scholarly journals Measurement of the water vapour vertical profile and of the Earth's outgoing far infrared flux

2007 ◽  
Vol 7 (6) ◽  
pp. 17741-17767 ◽  
Author(s):  
L. Palchetti ◽  
G. Bianchini ◽  
B. Carli ◽  
U. Cortesi ◽  
S. Del Bianco
Keyword(s):  
Water Vapour ◽  
Radiative Forcing ◽  
Far Infrared ◽  
Radiation Budget ◽  
Accurate Information ◽  
Uncooled Detectors ◽  
The Mean ◽  
Spectrally Resolved ◽  
Earth’S Radiation Budget ◽  
Good Agreement

Abstract. Our understanding of global warming depends on the accuracy with which the atmospheric components that modulate the Earth's radiation budget are known. Many uncertainties still exist on the radiative effect of water in the different spectral regions, among which the far infrared where few observations have been made. An assessment is shown of the atmospheric outgoing flux obtained from a balloon-borne platform with wideband spectrally resolved nadir measurements at the top-of-atmosphere over the full spectral range, including the far infrared, from 100 to 1400 cm−1, made by a Fourier transform spectrometer with uncooled detectors. From these measurements, we retrieve 15 pieces of information about water vapour and temperature profiles, and surface temperature, with a precision of 5% for the mean water vapour profile and a major improvement of the upper troposphere-lower stratosphere knowledge. The retrieved atmospheric state makes it possible to calculate the emitted radiance as a function of the zenith angle and to determine the outgoing radiation flux, proving that spectrally resolved observations can be used to derive accurate information on the integrated flux. While the retrieved temperature is in good agreement with ECMWF analysis, the retrieved water vapour profile differs significantly, and, depending on time and location, the derived flux differs in the far infrared (0–600 cm−1) from that derived from ECMWF by 2–3.5 W/m2±0.4 W/m2. The observed discrepancy is larger than current estimates of radiative forcing due to CO2 increases since pre-industrial time. The error with which the flux is determined is caused mainly by calibration uncertainties while detector noise has a negligible effect, proving that uncooled detectors are adequate for top of the atmosphere radiometry.

scholarly journals Measurement of the water vapour vertical profile and of the Earth's outgoing far infrared flux

2008 ◽  
Vol 8 (11) ◽  
pp. 2885-2894 ◽  
Author(s):  
L. Palchetti ◽  
G. Bianchini ◽  
B. Carli ◽  
U. Cortesi ◽  
S. Del Bianco
Keyword(s):  
Water Vapour ◽  
Far Infrared ◽  
Radiation Budget ◽  
Accurate Information ◽  
Spectral Radiation ◽  
Uncooled Detectors ◽  
Upper Troposphere ◽  
Atmospheric State ◽  
Spectrally Resolved ◽  
Earth’S Radiation Budget

Abstract. Our understanding of global warming depends on the accuracy with which the atmospheric components that modulate the Earth's radiation budget are known. Many uncertainties still exist as regards the radiative effect of water in the different spectral regions, among which is the far infrared, where very few observations have been made. An assessment is shown of the atmospheric outgoing flux obtained from a balloon-borne platform with wideband spectrally-resolved nadir measurements at the top of the atmosphere over the full spectral range, from 100 to 1400 cm−1, made by a Fourier transform spectrometer with uncooled detectors. From these measurements, we retrieved 15 pieces of information regarding water vapour and temperature profiles and surface temperature, with a major improvement in our knowledge of water vapour in the upper troposphere. The retrieved atmospheric state made it possible to calculate the emitted radiance also at frequencies and zenith angles that have not been observed and to determine the outgoing spectral radiation flux. This proves that spectrally resolved observations can be used to derive accurate information on the integrated flux. While the retrieved temperature was in agreement with ECMWF analysis, the retrieved water vapour profile differed significantly; depending on the time and the location, the derived flux in the far infrared (20–600 cm−1) differed by 2–3.5 W/m2 from that calculated using ECMWF. The error with which the far infrared flux is determined by REFIR-PAD is about 0.4 W/m2 and is caused mainly by calibration uncertainties, while detector noise has a negligible effect. This proves that uncooled detectors are adequate for top-of-the-atmosphere radiometry.

