skip to main content


Title: New calibration procedures for airborne turbulence measurements and accuracy of the methane fluxes during the AirMeth campaigns
Abstract. Low-level flights over tundra wetlands in Alaska and Canada have beenconducted during the Airborne Measurements of Methane Emissions (AirMeth) campaigns to measure turbulent methane fluxesin the atmosphere. In this paper we describe the instrumentation and newcalibration procedures for the essential pressure parameters required forturbulence sensing by aircraft that exploit suitable regular measurementflight legs without the need for dedicated calibration patterns. We estimatethe accuracy of the mean wind and the turbulence measurements. We show thatairborne measurements of turbulent fluxes of methane and carbon dioxide usingcavity ring-down spectroscopy trace gas analysers together with establishedturbulence equipment achieve a relative accuracy similar to that ofmeasurements of sensible heat flux if applied during low-level flights overnatural area sources. The inertial subrange of the trace gas fluctuationscannot be resolved due to insufficient high-frequency precision of theanalyser, but, since this scatter is uncorrelated with the vertical windvelocity, the covariance and thus the flux are reproduced correctly. In thecovariance spectra the -7/3 drop-off in the inertial subrange can bereproduced if sufficient data are available for averaging. For convectiveconditions and flight legs of several tens of kilometres we estimate the fluxdetection limit to be about4 mg m−2 d−1 forw′CH4′‾,1.4 g m−2 d−1 for w′CO2′‾ and4.2 W m−2 for the sensible heat flux.  more » « less
Award ID(s):
1724433
NSF-PAR ID:
10376509
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
Atmospheric Measurement Techniques
Volume:
11
Issue:
7
ISSN:
1867-8548
Page Range / eLocation ID:
4567 to 4581
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. We perform direct numerical simulations of a gas bubble dissolving in a surrounding liquid. The bubble volume is reduced due to dissolution of the gas, with the numerical implementation of an immersed boundary method, coupling the gas diffusion and the Navier–Stokes equations. The methods are validated against planar and spherical geometries’ analytical moving boundary problems, including the classic Epstein–Plesset problem. Considering a bubble rising in a quiescent liquid, we show that the mass transfer coefficient $k_L$ can be described by the classic Levich formula $k_L = (2/\sqrt {{\rm \pi} })\sqrt {\mathscr {D}_l\,U(t)/d(t)}$ , with $d(t)$ and $U(t)$ the time-varying bubble size and rise velocity, and $\mathscr {D}_l$ the gas diffusivity in the liquid. Next, we investigate the dissolution and gas transfer of a bubble in homogeneous and isotropic turbulence flow, extending Farsoiya et al. ( J. Fluid Mech. , vol. 920, 2021, A34). We show that with a bubble size initially within the turbulent inertial subrange, the mass transfer coefficient in turbulence $k_L$ is controlled by the smallest scales of the flow, the Kolmogorov $\eta$ and Batchelor $\eta _B$ microscales, and is independent of the bubble size. This leads to the non-dimensional transfer rate ${Sh}=k_L L^\star /\mathscr {D}_l$ scaling as ${Sh}/{Sc}^{1/2} \propto {Re}^{3/4}$ , where ${Re}$ is the macroscale Reynolds number ${Re} = u_{rms}L^\star /\nu _l$ , with $u_{rms}$ the velocity fluctuations, $L^*$ the integral length scale, $\nu _l$ the liquid viscosity, and ${Sc}=\nu _l/\mathscr {D}_l$ the Schmidt number. This scaling can be expressed in terms of the turbulence dissipation rate $\epsilon$ as ${k_L}\propto {Sc}^{-1/2} (\epsilon \nu _l)^{1/4}$ , in agreement with the model proposed by Lamont & Scott ( AIChE J. , vol. 16, issue 4, 1970, pp. 513–519) and corresponding to the high $Re$ regime from Theofanous et al. ( Intl J. Heat Mass Transfer , vol. 19, issue 6, 1976, pp. 613–624). 
    more » « less
  2. Abstract

