scholarly journals pCO2 Dynamics of Stratified Reservoir in Temperate Zone and CO2 Pulse Emissions During Turnover Events

Water ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1347 ◽  
Author(s):  
Hyungseok Park ◽  
Sewoong Chung
Keyword(s):  
Vertical Mixing ◽  
Temporal Variations ◽  
Mixing Processes ◽  
Atmospheric Flux ◽  
Partial Pressure Of Co2 ◽  
Physical Mixing ◽  
Field Campaigns ◽  
Stratified Reservoir ◽  
The Vertical Distribution ◽  
Measured Water

This study explores the dynamic changes in the partial pressure of CO2 (pCO2) with depth, and the temporal variations of CO2 net atmospheric flux (NAF) in a stratified reservoir. A total of 16 field campaigns were conducted from the summer stratification to fall turnover period in 2017. A random forest (RF) model was developed to estimate the pCO2 using concurrently measured water quality variables. The results showed that the vertical distribution of pCO2 and associated temporal variations of the NAF are closely related to the stratification strength of the reservoir. The reservoir surface pCO2 was supersaturated (1542 µatm) in summer (July 11), but this decreased to undersaturation as algae grew. Meanwhile, dissolved CO2 continuously accumulated below the reservoir mixed-layer due to the thermal stratification barrier and organic-rich floodwater intrusion. Vertical mixing began instantly as the stratification strength began to weaken in mid-October, and the surface pCO2 increased sharply up to 1934 µatm. Consequently, the NAF drastically increased to 3235 mg−CO2 m−2·day−1, which implies that the NAF changes seasonally and large CO2 pulsing occurs during the turnover events. The results provide valuable information about pCO2 variability and physical mixing processes, as well as carbon budget estimation in stratified reservoirs, and offer an improved understanding of these phenomena.

scholarly journals Studying boundary layer methane isotopy and vertical mixing processes at a rewetted peatland site using an unmanned aircraft system

2020 ◽  
Vol 13 (4) ◽  
pp. 1937-1952 ◽  
Author(s):  
Astrid Lampert ◽  
Falk Pätzold ◽  
Magnus O. Asmussen ◽  
Lennart Lobitz ◽  
Thomas Krüger ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Vertical Distribution ◽  
Isotopic Composition ◽  
Water Samples ◽  
Vertical Mixing ◽  
Temperature Inversion ◽  
Mixing Processes ◽  
Air Masses ◽  
The Vertical Distribution ◽  
Different Altitudes

Abstract. The combination of two well-established methods, of quadrocopter-borne air sampling and methane isotopic analyses, is applied to determine the source process of methane at different altitudes and to study mixing processes. A proof-of-concept study was performed to demonstrate the capabilities of quadrocopter air sampling for subsequently analysing the methane isotopic composition δ13C in the laboratory. The advantage of the system compared to classical sampling on the ground and at tall towers is the flexibility concerning sampling location, and in particular the flexible choice of sampling altitude, allowing the study of the layering and mixing of air masses with potentially different spatial origin of air masses and methane. Boundary layer mixing processes and the methane isotopic composition were studied at Polder Zarnekow in Mecklenburg–West Pomerania in the north-east of Germany, which has become a strong source of biogenically produced methane after rewetting the drained and degraded peatland. Methane fluxes are measured continuously at the site. They show high emissions from May to September, and a strong diurnal variability. For two case studies on 23 May and 5 September 2018, vertical profiles of temperature and humidity were recorded up to an altitude of 650 and 1000 m, respectively, during the morning transition. Air samples were taken at different altitudes and analysed in the laboratory for methane isotopic composition. The values showed a different isotopic composition in the vertical distribution during stable conditions in the morning (delta values of −51.5 ‰ below the temperature inversion at an altitude of 150 m on 23 May 2018 and at an altitude of 50 m on 5 September 2018, delta values of −50.1 ‰ above). After the onset of turbulent mixing, the isotopic composition was the same throughout the vertical column with a mean delta value of −49.9 ± 0.45 ‰. The systematically more negative delta values occurred only as long as the nocturnal temperature inversion was present. During the September study, water samples were analysed as well for methane concentration and isotopic composition in order to provide a link between surface and atmosphere. The water samples reveal high variability on horizontal scales of a few tens of metres for this particular case. The airborne sampling system and consecutive analysis chain were shown to provide reliable and reproducible results for two samples obtained simultaneously. The method presents a powerful tool for distinguishing the source process of methane at different altitudes. The isotopic composition showed clearly depleted delta values directly above a biological methane source when vertical mixing was hampered by a temperature inversion, and different delta values above, where the air masses originate from a different footprint area. The vertical distribution of methane isotopic composition can serve as tracer for mixing processes of methane within the atmospheric boundary layer.

scholarly journals A Hydrodynamical Model for Calculating the Vertical Temperature Profile in Lakes During Cooling

