| 1. |
- Lundberg, Angela, et al.
(författare)
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New approach to the measurement of interception evaporation
- 1997
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Ingår i: Journal of Atmospheric and Oceanic Technology. - 0739-0572 .- 1520-0426. ; 14:5, s. 1023-1035
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Tidskriftsartikel (refereegranskat)abstract
- Evaporation of water intercepted by vegetation represents an important (sometimes major) part of evapotranspiration in temperate regions. Interception evaporation is an important process where insufficient measurement techniques hamper progress in knowledge and modeling. An ideal technique to study the interception evaporation process should monitor intercepted mass (and its vertical distribution) and interception loss with high accuracy (0.1 mm) and time resolution (1 min), and give correct area estimates. The method should be inexpensive, require minor supervision during extended periods, and work in dense forests. Net precipitation techniques, in which interception evaporation is determined from the difference between gross precipitation (measured with funnels) and throughfall (measured with funnels, troughs, or plastic sheet net-rainfall gauges) fulfill many of the requirements but usually have a too-low accuracy and time resolution for process studies. Precipitation measurements are normally affected by distortion of the wind field around gauges as well as by adhesive and evaporative losses. Throughfall measurements with precipitation funnels, troughs, or plastic sheet net-rainfall gauges, manually emptied or combined with tipping buckets, usually have too-low accuracy and time resolution for process studies and are impaired by adhesive losses. A new loadcell-based system to determine interception evaporation from gross and net precipitation is presented. A weighing gauge with minimal wind loss is used for precipitation, and weighing troughs are used for throughfall measurements. The weighing troughs minimize adhesive-loss errors and react instantaneously. Preliminary results with the method confirm that it can be used for process studies with a high accuracy (0.1 mm) and a high time resolution (1 min).
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| 2. |
- Andersson, Andreas, et al.
(författare)
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Using a High-Frequency Fluorescent Oxygen Probe in Atmospheric Eddy Covariance Applications
- 2014
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Ingår i: Journal of Atmospheric and Oceanic Technology. - : American Meteorological Society. - 0739-0572 .- 1520-0426. ; 31:11, s. 2498-2511
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Tidskriftsartikel (refereegranskat)abstract
- During the years 2010-13, atmospheric eddy covariance measurement of oxygen was performed at the marine site Ostergarnsholm in the Baltic Sea. The fast response optode Microx TX3 was used with two different types of tapered sensors. In spite of the increased lifetime, the optical isolated sensor is limited by the slower response time and is unsuitable for ground-based eddy covariance measurements. The sensor without optical isolation shows a -2/3 slope within the inertial subrange and attains sufficient response time and precision to be used in air-sea applications during continuous periods of 1-4 days. Spectral and cospectral analysis shows oxygen measured with the nonoptical isolated sensor to follow the same shape as for CO2 and water vapor when normalized. The sampling rate of the Microx TX3 is 2Hz; however, the sensor was found to have a limited response and resolution, yielding a flux loss in the frequency range f > 0.3Hz. This can be corrected for by applying cospectral similarity simultaneously using measurements of latent heat as the reference signal. On average the magnitude of the cospectral correction added 20% to the uncorrected oxygen flux during neutral atmospheric stratification.
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| 3. |
- Heuzé, Céline, 1988, et al.
