Atmospheric Response to a Partial Solar Eclipse over a Cotton Field in Central California

2007 ◽  
Vol 46 (11) ◽  
pp. 1792-1803 ◽  
Author(s):  
Matthias Mauder ◽  
R. L. Desjardins ◽  
Steven P. Oncley ◽  
Ian MacPherson
Keyword(s):  
Carbon Dioxide ◽  
Water Vapor ◽  
Wavelet Analysis ◽  
Solar Eclipse ◽  
Sensible Heat Flux ◽  
Turbulent Fluxes ◽  
Cotton Field ◽  
Sensible Heat ◽  
Central California ◽  
Partial Solar Eclipse

Abstract The partial solar eclipse on 11 July 1991 in central California, with 58.3% maximum coverage, provided an exceptional opportunity to study the temporal response of processes in the atmospheric boundary layer to an abrupt change in solar radiation. Almost laboratory-like conditions were met over a cotton field, since no clouds disturbed the course of the eclipse. Tower-based and complementing aircraft-based systems monitored the micrometeorological conditions over the site. Temperature profile measurements indicated neutral stratification during the maximum eclipse in contrast to the unstable conditions before and after the eclipse. Accordingly, the sensible heat exchange completely stopped, as a wavelet analysis of the tower measurements and airborne eddy-covariance measurements showed. Turbulent fluxes of water vapor, carbon dioxide, and ozone were reduced by approximately ⅔ at the peak of the eclipse. Wavelet analysis further indicated that the same eddies contributed to the turbulent transport of water vapor and carbon dioxide, whereas sensible heat was transported by different ones. An analysis of the decay of turbulent kinetic energy followed a power law of time with an exponent of −1.25. The response of the sensible heat flux was 8–13 min delayed relative to the solar forcing, whereas no significant time lag could be detected for the turbulent fluxes of air constituents.

scholarly journals Canopy Resistance and Estimation of Evapotranspiration above a Humid Cypress Forest

2020 ◽  
Vol 2020 ◽  
pp. 1-16 ◽  
Author(s):  
Bau-Show Lin ◽  
Huimin Lei ◽  
Ming-Che Hu ◽  
Supattra Visessri ◽  
Cheng-I Hsieh
Keyword(s):  
Water Vapor ◽  
Seasonal Variations ◽  
Sensible Heat Flux ◽  
Sensible Heat ◽  
Canopy Resistance ◽  
Data Set ◽  
Water Vapor Flux ◽  
Vapor Flux ◽  
Evapotranspiration Estimation ◽  
Monteith Equation

This study presented a two-year data set of sensible heat and water vapor fluxes above a humid subtropical montane Cypress forest, located at 1650 m a.s.l. in northeastern Taiwan. The focuses of this study were to investigate (1) the diurnal and seasonal variations of canopy resistance and fluxes of sensible heat and water vapor above this forest; and (2) the mechanism of why a fixed canopy resistance could work when implementing the Penman–Monteith equation for diurnal hourly evapotranspiration estimation. Our results showed distinct seasonal variations in canopy resistance and water vapor flux, but on the contrary, the sensible heat flux did not change as much as the water vapor flux did with seasons. The seasonal variation patterns of the canopy resistance and water vapor flux were highly coupled with the meteorological factors. Also, the results demonstrated that a constant (fixed) canopy resistance was good enough for estimating the diurnal variation of evapotranspiration using Penman–Monteith equation. We observed a canopy resistance around 190 (s/m) for both the two warm seasons; and canopy resistances were around 670 and 320 (s/m) for the two cool seasons, respectively. In addition, our analytical analyses demonstrated that when the average canopy resistance is higher than 200 (s/m), the Penman–Monteith equation is less sensitive to the change of canopy resistance; hence, a fixed canopy resistance is suitable for the diurnal hourly evapotranspiration estimation. However, this is not the case when the average canopy resistance is less than 100 (s/m), and variable canopy resistances are needed. These two constraints (200 and 100) were obtained based on purely analytical analyses under a moderate meteorological condition (Rn = 600 W·m−2, RH = 60%, Ta = 20°C, U = 2 m·s−1) and a measurement height around two times of the canopy height.

