38 research outputs found
PHOTONS/AERONET sunphotometer network overview. Description â Activities - Results
Fourteenth International Symposium on Atmospheric and Ocean Optics/Atmospheric Physics celebrado del 24 al 30 de junio de 2007 en Buryatia, Russia
Quantification of surface water volume changes in the Mackenzie Delta using satellite multi-mission data
Quantification of surface water storage in extensive floodplains
and their dynamics are crucial for a better understanding of global
hydrological and biogeochemical cycles. In this study, we present estimates
of both surface water extent and storage combining multi-mission
remotely sensed observations and their temporal evolution over more than 15Â years
in the Mackenzie Delta. The Mackenzie Delta is located in the northwest of Canada and is the second largest delta in the Arctic Ocean. The delta
is frozen from October to May and the recurrent ice break-up provokes an
increase in the river's flows. Thus, this phenomenon causes intensive floods
along the delta every year, with dramatic environmental impacts. In this
study, the dynamics of surface water extent and volume are analysed from 2000
to 2015 by combining multi-satellite information from MODIS multispectral
images at 500âŻm spatial resolution and river stages derived from ERS-2
(1995â2003), ENVISAT (2002â2010) and SARAL (since 2013) altimetry data. The
surface water extent (permanent water and flooded area) peaked in June with
an area of 9600âŻkm2 (±200âŻkm2) on
average, representing approximately 70âŻ% of the delta's total surface.\ud
Altimetry-based water levels exhibit annual amplitudes ranging from 4âŻm in
the downstream part to more than 10âŻm in the upstream part of the Mackenzie
Delta. A high overall correlation between the satellite-derived and in situ
water heights (RâŻ>âŻ0.84) is found for the three altimetry missions.
Finally, using altimetry-based water levels and MODIS-derived surface water
extents, maps of interpolated water heights over the surface water extents
are produced. Results indicate a high variability of the water height
magnitude that can reach 10âŻm compared to the lowest water height in the
upstream part of the delta during the flood peak in June. Furthermore, the
total surface water volume is estimated and shows an annual variation of
approximately 8.5âŻkm3 during the whole study period, with a maximum of
14.4âŻkm3 observed in 2006. The good agreement between the total surface
water volume retrievals and in situ river discharges (Râ=ââŻ0.66) allows
for validation of this innovative multi-mission approach and highlights the high
potential to study the surface water extent dynamics
Aerosol optical properties and direct radiative forcing based on measurements from the China Aerosol Remote Sensing Network (CARSNET) in eastern China
Aerosol pollution in eastern China is an unfortunate consequence of the region's rapid economic and industrial growth. Here, sun photometer measurements from seven sites in the Yangtze River Delta (YRD) from 2011 to 2015 were used to characterize the climatology of aerosol microphysical and optical properties, calculate direct aerosol radiative forcing (DARF) and classify the aerosols based on size and absorption. Bimodal size distributions were found throughout the year, but larger volumes and effective radii of fine-mode particles occurred in June and September due to hygroscopic growth and/or cloud processing. Increases in the fine-mode particles in June and September caused AOD440ânmâ>â1.00 at most sites, and annual mean AOD440ânm values of 0.71-0.76 were found at the urban sites and 0.68 at the rural site. Unlike northern China, the AOD440ânm was lower in July and August (âŒâ0.40-0.60) than in January and February (0.71-0.89) due to particle dispersion associated with subtropical anticyclones in summer. Low volumes and large bandwidths of both fine-mode and coarse-mode aerosol size distributions occurred in July and August because of biomass burning. Single-scattering albedos at 440ânm (SSA440ânm) from 0.91 to 0.94 indicated particles with relatively strong to moderate absorption. Strongly absorbing particles from biomass burning with a significant SSA wavelength dependence were found in July and August at most sites, while coarse particles in March to May were mineral dust. Absorbing aerosols were distributed more or less homogeneously throughout the region with absorption aerosol optical depths at 440ânm âŒâ0.04-0.06, but inter-site differences in the absorption Angström exponent indicate a degree of spatial heterogeneity in particle composition. The annual mean DARF was â93â±â44 to â79â±â39âWâmâ2 at the Earth's surface and âŒââ40âWâmâ2 at the top of the atmosphere (for the solar zenith angle range of 50 to 80â) under cloud-free conditions. The fine mode composed a major contribution of the absorbing particles in the classification scheme based on SSA, fine-mode fraction and extinction Angström exponent. This study contributes to our understanding of aerosols and regional climate/air quality, and the results will be useful for validating satellite retrievals and for improving climate models and remote sensing algorithms
