13 research outputs found
Optical characterization of Polar winter aerosols and clouds
The Arctic region is particularly sensitive to climate change and has recently undergone major alterations including a dramatic decrease of sea-ice extent. Our ability to model and potentially mitigate climate change is limited, in part, by the uncertainties associated with radiative forcing due to direct and indirect aerosol effects which in turn are dependent on our understanding of aerosol and cloud processes. Aerosol loading can be characterized by aerosol optical depth (AOD) which is the most important (extensive or bulk) aerosol radiative parameter and arguably the most important regional indicator of aerosol behavior. One of the most important shortcomings in our understanding of Arctic aerosols is their behavior during the Polar winter. A major reason for this is the lack of night-time AOD measurements. In this work we use lidar and starphotometry instruments in the Arctic to obtain vertically resolved aerosol profiles and column in- tegrated representations of those profiles (AODs) respectively. In addition, data from a space-borne lidar (CALIOP) is used to provide a pan-Arctic context and seasonal statistics in support of ground based measurements
Characterisation of night-time aerosols using starphotometry
This is a study concerning the use of starphotometry to retrieve night-time aerosol optical depths (AODs). In the summer of 2007 a SPSTAR03 starphotometer was installed at a rural site at Egbert, Ontario for the purpose of the nighttime AOD measurements. Two series of daytime / nighttime AODs were acquired using the CIMEL CE 318 sunphotometer and the SPSTAR03 from Aug. 31 to Sept. 19 2007 and from June 30 to July 5, 2008. The measurements were complemented by vertical backscatter coefficient profiles acquired using a pulsed lidar. We found that starphotometer AOD estimates, based on the application of a two star method (TSM) to low and high elevation stars, are susceptible to atmospheric inhomogeneity effects. Starphotometer AOD estimates based on the one star method (OSM) reduce this sensitivity, but require absolute calibration values. A level of continuity was obtained between the daytime sunphotometry and nighttime starphotometry data. A continuity parameter (defined as the average difference between the measured nighttime and interpolated daytime values) was calculated over four distinct periods. It yielded the differences of 0.160, 0.053, 0.139 (total, fine and coarse mode optical depths) for the low star and 0.195, 0.070, 0.149 for the high star. We argue that cloud screening would have reduced the continuity parameter differences for the coarse and total optical depths. For 5 out of , 8 nights of lidar operation, a combination of the Angstrom and Spectral Deconvolution Algorithm (SDA) analysis provided an indication of the nature of the atmospheric features seen in the lidar data. Fine and coarse-mode events were detected during the measurement periods using the SDA. Lidar data was used to better understand complex atmospheric phenomena and was found especially effective for cloud detection and general signal increase/decrease analysis
La caracteĢrisation optique des aeĢrosols et des nuages pendant lāhiver polaire
RĆ©sumĆ© : LāArctique est particuliĆØrement sensible aux changements climatiques et a rĆ©cemment subi des modifications majeures incluant une diminution dramatique de lāextension de la glace de mer. Notre capacitĆ©Ģ aĢ modĆ©liser et aĢ potentiellement rĆ©duire les changements climatiques est limitĆ©e, en partie, par les incertitudes associeĢes au forcĢ§age radiatif induit par les effets directs et indirects des aeĢrosols, qui deĢpendent de notre compreĢhension des processus impliquant les nuages et les aeĢrosols. La charge des aeĢrosols est caracteĢriseĢe par lāeĢpaisseur optique des aeĢrosols (AOD) qui est le parameĢtre radiatif extensif le plus important et lāindicateur reĢgional du comportement des aeĢrosols sans doute le plus deĢcisif. Une de nos lacunes majeures dans la compreĢhension des aeĢrosols arctiques est leur comportement durant lāhiver polaire. Cela est