(författare)
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Optimization of Sea Surface Current Retrieval Using a Maximum Cross-Correlation Technique on Modeled Sea Surface Temperature
- 2017
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Ingår i: Journal of Atmospheric and Oceanic Technology. - : American Meteorological Society. - 1520-0426 .- 0739-0572. ; 34:10, s. 2245-2255
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Tidskriftsartikel (refereegranskat)abstract
- Using sea surface temperature from satellite images to retrieve sea surface currents is not a new idea, but so far its operational near-real-time implementation has not been possible. Validation studies are too region specific or uncertain, sometimes because of the satellite images themselves. Moreover, the sensitivity of the most common retrieval method, the maximum cross correlation, to the parameters that have to be set is unknown. Using model outputs instead of satellite images, biases induced by this method are assessed here, for four different seas of western Europe, and the best of nine settings and eight temporal resolutions are determined. The regions with strong currents return the most accurate results when tracking a 20-km pattern between two images separated by 6-9 h. The regions with weak currents favor a smaller pattern and a shorter time interval, although their main problem is not inaccurate results but missing results: where the velocity is too low to be picked by the retrieval. The results are not impaired by the restrictions imposed by ocean surface current dynamics and available satellite technology, indicating that automated sea surface current retrieval from sea surface temperature images is feasible, for pollution confinement, search and rescue, and even for more energy-efficient and comfortable ship navigation.
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| 4. |
- Heuzé, Céline, 1988, et al.
(författare)
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Optimization of Sea Surface Current Retrieval Using a Maximum Cross-Correlation Technique on Modeled Sea Surface Temperature
- 2017
-
Ingår i: Journal of Atmospheric and Oceanic Technology. - 0739-0572 .- 1520-0426. ; 34, s. 2245-2255
-
Tidskriftsartikel (refereegranskat)abstract
- Using sea surface temperature from satellite images to retrieve sea surface currents is not a new idea, but so far its operational near-real-time implementation has not been possible. Validation studies are too region specific or uncertain, sometimes because of the satellite images themselves. Moreover, the sensitivity of the most common retrieval method, the maximum cross correlation, to the parameters that have to be set is unknown. Using model outputs instead of satellite images, biases induced by this method are assessed here, for four different seas of western Europe, and the best of nine settings and eight temporal resolutions are determined. The regions with strong currents return the most accurate results when tracking a 20-km pattern between two images separated by 6–9 h. The regions with weak currents favor a smaller pattern and a shorter time interval, although their main problem is not inaccurate results but missing results: where the velocity is too low to be picked by the retrieval. The results are not impaired by the restrictions imposed by ocean surface current dynamics and available satellite technology, indicating that automated sea surface current retrieval from sea surface temperature images is feasible, for pollution confinement, search and rescue, and even for more energy-efficient and comfortable ship navigation.
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| 5. |
- Hieronymus, M., et al.
(författare)
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On the Application of Machine Learning Techniques to Regression Problems in Sea Level Studies
- 2019
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Ingår i: Journal of Atmospheric and Oceanic Technology. - : American Meteorological Society. - 0739-0572 .- 1520-0426. ; 36:9, s. 1889-1902
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Tidskriftsartikel (refereegranskat)abstract
- Long sea level records with high temporal resolution are of paramount importance for future coastal protection and adaptation plans. Here we discuss the application of machine learning techniques to some regression problems commonly encountered when analyzing such time series. The performance of artificial neural networks is compared with that of multiple linear regression models on sea level data from the Swedish coast. The neural networks are found to be superior when local sea level forcing is used together with remote sea level forcing and meteorological forcing, whereas the linear models and the neural networks show similar performance when local sea level forcing is excluded. The overall performance of the machine learning algorithms is good, often surpassing that of the much more computationally costly numerical ocean models used at our institute.
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| 6. |
- Jonsson, Patrik, 1968-, et al.
(författare)
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Infrared Thermometry in winter road maintenance
- 2012
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Ingår i: Journal of Atmospheric and Oceanic Technology. - 0739-0572 .- 1520-0426. ; 29:6, s. 846-856
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Tidskriftsartikel (refereegranskat)abstract
- There is significant interest among road authorities in measuring pavement conditions to perform appropriate winter road maintenance. The most common monitoring methods are based on pavement-mounted sensors. This study's hypothesis is that the temperature distribution in a pavement can be measured by means of a nonintrusive method to retrieve the topmost pavement temperature values. By utilizing the latest infrared (IR) technology, it is possible to retrieve additional information concerning both road temperatures and road conditions. The authors discovered that surface temperature readings from IR sensors are more reliable than data retrieved from traditional surface-mounted sensors during wet, snowy, or icyroad conditions. It was also possible to detect changes in the road condition by examining how the temperatures in wheel tracks and in between the wheel tracks differ from a reference dry road condition. The conclusion was that nonintrusive measurement of the road temperature is able to provide an increase in relation to the knowledge about both the road temperature and the road condition. Another conclusion was that the surface temperature should not be considered as being equal to the ground temperatures retrieved from traditional surface-mounted sensors except under conditions of dry, stable roadways. © 2012 American Meteorological Society.
