William O. J. Brown

Regional Environmental Prediction Over the Pacific Northwest

Abstract This paper examines the potential of regional environmental prediction by focusing on the local forecasting effort in the Pacific Northwest. A consortium of federal, state, and local agencies have funded the development and operation of a multifaceted numerical prediction system centered at the University of Washington that includes atmospheric, hydrologic, and air quality models, the collection of real-time regional weather data sources, and a number of realtime applications using both observations and model output. The manuscript reviews northwest modeling and data collection systems, describes the funding and management system established to support and guide the effort, provides some examples of regional real-time applications, and examines the national implications of regional environmental prediction.

The Persistent Cold-Air Pool Study

The Persistent Cold-Air Pool Study (PCAPS) was conducted in Utahs Salt Lake valley from 1 December 2010 to 7 February 2011. The field campaigns primary goal was to improve understanding of the physical processes governing the evolution of multiday cold-air pools (CAPs) that are common in mountain basins during the winter. Meteorological instrumentation deployed throughout the Salt Lake valley provided observations of the processes contributing to the formation, maintenance, and destruction of 10 persistent CAP episodes. The close proximity of PCAPS field sites to residences and the University of Utah campus allowed many undergraduate and graduate students to participate in the study. Ongoing research, supported by the National Science Foundation, is using the PCAPS dataset to examine CAP evolution. Preliminary analyses reveal that variations in CAP thermodynamic structure are attributable to a multitude of physical processes affecting local static stability: for example, synoptic-scale processes impact ...

Quality-Controlled Upper-Air Sounding Dataset for DYNAMO/CINDY/AMIE: Development and Corrections

AbstractThe upper-air sounding network for Dynamics of the Madden–Julian Oscillation (DYNAMO) has provided an unprecedented set of observations for studying the MJO over the Indian Ocean, where coupling of this oscillation with deep convection first occurs. With 72 rawinsonde sites and dropsonde data from 13 aircraft missions, the sounding network covers the tropics from eastern Africa to the western Pacific. In total nearly 26 000 soundings were collected from this network during the experiment’s 6-month extended observing period (from October 2011 to March 2012). Slightly more than half of the soundings, collected from 33 sites, are at high vertical resolution. Rigorous post–field phase processing of the sonde data included several levels of quality checks and a variety of corrections that address a number of issues (e.g., daytime dry bias, baseline surface data errors, ship deck heating effects, and artificial dry spikes in slow-ascent soundings).Because of the importance of an accurate description of ...

The Deep Propagating Gravity Wave Experiment (DEEPWAVE): An Airborne and Ground-Based Exploration of Gravity Wave Propagation and Effects from Their Sources throughout the Lower and Middle Atmosphere

AbstractThe Deep Propagating Gravity Wave Experiment (DEEPWAVE) was designed to quantify gravity wave (GW) dynamics and effects from orographic and other sources to regions of dissipation at high altitudes. The core DEEPWAVE field phase took place from May through July 2014 using a comprehensive suite of airborne and ground-based instruments providing measurements from Earth’s surface to ∼100 km. Austral winter was chosen to observe deep GW propagation to high altitudes. DEEPWAVE was based on South Island, New Zealand, to provide access to the New Zealand and Tasmanian “hotspots” of GW activity and additional GW sources over the Southern Ocean and Tasman Sea. To observe GWs up to ∼100 km, DEEPWAVE utilized three new instruments built specifically for the National Science Foundation (NSF)/National Center for Atmospheric Research (NCAR) Gulfstream V (GV): a Rayleigh lidar, a sodium resonance lidar, and an advanced mesosphere temperature mapper. These measurements were supplemented by in situ probes, dropson...

The canopy horizontal array turbulence study

The Canopy Horizontal Array Turbulence Study (CHATS) took place in spring 2007 and is the third in the series of Horizontal Array Turbulence Study (HATS) experiments. The HATS experiments have been instrumental in testing and developing subfilterscale (SFS) models for large-eddy simulation (LES) of planetary boundary layer (PBL) turbulence. The CHATS campaign took place in a deciduous walnut orchard near Dixon, California, and was designed to examine the impacts of vegetation on SFS turbulence. Measurements were collected both prior to and following leafout to capture the impact of leaves on the turbulence, stratification, and scalar source/sink distribution. CHATS utilized crosswind arrays of fast-response instrumentation to investigate the impact of the canopy-imposed distribution of momentum extraction and scalar sources on SFS transport of momentum, energy, and three scalars. To directly test and link with PBL parameterizations of canopy-modified turbulent exchange, CHATS also included a 30-m profile ...

Observations and Numerical Simulations of Subrotor Vortices during T-REX

High-resolution observations from scanning Doppler and aerosol lidars, wind profiler radars, as well as surface and aircraft measurements during the Terrain-induced Rotor Experiment (T-REX) provide the first comprehensive documentation of small-scale intense vortices associated with atmospheric rotors that form in the lee of mountainous terrain. Although rotors are already recognized as potential hazards for aircraft, it is proposed that these small-scale vortices, or subrotors, are the most dangerous features because of strong wind shear and the transient nature of the vortices. A life cycle of a subrotor event is captured by scanning Doppler and aerosol lidars over a 5-min period. The lidars depict an amplifying vortex, with a characteristic length scale of 500–1000 m, that overturns and intensifies to a maximum spanwise vorticity greater than 0.2 s−1. Radar wind profiler observations document a series of vortices, characterized by updraft/downdraft couplets and regions of enhanced reversed flow, that are generated in a layer of strong vertical wind shear and subcritical Richardson number. The observations and numerical simulations reveal that turbulent subrotors occur most frequently along the leading edge of an elevated sheet of horizontal vorticity that is a manifestation of boundary layer shear and separation along the lee slopes. As the subrotors break from the vortex sheet, intensification occurs through vortex stretching and in some cases tilting processes related to three-dimensional turbulent mixing. The subrotors and ambient vortex sheet are shown to intensify through a modest increase in the upstream inversion strength, which illustrates the predictability challenges for the turbulent characterization of rotors.