scholarly journals The impact of deforestation in the Amazonian atmospheric radiative balance: a remote sensing assessment

2012 ◽  
Vol 12 (6) ◽  
pp. 14837-14874 ◽  
Author(s):  
E. T. Sena ◽  
P. Artaxo ◽  
A. L. Correia
Keyword(s):  
Water Vapour ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Surface Albedo ◽  
Radiative Effect ◽  
Water Vapour Content ◽  
Albedo Change ◽  
Direct Radiative Forcing ◽  
The Mean ◽  
The Impact

Abstract. This paper addresses the Amazonian radiative budget after considering three aspects of deforestation: (i) the emission of aerosols from biomass burning due to forest fires; (ii) changes in surface albedo after deforestation and (iii) modifications in the column water vapour amount over deforested areas. Simultaneous Clouds and the Earth's Radiant Energy System (CERES) shortwave fluxes and aerosol optical depth (AOD) retrievals from the Moderate Resolution Imaging SpectroRadiometer (MODIS) were analysed during the peak of the biomass burning seasons (August and September) from 2000 to 2009. A discrete-ordinate radiative transfer (DISORT) code was used to extend instantaneous remote sensing radiative forcing assessments into 24-h averages. The mean direct radiative forcing of aerosols at the top of the atmosphere (TOA) during the biomass burning season for the 10-yr studied period was −5.6 ± 1.7 W m−2. Furthermore, the spatial distribution of the direct radiative forcing of aerosols over Amazon was obtained for the biomass burning season of each year. It was observed that for high AOD (larger than 1 at 550 nm) the imbalance in the radiative forcing at the TOA may be as high as −20 W m−2 locally. The surface reflectance plays a major role in the aerosol direct radiative effect. The study of the effects of biomass burning aerosols over different surface types shows that the direct radiative forcing is systematically more negative over forest than over savannah-like covered areas. Values of −15.7 ± 2.4 W m−2/τ550 nm and −9.3 ± 1.7 W m−2/τ550 nm were calculated for the mean daily aerosol forcing efficiencies over forest and savannah-like vegetation respectively. The overall mean annual albedo-change radiative forcing due to deforestation over the state of Rondônia, Brazil, was determined as −7.3 ± 0.9 W m−2. Biomass burning aerosols impact the radiative budget for approximately two months per year, whereas the surface albedo impact is observed throughout the year. Because of this difference, the estimated impact in the Amazonian annual radiative budget due to surface albedo-change is approximately 6 times higher than the impact due to aerosol emissions. The influence of atmospheric water vapour content in the radiative budget was also studied using AERONET column water vapour. It was observed that column water vapour is in average smaller by about 0.35 cm over deforested areas compared to forested areas. Our results indicate that this drying impact contributes to an increase in the shortwave radiative effect that varies from 0.4 W m−2 to 1.2 W m−2, depending on the column water vapour content before deforestation. The large radiative forcing values presented in this study point out that deforestation has strong implications in convection, cloud development and photosynthesis rate over the Amazon region.

scholarly journals Spatial variability of the direct radiative forcing of biomass burning aerosols and the effects of land use change in Amazonia

2013 ◽  
Vol 13 (3) ◽  
pp. 1261-1275 ◽  
Author(s):  
E. T. Sena ◽  
P. Artaxo ◽  
A. L. Correia
Keyword(s):  
Land Use ◽  
Land Use Change ◽  
Water Vapour ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Surface Albedo ◽  
Water Vapour Content ◽  
Direct Radiative Forcing ◽  
The Mean ◽  
The Impact