    The pre-ALPACA (Alaskan Layered Pollution And Chemical Analysis) 2019 winter campaign took place in Fairbanks, Alaska, in November–December 2019. One objective of the campaign was to study the life-cycle of surface-based temperature inversions and the associated surface energy budget changes. Several instruments, including a 4-component radiometer and sonic anemometer were deployed in the open, snow-covered University of Alaska Fairbanks (UAF) Campus Agricultural Field. A local flow from a connecting valley occurs at this site. This flow is characterized by locally elevated wind speeds (greater than 3 m s$$^{-1}$$-1) under clear-sky conditions and a north-westerly direction. It is notably different to the wind observed at the airport more than 3.5 km to the south-west. The surface energy budget at the UAF Field site exhibits two preferential modes. In the first mode, turbulent sensible heat and net longwave fluxes are close to 0 W m$$^{-2}$$-2, linked to the presence of clouds and generally low winds. In the second, the net longwave flux is around − 50 W m$$^{-2}$$-2and the turbulent sensible heat flux is around 15 W m$$^{-2}$$-2, linked to clear skies and elevated wind speeds. The development of surface-based temperature inversions at the field is hindered compared to the airport because the local flow sustains vertical mixing. In this second mode the residual of the surface energy budget is large, possibly due to horizontal temperature advection.

     
    more » « less
  3. The Baltimore Ecosystem Study (BES) has established a network of long-term permanent biogeochemical study plots. These plots will provide long-term data on vegetation, soil and hydrologic processes in the key ecosystem types within the urban ecosystem. The current network of study plots includes eight forest plots, chosen to represent the range of forest conditions in the area, and four grass plots. These plots are complemented by a network of 200 less intensive study plots located across the Baltimore metropolitan area. Plots are currently instrumented with lysimeters (drainage and tension) to sample soil solution chemistry, time domain reflectometry probes to measure soil moisture, dataloggers to measure and record soil temperature and trace gas flux chambers to measure the flux of carbon dioxide, nitrous oxide and methane from soil to the atmosphere. Measurements of in situ nitrogen mineralization, nitrification and denitrification were made at approximately monthly intervals from Fall 1998 - Fall 2000. Detailed vegetation characterization (all layers) was done in summer 1998. Data from these plots has been published in Groffman et al. (2006, 2009) and Groffman and Pouyat (2009). In November of 1998 four rural, forested plots were established at Oregon Ridge Park in Baltimore County northeast of the Gwynns Falls Watershed. Oregon Ridge Park contains Pond Branch, the forested reference watershed for BES. Two of these four plots are located on the top of a slope; the other two are located midway up the slope. In June of 2010 measurements at the mid-slope sites on Pond Branch were discontinued. Monuments and equipment remain at the two plots. These plots were replaced with two lowland riparian plots; Oregon upper riparian and Oregon lower riparian. Each riparian sites has four 5 cm by 1-2.5 meter depth slotted wells laid perpendicular to the stream, four tension lysimeters at 10 cm depth, five time domain reflectometry probes, and four trace gas flux chambers in the two dominant microtopographic features of the riparian zones - high spots (hummocks) and low spots (hollows). Four urban, forested plots were established in November 1998, two at Leakin Park and two adjacent to Hillsdale Park in west Baltimore City in the Gwynns Falls. One of the plots in Hillsdale Park was abandoned in 2004 due to continued vandalism. In May 1999 two grass, lawn plots were established at McDonogh School in Baltimore County west of the city in the Gwynns Falls. One of these plots is an extremely low intensity management area (mowed once or twice a year) and one is in a low intensity management area (frequent mowing, no fertilizer or herbicide use). In 2009, the McDonogh plots were abandoned due to management changes at the school. Two grass lawn plots were established on the campus of the University of Maryland, Baltimore County (UMBC) in fall 2000. One of these plots is in a medium intensity management area (frequent mowing, moderate applications of fertilizer and herbicides) and one is in a high intensity management area (frequent mowing, high applications of fertilizer and herbicides). Literature Cited Bowden R, Steudler P, Melillo J and Aber J. 1990. Annual nitrous oxide fluxes from temperate forest soils in the northeastern United States. J. Geophys. Res.-Atmos. 95, 13997 14005. Driscoll CT, Fuller RD and Simone DM (1988) Longitudinal variations in trace metal concentrations in a northern forested ecosystem. J. Environ. Qual. 17: 101-107 Goldman, M. B., P. M. Groffman, R. V. Pouyat, M. J. McDonnell, and S. T. A. Pickett. 1995. CH4 uptake and N availability in forest soils along an urban to rural gradient. Soil Biology and Biochemistry 27:281-286. Groffman PM, Holland E, Myrold DD, Robertson GP and Zou X (1999) Denitrification. In: Robertson GP, Bledsoe CS, Coleman DC and Sollins P (Eds) Standard Soil Methods for Long Term Ecological Research. (pp 272-290). Oxford University Press, New York Groffman PM, Pouyat RV, Cadenasso ML, Zipperer WC, Szlavecz K, Yesilonis IC,. Band LE and Brush GS. 2006. Land use context and natural soil controls on plant community composition and soil nitrogen and carbon dynamics in urban and rural forests. Forest Ecology and Management 236:177-192. Groffman, P.M., C.O. Williams, R.V. Pouyat, L.E. Band and I.C. Yesilonis. 2009. Nitrate leaching and nitrous oxide flux in urban forests and grasslands. Journal of Environmental Quality 38:1848-1860. Groffman, P.M. and R.V. Pouyat. 2009. Methane uptake in urban forests and lawns. Environmental Science and Technology 43:5229-5235. DOI: 10.1021/es803720h. Holland EA, Boone R, Greenberg J, Groffman PM and Robertson GP (1999) Measurement of Soil CO2, N2O and CH4 exchange. In: Robertson GP, Bledsoe CS, Coleman DC and Sollins P (Eds) Standard Soil Methods for Long Term Ecological Research. (pp 258-271). Oxford University Press, New York Robertson GP, Wedin D, Groffman PM, Blair JM, Holland EA, Nadelhoffer KJ and. Harris D. 1999. Soil carbon and nitrogen availability: Nitrogen mineralization, nitrification and carbon turnover. In: Standard Soil Methods for Long Term Ecological Research (Robertson GP, Bledsoe CS, Coleman DC and Sollins P (Eds) Standard Soil Methods for Long Term Ecological Research. (pp 258-271). Oxford University Press, New York Savva, Y., K. Szlavecz, R. V. Pouyat, P. M. Groffman, and G. Heisler. 2010. Effects of land use and vegetation cover on soil temperature in an urban ecosystem. Soil Science Society of America Journal 74:469-480." 
    more » « less
  4. Rapp, Anita (Ed.)
    Vertical motions over the complex terrain of Idaho’s Payette River Basin were observed by the Wyoming Cloud Radar (WCR) during 23 flights of the Wyoming King Air during the SNOWIE field campaign. The WCR measured radial velocity, V_r, which includes the reflectivity-weighted terminal velocity of hydrometeors (V_t), vertical air velocity (w), horizontal wind contributions as a result of aircraft attitude deviations, and aircraft motion. Aircraft motion was removed through standard processing. To retrieve vertical radial velocity (W), V_r was corrected using rawinsonde data and aircraft attitude measurements. w was then calculated by subtracting the mean W, (W ̅), at a given height along a flight leg long enough for W ̅ to equal the mean reflectivity weighted terminal velocity, (V_t ) ̅, at that height. The accuracy of the w and (V_t ) ̅ retrievals were dependent on satisfying assumptions along a given flight leg that the winds at a given altitude above/below the aircraft did not vary, the vertical air motions at a given altitude sum to 0 m s-1, and (V_t ) ̅ at a given altitude did not vary. The uncertainty in the w retrieval associated with each assumption is evaluated. Case studies and a project wide summary show that this methodology can provide estimates of w that closely match gust probe measurements of w at the aircraft level. Flight legs with little variation in equivalent reflectivity factor at a given height and large horizontal echo extent were associated with the least retrieval uncertainty. The greatest uncertainty occurred in regions with isolated convective turrets or at altitudes where split cloud layers were present. 
    more » « less
  5. Abstract

