Wind energy has been growing steadily in the U.S. and worldwide in the past decades. As wind farms are projected to increase in size and number, however, concerns are rising about possible undesirable effects of wind turbines near the Earth's surface. The literature is highly divided about what these effects could be, including warming, cooling, both, or neither. Only one mechanism, however, has been widely accepted (but never tested) to explain how wind turbines affect the lower boundary layer, namely that turbulence generated in wind turbine wakes enhances vertical mixing near the ground. Wakes are plume-like volumes downwind of wind turbines that are characterised by lower wind speeds and higher turbulent kinetic energy (TKE) than the undisturbed upwind flow. The few observational campaigns that have measured changes in near-surface properties by wind turbines have not provided an answer with respect to vertical mixing near the ground. To fill this knowledge gap, the VERTEX (VERTical Enhanced miXing) measurement campaign was conducted in August-October 2016 near a large wind turbine in coastal Delaware, using 15 surface flux towers, a 50-m meteorological tower, a radiometer, and two scanning lidars. During VERTEX, lidar scans and a wake detection algorithm were used to detect wake events and identify which sites were affected by the wake of the wind turbine. TKE, momentum and heat fluxes near the ground were compared between the sites below the wake and those outside of it. Preliminary findings based on two case studies (30 August and 20 September 2016) suggest a lack of enhancement of vertical mixing near the ground.

The Niwot Ridge Subalpine Forest AmeriFlux site (US-NR1) has been measuring eddy-covariance ecosystem fluxes of carbon dioxide, heat, and water vapor since 1 November 1998. Throughout this 17-year period there have been changes to the instrumentation and improvements to the data acquisition system. Here, in Part 1 of this three-part series of papers, we describe the hardware and software used for data-collection and metadata documentation. We made changes to the data acquisition system that aimed to reduce the system complexity, increase redundancy, and be as independent as possible from any network outages. Changes to facilitate these improvements were (1) switching to a PC/104-based computer running the National Center for Atmospheric Research (NCAR) In-Situ Data Acquisition Software (NIDAS) that saves the high-frequency data locally and over the network, and (2) time-tagging individual 10 Hz serial data samples using network time protocol (NTP) coupled to a GPS-based clock, providing a network-independent, accurate time base. Since making these improvements almost 2 years ago, the successful capture of high-rate data has been better than 99.98 %. We also provide philosophical concepts that shaped our design of the data system and are applicable to many different types of environmental data collection.

The second Meteor Crater Experiment (METCRAX II) was conducted in October 2013 at Arizona's Meteor Crater. The experiment was designed to investigate nighttime downslope windstorm-type flows that form regularly above the inner southwest sidewall of the 1.2-km diameter crater as a southwesterly mesoscale katabatic flow cascades over the crater rim. The objective of METCRAX II is to determine the causes of these strong, intermittent, and turbulent inflows that bring warm-air intrusions into the southwest part of the crater. This article provides an overview of the scientific goals of the experiment; summarizes the measurements, the crater topography, and the synoptic meteorology of the study period; and presents initial analysis results.

The construction and deployment of a portable trace-gas measurement system (TGaMS) is described. The air-collection system (dubbed HYDRA) collects air samples from 18 different locations and was connected to either one or two LI-COR LI-7000 gas analyzers to measure CO2. An in situ "field calibration" method, that uses four calibration gases with an uncertainty on the order of +/- 0.1 mu mol mol(-1) relative to the WMO CO2 mole fraction scale, revealed CO2 output from the LI-7000 had a slightly nonlinear relationship relative to the CO2 concentration of the calibration gases. The sensitivity of the field-calibrated CO2 to different forms of the field-calibration equation is investigated. To evaluate TGaMS performance, CO2 from collocated inlets, portable gas cylinders, and nearby independent CO2 instruments are compared. Results are as follows: 1) CO2 measurements from HYDRA multiple inlets are feasible with a reproducibility of +/- 0.4 mu mol mol(-1) (based on the standard deviation of the CO2 difference between collocated inlets when HYDRA was operating with two LI-7000s); 2) CO2 differences among the various field-calibration equations were on the order of +/- 0.3 mu mol mol(-1); and 3) comparison of midday hourly CO2 measurements at 30 m AGL between TGaMS and an independent high-accuracy CO2 measurement system (within 300 m of TGaMS) had a median difference and standard deviation of 0.04 +/- 0.81 mu mol mol(-1) over two months.

Multiplate radiation shield errors are examined using the following techniques: 1) ray tracing analysis, 2) wind tunnel experiments, 3) numerical flow simulations, and 4) field testing. The authors' objectives are to develop guidelines for radiation shield and temperature sensor design, to build an improved shield, and to determine factors that influence radiational heating errors. Guidelines For reducing radiational hearing errors are given that are based on knowledge of the temperature sensor to be used, with the shield chosen to match the sensor design.A new class of shield called a part-rime aspirated multiplate radiation shield is introduced. This type of shield consists of a multiplate design usually operated in a passive manner but equipped with fan-forced aspiration capability to be used when necessary (e.g., low wind speed). A prototype shield reduced radiational heating errors from 2 degrees to 1.2 degrees C. In addition, nighttime low wind speed errors were reduced from 1.6 degrees to 0.3 degrees C. Existing passive shields may be modified to incorporate part-time aspiration, thus making them cost effective.

The Portable Automated Mesonet II(PAM II) system was developed by NCAR to provide surface mesoscale data for the research needs of the atmospheric science community. The PAM system has 60 remote stations with planned growth to 300. In such a distributed system, data communication is a vital subsystem and, since it dictates some key system constraints, deserves special attention. The NOAA/NESDIS satellite, GOES, is used to link the remote stations to the base stations. This provides very wide areal coverage but limits the data rate.Special attention was given to the design of the sensor subsystems to minimize the possibility for human error and to maintain the calibration in field conditions while using interchangeable modules. This was achieved by using a dedicated microprocessor in the psychrometer and the barometer. The microprocessor in the sensor modules controls the sensors, applies the individual calibration coefficients, and transmits the sensor data to the master data acquisition module.The master base station collects the data, archives them and generates graphic displays of real-time or archived data for system control and scientific analysis. The field base stations provide real-time data for the user in the field environment.