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| 7. |
- Kottayil, Ajil, et al.
(författare)
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On the importance of Vaisala RS92 radiosonde humidity corrections for a better agreement between measured and modeled satellite radiances
- 2012
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Ingår i: Journal of Atmospheric and Oceanic Technology. - 0739-0572 .- 1520-0426. ; 29:2, s. 248-259
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Tidskriftsartikel (refereegranskat)abstract
- A study has been carried out to assess the importance of radiosonde corrections in improving the agreement between satellite and radiosonde measurements of upper-tropospheric humidity. Infrared [High Resolution Infrared Radiation Sounder (HIRS)-12] and microwave [Advanced Microwave Sounding Unit (AMSU)-18] measurements from the NOAA-17 satellite were used for this purpose. The agreement was assessed by comparing the satellite measurements against simulated measurements using collocated radiosonde profiles of the Atmospheric Radiation Measurement (ARM) Program undertaken at tropical and midlatitude sites. The Atmospheric Radiative Transfer Simulator (ARTS) was used to simulate the satellite radiances. The comparisons have been done under clear-sky conditions, separately for daytime and nighttime soundings. Only Vaisala RS92 radiosonde sensors were used and an empirical correction (EC) was applied to the radiosonde measurements. The EC includes correction for mean calibration bias and for solar radiation error, and it removes radiosonde bias relative to three instruments of known accuracy. For the nighttime dataset, the EC significantly reduces the bias from 0.63 to −0.10 K in AMSU-18 and from 1.26 to 0.35 K in HIRS-12. The EC has an even greater impact on the daytime dataset with a bias reduction from 2.38 to 0.28 K in AMSU-18 and from 2.51 to 0.59 K in HIRS-12. The present study promises a more accurate approach in future radiosonde-based studies in the upper troposphere.
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| 8. |
- Kuhn, Thomas, et al.
(författare)
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Improved imaging and image analysis system for application to measurement of small ice crystals
- 2012
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Ingår i: Journal of Atmospheric and Oceanic Technology. - 0739-0572 .- 1520-0426. ; 29:12, s. 1811-1824
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Tidskriftsartikel (refereegranskat)abstract
- Accurate knowledge of ice particle size and shape distribution is required for understanding of atmospheric microphysical processes. While larger ice particles are easily measured with a variety of sensors, the measurement of small ice particles with sizes down to a few micrometers remains challenging. Here the authors report the development of a system that measures the size and shape of small ice particles using a novel combination of high-resolution imaging and high-speed automated image classification. The optical system has a pixel resolution of 0.2 μm and a resolving power of approximately 1 μm. This imaging instrument is integrated into a cryogenic flow tube that allows precise control of experimental conditions.This study also describes an automated method for the high-speed analysis of high-resolution particle images. Each particle is located in the image using a Sobel edge detector, the border is vectorized, and a polygon representing the border is found. The vertices of this polygon are expressed in complex coordinates, and an analytic implementation of Fourier shape descriptors is used for piecewise integration along the edges of the polygon.The authors demonstrate the capabilities of this system in a study of the early-stage growth of ice particles, which are grown for approximately 1 min at fixed temperature and saturated water vapor concentrations in the cryogenic flowtube. Ice particle shapes and size distributions are reported and compared with habit diagrams found in the literature. The capability of the shape recognition system is verified by comparison with manual classification.