Abstract. This paper addresses the Amazonian shortwave radiative budget over cloud-free conditions after considering three aspects of deforestation: (i) the emission of aerosols from biomass burning due to forest fires; (ii) changes in surface albedo after deforestation; and (iii) modifications in the column water vapour amount over deforested areas. Simultaneous Clouds and the Earth's Radiant Energy System (CERES) shortwave fluxes and aerosol optical depth (AOD) retrievals from the Moderate Resolution Imaging SpectroRadiometer (MODIS) were analysed during the peak of the biomass burning seasons (August and September) from 2000 to 2009. A discrete-ordinate radiative transfer (DISORT) code was used to extend instantaneous remote sensing radiative forcing assessments into 24-h averages. The mean direct radiative forcing of aerosols at the top of the atmosphere (TOA) during the biomass burning season for the 10-yr studied period was −5.6 ± 1.7 W m−2. Furthermore, the spatial distribution of the direct radiative forcing of aerosols over Amazonia was obtained for the biomass burning season of each year. It was observed that for high AOD (larger than 1 at 550 nm) the maximum daily direct aerosol radiative forcing at the TOA may be as high as −20 W m−2 locally. The surface reflectance plays a major role in the aerosol direct radiative effect. The study of the effects of biomass burning aerosols over different surface types shows that the direct radiative forcing is systematically more negative over forest than over savannah-like covered areas. Values of −15.7 ± 2.4 W m−2τ550 nm and −9.3 ± 1.7 W m−2τ550 nm were calculated for the mean daily aerosol forcing efficiencies over forest and savannah-like vegetation respectively. The overall mean annual land use change radiative forcing due to deforestation over the state of Rondônia, Brazil, was determined as −7.3 ± 0.9 W m−2. Biomass burning aerosols impact the radiative budget for approximately two months per year, whereas the surface albedo impact is observed throughout the year. Because of this difference, the estimated impact in the Amazonian annual radiative budget due to surface albedo-change is approximately 6 times higher than the impact due to aerosol emissions. The influence of atmospheric water vapour content in the radiative budget was also studied using AERONET column water vapour. It was observed that column water vapour is on average smaller by about 0.35 cm (around 10% of the total column water vapour) over deforested areas compared to forested areas. Our results indicate that this drying contributes to an increase in the shortwave radiative forcing, which varies from 0.4 W m−2 to 1.2 W m−2 depending on the column water vapour content before deforestation. The large radiative forcing values presented in this study point out that deforestation could have strong implications in convection, cloud development and the ratio of direct to diffuse radiation, which impacts carbon uptake by the forest.

scholarly journals Emissivity Retrievals with FORUM's End-to-end Simulator: Challenges and Recommendations

2021 ◽  
Author(s):  
Maya Ben-Yami ◽  
Hilke Oetjen ◽  
Helen Brindley ◽  
William Cossich ◽  
Dulce Lajas ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Water Vapour ◽  
Spectral Region ◽  
Far Infrared ◽  
Spectral Emissivity ◽  
Water Vapour Content ◽  
Uncertainty Estimates ◽  
End To End ◽  
Spectrally Resolved ◽  
The Impact

