Observations of air–sea heat fluxes in the southwestern Atlantic under high‐frequency ocean and atmospheric perturbations

2020 ◽  
Vol 146 (733) ◽  
pp. 4226-4251
Author(s):  
M. F. Santini ◽  
R. B. Souza ◽  
L. P. Pezzi ◽  
S. Swart
Keyword(s):  
High Frequency ◽  
Heat Fluxes ◽  
Southwestern Atlantic ◽  
Atmospheric Perturbations

Ion–Electron Recombination and Heat Fluxes in High-Frequency Ion Thrusters

2019 ◽  
Vol 45 (2) ◽  
pp. 123-125
Author(s):  
V. K. Abgaryan ◽  
V. Yu. Gidaspov ◽  
A. B. Nadiradze ◽  
A. A. Semenov
Keyword(s):  
High Frequency ◽  
Heat Fluxes ◽  
Electron Recombination ◽  
Ion Thrusters

scholarly journals BVOC ecosystem flux measurements at a high latitude wetland site

2008 ◽  
Vol 8 (6) ◽  
pp. 21129-21169 ◽  
Author(s):  
T. Holst ◽  
A. Arneth ◽  
S. Hayward ◽  
A. Ekberg ◽  
M. Mastepanov ◽  
...  
Keyword(s):  
High Frequency ◽  
Boreal Forests ◽  
Sonic Anemometer ◽  
Proton Transfer Reaction ◽  
Heat Fluxes ◽  
Emission Rates ◽  
Water Vapour Concentration ◽  
Process Understanding ◽  
Emission Fluxes ◽  
Ecosystem Flux

Abstract. In this study, we present summertime concentrations and fluxes of biogenic volatile organic compounds (BVOCs) measured at a sub-arctic wetland in northern Sweden using a disjunct eddy-covariance (DEC) technique based on a proton transfer reaction mass spectrometer (PTR-MS). The vegetation at the site was dominated by Sphagnum, Carex and Eriophorum spp. The performance of the DEC system was assessed by comparing H3O+-ion cluster formed with water molecules (H3O+(H2O) at m37) with water vapour concentration measurements made using an adjacent humidity sensor, and from a comparison of sensible heat fluxes for high frequency and DEC data obtained from the sonic anemometer. These analyses showed no significant PTR-MS sensor drift over a period of several weeks and only a small flux-loss due to high-frequency spectrum omissions. This loss was within the range expected from other studies and the theoretical considerations. Standardised (20°C and 1000 μmol m−2 s−1 PAR) summer isoprene emission rates of 323 μg C m−2 (ground area) h−1 were comparable with findings from more southern boreal forests, and fen-like ecosystems. On a diel scale, measured fluxes indicated a stronger temperature dependence when compared with emissions from temperate or (sub)tropical ecosystems. For the first time, to our knowledge, we report ecosystem methanol fluxes from a sub-arctic ecosystem. Maximum daytime emission fluxes were around 270 μg m−2 h−1 (ca. 100 μg C m−2 h-1) and measurements indicated some nocturnal deposition. The measurements reported here covered a period of 50 days (1 August to 19 September 2006), approximately one half of the growing season at the site, and allowed to investigate the effect of vegetation senescence on daily BVOC fluxes and on their temperature and light responses. Long-term measurements of BVOC are still lacking for nearly all ecosystems and only a very few studies about seasonal or even interannual variation of BVOC emissions have been published so far, particularly for northern ecosystems. The results presented here will be useful for testing process understanding obtained in laboratory studies and for model evaluation, improving our understanding of biogeochemical cycles in a region which is likely to be sensitive to climate change and currently undergoes rapid changes due to global warming.

scholarly journals BVOC ecosystem flux measurements at a high latitude wetland site

2010 ◽  
Vol 10 (4) ◽  
pp. 1617-1634 ◽  
Author(s):  
T. Holst ◽  
A. Arneth ◽  
S. Hayward ◽  
A. Ekberg ◽  
M. Mastepanov ◽  
...  
Keyword(s):  
High Frequency ◽  
Boreal Forests ◽  
Sonic Anemometer ◽  
Proton Transfer Reaction ◽  
Heat Fluxes ◽  
Emission Rates ◽  
Water Vapour Concentration ◽  
Emission Fluxes ◽  
Flux Measurements ◽  
Ecosystem Flux

Abstract. In this study, we present summertime concentrations and fluxes of biogenic volatile organic compounds (BVOCs) measured at a sub-arctic wetland in northern Sweden using a disjunct eddy-covariance (DEC) technique based on a proton transfer reaction mass spectrometer (PTR-MS). The vegetation at the site was dominated by Sphagnum, Carex and \\textit{Eriophorum} spp. The measurements reported here cover a period of 50 days (1 August to 19 September 2006), approximately one half of the growing season at the site, and allowed to investigate the effect of day-to-day variation in weather as well as of vegetation senescence on daily BVOC fluxes, and on their temperature and light responses. The sensitivity drift of the DEC system was assessed by comparing H3O+-ion cluster formed with water molecules (H3O+(H2O) at m37) with water vapour concentration measurements made using an adjacent humidity sensor, and the applicability of the DEC method was analysed by a comparison of sensible heat fluxes for high frequency and DEC data obtained from the sonic anemometer. These analyses showed no significant PTR-MS sensor drift over a period of several weeks and only a small flux-loss due to high-frequency spectrum omissions. This loss was within the range expected from other studies and the theoretical considerations. Standardised (20 °C and 1000 μmol m−2 s−1 PAR) summer isoprene emission rates found in this study of 329 μg C m−2 (ground area) h−1 were comparable with findings from more southern boreal forests, and fen-like ecosystems. On a diel scale, measured fluxes indicated a stronger temperature dependence than emissions from temperate or (sub)tropical ecosystems. For the first time, to our knowledge, we report ecosystem methanol fluxes from a sub-arctic ecosystem. Maximum daytime emission fluxes were around 270 μg m−2 h−1 (ca. 100 μg C m−2 h−1), and during most nights small negative fluxes directed from the atmosphere to the surface were observed.

scholarly journals Ионно-электронная рекомбинация и тепловые потоки в высокочастотных ионных двигателях

2019 ◽  
Vol 45 (4) ◽  
pp. 3 ◽  
Author(s):  
В.К. Абгарян ◽  
В.Ю. Гидаспов ◽  
А.Б. Надирадзе ◽  
А.А. Семенов
Keyword(s):  
High Frequency ◽  
Numerical Models ◽  
Heat Fluxes ◽  
Temperature Fields ◽  
Structural Elements ◽  
Electron Recombination ◽  
Partial Reflection ◽  
Ion Thrusters ◽  
Radiation Fluxes ◽  
Ion Optical System

AbstractHeat fluxes emitted from plasma to the surface of structural elements of high-frequency (HF) ion thrusters with perforated electrodes of the ion-optical system have been studied. Radiation fluxes formed during ion–electron recombination on surfaces in contact with plasma are considered taking into account their spatial distribution and partial reflection from surfaces. New expressions for the heat fluxes are obtained that should be used as boundary conditions in numerical models for the calculation of temperature fields in HF ion thrusters.

A New Electromagnetic Heating Method to Study Spray Cooling

2015 ◽  
Vol 15 (1) ◽  
pp. 151-167
Author(s):  
M.E. Huerta-Larumbe ◽  
F.A. Acosta-González
Keyword(s):  
Heat Flux ◽  
High Frequency ◽  
Spray Cooling ◽  
Heat Fluxes ◽  
Digital Controller ◽  
Film Boiling ◽  
Metallic Surfaces ◽  
Coil Current ◽  
Frequency Generator ◽  
High Frequency Generator

AbstractThis work shows measured heat fluxes that are removed by air-mist jets under steady-state conditions from different metallic surfaces at temperatures up to 1,200°C. A sample disk is subjected simultaneously to induction heating and spray cooling. In order to reach a set-point temperature for the disk, a digital controller adjusts the power delivered by a 5 kW high-frequency generator to compensate the heat removed by the spray. The heat flux removed by the impinging jet is determined from the measured values of coil current and disk temperature, and from the coupled numerical solution of the Maxwell’s equations together with the heat conduction equation. This method determines heat fluxes within 10% uncertainty. The obtained boiling curves for Pt, Ni and Inconel show that heat flux is described by a single curve in the stable film boiling regime for these metals.

Preliminary Experiments While Designing a Cold Crucible for Metal Melting

2019 ◽  
Vol 5 (3) ◽  
Author(s):  
David Rot ◽  
Jakub Jiřinec
Keyword(s):  
Numerical Simulations ◽  
High Frequency ◽  
Electromagnetic Induction ◽  
Heat Fluxes ◽  
Final Part ◽  
Cold Crucible ◽  
High Frequency Transformer ◽  
Final Design ◽  
Electric Parameters ◽  
Metal Melting

This article deals with issues arising during the design and production of a cold crucible (CC) for melting metals and alloys using electromagnetic induction. The article deals particularly with the results from tests and numerical simulations for designing the CC. The heat fluxes from different metals and their alloys to two different CCs and one calorimeter were measured during the tests. The required magnetohydrodynamic effects on the melted load were verified, and related (independent) electrical and thermal quantities were measured. The dependent electric parameters (R, L, Z) were measured on the inductor and on the primary side of the high frequency transformer. The experiments were numerically simulated first, and the experimental and simulated results were then compared. The final part of the article contains the final design of the CC. The final CC was tested for the transfer of energy from the inductor into a load placed inside the CC and the required magnetohydrodynamic effects on the melted load inside the CC were partly verified too.

scholarly journals The Role of Transient Eddies in North Pacific Blocking Formation and Its Seasonality

