Scanning 10-W Water Vapor DIAL for the Investigation of Atmospheric Turbulence and Land-Atmosphere Feedback

2021 ◽  
Author(s):  
Andreas Behrendt ◽  
Florian Spaeth ◽  
Volker Wulfmeyer
Keyword(s):  
Heat Flux ◽  
Water Vapor ◽  
Latent Heat ◽  
Atmospheric Turbulence ◽  
Latent Heat Flux ◽  
Climate Models ◽  
Weather Forecast ◽  
Surface Characteristics ◽  
Scanning System ◽  
Forecast Models

<p>We will present recent measurements made with the water vapor differential absorption lidar (DIAL) of University of Hohenheim (UHOH). This scanning system has been developed in recent years for the investigation of atmospheric turbulence and land-atmosphere feedback processes.</p><p>The lidar is housed in a mobile trailer and participated in recent years in a number of national and international field campaigns. We will present examples of vertical pointing and scanning measurements, especially close to the canopy. The water vapor gradients in the surface layer are related to the latent heat flux. Thus, with such low-elevation scans, the latent heat flux distribution over different surface characteristics can be monitored, which is important to verify and improve both numerical weather forecast models and climate models.</p><p>The transmitter of the UHOH DIAL consists of a diode-pumped Nd:YAG laser which pumps a Ti:sapphire laser. The output power of this laser is up to 10 W. Two injection seeders are used to switch pulse-to-pulse between the online and offline signals. These signals are then either directly sent into the atmosphere or coupled into a fiber and guided to a transmitting telescope which is attached to the scanner unit. The receiving telescope has a primary mirror with a dimeter of 80 cm. The backscatter signals are recorded shot to shot and are typically averaged over 0.1 to 1 s.</p>

scholarly journals Latent Heat Flux Profiles from Collocated Airborne Water Vapor and Wind Lidars during IHOP_2002

2007 ◽  
Vol 24 (4) ◽  
pp. 627-639 ◽  
Author(s):  
C. Kiemle ◽  
G. Ehret ◽  
A. Fix ◽  
M. Wirth ◽  
G. Poberaj ◽  
...  
Keyword(s):  
Heat Flux ◽  
Water Vapor ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Deep Convection ◽  
Minor Role ◽  
Flux Divergence ◽  
Convective Boundary ◽  
Budget Analysis ◽  
Wind Lidar

Abstract Latent heat flux profiles in the convective boundary layer (CBL) are obtained for the first time with the combination of the Deutsches Zentrum für Luft- und Raumfahrt (DLR) water vapor differential absorption lidar (DIAL) and the NOAA high resolution Doppler wind lidar (HRDL). Both instruments were integrated nadir viewing on board the DLR Falcon research aircraft during the International H2O Project (IHOP_2002) over the U.S. Southern Great Plains. Flux profiles from 300 to 2500 m AGL are computed from high spatial resolution (150 m horizontal and vertical) two-dimensional water vapor and vertical velocity lidar cross sections using the eddy covariance technique. Three flight segments on 7 June 2002 between 1000 and 1300 LT over western Oklahoma and southwestern Kansas are analyzed. On two segments with strong convection, the latent heat flux peaks at (700 ± 200) W m−2 in the entrainment zone and decreases linearly to (200 ± 100) W m−2 in the lower CBL. A water vapor budget analysis reveals that this flux divergence [(0.9 ± 0.4) g kg−1 h−1] plus the advection (0.3 g kg−1 h−1) are nearly balanced by substantial CBL drying [(1.5 ± 0.2) g kg−1 h−1] observed by airborne and surface in situ instruments, within the limits of the overall budget rms error of 0.5 g kg−1 h−1. Entrainment of dry air from aloft and net upward humidity transport caused the CBL drying and finally inhibited the initiation of deep convection. All cospectra show significant contributions to the flux between 1- and 10-km wavelength, with peaks between 2 and 6 km, originating from large eddies. The main flux uncertainty is due to low sampling (55% rmse at mid-CBL), while instrument noise (15%) and systematic errors (7%) play a minor role. The combination of a water vapor and a wind lidar on an aircraft appears as an attractive new tool that allows measuring latent heat flux profiles from a single overflight of the investigated area.