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| 9. |
- Liang, Xi, et al.
(författare)
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Assimilating Copernicus SST Data into a Pan-Arctic Ice–Ocean Coupled Model with a Local SEIK Filter
- 2017
-
Ingår i: Journal of Atmospheric and Oceanic Technology. - : American Meteorological Society. - 0739-0572 .- 1520-0426. ; 34:9, s. 1985-1999
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Tidskriftsartikel (refereegranskat)abstract
- Sea surface temperature (SST) data from the Copernicus Marine Environment Monitoring Service are assimilated into a pan-Arctic ice–ocean coupled model using the ensemble-based local singular evolutive interpolated Kalman (LSEIK) filter. This study found that the SST deviation between model hindcasts and independent SST observations is reduced by the assimilation. Compared with model results without data assimilation, the deviation between the model hindcasts and independent SST observations has decreased by up to 0.2°C at the end of summer. The strongest SST improvements are located in the Greenland Sea, the Beaufort Sea, and the Canadian Arctic Archipelago. The SST assimilation also changes the sea ice concentration (SIC). Improvements of the ice concentrations are found in the Canadian Arctic Archipelago, the Beaufort Sea, and the central Arctic basin, while negative effects occur in the west area of the eastern Siberian Sea and the Laptev Sea. Also, sea ice thickness (SIT) benefits from ensemble SST assimilation. A comparison with upward-looking sonar observations reveals that hindcasts of SIT are improved in the Beaufort Sea by assimilating reliable SST observations into light ice areas. This study illustrates the advantages of assimilating SST observations into an ice–ocean coupled model system and suggests that SST assimilation can improve SIT hindcasts regionally during the melting season.
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| 10. |
- Meier, HEM, et al.
(författare)
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Performance analysis of a multiprocessor coupled ice-ocean model for the Baltic Sea
- 2002
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Ingår i: Journal of Atmospheric and Oceanic Technology. - 0739-0572 .- 1520-0426. ; 19:1, s. 114-124
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Tidskriftsartikel (refereegranskat)abstract
- Within the Swedish Regional Climate Modelling Programme (SWECLIM) a 3D coupled ice-ocean model for the Baltic Sea has been developed to simulate physical processes on timescales of hours to decades. The model code is based on the global ocean GCM of the Ocean Circulation Climate Advanced Modelling (OCCAM) project and has been optimized for massively parallel computer architectures. The Hibler-type dynamic-thermodynamic sea ice model utilizes elastic-viscous-plastic rheology resulting in a fully explicit numerical scheme that improves computational efficiency. A detailed performance analysis shows that the ice model causes generic workload imbalance between involved processors. An improved domain partitioning technique minimizes load imbalance, but cannot solve the problem completely. However, it is shown that the total load imbalance is not more than 13% for a mild winter and about 8% for a severe winter. With respect to parallel processor performance, the code makes the best use of available computer resources.
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| 11. |
- Mensah, Vigan, et al.
(författare)
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A Correction for the Thermal Mass-Induced Errors of CTD Tags Mounted on Marine Mammals
- 2018
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Ingår i: Journal of Atmospheric and Oceanic Technology. - 0739-0572 .- 1520-0426. ; 35:6, s. 1237-1252
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Tidskriftsartikel (refereegranskat)abstract
- The effect of thermal mass on the salinity estimate from conductivity-temperature-depth (CTD) tags sensor mounted on marine mammals is documented, and a correction scheme is proposed to mitigate its impact. The algorithm developed here allows for a direct correction of the salinity data, rather than a correction of the sample's conductivity and temperature. The amplitude of the thermal mass-induced error on salinity and its correction are evaluated via comparison between data from CTD tags and from Sea-Bird Scientific CTD used as a reference. Thermal mass error on salinity appears to be generally O(10(-2)) g kg(-1), it may reach O(10(-1)) g kg(-1), and it tends to increase together with the magnitude of the cumulated temperature gradient (T-HP) within the water column. The correction we propose yields an error decrease of up to similar to 60% if correction coefficients specific to a certain tag or environment are calculated, and up to 50% if a default value for the coefficients is provided. The correction with the default coefficients was also evaluated using over 22 000 in situ dive data from five tags deployed in the Southern Ocean and is found to yield significant and systematic improvements on the salinity data, including for profiles whose T-HP was weak and the error small. The correction proposed here yields substantial improvements in the density estimates, although a thermal mass-induced error in temperature measurements exists for very large T-HP and has yet to be corrected.