principalement duĢ au manque de mesures nocturnes dāAOD. Dans ce travail, on utilise des instruments (lidar et photomeĢtre stellaire) installeĢs en Arctique pour mesurer, respectivement, les profils verticaux des aeĢrosols et une valeur inteĢgreĢe dans la colonne (AOD) de ces profils. En outre, les donneĢes dāun lidar spatial (CALIOP) sont utiliseĢes pour fournir un contexte pan-arctique et des statistiques saisonnieĢres pour supporter les mesures au sol. Ces dernieĢres ont eĢteĢ obtenues aux stations arctiques dāEureka (80ā¦ N, 86ā¦ W) et de Ny AĢlesund (79ā¦ N, 12ā¦ E) durant les hivers polaires de 2010-2011 et 2011-2012. Lāimportance physique des pe- tites variations dāamplitude de lāAOD est typique de lāhiver polaire en Arctique, mais suppose une veĢrification pour sāassurer que des artefacts ne contribuent pas aĢ ces variations (par exemple un masque de nuage insuffisant). Une analyse des processus baseĢe sur des eĢveĢnements (avec une reĢsolution temporelle ā une minute) est essentielle pour sāassurer que les parameĢtres optiques et microphysiques extensifs (grossiers) et intensifs (par particules) sont coheĢrents et physiquement conformes. La synergie photomĆØtre stellaire-lidar nous permet de caracteĢriser plusieurs eĢveĢnements distincts au cours des peĢriodes de mesures, en particulier : des aeĢrosols, des cristaux de glace, des nuages fins et des nuages polaires stratospheĢriques (PSC). Dans lāensemble, les modes fin (1Ī¼m) de lāAOD obtenus par photomeĢtrie stellaire (Ļ[indice infĆ©rieur f] et Ļ[indice infĆ©rieur c]) sont coheĢrents avec leurs analogues produits aĢ partir des profils inteĢgreĢs du lidar. Cependant certaines inconsistances causeĢes par des facteurs instrumentaux et environnementaux ont aussi eĢteĢ trouveĢes. La division de lāAOD du photomeĢtre stellaire Ļ[indice infĆ©rieur f] et Ļ[indice infĆ©rieur c] a eĢteĢ davantage exploiteĢe afin dāeĢliminer les eĢpaisseurs optiques du mode grossier (le filtrage spectral de nuages) et, par la suite, de comparer Ļ[indice infĆ©rieur]f avec les AODs obtenues par le filtrage de nuages traditionnel (temporel). Alors que les filtrages temporel et spectral des nuages des cas eĢtudieĢs au niveau des processus ont conduit aĢ des reĢsultats bons aĢ modeĢreĢs en termes de coheĢrence entre les donneĢes filtreĢes spectralement et temporellement (les eĢpaisseurs optiques des photomeĢtres stellaires et lidars eĢtant toutes deux filtreĢes temporellement), les reĢsultats saisonniers semblent eĢtre encore contamineĢs par les nuages. En imposant un accord en utilisant un second filtre, plus restrictif, avec un criteĢre de ciel clair ("enveloppe minimale du nuage"), les valeurs saisonnieĢres moyennes obtenues eĢtaient de 0.08 aĢ Eureka et 0.04 aĢ Ny AĢlesund durant lāhiver 2010-2011. En 2011-2012, ces valeurs eĢtaient, respectivement, de 0.12 et 0.09. En revanche les valeurs dāeĢpaisseur optique de CALIOP (estimeĢes entre 0 et 8 km) ont leĢgeĢrement diminueĢ de 2010-2011 aĢ 2011-2012 (0.04 vs. 0.03). // Abstract : The Arctic region is particularly sensitive to climate change and has recently undergone major alterations including a dramatic decrease of sea-ice extent. Our ability to model and potentially mitigate climate change is limited, in part, by the uncertainties associated with radiative forcing due to direct and indirect aerosol effects which in turn are dependent on our understanding of aerosol and cloud processes. Aerosol loading can be characterized by aerosol optical depth (AOD) which is the most important (extensive or bulk) aerosol radiative parameter and arguably the most important regional indicator of aerosol behavior. One of the most important shortcomings in our understanding of Arctic aerosols is their behavior during the Polar winter. A major reason for this is the lack of night-time AOD measurements. In this work we use lidar and starphotometry instruments in the Arctic to obtain vertically resolved aerosol profiles and column integrated representations of those profiles (AODs) respectively. In addition, data from a space-borne lidar (CALIOP) is used to provide a pan-Arctic context and seasonal statistics in support of ground based measurements. The latter were obtained at the Eureka (80 ā¦ N, 86 ā¦ W) and Ny Ć