Abstract. Spectral emissivity is a key property of the Earth surface of which only very few measurements exist so far in the far-infrared (FIR) spectral region, even though recent work has shown its FIR contribution is important for accurate modelling of global climate. The European Space Agency's 9th Earth Explorer, FORUM (Far-infrared Outgoing Radiation Understanding and Monitoring) will provide the first global spectrally resolved measurements of the Earth's top-of-the-atmosphere (TOA) spectrum in the FIR. In clear-sky conditions with low water vapour content, these measurements will provide a unique opportunity to retrieve spectrally resolved FIR surface emissivity. In preparation for the FORUM mission with an expected launch in 2026, this study takes the first steps towards the development of an operational emissivity retrieval for FORUM by investigating the sensitivity of the emissivity product of a full spectrum optimal estimation retrieval method to different physical and operational parameters. The tool used for the sensitivity tests is the FORUM mission's end-to-end simulator. These tests show that spectral emissivity of most surface types can be retrieved for dry scenes in the 350–600 cm−1 region with an uncertainty ranging from 0.005 to 0.01. In addition, the quality of retrieval is quantified with respect to the precipitable water vapour content of the scene, and the uncertainty caused by the correlation of emissivity with surface temperature is investigated. Two main recommendations are made based on these investigations: (1) As the extent of TOA sensitivity to the surface in the FIR depends on the atmospheric state, the spectral region of the emissivity product should be decided using a so-called information quantifier, calculated from the ratio of the retrieval uncertainty to the a-priori uncertainty. (2) Depending on retrieval input parameters, the correlation of emissivity with surface temperature allows for retrieved emissivities within a small range around the true emissivity. Thus the impact of this correlation on the uncertainty estimates of the product should be quantified in detail during further development of the operational retrieval.

scholarly journals Competition for water vapour results in suppression of ice formation in mixed phase clouds

2017 ◽  
Author(s):  
Emma L. Simpson ◽  
Paul J. Connolly ◽  
Gordon B. McFiggans
Keyword(s):  
Water Vapour ◽  
Elevated Temperatures ◽  
Dominant Role ◽  
Cloud Condensation Nuclei ◽  
Radiation Budget ◽  
Ice Formation ◽  
Condensed Water ◽  
Mixed Phase Clouds ◽  
Earth’S Radiation Budget ◽  
Made In

Abstract. The formation of ice in clouds can initiate precipitation and influence a cloud's reflectivity and lifetime, affecting climate to a highly uncertain degree. Nucleation of ice at elevated temperatures requires an ice nucleating particle (INP): so-called heterogeneous freezing. Previously reported measurements for the ability of a particle to nucleate ice have been made in the absence of other aerosol which will act as cloud condensation nuclei (CCN) and are ubiquitous in the atmosphere. Here we show that CCN can outcompete INPs for available water vapour thus suppressing ice formation, which has the potential to significantly affect the Earth's radiation budget. The magnitude of this suppression is shown to be dependent on the mass of condensed water required for freezing. Here we show that ice formation in a state-of-the-art cloud parcel model is strongly dependent on the criteria for heterogeneous freezing selected from those previously hypothesised. We have developed two alternative criteria which agree well with observations from cloud chamber experiments. This study highlights the dominant role that competition for water vapour can play in ice formation, highlighting both a need for clarity in the requirements for heterogeneous freezing and for measurements under atmospherically appropriate conditions.

scholarly journals Radiative impact of an extreme Arctic biomass-burning event

2018 ◽  
Vol 18 (12) ◽  
pp. 8829-8848 ◽  
Author(s):  
Justyna Lisok ◽  
Anna Rozwadowska ◽  
Jesper G. Pedersen ◽  
Krzysztof M. Markowicz ◽  
Christoph Ritter ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Radiation Budget ◽  
Plane Parallel ◽  
Direct Radiative Forcing ◽  
The Mean ◽  
The Impact