Coalition governance and foreign policy decision making
This article explores processes of coalition governance in foreign policy. Specifically, it argues that such processes are shaped by two interrelated dimensions of coalition set-up: first, the allocation of the foreign ministry to the senior or a junior coalition partner and, second, the degree of policy discretion which is delegated to that ministry. Bringing these two dimensions together, the article distinguishes four types of coalition arrangement for the making of foreign policy, which are expected to have predictable implications for the process of foreign policy-making and, ultimately, for the foreign policy outputs of multi-party coalitions and their quality
Assessment of Sun photometer Langley calibration at the high-elevation sites Mauna Loa and Izaña
The aim of this paper is to analyze the suitability of the high-mountain
stations Mauna Loa and Izaña for Langley plot calibration of Sun
photometers. Thus the aerosol optical depth (AOD) characteristics and
seasonality, as well as the cloudiness, have been investigated in order to
provide a robust estimation of the calibration uncertainty as well as the
number of days that are suitable for Langley calibrations. The data used for
the investigations belong to the AERONET and GAW-PFR networks, which maintain
reference Sun photometers at these stations with long measurement records:
22 years at Mauna Loa and 15 years at Izaña. In terms of clear-sky and
stable aerosol conditions, Mauna Loa (3397 m a.s.l.) exhibits on average
377 Langley plots (243 morning and 134 afternoon)
per year suitable for Langley plot calibration, whereas Izaña
(2373 m a.s.l.) shows 343 Langley plots (187 morning and 155 afternoon) per
year. The background AOD (500 nm) values, on days that are favorable for
Langley calibrations, are in the range 0.01â0.02 throughout the year, with
well-defined seasonality that exhibits a spring maximum at both stations plus
a slight summer increase at Izaña. The statistical analysis of the
long-term determination of extraterrestrial signals yields to a calibration
uncertainty of ââŒâ 0.25â0.5 %, this uncertainty being smaller in the
visible and near-infrared wavelengths and larger in the ultraviolet
wavelengths. This is due to atmospheric variability produced by changes in
several factors, mainly the AOD. The uncertainty cannot be reduced based only
on quality criteria of individual Langley plots and averaging over several
days is shown to reduce the uncertainty to the needed levels for reference
Sun photometers.</p
Overview of the Chemistry-Aerosol Mediterranean Experiment/Aerosol Direct Radiative Forcing on the Mediterranean Climate (ChArMEx/ADRIMED) summer 2013 campaign
The Chemistry-Aerosol Mediterranean Experiment (ChArMEx; http://charmex.lsce.ipsl.fr) is a collaborative research program federating international activities to investigate Mediterranean regional chemistry-climate interactions. A special observing period (SOP-1a) including intensive airborne measurements was performed in the framework of the Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region (ADRIMED) project during the Mediterranean dry season over the western and central Mediterranean basins, with a focus on aerosol-radiation measurements and their modeling. The SOP-1a took place from 11 June to 5 July 2013. Airborne measurements were made by both the ATR-42 and F-20 French research aircraft operated from Sardinia (Italy) and instrumented for in situ and remote-sensing measurements, respectively, and by sounding and drifting balloons, launched in Minorca. The experimental setup also involved several ground-based measurement sites on islands including two ground-based reference stations in Corsica and Lampedusa and secondary monitoring sites in Minorca and Sicily. Additional measurements including lidar profiling were also performed on alert during aircraft operations at EARLINET/ACTRIS stations at Granada and Barcelona in Spain, and in southern Italy. Remote-sensing aerosol products from satellites (MSG/SEVIRI, MODIS) and from the AERONET/PHOTONS network were also used. Dedicated meso-scale and regional modeling experiments were performed in relation to this observational effort. We provide here an overview of the different surface and aircraft observations deployed during the ChArMEx/ADRIMED period and of associated modeling studies together with an analysis of the synoptic conditions that determined the aerosol emission and transport. Meteorological conditions observed during this campaign (moderate temperatures and southern flows) were not favorable to producing high levels of atmospheric pollutants or intense biomass burning events in the region. However, numerous mineral dust plumes were observed during the campaign, with the main sources located in Morocco, Algeria and Tunisia, leading to aerosol optical depth (AOD) values ranging