2020 ◽  
Vol 77 (7) ◽  
pp. 2453-2470 ◽  
Author(s):  
Jaeyoung Hwang ◽  
Patrick Martineau ◽  
Seok-Woo Son ◽  
Takafumi Miyasaka ◽  
Hisashi Nakamura
Keyword(s):  
North Pacific ◽  
High Frequency ◽  
Wave Breaking ◽  
Low Frequency ◽  
Heat Fluxes ◽  
Background Flow ◽  
Budget Analysis ◽  
The Cross ◽  
A Minor

AbstractThe mechanism of North Pacific (NP) blocking formation is investigated by conducting a reanalysis-based budget analysis of the quasigeostrophic geopotential tendency equation. It is confirmed that the amplification of NP blocking anomalies primarily results from vorticity fluxes with a minor contribution of heat fluxes. In winter, the cross-frequency vorticity fluxes, resulting from interactions between high-frequency eddies and the slowly varying background flow, dominate the blocking formation. The cross-frequency vorticity fluxes, however, become substantially weaker and comparable to the low-frequency vorticity fluxes in summer. This seasonality indicates that the mechanism of NP blocking formation varies with seasons due to the different background flow. It is further found that NP blocking formation is not sensitive to the region of formation (i.e., western vs eastern NP) nor to the type of wave breaking (i.e., cyclonic vs anticyclonic wave breaking).

scholarly journals Optimizing Mooring Placement to Constrain Southern Ocean Air–Sea Fluxes

2020 ◽  
Vol 37 (8) ◽  
pp. 1365-1385
Author(s):  
Yanzhou Wei ◽  
Sarah T. Gille ◽  
Matthew R. Mazloff ◽  
Veronica Tamsitt ◽  
Sebastiaan Swart ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Numerical Weather Prediction ◽  
High Frequency ◽  
Weather Prediction ◽  
Low Frequency ◽  
Heat Fluxes ◽  
Test Case ◽  
Numerical Weather ◽  
Ocean Observing

AbstractProposals from multiple nations to deploy air–sea flux moorings in the Southern Ocean have raised the question of how to optimize the placement of these moorings in order to maximize their utility, both as contributors to the network of observations assimilated in numerical weather prediction and also as a means to study a broad range of processes driving air–sea fluxes. This study, developed as a contribution to the Southern Ocean Observing System (SOOS), proposes criteria that can be used to determine mooring siting to obtain best estimates of net air–sea heat flux (Qnet). Flux moorings are envisioned as one component of a multiplatform observing system, providing valuable in situ point time series measurements to be used alongside satellite data and observations from autonomous platforms and ships. Assimilating models (e.g., numerical weather prediction and reanalysis products) then offer the ability to synthesize the observing system and map properties between observations. This paper develops a framework for designing mooring array configurations to maximize the independence and utility of observations. As a test case, within the meridional band from 35° to 65°S we select eight mooring sites optimized to explain the largest fraction of the total variance (and thus to ensure the least variance of residual components) in the area south of 20°S. Results yield different optimal mooring sites for low-frequency interannual heat fluxes compared with higher-frequency subseasonal fluxes. With eight moorings, we could explain a maximum of 24.6% of high-frequency Qnet variability or 44.7% of low-frequency Qnet variability.

scholarly journals The process of high-frequency intraseasonal oscillation associated with a persistent rainfall event over South China

2021 ◽  
Author(s):  
Bin Zheng ◽  
Yanyan Huang ◽  
Ailan Lin
Keyword(s):  
South China ◽  
High Frequency ◽  
Intraseasonal Oscillation ◽  
Low Frequency ◽  
Zonal Flow ◽  
Heat Fluxes ◽  
Rainfall Event ◽  
Radiative Heating ◽  
Low Level ◽  
Zonal Advection

AbstractIn the present study, the moist static energy (MSE) budget associated with a persistent rainfall event that occurred over South China in late August 2018 (PR1808) was analyzed using ERA-Interim reanalysis data. The results revealed that the PR1808 event was closely related to a 12–30-day intraseasonal oscillation (ISO), with a significant westward-propagating mode. The recharge of MSE occurred before ISO deep convection, and the MSE was discharged during and after the peak precipitation. This result indicates that the recharge-discharge cycle of MSE played an important role in regulating the high-frequency ISO (HF-ISO) process during the PR1808 event. However, the mid-level MSE tendency, rather than the low-level tendency, controlled the column-integrated MSE change in this case, and there was no low-level MSE tendency ahead of HF-ISO convection, which is different from previous studies, implying that shallow convection was not a key factor in this case. The recharge of MSE related to the mid-level MSE change mode was mainly attributed to zonal advection, while the forcing related to radiative heating (longwave and shortwave radiation) and heat fluxes (latent and sensible heat fluxes) contributed little to the change in MSE. Furthermore, for the zonal advection of MSE, the main contribution originated from the advection by the low-frequency zonal flow across the low-frequency MSE gradient, and interactions between high- (low-) frequency zonal flow and low- (high-) frequency MSE. In addition, the disturbances from higher latitudes enhanced the persistent rainfall in this case over South China through the southward shift of baroclinic vorticity.

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