The dryline on 22 May 2002 during IHOP_2002: Convective-scale measurements at the profiling site

Abstract A detailed analysis of the structure of a double dryline observed over the Oklahoma panhandle during the first International H2O Project (IHOP_2002) convective initiation (CI) mission on 22 May 2002 is presented. A unique and unprecedented set of high temporal and spatial resolution measurements of water vapor mixing ratio, wind, and boundary layer structure parameters were acquired using the National Aeronautics and Space Administration (NASA) scanning Raman lidar (SRL), the Goddard Lidar Observatory for Winds (GLOW), and the Holographic Airborne Rotating Lidar Instrument Experiment (HARLIE), respectively. These measurements are combined with the vertical velocity measurements derived from the National Center for Atmospheric Research (NCAR) Multiple Antenna Profiler Radar (MAPR) and radar structure function from the high-resolution University of Massachusetts frequency-modulated continuous-wave (FMCW) radar to reveal the evolution and structure of the late afternoon double-dryline boundary layer...

Cross-correlation ratio method to estimate cross-beam wind and comparison with a full correlation analysis

[1] Cross-beam wind is usually estimated using a full correlation analysis (FCA) method applied to signals from spaced antennas. In this paper we present a cross-correlation ratio (CCR) method for wind measurements. The CCR method is illustrated using theory, and data obtained with the National Center for Atmospheric Research’s multiple antenna profiling radar. The standard errors of estimated cross-beam wind using CCR and a FCA are studied based on a rigorous analysis of the variance of the cross-correlation estimates. The results of the analysis are compared with previous works. It is shown that the current method is easy to implement and has smaller error for receiving antenna spacing small compared to the transmitting antenna dimensions. INDEX TERMS: 1869 Hydrology: Stochastic processes; 6952 Radio Science: Radar atmospheric physics; 6969 Radio Science: Remote sensing; 6974 Radio Science: Signal processing; 6994 Radio Science: Instruments and techniques; KEYWORDS: spaced antenna technique, cross-beam wind, cross-correlation, cross-correlation ratio (CCR), full correlation analysis (FCA), wind profilers

Vertical Air Motion from T-REX Radiosonde and Dropsonde Data

Abstract The primary goal of this study is to explore the potential for estimating the vertical velocity (VV) of air from the surface to the stratosphere, using widely available radiosonde and dropsonde data. The rise and fall rates of radiosondes and dropsondes, respectively, are a combination of the VV of the atmosphere and still-air rise–fall rates. The still-air rise–fall rates are calculated using basic fluid dynamics and characteristics of radiosonde and dropsonde systems. This study validates the technique to derive the VV from radiosonde and dropsonde data and demonstrates its value. This technique can be easily implemented by other users for various scientific applications. The technique has been applied to the Terrain-induced Rotor Experiment (T-REX) dropsonde and radiosonde data. Comparisons among radiosonde, dropsonde, aircraft, and profiling radar vertical velocities show that the sonde-estimated VV is able to capture and describe events with strong vertical motions (larger than ∼1 m s−1) obs...

Coevolution of Down-Valley Flow and the Nocturnal Boundary Layer in Complex Terrain

An enhanced National Center for Atmospheric Research (NCAR) integrated sounding system (ISS) was deployed as part of the Vertical Transport and Mixing (VTMX) field experiment, which took place in October of 2000. The enhanced ISS was set up at the southern terminus of the Great Salt Lake Valley just north of a gap in the Traverse Range (TR), which separates the Great Salt Lake and Utah Lake basins. This location was chosen to sample the dynamic and thermodynamic properties of the flow as it passes over the TR separating the two basins. The enhanced ISS allowed for near-continuous sampling of the nocturnal boundary layer (NBL) and low-level winds associated with drainage flow through the gap in the TR. Diurnally varying winds were observed at the NCAR site on days characterized by weak synoptic forcing and limited cloud cover. A down-valley jet (DVJ) was observed on about 50% of the nights during VTMX, with the maximum winds usually occurring within 150 m of the surface. The DVJ was associated with abrupt warming at low levels as a result of downward mixing and vertical transport of warm air from the inversion layer above. Several processes were observed to contribute to vertical transport and mixing at the NCAR site. Pulses in the strength of the DVJ contributed to vertical transport by creating localized areas of low-level convergence. Gravity waves and Kelvin–Helmholtz waves, which facilitated vertical mixing near the surface and atop the DVJ, were observed with a sodar and an aerosol backscatter lidar that were deployed as part of the enhanced ISS. The nonlocal nature of the processes responsible for generating turbulence in strongly stratified surface layers in complex terrain confounds surface flux parameterizations typically used in mesoscale models that rely on Monin–Obukhov similarity theory. This finding has major implications for modeling NBL structure and drainage flows in regions of complex terrain.