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| 12. |
- Muchowski, Julia, et al.
(författare)
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Potential and Limitations of a Commercial Broadband Echo Sounder for Remote Observations of Turbulent Mixing
- 2022
-
Ingår i: Journal of Atmospheric and Oceanic Technology. - 0739-0572 .- 1520-0426. ; 39:12, s. 1985-2003
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Tidskriftsartikel (refereegranskat)abstract
- Stratified oceanic turbulence is strongly intermittent in time and space, and therefore generally underresolved by currently available in situ observational approaches. A promising tool to at least partly overcome this constraint are broadband acoustic observations of turbulent microstructure that have the potential to provide mixing parameters at orders of magnitude higher resolution compared to conventional approaches. Here, we discuss the applicability, limitations, and measurement uncertainties of this approach for some prototypical turbulent flows (stratified shear layers, turbulent flow across a sill), based on a comparison of broadband acoustic observations and data from a free-falling turbulence microstructure profiler. We find that broadband acoustics are able to provide a quantitative description of turbulence energy dissipation in stratified shear layers (correlation coefficient r = 0.84) if the stratification parameters required by the method are carefully preprocessed. Essential components of our suggested preprocessing algorithm are 1) a vertical low-pass filtering of temperature and salinity profiles at a scale slightly larger than the Ozmidov length scale of turbulence and 2) an automated elimination of weakly stratified layers according to a gradient threshold criterion. We also show that in weakly stratified conditions, the acoustic approach may yield acceptable results if representative averaged vertical temperature and salinity gradients rather than local gradients are used. Our findings provide a step toward routine turbulence measurements in the upper ocean from moving vessels by combining broadband acoustics with in situ CTD profiles.
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| 13. |
- Nilsson, Erik, 1983-, et al.
(författare)
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Evaluating humidity and sea salt disturbances on CO2 flux measurements
- 2018
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Ingår i: Journal of Atmospheric and Oceanic Technology. - 0739-0572 .- 1520-0426. ; 35, s. 859-875
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Tidskriftsartikel (refereegranskat)abstract
- Global oceans are an important sink of atmospheric carbon dioxide (CO2). Therefore, understanding the air-sea flux of CO2 is a vital part in describing the global carbon balance. Eddy covariance (EC) measurements are often used to study CO2 fluxes from both land and ocean. CO2 are usually measured with infrared absorption sensors, which at the same time measure water vapor. Studies have shown that presence of water vapor fluctuations in the sampling air potentially result in erroneous CO2 flux measurements due to cross-sensitivity of the sensor. Here we compare measured CO2 fluxes from both enclosed path Li-Cor 7200 sensors and open-path Li-Cor 7500 instruments from an inland measurement site and a marine site. We also introduce new quality control criteria based upon a Relative Signal Strength Indicator (RSSI). The sampling gas in one of the Li-Cor 7200 instruments was dried by means of a multi-tube diffusion dryer so that the water vapor fluxes were close to zero. With this setup we investigated the effect that cross-sensitivity of the CO2 signal to water vapor can have on the CO2 fluxes. The dryer had no significant effect on the CO2 fluxes. We tested the hypothesis that the cross-sensitivity effect is caused by hygroscopic particles such as sea salt by spraying a saline solution on the windows of the Li-Cor 7200 instruments during the inland field test. Our results confirm earlier findings that sea salt contamination can affect CO2 fluxes significantly and confirm earlier findings, that drying the sampling air for the gas analyzer is an effective method to reduce this signal contamination.