Abstract. The aim of the presented study was to investigate the impact on the radiation budget of a biomass-burning plume, transported from Alaska to the High Arctic region of Ny-Ålesund, Svalbard, in early July 2015. Since the mean aerosol optical depth increased by the factor of 10 above the average summer background values, this large aerosol load event is considered particularly exceptional in the last 25 years. In situ data with hygroscopic growth equations, as well as remote sensing measurements as inputs to radiative transfer models, were used, in order to estimate biases associated with (i) hygroscopicity, (ii) variability of single-scattering albedo profiles, and (iii) plane-parallel closure of the modelled atmosphere. A chemical weather model with satellite-derived biomass-burning emissions was applied to interpret the transport and transformation pathways. The provided MODTRAN radiative transfer model (RTM) simulations for the smoke event (14:00 9 July–11:30 11 July) resulted in a mean aerosol direct radiative forcing at the levels of −78.9 and −47.0 W m−2 at the surface and at the top of the atmosphere, respectively, for the mean value of aerosol optical depth equal to 0.64 at 550 nm. This corresponded to the average clear-sky direct radiative forcing of −43.3 W m−2, estimated by radiometer and model simulations at the surface. Ultimately, uncertainty associated with the plane-parallel atmosphere approximation altered results by about 2 W m−2. Furthermore, model-derived aerosol direct radiative forcing efficiency reached on average −126 W m-2/τ550 and −71 W m-2/τ550 at the surface and at the top of the atmosphere, respectively. The heating rate, estimated at up to 1.8 K day−1 inside the biomass-burning plume, implied vertical mixing with turbulent kinetic energy of 0.3 m2 s−2.

scholarly journals Impact of a Strong Biomass Burning Event on the Radiative Forcing in the Arctic

2017 ◽  
Author(s):  
Justyna Lisok ◽  
Anna Rozwadowska ◽  
Jesper G. Pedersen ◽  
Krzysztof M. Markowicz ◽  
Christoph Ritter ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Radiation Budget ◽  
The Arctic ◽  
Plane Parallel ◽  
Direct Radiative Forcing ◽  
The Mean ◽  
The Impact

Abstract. The aim of the presented study was to investigate the impact on the radiation budget of biomass burning smoke plume transported from Alaska to high Arctic region (Ny-Alesund, Svalbard) in early July 2015. This high aerosol load event is considered exceptional in the last 25 years with mean aerosol optical depth increased by the factor of 10 in comparison to the average summer background values. We utilised in-situ data with hygroscopic growth equations as well as remote sensing measurements as inputs to radiative transfer models with an objective to estimate biases associated with (i) hygroscopicity, (ii) variability of ω profiles and (iii) plane-parallel closure of the modelled atmosphere. A chemical weather model with satellite-derived biomass burning emissions was used to interpret the transport and transformations pathways. Provided MODTRAN simulations resulted in the mean aerosol direct radiative forcing on the level of −78.9 W m−2 and −47.0 W m−2 at the surface and the top of the atmosphere respectively for the mean value of aerosol optical depth equal to 0.64 at 550 nm. It corresponded to the average clear-sky direct radiative forcing of −43.3 W m−2 estimated by radiometers and model simulations. Furthermore, model-derived aerosol direct radiative forcing efficiency reached on average −126 W m−2 / τ550 and −71 W m−2 / τ550 at the surface and at the top of the atmosphere. Estimated heating rate up to 1.8 K day−1 inside the BB plume implied vertical mixing with the turbulent kinetic energy of 0.3 m2 s−2. Ultimately, uncertainty connected with the plane-parallel atmosphere approximation altered results by about 2 W m−2.

scholarly journals Competition for water vapour results in suppression of ice formation in mixed-phase clouds

2018 ◽  
Vol 18 (10) ◽  
pp. 7237-7250 ◽  
Author(s):  
Emma L. Simpson ◽  
Paul J. Connolly ◽  
Gordon McFiggans
Keyword(s):  
Water Vapour ◽  
Elevated Temperatures ◽  
Dominant Role ◽  
Cloud Condensation Nuclei ◽  
Radiation Budget ◽  
Ice Formation ◽  
Condensed Water ◽  
Mixed Phase Clouds ◽  
Earth’S Radiation Budget ◽  
Made In

