Influence of large scale oscillations on upwelling-favorable coastal wind off central Chile

This is the publisher's version, also available electronically from http://onlinelibrary.wiley.com/doi/10.1029/2012JD018016/abstract;jsessionid=258F6DB5E58E8470DF18F233E18F918C.f01t02.Along the central coast of Chile is typically equatorward, upwelling-favorable wind associated with the southeast Pacific anticyclone. A coastal low-level jet often develops, and its wind speed is mostly controlled by the meridional pressure gradient. While the low-level jet is a mesoscale feature forced by an interaction between synoptic conditions and coastal topography, regional sea level pressure anomalies are associated with changes of the Antarctic, Madden Julian, and El Niño–Southern Oscillation. The connection between the alongshore wind and changes to the large-scale circulation is examined and quantified using 31 years of the Climate Forecast System Reanalysis, which resolves coastal features better than previous, coarser analyses. Composites based on each index reveal the modulation of the sea level pressure and significant alongshore wind anomalies of ±0.5–1.5 m s−1 that correlate well to meridional surface pressure gradient changes and are centered near 35°S. Constructive and destructive interference exists between the three indices that either enhance or cancel the alongshore wind anomaly. During favorable upwelling conditions the distribution of meridional wind is generally clustered around positive anomalies with a tail toward negative values, representing a stronger and persistent anticyclone. During unfavorable upwelling conditions the anomalies are generally more normally distributed, representing a weaker anticyclone and the passage of more cyclones

A Study of the Forcing of the 22–25 June 2006 Coastally Trapped Wind Reversal Based on Numerical Simulations and Aircraft Observations

This is the publisher's version, also available electronically from http://journals.ametsoc.org/doi/abs/10.1175/2008MWR2361.1.Coastally trapped wind reversals (CTWRs) occur periodically in the lowest several hundred meters of the marine boundary layer west of California and disrupt the northerly flow that typically occurs during summer. South winds and coastal fog or low stratus accompany the CTWR, which propagates northward along the coast. A CTWR was observed off the California coast during late June 2006 that originated in the California Bight and propagated northward to Cape Mendocino during the subsequent 2-day period. This CTWR event was explored by the University of Wyoming King Air research aircraft to document the primary characteristics of the wind reversal. Numerical simulations of the CTWR event using the Weather Research and Forecast modeling system were conducted to compare with observations and to provide a broader picture of the CTWR structure and evolution. An analysis of the forcing mechanisms responsible for the June 2006 CTWR event is presented. It is demonstrated that the mature CTWR for this case is a density current propagating northward along the coast in response to the density gradient found to the north of the CTWR with maximum speed during the nighttime hours. Establishment of the density contrast is largely a result of cloud-top longwave radiative cooling of the stratus that accompanies the CTWR, which serves to cool and deepen the boundary layer during the night. Density contrast between the cloudy CTWR air and the ambient environment is enhanced by the persistent offshore flow to the north of the CTWR with attendant warming and a flattening of the horizontal pressure gradient in the marine layer

Cessation of the 22–25 June 2006 Coastally Trapped Wind Reversal

This is the publisher's version, also available electronically from http://journals.ametsoc.org/doi/abs/10.1175/2010JAMC2242.1.Coastally trapped wind reversals (CTWRs) occur periodically in the marine boundary layer off the western coast of the United States and dramatically change the low-level wind regime and coastal weather. Southerly flow becomes established with the passage of a CTWR along with cooler temperatures and a low stratus deck in a narrow band along the coast. CTWRs can propagate northward along the coast for hundreds of kilometers. A strong CTWR commenced in southern California on 22 June 2006 and moved north along the California coastline before stalling at Cape Mendocino on 24 June 2006. A transcritical Froude number differentiates the CTWR layer from the climatologically favored northern wind regime to the north of Cape Mendocino and indicates a barrier to the movement of a density current. A well-defined cloud boundary is present as detected by radar and satellite imagery and sharp gradients exist in the basic-state parameters as measured by instrumented aircraft. As the Pacific high migrates back offshore, the horizontal pressure field near Cape Mendocino becomes increasingly adverse to the continued northward movement of the CTWR layer and typical summertime conditions are reestablished. Observations and modeling results show that the cessation phase of this CTWR was characterized by a surprising lack of topographic blocking due to the mountainous coastal terrain and Cape Mendocino massif. The horizontal pressure field over the ocean to the north of the CTWR was the key impeding force to continued propagation of this event

