Spatial variability of ocean waves, from in-situ measurements

2013 ◽  
Vol 57 ◽  
pp. 83-98 ◽  
Author(s):  
I.G.C. Ashton ◽  
J-B. Saulnier ◽  
G.H. Smith
Keyword(s):  
Spatial Variability ◽  
Ocean Waves ◽  
In Situ Measurements

scholarly journals Permafrost Variability over the Northern Hemisphere Based on the MERRA-2 Reanalysis

2018 ◽  
Author(s):  
Jing Tao ◽  
Randal D. Koster ◽  
Rolf H. Reichle ◽  
Barton A. Forman ◽  
Yuan Xue ◽  
...  
Keyword(s):  
Spatial Variability ◽  
Northern Hemisphere ◽  
Snow Water Equivalent ◽  
Snow Accumulation ◽  
In Situ Measurements ◽  
Active Layer Thickness ◽  
Permafrost Region ◽  
Meteorological Forcing ◽  
Northern Alaska

Abstract. This study introduces and evaluates a comprehensive, model-generated dataset of Northern Hemisphere permafrost conditions. Surface meteorological forcing fields from the Modern-Era Retrospective Analysis for Research and Applications-2 (MERRA-2) reanalysis data were used to drive an improved version of the land component of MERRA-2 in middle-to-high northern latitudes from 1980 to 2017. The resulting simulated permafrost distribution across the Northern Hemisphere captures well the observed extent of continuous permafrost except in Western Siberia, which is permafrost-free in the simulation. Noticeable discrepancies also appear along the southern edge of the permafrost region where sporadic and isolated permafrost types dominate. The evaluation of the simulated active layer thickness (ALT) climatology against in-situ measurements demonstrates reasonable skill except in Mongolia. In northern Alaska, both ALT retrievals from airborne remote sensing for 2015 and the corresponding simulated ALT exhibit reasonable accuracy vs. in-situ measurements. However, the remotely sensed ALT retrievals generally demonstrate lower levels of spatial variability than both the observed and simulated ALT. Controls on the spatial variability of ALT are examined with idealized numerical experiments focusing on northern Alaska; meteorological forcing and soil type are found to have dominant impacts on the spatial variability of ALT, with vegetation also playing a role through its modulation of snow accumulation. A correlation analysis further reveals that accumulated air temperature and maximum snow water equivalent (SWE) explain most of the year-to-year variability of ALT nearly everywhere over the model-simulated permafrost regions. Simulated ALT trends from 1980 to 2017 indicate that some permafrost areas are experiencing significant degradation, with ALT increasing up to 0.5 cm/year.

scholarly journals Description and applications of a mobile system performing on-road aerosol remote sensing and in situ measurements

2018 ◽  
Author(s):  
Ioana Elisabeta Popovici ◽  
Philippe Goloub ◽  
Thierry Podvin ◽  
Luc Blarel ◽  
Rodrigue Loisil ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Spatial Variability ◽  
Mass Concentration ◽  
In Situ Measurements ◽  
Quality Data ◽  
The Sun ◽  
Mobile System ◽  
Modis Aod ◽  
Sun Photometer

Abstract. The majority of ground-based aerosols observations are limited to fixed locations, narrowing the knowledge on their spatial variability. In order to overcome this issue, a compact Mobile Aerosol Monitoring System (MAMS) was developed to explore the aerosol vertical and spatial variability. This mobile laboratory is equipped with a micropulse lidar, a sun-photometer and an aerosol spectrometer. It is distinguished by other transportable platforms through its ability to perform on-road measurements and its unique feature lies in the sun-photometer capable to track the sun during motion. The system presents a great flexibility, being able to respond quickly in case of sudden aerosol events such as pollution episodes, dust, fire or volcano outbreaks. On-road mapping of aerosol physical parameters such as attenuated aerosol backscatter, aerosol optical depth, particle number and mass concentration and size distribution is achieved through the MAMS. The performance of remote sensing instruments on-board has been evaluated through intercomparison with instruments in reference networks (i.e. AERONET and EARLINET), showing that the system is capable of providing high quality data. This also illustrates the application of such system for instrument intercomparison field campaigns. Applications of the mobile system have been exemplified through two case studies in northern France. MODIS AOD data was compared to ground-based mobile sun-photometer data. A good correlation was observed with R2 of 0.76, showing the usefulness of the mobile system for validation of satellite-derived products. The performance of BSC-DREAM8b dust model has been tested by comparison of results from simulations to the lidar-sun-photometer derived extinction coefficient and mass concentration profiles. The comparison indicated that observations and model are in good agreement in describing the vertical variability of dust layers. Moreover, on-road measurements of PM10 were compared with modelled PM10 concentrations and with ATMO Hauts-de-France and AIRPARIF air quality in situ measurements, presenting an excellent agreement in horizontal spatial representativity of PM10. This proves a possible application of mobile platforms for evaluating the chemistry-models performances.