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| 14. |
- Nilsson, Erik O., 1983-, et al.
(författare)
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Flux attenuation due to sensor displacement over sea
- 2010
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Ingår i: Journal of Atmospheric and Oceanic Technology. - 45 Beacon Street Boston, MA 02108-3693 : American Meteorological Society. - 0739-0572 .- 1520-0426. ; 27:5, s. 856-868
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Tidskriftsartikel (refereegranskat)abstract
- When using the eddy correlation method to measure turbulent scalar fluxes, there is often a spatial separation between the instruments measuring the scalar and the vertical velocity. The attenuation of the flux due to this separation is studied here for marine conditions. Measurements of a two-point covariance between vertical velocity and temperature are compared to covariance measurements from collocated sensors for both horizontal and vertical displacements, with the purpose of finding the approximate functions to describe the flux loss for typical separation distances. On the basis of this study’s measurements, there is only a slight directional dependence (i.e., streamwise or crosswind separation) of the flux loss for sensor separation distances less than 1 m but an increasing dependence with increasing displacement distance. For a vertical displacement, observations from this study confirm that flux loss is less with the scalar sensor positioned below the velocity sensor than at an equal distance above. Furthermore, the data show a clear dependence on atmospheric stability with increasing flux loss for increasing stable stratification, but it is not as large as that found in previous studies of flux attenuation over land. For example, the authors compare estimated flux loss for neutral and moderately stable (z/L = 0.3) stratification at a measuring height of z = 10 m and a sensor displacement r = 0.3 m, where L is the Obukhov length. For neutral (stable, z/L = 0.3) stratification the estimated loss of flux is 3% (5%) of the total flux for horizontal displacement. Whereas for an equal vertical separation the estimates are 2% (4%) when the scalar sensor is placed above the anemometer but less than 1% (2%) if it is placed below. Thus, the authors conclude that placing the scalar sensor below the anemometer minimizes the flux loss due to sensor separation, and that a simple correction function can be used to quantify the mean flux loss due to sensor separation over sea.
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| 15. |
- Ribas-Ribas, Mariana, et al.
(författare)
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Sea surface scanner (S3) : A catamaran for high-resolution measurements of biogeochemical properties of the sea surface microlayer
- 2017
-
Ingår i: Journal of Atmospheric and Oceanic Technology. - : American Meteorological Society. - 0739-0572 .- 1520-0426. ; 34:7, s. 1433-1448
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes a state-of-the-art research catamaran to investigate processes such as air–sea gas exchange, heat exchange, surface blooms, and photochemistry at the sea surface microlayer (SML) with high-resolution measurements of 0.1-Hz frequency. As the boundary layer between the ocean and the atmosphere, the SML covers 70% of Earth. The remote-controlled Sea Surface Scanner is based on a glass disk sampler to automate the sampling of the thin SML, overcoming the disadvantages of techniques such as low volume sampling and ex situ measurement of the SML. A suite of in situ sensors for seven biogeochemical parameters (temperature, pH, dissolved oxygen, salinity, chromophoric dissolved organic matter, chlorophyll-a, and photosynthetic efficiency) was implemented to characterize the SML in reference to the mixed bulk water. The Sea Surface Scanner has the capability to collect 24 discrete water samples with a volume of 1 L each for further laboratory analysis. Meteorological parameters such as wind speed influence SML properties and are continuously monitored. This paper reports the use of the Sea Surface Scanner to identify and study (i) upwelling regions and associated fronts, (ii) rain events, and (iii) the occurrence of surface blooms. The high patchiness of the SML was detected during the observed sea surface phenomena, and high-resolution mapping of the biogeochemical parameters of the oceanic boundary layer to the atmosphere are presented for the first time. The Sea Surface Scanner is a new technology to map and understand sea surface processes and, ultimately, to fill the gaps in knowledge about ocean–atmosphere interactions relevant to ocean and climate science.