lesund (79 ā¦ N, 12 ā¦ E) high Arctic stations during the Polar Winters of 2010-11 and 2011-12. The physical significance of the variation of the small-amplitude AODs that are typical of the Arctic Polar Winter, requires verification to ensure that artifactual contributions (such as incomplete cloud screening) do not contribute to these variations. A process-level event-based analysis (with a time resolution of ā minutes), is essential to ensure that extracted extensive (bulk) and intensive (per particle) optical and microphysical indicators are coherent and physically consistent. Using the starphotometry-lidar synergy we characterized several distinct events throughout the measurement period: these included aerosol, ice crystal, thin cloud and polar stratospheric cloud (PSC) events. In general fine (1 Ī¼m )modeAODs from starphotometry ( Ļ[subscript f] and Ļ [subscript c] ) were coherent with their lidar analogues produced from integrated profiles : however several inconsistencies related to instrumental and environmental factors were also found. The division of starphotometer AODs into Ļ[subscript ]f and Ļ [subscript c] components was further exploited to eliminate coarse mode cloud optical depths (spectral cloud screening) and subsequently compare Ļ [subscript f] with cloud-screened AODs using a traditional (temporal based) approach. While temporal and spectral cloud screening case studies at process level resolutions yielded good to moderate results in terms of the coherence between spectrally and temporally cloud screened data (both temporally screened starphotometer and lidar optical depths), seasonal results apparently still contained cloud contaminated data. Forcing an agreement using a more restrictive, second-pass, clear sky criterion ("minimal cloud envelope") produced mean 2010-11 AOD seasonal values of 0.08 and 0.04 for Eureka and Ny Ć
lesund respectively. In 2011-12 these values were 0.12 and 0.09. Conversely, CALIOP AODs (0 to 8 km) for the high Arctic showed a slight decrease from 2010-2011 to 2011-2012 (0.04 vs 0.03)
Optische Charakterisierung von polaren Winteraerosolen und Wolken
The Arctic region is particularly sensitive to climate change and has recently undergone major alterations including a dramatic decrease of sea-ice extent. Our ability to model and potentially mitigate climate change is limited, in part, by the uncertainties associated with radiative forcing due to direct and indirect aerosol effects which in turn are dependent on our understanding of aerosol and cloud processes. Aerosol loading can be characterized by aerosol optical depth (AOD) which is the most important (extensive or bulk) aerosol radiative parameter and arguably the most important regional indicator of aerosol behavior. One of the most important shortcomings in our understanding of Arctic aerosols is their behavior during the Polar winter. A major reason for this is the lack of night-time AOD measurements. In this work we use lidar and starphotometry instruments in the Arctic to obtain vertically resolved aerosol profiles and column in- tegrated representations of those profiles (AODs) respectively. In addition, data from a space-borne lidar (CALIOP) is used to provide a pan-Arctic context and seasonal statistics in support of ground based measurements
Characterisation of night-time aerosols using starphotometry
This is a study concerning the use of starphotometry to retrieve night-time aerosol optical depths (AODs). In the summer of 2007 a SPSTAR03 starphotometer was installed at a rural site at Egbert, Ontario for the purpose of the nighttime AOD measurements. Two series of daytime / nighttime AODs were acquired using the CIMEL CE 318 sunphotometer and the SPSTAR03 from Aug. 31 to Sept. 19 2007 and from June 30 to July 5, 2008. The measurements were complemented by vertical backscatter coefficient profiles acquired using a pulsed lidar. We found that starphotometer AOD estimates, based on the application of a two star method (TSM) to low and high elevation stars, are susceptible to atmospheric