Marine boundary layer over the subtropical southeast Pacific during VOCALS-REx – Part 1: Mean structure and diurnal cycle

This is the publisher's version, also available electronically from http://www.atmos-chem-phys.net/10/4491/2010/acp-10-4491-2010.html.Atmospheric subsidence over the subtropical southeast Pacific (SEP) leads to a low-level anticyclonic circulation, a cool sea surface and a cloud-topped marine boundary layer (MBL). Observations in this region from a major field campaign during October and November 2008, the VOCALS Regional Experiment, provide ample data to characterize the lower atmospheric features over the SEP. The observations are also useful to test the ability of an area-limited, high-resolution atmospheric model to simulate the SEP conditions. Observations and model-results (where appropriate) improve the characterization of the mean state (Part 1) and variability (Part 2) of the lower troposphere including circulation, MBL characteristics and the upsidence wave. Along 20° S the MBL is generally deeper offshore (1600 m at 85° W) but there is also considerable variability. MBL depth and variability decrease towards the coast and maximum inversion strength is detected between 74–76° W. Weather Research and Forecasting (WRF) simulations underestimate MBL height the most near the coast but improve offshore. Southeasterly trades prevail within the MBL although the wind speed decreases toward the coast. Above the MBL along the coast of Chile, flow is northerly, has a maximum at 3 km, and extends westward to ~74° W, apparently due to the mechanical blocking exerted by the Andes upon the westerly flow aloft. Mean MBL features along northern Chile (18–25° S) are remarkably similar (e.g., MBL depth just below 1 km) in spite of different SST. Observed diurnal cycles of the temperature at the coast and further offshore exhibit a number of conspicuous features that are consistent with the southwestward propagation of an upsidence wave initiated during late evening along the south Peru coast. Furthermore, the passage of the vertical motion results in either constructive or deconstructive interference with the radiatively-forced diurnal cycle of MBL depth. Interference is clearly seen in the soundings at Iquique which are driven by a strong upsidence wave contrary to the radiation-driven cycle, leading to a diurnal cycle opposite of the other sites. Because WRF simulations have a lower MBL height, the speed of the simulated gravity wave is slower than observations and accounts for most of the discrepancy between observed and simulated phase speeds

Marine boundary layer over the subtropical southeast Pacific during VOCALS-REx – Part 2: Synoptic variability

This is the publisher's version, also available electronically from http://www.atmos-chem-phys.net/10/4507/2010/acp-10-4507-2010.htmlIn the second part of this work we study the day-to-day variability of the marine atmospheric boundary layer (MBL) over the subtropical southeast Pacific using primarily results from a numerical simulation that covered the whole VOCALS-REx period (October–November 2008). In situ and satellite-derived observations of the MBL height in the offshore region indicate rapid, significant variations (from 500 m to 1700 m a.s.l. over a few days) during October. These MBL changes are connected with the passage of midlatitude troughs that altered the large-scale environment over the VOCALS-REx region. In contrast, the synoptic forcing and MBL changes were less prominent during November. Modelled and observed MBL depth at Point Omega (20° S, 85° W) compare quite well during October (but the simulation is on average 200 m lower) while in November the simulation does not perform as well. In the prognostic local MBL height equation the height change, the horizontal MBL height advection, and the large scale vertical velocity at MBL top are calculated explicitly from the simulation. The entrainment velocity is calculated as the residual of the other terms in the equation. While the vertical velocity and residual terms are opposing and generally have the largest magnitude on average, it is the variability in the advection that explains most of the large changes in the MBL depth. Examination of several cases during VOCALS-REx suggests that the advective term is in turn largely controlled by changes in wind direction, driven by midlatitude activity, acting on a MBL that generally slopes down toward the coast. In one phase, the subtropical anticyclone is reinforced and extends toward the Chilean coast, leading to easterly wind that advects low MBL heights from the coast as far as Point Omega. The opposite phase occurs after the passage of an extratropical cyclone over southern Chile, leading to southwesterly wind that advects a deeper MBL towards subtropical latitudes