between 0.2 and 0.6 (at 440 nm) over the western and central Mediterranean basins. One important point of this experiment concerns the direct observations of aerosol extinction onboard the ATR-42, using the CAPS system, showing local maxima reaching up to 150Mm(-1) within the dust plume. Non-negligible aerosol extinction (about 50Mm(-1)) has also been observed within the marine boundary layer (MBL). By combining the ATR- 42 extinction coefficient observations with absorption and scattering measurements, we performed a complete optical closure revealing excellent agreement with estimated optical properties. This additional information on extinction properties has allowed calculation of the dust single scattering albedo (SSA) with a high level of confidence over the western Mediterranean. Our results show a moderate variability from 0.90 to 1.00 (at 530 nm) for all flights studied compared to that reported in the literature on this optical parameter. Our results underline also a relatively low difference in SSA with values derived near dust sources. In parallel, active remote-sensing observations from the surface and onboard the F-20 aircraft suggest a complex vertical structure of particles and distinct aerosol layers with sea spray and pollution located within the MBL, and mineral dust and/or aged North American smoke particles located above (up to 6â7 km in altitude). Aircraft and balloon-borne observations allow one to investigate the vertical structure of the aerosol size distribution showing particles characterized by a large size (> 10 ÎŒm in diameter) within dust plumes. In most of cases, a coarse mode characterized by an effective diameter ranging between 5 and 10 ÎŒm, has been detected above the MBL. In terms of shortwave (SW) direct forcing, in situ surface and aircraft observations have been merged and used as inputs in 1-D radiative transfer codes for calculating the aerosol direct radiative forcing (DRF). Results show significant surface SW instantaneous forcing (up to (-90)Wm(-2) at noon). Aircraft observations provide also original estimates of the vertical structure of SW and LW radiative heating revealing significant instantaneous values of about 5 K per day in the solar spectrum (for a solar angle of 30 ) within the dust layer. Associated 3-D modeling studies from regional climate (RCM) and chemistry transport (CTM) models indicate a relatively good agreement for simulated AOD compared with observations from the AERONET/PHOTONS network and satellite data, especially for long-range dust transport. Calculations of the 3-D SW (clear-sky) surface DRF indicate an average of about -10 to -20Wm(-2) (for the whole period) over the Mediterranean Sea together with maxima (-50Wm(-2)) over northern Africa. The top of the atmosphere (TOA) DRF is shown to be highly variable within the domain, due to moderate absorbing properties of dust and changes in the surface albedo. Indeed, 3-D simulations indicate negative forcing over the Mediterranean Sea and Europe and positive forcing over northern Africa. Finally, a multiyear simulation, performed for the 2003 to 2009 period and including an oceanâatmosphere (OâA) coupling, underlines the impact of the aerosol direct radiative forcing on the sea surface temperature, OâA fluxes and the hydrological cycle over the Mediterranean.French National Research Agency (ANR)
ANR-11-BS56-0006ADEMEFrench Atomic Energy CommissionCNRS-INSU and Meteo-France through the multidisciplinary programme MISTRALS (Mediterranean Integrated Studies aT Regional And Local Scales)CORSiCA project - Collectivite Territoriale de Corse through Fonds Europeen de Developpement Regional of the European Operational ProgramContrat de Plan Etat-RegionEuropean Union's Horizon 2020 research and innovation program
654169Spanish Ministry of Economy and Competitivity
TEC2012-34575Science and Innovation
UNPC10-4E-442European Union (EU)Department of Economy and Knowledge of the Catalan Autonomous Government
SGR 583Andalusian Regional Government
P12-RNM-2409Spanish Government
CGL2013-45410-R
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Altimetry for the future: Building on 25 years of progress
In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the âGreenâ Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instrumentsâ development and satellite missionsâ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion
Altimetry for the future: Building on 25 years of progress
In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ââGreenâ Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instrumentsâ development and satellite missionsâ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion
Altimetry for the future: building on 25 years of progress
In 2018 we celebrated 25âŻyears of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology.
The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the âGreenâ Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instrumentsâ development and satellite missionsâ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion