 1996

Some of the highlights of an experiment designed to study coastal atmospheric phenomena along the California coast (Coastal Waves 1996 experiment) are described. This study was designed to address ...

Coastally Trapped Wind Reversals: Progress toward Understanding

Abstract Coastally trapped wind reversals along the U.S. west coast, which are often accompanied by a northward surge of fog or stratus, are an important warm—season forecast problem due to their impact on coastal maritime activities and airport operations. Previous studies identified several possible dynamic mechanisms that could be responsible for producing these events, yet observational and modeling limitations at the time left these competing interpretations open for debate. In an effort to improve our physical understanding, and ultimately the prediction, of these events, the Office of Naval Research sponsored an Accelerated Research Initiative in Coastal Meteorology during the years 1993—98 to study these and other related coastal meteorological phenomena. This effort included two field programs to study coastally trapped disturbances as well as numerous modeling studies to explore key dynamic mechanisms. This paper describes the various efforts that occurred under this program to provide an advanc...

Adjustment of the Summer Marine Boundary Layer around Point Sur, California

An instrumented C-130 aircraft flew over water around Point Sur, California, on 17 June 1996 under strong northwest wind conditions and a strong marine inversion. Patterns were flown from 30- to 1200-m elevation and up to 120 km offshore. Nearshore, marine air accelerated past Point Sur, reaching a surface maximum of 17 ms 21 in the lee. Winds measured over water in and above the marine layer were alongshore with no significant cross-shore flow. Sea level pressure, 10-m air temperature, and air temperature inversion base generally decreased toward the coast and were an absolute minimum just downcoast of the wind speed maximum. The sea surface temperature also decreased toward the coast, but was an absolute minimum directly off Point Sur. The nearcoast, air temperature inversion base height was 400 m north of Point Sur, decreased to a minimum of 50 m in the lee of Point Sur, then increased farther to the south. Wind speeds were at a maximum centered along the air temperature inversion base; the fastest was 27 m s 21 in the lee of Point Sur. Using a Froude number calculation that includes the lower half of the capping layer, the marine layer in the area is determined to have been supercritical. Most of the marine layer had Froude numbers between 1.0 and 2.0 with the extreme range of 0.8‐2.8. Temperatures in the air temperature inversion in the lee were substantially greater than elsewhere, modifying the surface pressure gradient. The overall structure was a hydraulic supercritical expansion fan in the lee of Point Sur under the influence of rotation and surface friction. The Naval Research Laboratory nonhydrostatic Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) indicated a broad, supercritical marine boundary layer moving to the south along central California and Point Sur during the aircraft flight. The marine boundary layer thinned and accelerated into the lee of Point Sur, which was the site of the fastest sea level wind speed along central California. Isotherms dip and speeds decreased in the lee of Point Sur in the capping inversion well above the marine layer. COAMPS forecasted a compression shock wave initiating off the upwind side of the topography behind Point Sur and other coastal points to the north. Evidence from the model and the aircraft supports the existence of an oblique hydraulic jump on the north side of Point Sur.

Observations and Analysis of the 10–11 June 1994 Coastally Trapped Disturbance

Abstract A coastally trapped disturbance (CTD), characterized by southerly flow at the surface on 10–11 June 1994, was observed from the California Bight to Bodega Bay during a field experiment along the California coast. (North–south approximates the coast-parallel direction.) Data from a special observational network of wind profilers, radio acoustic sounding systems, special surface data, balloon ascents, and a research aircraft were used with satellite and synoptic data to explore both the CTD structure and the regional-scale changes before the event. The disruption of the climatological northerly flow along the central California coast, which preconditioned the area for the development of a CTD, began with the eastward movement of a surface high into Washington and Oregon and the amplification of a thermal low in northern California. As with most CTDs in the region, this occurred over the 2–3 days preceding the CTD’s initiation. These large-scale changes caused westward advection of warm continental ...

Kelvin Waves and Internal Bores in the Marine Boundary Layer Inversion and Their Relationship to Coastally Trapped Wind Reversals

Abstract Detailed observations of a coastally trapped disturbance, or wind reversal, on 10–11 June 1994 along the California coast provide comprehensive documentation of its structure, based on aircraft, wind profiler, radio acoustic sounding system, and buoy measurements. Unlike the expectations from earlier studies based on limited data, which concluded that the deepening of the marine boundary layer (MBL) was a key factor, the 1994 data show that the perturbation was better characterized as an upward thickening of the inversion capping the MBL. As the event propagated over a site, the reversal in the alongshore wind direction occurred first within the inversion and then 3–4 h later at the surface. A node in the vertical structure (defined here as the altitude of zero vertical displacement) is found just above the inversion base, with up to 200-m upward displacements of isentropic surfaces above the node, and 70-m downward displacements below. Although this is a single event, it is shown that the vertic...

Data quality issues in visualization

Recent efforts in visualization have concentrated on high volume data sets from numerical simulations and medical imaging. There is another large class of data, characterized by their spatial sparsity with noisy and possibly missing data points, that also need to be visualized. Two places where these type of data sets can be found are in oceanographic and atmospheric science studies. In such cases, it is not uncommon to have on the order on one percent of sampled data available within a space volume. Techniques that attempt to deal with the problem of filling in the holes range in complexity from simple linear interpolation to more sophisticated multiquadric and optimal interpolation techniques. These techniques will generally produce results that do not fully agree with each other. To avoid misleading the users, it is important to highlight these differences and make sure the users are aware of the idiosyncrasies of the different methods. This paper compares some of these interpolation techniques on sparse data sets and also discusses how other parameters such as confidence levels and drop-off rates may be incorporated into the visual display.

CASPER: Coupled Air-Sea Processes and Electromagnetic (EM) ducting Research

CapsuleCASPER objective is to improve our capability to characterize the propagation of radio frequency (RF) signals through the marine atmosphere with coordinated efforts in data collection, data analyses, and modeling of the air-sea interaction processes, refractive environment, and RF propagation.

Eighth Cyclone Workshop Scientific Summary, Val Morin, Quebec, Canada, 12–16 October 1992

The Eighth Cyclone Workshop was held at the Far Hills Inn and Conference Center in Val Morin, Quebec, Canada, 12–16 October 1992. The workshop was arranged around several scientific themes of current research interest. The most widely debated theme was the applicability of “potential vorticity thinking” to theoretical, observational, and numerical studies of the life cycle of cyclones and the interaction of these cyclones with their environment on all spatial and temporal scales. A combination of invited and contributed talks, with preference given to younger scientists, made up the workshop.

Terrain-influenced local wind forecasting for the Sasebo typhoon haven: Improved empirical techniques

Although the Sasebo, Japan harbor is usually a “typhoon haven” from tropical cyclone (TC) winds due to terrain-blocking effects, in rare cases damaging winds occur that may be attributed to terrain channeling. An empirical parametric model technique is developed and tested that includes consideration of the TC wind structure, land frictional effects, and terrain influences affecting the maximum wind speeds in the harbor when TCs pass within 200 nautical miles of Sasebo. The terrain influence is represented by two sets of wind direction-dependent acceleration factors. The first set, which is directly from the ratio of the local wind to the adjusted parametric wind for TCs passages during 2003–2010, provides mean values that represent the terrain blocking and channeling effects, but the variability with wind direction may be suspect. The second set derived from a large sample of reanalysis winds not limited to TCs has better variability properties, but is not easily related to just the TC passages. A new nomogram modified to include TC wind structure has higher estimates of Sasebo sustained winds for some TC tracks that may be related to terrain influences, but is limited due to the number of TC structure estimates in the developmental sample. These empirical models have the advantage of ease and low cost for future use in also estimating the combined uncertainty in the local winds in Sasebo harbor due to TCs.

Environmental Science Computing

The sections in this article are 1 Numerical Modeling 2 Display and Visualization Requirements 3 Instrumentation and Data Collection 4 Numerical Modeling 5 Display and Visualization Software 6 Data Collection and Management Software 7 Future Directions