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| 16. |
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| 17. |
- Siegelman, L., et al.
(författare)
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Correction and Accuracy of High- and Low-Resolution CTD Data from Animal-Borne Instruments
- 2019
-
Ingår i: Journal of Atmospheric and Oceanic Technology. - : American Meteorological Society. - 0739-0572 .- 1520-0426. ; 36:5, s. 745-760
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Tidskriftsartikel (refereegranskat)abstract
- Most available CTD Satellite Relay Data Logger (CTD-SRDL) profiles are heavily compressed before satellite transmission. High-resolution profiles recorded at the sampling frequency of 0.5 Hz are, however, available upon physical retrieval of the logger. Between 2014 and 2018, several loggers deployed on elephant seals in the Southern Ocean have been set in continuous recording mode, capturing both the ascent and descent for over 60 profiles per day during several months, opening new horizons for the physical oceanography community. Taking advantage of a new dataset made of seven such loggers, a postprocessing procedure is proposed and validated to improve the quality of all CTD-SRDL data: that is, both high-resolution profiles and compressed low-resolution ones. First, temperature and conductivity are corrected for a thermal mass effect. Then salinity spiking and density inversion are removed by adjusting salinity while leaving temperature unchanged. This method, applied here to more than 50 000 profiles, yields significant and systematic improvements in both temperature and salinity, particularly in regions of rapid temperature variation. The continuous high-resolution dataset is then used to provide updated accuracy estimates of CTD-SRDL data. For high-resolution data, accuracies are estimated to be of +/- 0.02 degrees C for temperature and +/- 0.03 g kg(-1) for salinity. For low-resolution data, transmitted data points have similar accuracies; however, reconstructed temperature profiles have a reduced accuracy associated with the vertical interpolation of +/- 0.04 degrees C and a nearly unchanged salinity accuracy of +/- 0.03 g kg(-1).
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| 18. |
- Thornton, Brett F., et al.
(författare)
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A High-Volume Cryosampler and Sample Purification System for Bromine Isotope Studies of Methyl Bromide
- 2013
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Ingår i: Journal of Atmospheric and Oceanic Technology. - 0739-0572 .- 1520-0426. ; 30:9, s. 2095-2107
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Tidskriftsartikel (refereegranskat)abstract
- A system was developed for collecting from the ambient atmosphere the methyl halides CH3Cl and CH3Br in quantities sufficient for chlorine and bromine isotope analysis. The construction and operation of the novel cryogenic collection system (cryosampler) and sample purification system developed for this task are described. This study demonstrates the capability of the cryosampler by quantifying the CH3Cl and CH3Br collected from atmospheric samples and the nonfractionating bromine isotope fingerprint of CH3Br from synthetic air samples of controlled composition. An optimized cryosampler operation time of 4 h at a flow rate of 15 L min(-1) is applied to yield the nearly 40 ng required for subsequent Br-81-CH3Br analyses. The sample purification system is designed around a packed column gas chromatography-quadropole-mass spectrometry (GCqMS) system with three additional cryotraps and backflushing capacity. The system's suitability was tested by observing both the mass recovery and the lack of Br-81 isotope fractionation induced during sample purification under varying flow rates and loading scenarios. To demonstrate that the entire system samples and dependably delivers CH3Br to the isotope analysis system without inducing isotope fractionation, diluted synthetic air mixtures prepared from standard gases were processed through the entire system, yielding a Br-81-CH3Br of +0.03 parts per thousand +/- 0.10 parts per thousand relative to their starting composition. Finally, the combined cryosampler-purification and analysis system was applied to demonstrate the first-ever Br-81-CH3Br in the ambient atmosphere with two samples collected in the autumn of 2011, yielding -0.08 parts per thousand +/- 0.43 parts per thousand and +1.75 parts per thousand +/- 0.13 parts per thousand versus standard mean ocean bromide for samples collected at a suburban Stockholm, Sweden, site.