inhomogeneity effects. Starphotometer AOD estimates based on the one star method (OSM) reduce this sensitivity, but require absolute calibration values. A level of continuity was obtained between the daytime sunphotometry and nighttime starphotometry data. A continuity parameter (defined as the average difference between the measured nighttime and interpolated daytime values) was calculated over four distinct periods. It yielded the differences of 0.160, 0.053, 0.139 (total, fine and coarse mode optical depths) for the low star and 0.195, 0.070, 0.149 for the high star. We argue that cloud screening would have reduced the continuity parameter differences for the coarse and total optical depths. For 5 out of , 8 nights of lidar operation, a combination of the Angstrom and Spectral Deconvolution Algorithm (SDA) analysis provided an indication of the nature of the atmospheric features seen in the lidar data. Fine and coarse-mode events were detected during the measurement periods using the SDA. Lidar data was used to better understand complex atmospheric phenomena and was found especially effective for cloud detection and general signal increase/decrease analysis
La caracteĢrisation optique des aeĢrosols et des nuages pendant lāhiver polaire
RĆ©sumĆ© : LāArctique est particuliĆØrement sensible aux changements climatiques et a rĆ©cemment subi des modifications majeures incluant une diminution dramatique de lāextension de la glace de mer. Notre capacitĆ©Ģ aĢ modĆ©liser et aĢ potentiellement rĆ©duire les changements climatiques est limitĆ©e, en partie, par les incertitudes associeĢes au forcĢ§age radiatif induit par les effets directs et indirects des aeĢrosols, qui deĢpendent de notre compreĢhension des processus impliquant les nuages et les aeĢrosols. La charge des aeĢrosols est caracteĢriseĢe par lāeĢpaisseur optique des aeĢrosols (AOD) qui est le parameĢtre radiatif extensif le plus important et lāindicateur reĢgional du comportement des aeĢrosols sans doute le plus deĢcisif. Une de nos lacunes majeures dans la compreĢhension des aeĢrosols arctiques est leur comportement durant lāhiver polaire. Cela est principalement duĢ au manque de mesures nocturnes dāAOD. Dans ce travail, on utilise des instruments (lidar et photomeĢtre stellaire) installeĢs en Arctique pour mesurer, respectivement, les profils verticaux des aeĢrosols et une valeur inteĢgreĢe dans la colonne (AOD) de ces profils. En outre, les donneĢes dāun lidar spatial (CALIOP) sont utiliseĢes pour fournir un contexte pan-arctique et des statistiques saisonnieĢres pour supporter les mesures au sol. Ces dernieĢres ont eĢteĢ obtenues aux stations arctiques dāEureka (80ā¦ N, 86ā¦ W) et de Ny AĢlesund (79ā¦ N, 12ā¦ E) durant les hivers polaires de 2010-2011 et 2011-2012. Lāimportance physique des pe- tites variations dāamplitude de lāAOD est typique de lāhiver polaire en Arctique, mais suppose une veĢrification pour sāassurer que des artefacts ne contribuent pas aĢ ces variations (par exemple un masque de nuage insuffisant). Une analyse des processus baseĢe sur des eĢveĢnements (avec une reĢsolution temporelle ā une minute) est essentielle pour sāassurer que les parameĢtres optiques et microphysiques extensifs (grossiers) et intensifs (par particules) sont coheĢrents et physiquement conformes. La synergie photomĆØtre stellaire-lidar nous permet de caracteĢriser plusieurs eĢveĢnements distincts au cours des peĢriodes de mesures, en particulier : des aeĢrosols, des cristaux de glace, des nuages fins et des nuages polaires stratospheĢriques (PSC). Dans lāensemble, les modes fin (1Ī¼m) de lāAOD obtenus par photomeĢtrie stellaire (Ļ[indice infĆ©rieur f] et Ļ[indice infĆ©rieur c]) sont coheĢrents avec leurs analogues produits aĢ partir des profils inteĢgreĢs du lidar. Cependant certaines inconsistances causeĢes par des facteurs instrumentaux et environnementaux ont aussi eĢteĢ trouveĢes. La division de lāAOD du photomeĢtre stellaire Ļ[indice infĆ©rieur f] et Ļ[indice infĆ©rieur c] a eĢteĢ davantage exploiteĢe afin dāeĢliminer les eĢpaisseurs optiques du mode grossier (le filtrage spectral de nuages) et, par la suite, de comparer Ļ[indice