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William J. Massman

Abstract

The neutral buoyant oscillation of a spherical balloon floating in the upper troposphere or lower stratosphere is predicted to be between 3 and 4 min for the simplest theoretical case. Variance spectra of balloonborne sensor data, as well as ground-based radar data, show the period of this motion to be roughly between 3 and 6 min. Other balloon oscillations with much longer periods are shown to be largely in response to sinusoidal motions of its equilibrium density surface rather than in response to sinusoidal variations of the vertical velocity of the atmosphere. A term which accounts for the time dependence of the balloon's equilibrium density surface is explicitly included in the equation of motion for a spherical balloon and various solutions are then presented.

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William J. Massman and Karl F. Zeller

Abstract

A fast algorithm to correct for the non-cosine response of the three-component Gill Propeller Anemometer is presented. Its intended use is for real time in-situ correction of the horizontal and vertical components of the wind velocity for high frequency turbulent flux measurement. Comparisons between this new method and the original Horst correction (Horst 1973) are presented. It is also shown that without a correction for the non-cosine response, the Gill propeller anemometers can underestimate heat and momentum fluxes by about 30%.

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Nadav Levanon, Robert A. Oehlkers, Scott D. Ellington, William J. Massman, and Verner E. Suomi

Abstract

This paper presents measured data related to the question of how constant are “constant-level” balloons. The simultaneous use of two balloon-borne instruments, a radio altimeter and a pressure sensor, operating on entirely different principles, help to distinguish between sensor noise and true balloon altitude fluctuation. Four types of superpressure balloon altitude changes at the level of 150 mb were observed: (i) neutral buoyancy oscillations (NBO) with a period of about 200 sec and with peak-to-peak amplitude of up to 50 m, (ii) short-term oscillations with a period of ∼1.2 hr and peak-to-peak amplitudes of up to 80 m, (iii) diurnal half-cycle (day observations only) with an amplitude of up to 150 m, and (iv) possible trends of up to 120 m per day.

The data were obtained during four superpressure-balloon 150-mb flights in the Southern Hemisphere. These balloon flights were part of a test program for the TWERL Experiment. NCAR's GHOST balloons and navigation system were used, with the final version of the TWERLE radio altimeter and an early version of the pressure sensor.

The data are presented with a discussion of their limitations, mainly aliasing, ambiguity, and the absolute accuracy of the pressure sensor. A theoretical analysis of the NBO, with a spectrum analysis of supporting ground radar data, are given in the Appendix.

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John M. Frank, William J. Massman, Edward Swiatek, Herb A. Zimmerman, and Brent E. Ewers

Abstract

Sonic anemometry is fundamental to all eddy-covariance studies of surface energy and ecosystem carbon and water balance. Recent studies have shown that some nonorthogonal anemometers underestimate vertical wind. Here it is hypothesized that this is due to a lack of transducer and structural shadowing correction. This is tested with a replicated intercomparison experiment between orthogonal (K-probe, Applied Technologies, Inc.) and nonorthogonal (A-probe, Applied Technologies, Inc.; and CSAT3 and CSAT3V, Campbell Scientific, Inc.) anemometer designs. For each of the 12 weeks, five randomly selected and located anemometers were mounted both vertically and horizontally. Bayesian analysis was used to test differences between half-hourly anemometer measurements of the standard deviation of wind (σu, συ, and σw) and temperature, turbulent kinetic energy (TKE), the ratio between vertical/horizontal TKE (VHTKE), and sensible heat flux (H). Datasets were analyzed with various applications of transducer shadow correction. Using the manufacturer’s current recommendations, orthogonal anemometers partitioned higher VHTKE and measured about 8%–9% higher σw and ~10% higher H. This difference can be mitigated by adding shadow correction to nonorthogonal anemometers. The horizontal manipulation challenged each anemometer to measure the three dimensions consistently, which allowed for testing two hypotheses explaining the underestimate in vertical wind. While measurements were essentially unchanged when the orthogonal anemometers were mounted sideways, the nonorthogonal anemometers changed substantially and confirmed the lack of shadow correction. Considering the ubiquity of nonorthogonal anemometers, these results are consequential across flux networks and could potentially explain half of the ~20% missing energy that is typical at most flux sites.

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Fei Chen, Guo Zhang, Michael Barlage, Ying Zhang, Jeffrey A. Hicke, Arjan Meddens, Guangsheng Zhou, William J. Massman, and John Frank

Abstract

Bark beetle outbreaks have killed billions of trees and affected millions of hectares of forest during recent decades. The objective of this study was to quantify responses of surface energy and hydrologic fluxes 2–3 yr following a spruce beetle outbreak using measurements and modeling. The authors used observations at the Rocky Mountains Glacier Lakes Ecosystem Experiments Site (GLEES), where beetles killed 85% of the basal area of spruce from 2005–07 (prebeetle) to 2009/10 (postbeetle). Observations showed increased albedo following tree mortality, more reflected solar radiation, and less net radiation, but these postoutbreak radiation changes are smaller than or comparable to their annual preoutbreak variability. The dominant signals from observations were a large reduction (27%) in summer daytime evaporation and a large increase (25%) in sensible heat fluxes. Numerous Noah LSM with multiparameterization options (Noah-MP) simulations incorporating beetle-caused tree mortality effects were conducted to assess their impact on the surface hydrological cycle components that were not directly observed. Model results revealed substantial seasonal variations: more spring snowmelt and runoff, less spring–summer transpiration, and drier soil in summer and fall. This modeled trend is similar to observed runoff changes in harvested forests where reduced forest density resulted in more spring snowmelt and annual water yields. Model results showed that snow albedo changes due to increased litter cover beneath killed trees altered the seasonal pattern of simulated snowmelt and snow water equivalent, but these changes are small compared to the effect of leaf loss. This study highlights the need to include the transient effects of forest disturbances in modeling land–atmosphere interactions and their potential impacts on regional weather and climate.

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Edward G. Patton, Thomas W. Horst, Peter P. Sullivan, Donald H. Lenschow, Steven P. Oncley, William O. J. Brown, Sean P. Burns, Alex B. Guenther, Andreas Held, Thomas Karl, Shane D. Mayor, Luciana V. Rizzo, Scott M. Spuler, Jielun Sun, Andrew A. Turnipseed, Eugene J. Allwine, Steven L. Edburg, Brian K. Lamb, Roni Avissar, Ronald J. Calhoun, Jan Kleissl, William J. Massman, Kyaw Tha Paw U, and Jeffrey C. Weil

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 tower instrumented with turbulence instrumentation, fast and slow chemical sensors, aerosol samplers, and radiation instrumentation. A highresolution scanning backscatter lidar characterized the turbulence structure above and within the canopy; a scanning Doppler lidar, mini sodar/radio acoustic sounding system (RASS), and a new helicopter-observing platform provided details of the PBL-scale flow. Ultimately, the CHATS dataset will lead to improved parameterizations of energy and scalar transport to and from vegetation, which are a critical component of global and regional land, atmosphere, and chemical models. This manuscript presents an overview of the experiment, documents the regime sampled, and highlights some preliminary key findings.

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