Concerning the Measurement and Magnitude of Heat, Water Vapor, and Carbon Dioxide Exchange from a Semiarid Grassland

2009 ◽  
Vol 48 (5) ◽  
pp. 982-996 ◽  
Author(s):  
Joseph G. Alfieri ◽  
Peter D. Blanken ◽  
David Smith ◽  
Jack Morgan
Keyword(s):  
Carbon Dioxide ◽  
Energy Balance ◽  
Latent Heat ◽  
Land Surface ◽  
Turbulent Fluxes ◽  
Carbon Dioxide Exchange ◽  
Sensible Heat ◽  
Seasonal Behavior ◽  
Eddy Diffusivities ◽  
Using Data

Abstract Grassland environments constitute approximately 40% of the earth’s vegetated surface, and they play a key role in a number of processes linking the land surface with the atmosphere. To investigate these linkages, a variety of techniques, including field and modeling studies, are required. Using data collected at the Central Plains Experimental Range (CPER) in northeastern Colorado from 25 March to 10 November 2004, this study compares two common ways of measuring turbulent fluxes of latent heat, sensible heat, and carbon dioxide in the field: the eddy covariance (EC) and Bowen ratio energy balance (BREB) methods. The turbulent fluxes measured by each of these methods were compared in terms of magnitude and seasonal behavior and were combined to calculate eddy diffusivities and examine turbulent transport. Relative to the EC method, the BREB method tended to overestimate the magnitude of the sensible heat, latent heat, and carbon dioxide fluxes. As a result, substantial differences in both the diurnal pattern and long-term magnitudes of the water and carbon budgets were apparent depending on which method was used. These differences arise from (i) the forced closure of the surface energy balance and (ii) the assumption of similarity between the eddy diffusivities required by the BREB method. An empirical method was developed that allows the BREB and EC datasets to be reconciled; this method was tested successfully using data collected at the CPER site during 2005. Ultimately, however, the BREB and EC methods show important differences that must be recognized and taken into account when analyzing issues related to the energy, water, or carbon cycles.

scholarly journals Venting of Heat and Carbon Dioxide from Urban Canyons at Night

2005 ◽  
Vol 44 (8) ◽  
pp. 1180-1194 ◽  
Author(s):  
J. A. Salmond ◽  
T. R. Oke ◽  
C. S. B. Grimmond ◽  
S. Roberts ◽  
B. Offerle
Keyword(s):  
Carbon Dioxide ◽  
Boundary Layer ◽  
Time Series ◽  
Wavelet Analysis ◽  
Air Temperature ◽  
Urban Boundary Layer ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Canopy Layer ◽  
Street Canyons

Abstract Turbulent fluxes of carbon dioxide and sensible heat were observed in the surface layer of the weakly convective nocturnal boundary layer over the center of the city of Marseille, France, during the Expérience sur Sites pour Contraindre les Modèles de Pollution Atmosphérique et de Transport d’Emission (ESCOMPTE) field experiment in the summer of 2001. The data reveal intermittent events or bursts in the time series of carbon dioxide (CO2) concentration and air temperature that are superimposed upon the background values. These features relate to intermittent structures in the fluxes of CO2 and sensible heat. In Marseille, CO2 is primarily emitted into the atmosphere at street level from vehicle exhausts. In a similar way, nocturnal sensible heat fluxes are most likely to originate in the deep street canyons that are warmer than adjacent roof surfaces. Wavelet analysis is used to examine the hypothesis that CO2 concentrations can be used as a tracer to identify characteristics of the venting of pollutants and heat from street canyons into the above-roof nocturnal urban boundary layer. Wavelet analysis is shown to be effective in the identification and analysis of significant events and coherent structures within the turbulent time series. Late in the evening, there is a strong correlation between the burst structures observed in the air temperature and CO2 time series. Evidence suggests that the localized increases of temperature and CO2 observed above roof level in the urban boundary layer (UBL) are related to intermittent venting of sensible heat from the warmer urban canopy layer (UCL). However, later in the night, local advection of CO2 in the UBL, combined with reduced traffic emissions in the UCL, limit the value of CO2 as a tracer of convective plumes in the UBL.

scholarly journals Carbon dioxide, water vapor and sensible heat fluxes over a tallgrass prairie

1989 ◽  
Vol 46 (1-2) ◽  
pp. 53-67 ◽  
Author(s):  
Shashi B. Verma ◽  
Joon Kim ◽  
Robert J. Clement
Keyword(s):  
Carbon Dioxide ◽  
Water Vapor ◽  
Tallgrass Prairie ◽  
Heat Fluxes ◽  
Sensible Heat

scholarly journals RELAÇÃO ENTRE VELOCIDADE DO VENTO E ENERGIA CINÉTICA TURBULENTA EM MODELOS SIMPLIFICADOS DA CAMADA LIMITE NOTURNA