1983 ◽  
Vol 14 (4) ◽  
pp. 239-254 ◽  
Author(s):  
Jörgen Sahlberg
Keyword(s):  
Heat Flux ◽  
Temperature Profile ◽  
Vertical Mixing ◽  
Hydrodynamical Model ◽  
Measured Temperature ◽  
Vertical Temperature ◽  
Mixing Rate ◽  
Mixing Processes ◽  
Vertical Temperature Profile ◽  
Radiation Fluxes

A one-dimensional hydrodynamical model is used for simulating the vertical temperature profile in a lake during cooling conditions. The vertical mixing rate is calculated by solving the equations for turbulent kinetic energy, k, and dissipation of energy, ε. The heat exchange between the water and atmosphere consists of the radiation fluxes, sensible and latent heat flux. Temperature measurements from Lake Väsman during November-December, 1981, were used in the verification study. The agreement between calculated and measured temperature profiles is very good. This indicates that both the mixing processes and the net heat flux are well described in the model.

scholarly journals The sensitivity of aerosol in Europe to two different emission inventories and temporal distribution of emissions

2006 ◽  
Vol 6 (12) ◽  
pp. 4287-4309 ◽  
Author(s):  
A. de Meij ◽  
M. Krol ◽  
F. Dentener ◽  
E. Vignati ◽  
C. Cuvelier ◽  
...  
Keyword(s):  
Emission Inventory ◽  
Dominant Role ◽  
Temporal Distribution ◽  
Temporal Variations ◽  
Anthropogenic Emissions ◽  
Emission Inventories ◽  
Global Transport ◽  
Modelling Uncertainties ◽  
The Vertical Distribution ◽  
Nitrate Aerosol

Abstract. The sensitivity to two different emission inventories, injection altitude and temporal variations of anthropogenic emissions in aerosol modelling is studied, using the two way nested global transport chemistry model TM5 focussing on Europe in June and December 2000. The simulations of gas and aerosol concentrations and aerosol optical depth (AOD) with the EMEP and AEROCOM emission inventories are compared with EMEP gas and aerosol surface based measurements, AERONET sun photometers retrievals and MODIS satellite data. For the aerosol precursor gases SO2 and NOx in both months the model results calculated with the EMEP inventory agree better (overestimated by a factor 1.3 for both SO2 and NOx) with the EMEP measurements than the simulation with the AEROCOM inventory (overestimated by a factor 2.4 and 1.9, respectively). Besides the differences in total emissions between the two inventories, an important role is also played by the vertical distribution of SO2 and NOx emissions in understanding the differences between the EMEP and AEROCOM inventories. In December NOx and SO2 from both simulations agree within 50% with observations. In June SO4= evaluated with the EMEP emission inventory agrees slightly better with surface observations than the AEROCOM simulation, whereas in December the use of both inventories results in an underestimate of SO4 with a factor 2. Nitrate aerosol measured in summer is not reliable, however in December nitrate aerosol calculations with the EMEP and AEROCOM emissions agree with 30%, and 60%, respectively with the filter measurements. Differences are caused by the total emissions and the temporal distribution of the aerosol precursor gases NOx and NH3. Despite these differences, we show that the column integrated AOD is less sensitive to the underlying emission inventories. Calculated AOD values with both emission inventories underestimate the observed AERONET AOD values by 20–30%, whereas a case study using MODIS data shows a high spatial agreement. Our evaluation of the role of temporal distribution of anthropogenic emissions on aerosol calculations shows that the daily and weekly temporal distributions of the emissions are only important for NOx, NH3 and aerosol nitrate. However, for all aerosol species SO4=, NH4+, POM, BC, as well as for AOD, the seasonal temporal variations used in the emission inventory are important. Our study shows the value of including at least seasonal information on anthropogenic emissions, although from a comparison with a range of measurements it is often difficult to firmly identify the superiority of specific emission inventories, since other modelling uncertainties, e.g. related to transport, aerosol removal, water uptake, and model resolution, play a dominant role.

Key factors in vertical mixing processes in a reservoir bordering the Pantanal floodplain, Brazil

2015 ◽  
Vol 60 (9) ◽  
pp. 1508-1519 ◽  
Author(s):  
Ibraim Fantin-Cruz ◽  
Olavo Pedrollo ◽  
Cláudia C. Bonecker ◽  
Peter Zeilhofer
Keyword(s):  
Vertical Mixing ◽  
Key Factors ◽  
Mixing Processes

Mechanisms for nitrogen supply to the Australian North West Shelf

1985 ◽  
Vol 36 (6) ◽  
pp. 753 ◽  
Author(s):  
PE Holloway ◽  
SE Humphries ◽  
M Atkinson ◽  
J Imberger
Keyword(s):  
River Flow ◽  
Tidal Flow ◽  
Vertical Mixing ◽  
Low Frequency ◽  
Transport Processes ◽  
Physical Processes ◽  
Mixing Processes ◽  
North West ◽  
Tidal Motion ◽  
The North