scholarly journals Measuring turbulent CO<sub>2</sub> fluxes with a closed-path gas analyzer in a marine environment

2018 ◽  
Vol 11 (9) ◽  
pp. 5335-5350 ◽  
Author(s):  
Martti Honkanen ◽  
Juha-Pekka Tuovinen ◽  
Tuomas Laurila ◽  
Timo Mäkelä ◽  
Juha Hatakka ◽  
...  
Keyword(s):  
Heat Flux ◽  
Water Vapor ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Flux Measurement ◽  
Sea Spray ◽  
Closed Path ◽  
Co2 Fluxes ◽  
Gas Analyzer ◽  
Virtual Impactor

Abstract. In this study, we introduce new observations of sea–air fluxes of carbon dioxide using the eddy covariance method. The measurements took place at the Utö Atmospheric and Marine Research Station on the island of Utö in the Baltic Sea in July–October 2017. The flux measurement system is based on a closed-path infrared gas analyzer (LI-7000, LI-COR) requiring only occasional maintenance, making the station capable of continuous monitoring. However, such infrared gas analyzers are prone to significant water vapor interference in a marine environment, where CO2 fluxes are small. Two LI-7000 analyzers were run in parallel to test the effect of a sample air drier which dampens water vapor fluctuations and a virtual impactor, included to remove liquid sea spray, both of which were attached to the sample air tubing of one of the analyzers. The systems showed closely similar (R2=0.99) sea–air CO2 fluxes when the latent heat flux was low, which proved that neither the drier nor the virtual impactor perturbed the CO2 flux measurement. However, the undried measurement had a positive bias that increased with increasing latent heat flux, suggesting water vapor interference. For both systems, cospectral densities between vertical wind speed and CO2 molar fraction were distributed within the expected frequency range, with a moderate attenuation of high-frequency fluctuations. While the setup equipped with a drier and a virtual impactor generated a slightly higher flux loss, we opt for this alternative for its reduced water vapor cross-sensitivity and better protection against sea spray. The integral turbulence characteristics were found to agree with the universal stability dependence observed over land. Nonstationary conditions caused unphysical results, which resulted in a high percentage (65 %) of discarded measurements. After removing the nonstationary cases, the direction of the sea–air CO2 fluxes was in good accordance with independently measured CO2 partial pressure difference between the sea and the atmosphere. Atmospheric CO2 concentration changes larger than 2 ppm during a 30 min averaging period were found to be associated with the nonstationarity of CO2 fluxes.

scholarly journals Application of MJO Simulation Diagnostics to Climate Models

2009 ◽  
Vol 22 (23) ◽  
pp. 6413-6436 ◽  
Author(s):  
D. Kim ◽  
K. Sperber ◽  
W. Stern ◽  
D. Waliser ◽  
I.-S. Kang ◽  
...  
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Principal Components ◽  
Zonal Wind ◽  
Time Scale ◽  
Vertical Structure ◽  
Climate Models ◽  
Moisture Convergence ◽  
Low Level