scholarly journals Permafrost variability over the Northern Hemisphere based on the MERRA-2 reanalysis

2019 ◽  
Vol 13 (8) ◽  
pp. 2087-2110 ◽  
Author(s):  
Jing Tao ◽  
Randal D. Koster ◽  
Rolf H. Reichle ◽  
Barton A. Forman ◽  
Yuan Xue ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Spatial Variability ◽  
Northern Hemisphere ◽  
Snow Accumulation ◽  
In Situ Measurements ◽  
Active Layer Thickness ◽  
Meteorological Forcing ◽  
Northern Alaska ◽  
Permafrost Regions

Abstract. This study introduces and evaluates a comprehensive, model-generated dataset of Northern Hemisphere permafrost conditions at 81 km2 resolution. Surface meteorological forcing fields from the Modern-Era Retrospective Analysis for Research and Applications 2 (MERRA-2) reanalysis were used to drive an improved version of the land component of MERRA-2 in middle-to-high northern latitudes from 1980 to 2017. The resulting simulated permafrost distribution across the Northern Hemisphere mostly captures the observed extent of continuous and discontinuous permafrost but misses the ecosystem-protected permafrost zones in western Siberia. Noticeable discrepancies also appear along the southern edge of the permafrost regions where sporadic and isolated permafrost types dominate. The evaluation of the simulated active layer thickness (ALT) against remote sensing retrievals and in situ measurements demonstrates reasonable skill except in Mongolia. The RMSE (bias) of climatological ALT is 1.22 m (−0.48 m) across all sites and 0.33 m (−0.04 m) without the Mongolia sites. In northern Alaska, both ALT retrievals from airborne remote sensing for 2015 and the corresponding simulated ALT exhibit limited skill versus in situ measurements at the model scale. In addition, the simulated ALT has larger spatial variability than the remotely sensed ALT, although it agrees well with the retrievals when considering measurement uncertainty. Controls on the spatial variability of ALT are examined with idealized numerical experiments focusing on northern Alaska; meteorological forcing and soil types are found to have dominant impacts on the spatial variability of ALT, with vegetation also playing a role through its modulation of snow accumulation. A correlation analysis further reveals that accumulated above-freezing air temperature and maximum snow water equivalent explain most of the year-to-year variability of ALT nearly everywhere over the model-simulated permafrost regions.

scholarly journals Description and applications of a mobile system performing on-road aerosol remote sensing and in situ measurements

2018 ◽  
Vol 11 (8) ◽  
pp. 4671-4691 ◽  
Author(s):  
Ioana Elisabeta Popovici ◽  
Philippe Goloub ◽  
Thierry Podvin ◽  
Luc Blarel ◽  
Rodrigue Loisil ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Spatial Variability ◽  
Mass Concentration ◽  
In Situ Measurements ◽  
Quality Data ◽  
The Sun ◽  
Mobile System ◽  
Modis Aod ◽  
Sun Photometer