E-Business for Entrepreneurs: A Turnkey Experiential Based Course for Teaching Faculty

This workshop is targeted at faculty teaching entrepreneurship courses who desire a hands-on experiential approach. Specific entrepreneurship courses that this method would apply to include, but are not limited to, introduction to entrepreneurship, opportunity analysis, and business model courses. The course materials are designed for non-technical instructors and students, but can be customized for those with significant tech skills. Each part of the e-Business model is covered individually and as an integrated part of the e-Business. Key e-Business processes are implemented and evaluated. Students come away from the course understanding how to run the online portion of a business

Diagnosis of the Forcing and Structure of the Coastal Jet near Cape Mendocino Using In Situ Observations and Numerical Simulations

This is the publisher's version, also available electronically from http://journals.ametsoc.org/doi/abs/10.1175/JAM2546.1.Several flights were conducted by the University of Wyoming King Air near Cape Mendocino, California, during June 2004 to examine finescale features of the coastal low-level jet (CJ) that frequently forms during summer over the ocean off the West Coast of the United States. The primary goal of these flights was to measure the horizontal pressure gradient force (PGF) and hence to determine the forcing of the CJ directly. By flying a series of redundant legs on an isobaric surface, heights of the pressure surface can be obtained from radar altimeter measurements and refined position estimates from an onboard global positioning system receiver. The slope of the isobaric surface height is proportional to the PGF. Results are shown for the 22 June 2004 case study conducted to the south of Cape Mendocino. The forcing of a CJ under weak synoptic forcing and the role of the elevated terrain near Cape Mendocino are explored. Ten isobaric legs approximately 70 km in length and directed east–west were conducted near the level of the maximum CJ wind speed. The vertical structure of the CJ was obtained from sawtooth legs conducted along an east–west flight leg. Numerical simulations have been performed for this case using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) for comparison with in situ measurements. Model simulations show pressure perturbations in the vicinity of the cape as the northerly winds associated with the CJ interact with the coastal topography. Close agreement is found between in situ measurements and MM5 analyses of the various state parameters and the PGF along the east–west flight track in the lee of Cape Mendocino. Strong variation in the PGF is observed along the flight path. Large ageostrophic accelerations are present in response to the adjustment of the CJ with Cape Mendocino, reflecting the force imbalance between the observed PGF and Coriolis force

Airborne Observations of a Catalina Eddy

This is the publisher's version, also available electronically from http://journals.ametsoc.org/doi/abs/10.1175/MWR-D-13-00029.1Summertime low-level winds over the ocean adjacent to the California coast are typically from the north, roughly parallel to the coastline. Past Point Conception the flow often turns eastward, thereby generating cyclonic vorticity in the California Bight. Clouds are frequently present when the cyclonic motion is well developed and at such times the circulation is referred to as a Catalina eddy. Onshore flow south of the California Bight associated with the eddy circulation can result in a thickening of the low-level marine stratus adjacent to the coast. During nighttime hours the marine stratus typically expands over a larger area and moves northward along the coast with the cyclonic circulation. A Catalina eddy was captured during the Precision Atmospheric Marine Boundary Layer Experiment in June of 2012. Measurements were made of the cloud structure in the marine layer and the horizontal pressure field associated with the cyclonic circulation using the University of Wyoming King Air research aircraft. Airborne measurements show that the coastal mountains to the south of Los Angeles block the flow, resulting in enhanced marine stratus heights and a local pressure maximum near the coast. The horizontal pressure field also supports a south–north movement of marine stratus. Little evidence of leeside troughing south of Santa Barbara, California, was observed for this case, implying that the horizontal pressure field is forced primarily through topographic blocking by the coastal terrain south of Los Angeles, California, and the ambient large-scale circulation associated with the mean flow