2016 ◽  
Vol 38 ◽  
pp. 75
Author(s):  
Rafael Maroneze ◽  
Otávio Costa Acevedo ◽  
Felipe Denardin Costa
Keyword(s):  
Heat Flux ◽  
Sensible Heat Flux ◽  
Turbulent Fluxes ◽  
Turbulent Intensity ◽  
Simplified Model ◽  
Sensible Heat ◽  
Temperature Variance ◽  
Stable Conditions ◽  
Atmospheric Coupling

The determination of the turbulent fluxes in very stable conditions is done, generally, through parameterizations. In this work the turbulent fluxes are estimated, by using a simplified model, through prognostic equations for the turbulent intensity, the sensible heat flux and the temperature variance. The results indicate that the model is able to reproduce both atmospheric coupling and the intermittent character of the turbulence in very stable conditions.

scholarly journals Micrometeorological processes driving snow ablation in an Alpine catchment

2011 ◽  
Vol 5 (4) ◽  
pp. 1083-1098 ◽  
Author(s):  
R. Mott ◽  
L. Egli ◽  
T. Grünewald ◽  
N. Dawes ◽  
C. Manes ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Energy Balance ◽  
Snow Cover ◽  
Sensible Heat Flux ◽  
Internal Boundary Layer ◽  
Turbulent Fluxes ◽  
Eddy Correlation ◽  
Internal Boundary ◽  
Sensible Heat ◽  
Regional Prediction

Abstract. Mountain snow covers typically become patchy over the course of a melting season. The snow pattern during melt is mainly governed by the end of winter snow depth distribution and the local energy balance. The objective of this study is to investigate micro-meteorological processes driving snow ablation in an Alpine catchment. For this purpose we combine a meteorological boundary-layer model (Advanced Regional Prediction System) with a fully distributed energy balance model (Alpine3D). Turbulent fluxes above melting snow are further investigated by using data from eddy-correlation systems. We compare modeled snow ablation to measured ablation rates as obtained from a series of Terrestrial Laser Scanning campaigns covering a complete ablation season. The measured ablation rates indicate that the advection of sensible heat causes locally increased ablation rates at the upwind edges of the snow patches. The effect, however, appears to be active over rather short distances of about 4–6 m. Measurements suggest that mean wind velocities of about 5 m s−1 are required for advective heat transport to increase snow ablation over a long fetch distance of about 20 m. Neglecting this effect, the model is able to capture the mean ablation rates for early ablation periods but strongly overestimates snow ablation once the fraction of snow coverage is below a critical value of approximately 0.6. While radiation dominates snow ablation early in the season, the turbulent flux contribution becomes important late in the season. Simulation results indicate that the air temperatures appear to overestimate the local air temperature above snow patches once the snow coverage is low. Measured turbulent fluxes support these findings by suggesting a stable internal boundary layer close to the snow surface causing a strong decrease of the sensible heat flux towards the snow cover. Thus, the existence of a stable internal boundary layer above a patchy snow cover exerts a dominant control on the timing and magnitude of snow ablation for patchy snow covers.

scholarly journals An Assessment of Coordinate Rotation Methods in Sonic Anemometer Measurements of Turbulent Fluxes over Complex Mountainous Terrain

Atmosphere ◽  
2019 ◽  
Vol 10 (6) ◽  
pp. 324 ◽  
Author(s):  
Alessio Golzio ◽  
Irene Maria Bollati ◽  
Silvia Ferrarese
Keyword(s):  
Quality Assessment ◽  
Sonic Anemometer ◽  
Sensible Heat Flux ◽  
Stationary Flow ◽  
Turbulent Fluxes ◽  
Quality Level ◽  
Mountainous Terrain ◽  
Sensible Heat ◽  
Coordinate Rotation ◽  
Ultrasonic Anemometer

The measurement of turbulent fluxes in the atmospheric boundary layer is usually performed using fast anemometers and the Eddy Covariance technique. This method has been applied here and investigated in a complex mountainous terrain. A field campaign has recently been conducted at Alpe Veglia (the Central-Western Italian Alps, 1746 m a.s.l.) where both standard and micrometeorological data were collected. The measured values obtained from an ultrasonic anemometer were analysed using a filtering procedure and three different coordinate rotation procedures: Double (DR), Triple Rotation (TR) and Planar Fit (PF) on moving temporal windows of 30 and 60 min. A quality assessment was performed on the sensible heat and momentum fluxes and the results show that the measured turbulent fluxes at Alpe Veglia were of a medium-high quality level and rarely passed the stationary flow test. A comparison of the three coordinate procedures, using quality assessment and sensible heat flux standard deviations, revealed that DR and TR were comparable, with significant differences, mainly under low-wind conditions. The PF method failed to satisfy the physical requirement for the multiple planarity of the flow, due to the complexity of the mountainous terrain.

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