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| 19. |
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| 20. |
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| 21. |
- Wu, Lichuan, et al.
(författare)
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Surface Wave Impact When Simulating Midlatitude Storm Development
- 2017
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Ingår i: Journal of Atmospheric and Oceanic Technology. - 0739-0572 .- 1520-0426. ; 34:1, s. 233-248
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Tidskriftsartikel (refereegranskat)abstract
- Surface gravity waves, present at the air–sea interface, can affect the momentum flux and heat fluxes by modifying turbulence in the lower layers of the atmosphere. How to incorporate wave impacts into model parameterizations is still an open issue. In this study, the influence of a dynamic roughness length (considering instantaneous wave-induced stress), horizontal resolution, and the coupling time resolution between waves and the atmosphere on storm simulations are investigated using sensitivity experiments. Based on the sim- ulations of six midlatitude storms using both an atmosphere–wave coupled model and an atmospheric stand- alone model, the impacts are investigated. Adding the wave-induced stress weakens the storm intensity. Applying a roughness length tuned to an average friction velocity is not enough to capture the simulation results from ‘‘true’’ wave-related roughness length. High-horizontal-resolution models intensify the simula- tion of storms, which is valid for both coupled and uncoupled models. Compared with the atmospheric stand- alone model, the coupled model (considering the influence of dynamic roughness length) is more sensitive to the model horizontal resolution. During reasonable ranges, the coupling time resolution does not have a significant impact on the storm intensity based on the limited experiments used in this study. It is concluded that the dynamic wave influence (instantaneous wave influence) and the model resolution should be taken into account during the development of forecast and climate models.
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| 22. |
- Abessolo Ondoa, Gregoire, et al.
(författare)
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Sea level at the coast from video-sensed waves : Comparison to tidal gauges and satellite altimetry
- 2019
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Ingår i: Journal of Atmospheric and Oceanic Technology. - 0739-0572. ; 36:8, s. 1591-1603
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Tidskriftsartikel (refereegranskat)abstract
- Nearshore complex and energetic hydrodynamic conditions make observing evolving processes during extreme and short-term events difficult. In particular, total sea levels at the coast are hard to measure with current techniques. Sea level is commonly measured with tidal gauges and spaceborne altimetry, which lack essential details of spatial and wave-related sea level variability along the coast. Hence, novel techniques, adapted to nearshore areas, are required. This paper presents the first-time use of video cameras to derive the total sea level at the coast. This novel approach consists of estimating time-varying total water levels by applying a celerity-based depth inversion method, which is conventionally used to estimate bathymetry from video. The video-derived total sea levels are compared to sea levels derived from an in situ acoustic Doppler current profiler (ADCP), the nearest tide gauge, and altimetry. A tidal harmonic analysis is performed on the video-derived water levels, yielding an accurate determination of the dominant tidal harmonics. However, it remains difficult to separate bathymetric changes due to the waves on beaches when rapid morphological changes occur under energetic conditions. Nonetheless, video-derived water-level anomalies are in good agreement with state-of-the-art altimetry products. Although there is still work to be done, the results show the potential to measure total sea level at the coast using video camera systems.
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| 23. |
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| 24. |
- TJERNSTROM, M, et al.
(författare)
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THE EFFECT OF INERTIAL NAVIGATION SYSTEM TIME RESPONSE ON AIRBORNE TURBULENCE MEASUREMENTS
- 1995
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Ingår i: JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY. - : AMER METEOROLOGICAL SOC. - 0739-0572. ; 12:6, s. 1196-1213
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Tidskriftsartikel (refereegranskat)abstract
- Wind calculations from a radome gust probe system, in combination with a wander-angle Inertial Navigation System (INS), are used to calculate turbulence (variance and fluxes) by eddy correlation. The difference in time response between the air motion gus
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