Abstract. The formation of ice in clouds can initiate precipitation and influence a cloud's reflectivity and lifetime, affecting climate to a highly uncertain degree. Nucleation of ice at elevated temperatures requires an ice nucleating particle (INP), which results in so-called heterogeneous freezing. Previously reported measurements for the ability of a particle to nucleate ice have been made in the absence of other aerosol which will act as cloud condensation nuclei (CCN) and are ubiquitous in the atmosphere. Here we show that CCN can outcompete INPs for available water vapour thus suppressing ice formation, which has the potential to significantly affect the Earth's radiation budget. The magnitude of this suppression is shown to be dependent on the mass of condensed water required for freezing. Here we show that ice formation in a state-of-the-art cloud parcel model is strongly dependent on the criteria for heterogeneous freezing selected from those previously hypothesised. We have developed an alternative criteria which agrees well with observations from cloud chamber experiments. This study demonstrates the dominant role that competition for water vapour can play in ice formation, highlighting both a need for clarity in the requirements for heterogeneous freezing and for measurements under atmospherically appropriate conditions.

scholarly journals Impact of ship emissions on the microphysical, optical and radiative properties of marine stratus: a case study

2006 ◽  
Vol 6 (1) ◽  
pp. 1023-1071 ◽  
Author(s):  
M. Schreier ◽  
A. A. Kokhanovsky ◽  
V. Eyring ◽  
L. Bugliaro ◽  
H. Mannstein ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Radiative Forcing ◽  
Surface Radiation ◽  
Radiative Properties ◽  
Radiation Budget ◽  
Atmospheric Effects ◽  
Climatic Effects ◽  
The North ◽  
The Mean ◽  
Ship Tracks

Abstract. Modifications of existing clouds by the exhaust of ships are well-known but poorly studied atmospheric effects which could contribute to climate change. The perturbation of a cloud layer by ship-generated aerosol changes the cloud reflectivity and is identified by long curves in satellite images, known as ship tracks. As ship tracks indicate a pollution of a very clean marine environment and also affect the radiation budget below and above the cloud, it is important to investigate their radiative and climatic effects. Satellite-data from MODIS on Terra are used to examine a scene from 10 February 2003 where ship tracks were detected close to the North American West-Coast. The cloud optical and microphysical properties are derived using a semi-analytical retrieval technique combined with a look-up-table approach. Ship-track-pixels are distinguished from the unperturbed cloud pixels and the optical properties of the former are compared to those of the latter. Within the ship tracks a significant change in the droplet number concentration, the effective radius and the optical thickness are found compared to the unaffected cloud. Significant increase of liquid water could not be confirmed. The resulting cloud properties are used to calculate the radiation budget below and above the cloud. Assuming a mean solar zenith angle, the mean surface radiation below the ship track is decreased by 43.25 Wm−2 and the mean reflectance at TOA is increased by 40.73 Wm−2. For the selected scene the ship emission decreases the solar radiation at the surface by 2.10 Wm−2 and increases the backscattered solar radiation at top of the atmosphere (TOA) by 2.00 Wm−2. Increased backscattered radiation is partly compensated by a decrease of the thermal radiation of 0.43 Wm−2. The resulting net-effect at TOA is an increase of 1.57 Wm−2 corresponding to a negative radiative forcing and a cooling.

Computational Investigation of Different Turbulent Models When Predicting Airflow in an Enclosure

2008 ◽  
Author(s):  
Xi Wang ◽  
Hassan Naji ◽  
Ahmed Mezrhab
Keyword(s):  
Numerical Investigation ◽  
Turbulence Models ◽  
Turbulent Stress ◽  
Computational Investigation ◽  
Isothermal Case ◽  
The Mean ◽  
Turbulent Models ◽  
Rsm Model ◽  
Cold Case ◽  
Good Agreement

In the present study, a numerical investigation is carried out for an isothermal case, a hot case and a cold case with FLUENT code. Three turbulence models are considered: the k-ε realisable model, the RNG k-ε model and the RSM linear model. The obtained results are compared to experiments and show generally a good agreement for the mean velocities and temperatures, but less satisfactory for the turbulent stress. The performance of the RSM model is remarkable. Even if none of the models is able to give the exact experimental pattern on the map of turbulence, the RSM model seems able to predict such configuration.

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