    Vertical energy transports due to dissipating gravity waves in the mesopause region (85–100 km) are analyzed using over 400 h of observational data obtained from a narrow‐band sodium wind‐temperature lidar located at Andes Lidar Observatory (ALO), Cerro Pachón (30.25°S, 70.73°W), Chile. Sensible heat flux is directly estimated using measured temperature and vertical wind; energy flux is estimated from the vertical wavenumber and frequency spectra of temperature perturbations; and enthalpy flux is derived based on its relationship with sensible heat and energy fluxes. Sensible heat flux is mostly downward throughout the region. Enthalpy flux exhibits an annual oscillation with maximum downward transport in July above 90 km. The dominant feature of energy flux is the exponential decrease from 10−2to 10−4 W m−2with the altitude increases from 85 to 100 km and is larger during austral winter. The annual mean thermal diffusivity inferred from enthalpy flux decreases from 303 m2s−1at 85 km to minimum 221 m2s−1at 90 km then increases to 350 m2s−1at 99 km. Results also show that shorter period gravity waves tend to dissipate at higher altitudes and generate more heat transport. The averaged vertical group velocities for high, medium, and low frequency waves are 4.15 m s−1, 1.15 m s−1, and 0.70 m s−1, respectively. Gravity wave heat transport brings significant cooling in the mesopause region at an average cooling rate of 6.7 ± 1.1 K per day.

     
    more » « less