An upper bound for the rate of supply of new nitrate required to maintain the observed primary production on the North West Shelf is estimated to be 0.1 g N m-2 day -1. Nitrate concentrations over the shelf and slope regions are high ( > 100 mg N m-3, in water deeper than - 100 m and usually low (~10 mg N m-3), on the shelf. River flow is weak and carries little nutrient into the shelf waters and so it remains for ocean physical processes to advect and mix the nutrient-rich deep waters onto the shallower shelf regions to meet the nutrient demand. Several mechanisms are reviewed to determine their potential in carrying out the required transport processes. Estimates of the advection of nitrate onto the shelf show that both semi-diurnal tidal flow and low-frequency (periods > 35 h) upwelling events can each contribute approximately half the required demand, providing there is rapid use of nutrients. The upwelling events occur in summer and are associated with reversals of the south-west-flowing Leeuwin Current. Tropical cyclones are also shown to be capable of meeting a small, but significant, portion of the demand through enrichment of the surface layers in the offshelf waters by upwelling and vertical mixing. The enriched water can then be advected onto the shelf. Both tidal and internal tidal motion have the potential to transport nitrate onto the shelf from deeper water through vertical and horizontal mixing processes. However, these processes are difficult to quantify accurately. It is concluded that nitrogen is supplied to this shelf ecosystem by physical processes that are regular throughout the year, as opposed to large sporadic events that occur only once or twice a year.

scholarly journals The influence of the vertical distribution of emissions on tropospheric chemistry

2009 ◽  
Vol 9 (4) ◽  
pp. 16051-16083
Author(s):  
A. Pozzer ◽  
P. Jöckel ◽  
J. Van Aardenne
Keyword(s):  
Vertical Distribution ◽  
Atmospheric Chemistry ◽  
General Circulation ◽  
Circulation Model ◽  
Tropospheric Chemistry ◽  
Aircraft Observations ◽  
Field Campaigns ◽  
The Vertical Distribution ◽  
Lower Correlation ◽  
Model Layer

Abstract. The atmospheric chemistry general circulation model EMAC (ECHAM5/MESSy atmospheric chemistry) is used to investigate the effect of height dependent emissions on tropospheric chemistry. In a sensitivity simulation, anthropogenic and biomass burning emissions are released in the lowest model layer. The resulting tracer distributions are compared to those of a former simulation applying height dependent emissions. Although the differences between the two simulations in the free troposphere are small (less than 5%), large differences are present in polluted regions at the surface, in particular for NOx (more than 100%) and non-methane hydrocarbons (up to 30%), whereas for OH the differences at the same locations are somewhat lower (15%). Global ozone formation is virtually unaffected by the choice of the vertical distribution of emissions. Nevertheless, local ozone changes can be up to 30%. Model results of both simulations are further compared to observations from field campaigns and to data from measurement stations. The two simulations show no significant differences when compared to aircraft observations. In contrast, for measurements from surface stations, the simulation with emissions in the lowest model layer gives a 20% lower correlation to the observations compared to the simulation with height dependent emissions.

scholarly journals An Ocean Modeling Study To Quantify Wind Forcing and Oceanic Mixing Effects on The Tropical North Pacific Subsurface Warm Bias in CMIP and OMIP Simulations

2021 ◽  
Author(s):  
Yuchao Zhu ◽  
Rong-Hua Zhang ◽  
Delei Li
Keyword(s):  
Boundary Layer ◽  
North Pacific ◽  
Thermal Structure ◽  
Vertical Mixing ◽  
Upper Ocean ◽  
Subsurface Temperature ◽  
Mixing Processes ◽  
Warm Bias ◽  
The Past ◽  
Upper Boundary

Abstract Sea surface temperature (SST) bias in the climate models has been a focus in the past, but subsurface temperature biases have not been received much attention yet. In this study, subsurface temperature biases in the Tropical North Pacific (TNP) are investigated by analyzing the CMIP6, CMIP5 and OMIP products, and performing ocean model simulations. It is found that almost all the CMIP and OMIP simulations have a pronounced subsurface warm bias (SWB) in the northeastern tropical Pacific (NETP), and the model developments over the past decade do not indicate obvious improvements in bias pattern and magnitude from CMIP5 to the latest version CMIP6. This SWB is primarily caused by the model deficiencies in the simulated surface wind stress curl (WSC) in the NETP, which is too weak to produce a sufficient Ekman upwelling, a bias that also exists in OMIP simulations. The uncertainties in the parameterizations of the oceanic vertical mixing processes also make a great contribution, and it is demonstrated that the estimated oceanic vertical diffusivities are overestimated both in the upper boundary layer and the interior in the CMIP and OMIP simulations. The relationship between the SWB and the misrepresented oceanic vertical mixing processes are investigated by conducting several ocean-only experiments, in which the upper boundary layer mixing is modified by reducing the wind stirring effect in the Kraus-Turner type bulk mixed-layer approach, and the interior mixing is constrained by using the Argo-derived diffusivity. By applying these modifications to oceanic vertical mixing schemes, the SWB is greatly reduced in the NETP. The consequences of this SWB are further analyzed. Because the thermal structure in the NETP can influence the simulations of oceanic circulations and equatorial upper-ocean thermal structure, the large SWB in the CMIP6 models tends to produce a weak equatorward water transport in the subsurface TNP, a weak equatorial upwelling and a warm equatorial upper ocean.

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