Abstract. The majority of ground-based aerosols observations are limited to fixed locations, narrowing the knowledge on their spatial variability. In order to overcome this issue, a compact Mobile Aerosol Monitoring System (MAMS) was developed to explore the aerosol vertical and spatial variability. This mobile laboratory is equipped with a micropulse lidar, a sun photometer and an aerosol spectrometer. It is distinguished from other transportable platforms through its ability to perform on-road measurements and its unique feature lies in the sun photometer's capacity for tracking the sun during motion. The system presents a great flexibility, being able to respond quickly in case of sudden aerosol events such as pollution episodes, dust, fire or volcano outbreaks. On-road mapping of aerosol physical parameters such as attenuated aerosol backscatter, aerosol optical depth, particle number and mass concentration and size distribution is achieved through the MAMS. The performance of remote sensing instruments on-board has been evaluated through intercomparison with instruments in reference networks (i.e. AERONET and EARLINET), showing that the system is capable of providing high quality data. This also illustrates the application of such a system for instrument intercomparison field campaigns. Applications of the mobile system have been exemplified through two case studies in northern France. MODIS AOD data was compared to ground-based mobile sun photometer data. A good correlation was observed with R2 of 0.76, showing the usefulness of the mobile system for validation of satellite-derived products. The performance of BSC-DREAM8b dust model has been tested by comparison of results from simulations for the lidar–sun-photometer derived extinction coefficient and mass concentration profiles. The comparison indicated that observations and the model are in good agreement in describing the vertical variability of dust layers. Moreover, on-road measurements of PM10 were compared with modelled PM10 concentrations and with ATMO Hauts-de-France and AIRPARIF air quality in situ measurements, presenting an excellent agreement in horizontal spatial representativity of PM10. This proves a possible application of mobile platforms for evaluating the chemistry-models performances.

Spatial variability of waves within a marine energy site using in-situ measurements and a high resolution spectral wave model

Energy ◽  
2014 ◽  
Vol 66 ◽  
pp. 699-710 ◽  
Author(s):  
I. Ashton ◽  
J.C.C. Van-Nieuwkoop-McCall ◽  
H.C.M. Smith ◽  
L. Johanning
Keyword(s):  
High Resolution ◽  
Spatial Variability ◽  
Wave Model ◽  
In Situ Measurements ◽  
Spectral Wave Model ◽  
Marine Energy

scholarly journals In situ measurements and analysis of ocean waves in the Antarctic marginal ice zone

2014 ◽  
Vol 41 (14) ◽  
pp. 5046-5051 ◽  
Author(s):  
Michael H. Meylan ◽  
Luke G. Bennetts ◽  
Alison L. Kohout
Keyword(s):  
Ocean Waves ◽  
In Situ Measurements ◽  
Marginal Ice Zone ◽  
The Antarctic

The Carbon:²³⁴Thorium ratios of sinking particles in the California Current Ecosystem 2: Examination of a thorium sorption, desorption, and particle transport model

2019 ◽  
Author(s):  
Michael Stukel ◽  
Thomas Kelly
Keyword(s):  
Organic Carbon ◽  
Water Column ◽  
Particulate Organic Carbon ◽  
Transport Model ◽  
California Current ◽  
In Situ Measurements ◽  
Power Law Distribution ◽  
Sinking Particles ◽  
Organic Carbon Concentration

Thorium-234 (234Th) is a powerful tracer of particle dynamics and the biological pump in the surface ocean; however, variability in carbon:thorium ratios of sinking particles adds substantial uncertainty to estimates of organic carbon export. We coupled a mechanistic thorium sorption and desorption model to a one-dimensional particle sinking model that uses realistic particle settling velocity spectra. The model generates estimates of 238U-234Th disequilibrium, particulate organic carbon concentration, and the C:234Th ratio of sinking particles, which are then compared to in situ measurements from quasi-Lagrangian studies conducted on six cruises in the California Current Ecosystem. Broad patterns observed in in situ measurements, including decreasing C:234Th ratios with depth and a strong correlation between sinking C:234Th and the ratio of vertically-integrated particulate organic carbon (POC) to vertically-integrated total water column 234Th, were accurately recovered by models assuming either a power law distribution of sinking speeds or a double log normal distribution of sinking speeds. Simulations suggested that the observed decrease in C:234Th with depth may be driven by preferential remineralization of carbon by particle-attached microbes. However, an alternate model structure featuring complete consumption and/or disaggregation of particles by mesozooplankton (e.g. no preferential remineralization of carbon) was also able to simulate decreasing C:234Th with depth (although the decrease was weaker), driven by 234Th adsorption onto slowly sinking particles. Model results also suggest that during bloom decays C:234Th ratios of sinking particles should be higher than expected (based on contemporaneous water column POC), because high settling velocities minimize carbon remineralization during sinking.

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