Abstract The ability of eight climate models to simulate the Madden–Julian oscillation (MJO) is examined using diagnostics developed by the U.S. Climate Variability and Predictability (CLIVAR) MJO Working Group. Although the MJO signal has been extracted throughout the annual cycle, this study focuses on the boreal winter (November–April) behavior. Initially, maps of the mean state and variance and equatorial space–time spectra of 850-hPa zonal wind and precipitation are compared with observations. Models best represent the intraseasonal space–time spectral peak in the zonal wind compared to that of precipitation. Using the phase–space representation of the multivariate principal components (PCs), the life cycle properties of the simulated MJOs are extracted, including the ability to represent how the MJO evolves from a given subphase and the associated decay time scales. On average, the MJO decay (e-folding) time scale for all models is shorter (∼20–29 days) than observations (∼31 days). All models are able to produce a leading pair of multivariate principal components that represents eastward propagation of intraseasonal wind and precipitation anomalies, although the fraction of the variance is smaller than observed for all models. In some cases, the dominant time scale of these PCs is outside of the 30–80-day band. Several key variables associated with the model’s MJO are investigated, including the surface latent heat flux, boundary layer (925 hPa) moisture convergence, and the vertical structure of moisture. Low-level moisture convergence ahead (east) of convection is associated with eastward propagation in most of the models. A few models are also able to simulate the gradual moistening of the lower troposphere that precedes observed MJO convection, as well as the observed geographical difference in the vertical structure of moisture associated with the MJO. The dependence of rainfall on lower tropospheric relative humidity and the fraction of rainfall that is stratiform are also discussed, including implications these diagnostics have for MJO simulation. Based on having the most realistic intraseasonal multivariate empirical orthogonal functions, principal component power spectra, equatorial eastward propagating outgoing longwave radiation (OLR), latent heat flux, low-level moisture convergence signals, and vertical structure of moisture over the Eastern Hemisphere, the superparameterized Community Atmosphere Model (SPCAM) and the ECHAM4/Ocean Isopycnal Model (OPYC) show the best skill at representing the MJO.

scholarly journals Measuring turbulent CO<sub>2</sub> fluxes with a closed-path gas analyzer in marine environment

2018 ◽  
Author(s):  
Martti Honkanen ◽  
Juha-Pekka Tuovinen ◽  
Tuomas Laurila ◽  
Timo Mäkelä ◽  
Juha Hatakka ◽  
...  
Keyword(s):  
Heat Flux ◽  
Water Vapor ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Flux Measurement ◽  
Sea Spray ◽  
Closed Path ◽  
Co2 Fluxes ◽  
Gas Analyzer ◽  
Virtual Impactor

Abstract. Sea-air fluxes of carbon dioxide (CO2) were measured using the eddy covariance method at a new station established on the Utö Island in the Baltic Sea. The flux measurement system is based on a closed-path infrared gas analyzer (LI-7000, LI-COR) requiring only occasional maintenance, so the station is capable of continuous monitoring. However, such infrared gas analyzers are prone to significant water vapor interference in a marine environment, where CO2 fluxes are small. In July–October 2017, two LI-7000 analyzers were run in parallel to test the effect of a sample air drier which dampens water vapor fluctuations, and a virtual impactor, included to remove liquid sea spray, both of which were attached to the sample air tubing of one of the analyzers. The systems showed closely similar (R2 = 0.99) sea-air CO2 fluxes when the latent heat flux was low, which proved that neither the drier nor the virtual impactor perturbed the CO2 flux measurement. However, the undried measurement had a positive bias that increased with increasing latent heat flux, suggesting water vapor interference. For both systems, cospectral densities between vertical wind speed and CO2 were distributed within the expected frequency range, with a moderate attenuation of high frequency fluctuations. While the setup equipped with a drier and a virtual impactor generated a slightly higher flux loss, we opt for this alternative for its reduced water vapor cross-sensitivity and better protection against sea spray. The integral turbulence characteristics were found to agree with the universal stability dependence observed over land. Non-stationary flow conditions caused unphysical results, which resulted in a high percentage (up to 63 %) of discarded measurements. After removing the non-stationary cases, the direction of the sea-air CO2 fluxes was in good accordance with the measured CO2 partial pressure difference between the sea and the atmosphere. Atmospheric CO2 concentration changes larger than 2 ppm during a 30 min averaging period were found to be associated with the non-stationarity of CO2 fluxes. The Utö Atmospheric and Marine Research Station continues to monitor the regional CO2 exchange between the sea and the atmosphere, utilizing the results of this work.

scholarly journals Identifying the Sources of Continental Summertime Temperature Variance Using a Diagnostic Model of Land–Atmosphere Interactions

2020 ◽  
Vol 33 (9) ◽  
pp. 3547-3564 ◽  
Author(s):  
L. R. Vargas Zeppetello ◽  
Étienne Tétreault-Pinard ◽  
D. S. Battisti ◽  
M. B. Baker
Keyword(s):  
Heat Flux ◽  
Soil Moisture ◽  
Surface Temperature ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Air Temperature ◽  
Climate Models ◽  
Temperature Variability ◽  
Diagnostic Model ◽  
Temperature Variance

AbstractClimate models show that soil moisture and its subseasonal fluctuations have important impacts on the surface latent heat flux, thus regulating surface temperature variations. Using correlations between monthly anomalies in net absorbed radiative fluxes, precipitation, 2-m air temperature, and soil moisture in the ERA-Interim reanalysis and the HadCM3 climate model, we develop a linear diagnostic model to quantify the major effects of land–atmosphere interactions on summertime surface temperature variability. The spatial patterns in 2-m air temperature and soil moisture variance from the diagnostic model are consistent with those from the products from which it was derived, although the diagnostic model generally underpredicts soil moisture variance. We use the diagnostic model to quantify the impact of soil moisture, shortwave radiation, and precipitation anomalies on temperature variance in wet and dry regions. Consistent with other studies, we find that fluctuations in soil moisture amplify temperature variance in dry regions through their impact on latent heat flux, whereas in wet regions temperature variability is muted because of high mean evapotranspiration rates afforded by plentiful surface soil moisture. We demonstrate how the diagnostic model can be used to identify sources of temperature variance bias in climate models.

Land-Atmosphere Interactions

Geography ◽  
2020 ◽  
Author(s):  
Geoffrey M. Henebry ◽  
Nathan J. Moore ◽  
Jiquan Chen
Keyword(s):  
Heat Flux ◽  
Water Vapor ◽  
Solar Radiation ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Land Surface ◽  
Longwave Radiation ◽  
Coupled Processes ◽  
Shortwave Radiation ◽  
Ground Heat Flux

Land-atmosphere interactions encompass a multitude of processes that link the land surface with the atmospheric boundary layer. Interactions are bidirectional, include energy and material exchanges, and can include feedbacks that can amplify or attenuate coupled processes. Shortwave radiation drives most of the biogeophysical processes at the land surface. Photosynthetically active radiation (PAR) is the subset of shortwave radiation (400–700 nanometers) and is critical for most life on the planet. Thermal infrared is the more energetic subset of terrestrial radiation that results primarily from interactions of solar radiation with the land surface. Microwaves are an important subset of terrestrial radiation that facilitate monitoring both atmosphere and land surface. Net radiation is the energy left over after accounting for incoming direct and indirect solar radiation less outgoing solar radiation reflected by the surface, plus incoming longwave radiation (from water vapor and other gases in the atmosphere and terrestrial materials within view of the surface), less outgoing longwave radiation from the land surface. This radiation remaining at an “ideal surface” can be simply partitioned into energy transferred into the surface (ground heat flux) plus energy transferred to heat the atmosphere above the surface (sensible heat flux) plus energy transferred via evapotranspiration (latent heat flux) to moisten the atmosphere. Additionally, objects on the surface can absorb radiation and later radiate this stored heat. Photosynthesis uses only a small portion of incident energy. Precipitation on the surface may (1) return to the atmosphere as water vapor (latent heat flux), (2) move as liquid laterally to another surface point (runoff), (3) move as liquid below the surface (drainage), (4) be retained at or below the surface, including in the soil (storage), (5) be transported away, if frozen, from the surface by wind (advection), or combinations of these. Material exchanges between surface and atmosphere include mineral dust, organic particles, biota, and biological materials such as pollen, seeds, combustion products, volcanic ash and ejecta, trace gas emissions, and anthropogenic emissions from stationary and mobile sources. Interactions between the land surface and lower portion of the atmosphere at various time scales from seconds to centuries are influenced by the amount and type of incident sunlight, radiative characteristics of the materials at the surface, amount of moisture at and below the surface, vegetation amount and type, soils and substrate, vertical structures at the surface that affect wind, land cover type and arrangement, atmospheric constituents, and recent weather. Here we focus on interactions moving from land to the atmosphere.

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