infĆ©rieur]f avec les AODs obtenues par le filtrage de nuages traditionnel (temporel). Alors que les filtrages temporel et spectral des nuages des cas eĢtudieĢs au niveau des processus ont conduit aĢ des reĢsultats bons aĢ modeĢreĢs en termes de coheĢrence entre les donneĢes filtreĢes spectralement et temporellement (les eĢpaisseurs optiques des photomeĢtres stellaires et lidars eĢtant toutes deux filtreĢes temporellement), les reĢsultats saisonniers semblent eĢtre encore contamineĢs par les nuages. En imposant un accord en utilisant un second filtre, plus restrictif, avec un criteĢre de ciel clair ("enveloppe minimale du nuage"), les valeurs saisonnieĢres moyennes obtenues eĢtaient de 0.08 aĢ Eureka et 0.04 aĢ Ny AĢlesund durant lāhiver 2010-2011. En 2011-2012, ces valeurs eĢtaient, respectivement, de 0.12 et 0.09. En revanche les valeurs dāeĢpaisseur optique de CALIOP (estimeĢes entre 0 et 8 km) ont leĢgeĢrement diminueĢ de 2010-2011 aĢ 2011-2012 (0.04 vs. 0.03). // Abstract : The Arctic region is particularly sensitive to climate change and has recently undergone major alterations including a dramatic decrease of sea-ice extent. Our ability to model and potentially mitigate climate change is limited, in part, by the uncertainties associated with radiative forcing due to direct and indirect aerosol effects which in turn are dependent on our understanding of aerosol and cloud processes. Aerosol loading can be characterized by aerosol optical depth (AOD) which is the most important (extensive or bulk) aerosol radiative parameter and arguably the most important regional indicator of aerosol behavior. One of the most important shortcomings in our understanding of Arctic aerosols is their behavior during the Polar winter. A major reason for this is the lack of night-time AOD measurements. In this work we use lidar and starphotometry instruments in the Arctic to obtain vertically resolved aerosol profiles and column integrated representations of those profiles (AODs) respectively. In addition, data from a space-borne lidar (CALIOP) is used to provide a pan-Arctic context and seasonal statistics in support of ground based measurements. The latter were obtained at the Eureka (80 ā¦ N, 86 ā¦ W) and Ny Ć
lesund (79 ā¦ N, 12 ā¦ E) high Arctic stations during the Polar Winters of 2010-11 and 2011-12. The physical significance of the variation of the small-amplitude AODs that are typical of the Arctic Polar Winter, requires verification to ensure that artifactual contributions (such as incomplete cloud screening) do not contribute to these variations. A process-level event-based analysis (with a time resolution of ā minutes), is essential to ensure that extracted extensive (bulk) and intensive (per particle) optical and microphysical indicators are coherent and physically consistent. Using the starphotometry-lidar synergy we characterized several distinct events throughout the measurement period: these included aerosol, ice crystal, thin cloud and polar stratospheric cloud (PSC) events. In general fine (1 Ī¼m )modeAODs from starphotometry ( Ļ[subscript f] and Ļ [subscript c] ) were coherent with their lidar analogues produced from integrated profiles : however several inconsistencies related to instrumental and environmental factors were also found. The division of starphotometer AODs into Ļ[subscript ]f and Ļ [subscript c] components was further exploited to eliminate coarse mode cloud optical depths (spectral cloud screening) and subsequently compare Ļ [subscript f] with cloud-screened AODs using a traditional (temporal based) approach. While temporal and spectral cloud screening case studies at process level resolutions yielded good to moderate results in terms of the coherence between spectrally and temporally cloud screened data (both temporally screened starphotometer and lidar optical depths), seasonal results apparently still contained cloud contaminated data. Forcing an agreement using a more restrictive, second-pass, clear sky criterion ("minimal cloud envelope") produced mean 2010-11 AOD seasonal values of 0.08 and 0.04 for Eureka and Ny Ć
lesund respectively. In 2011-12 these values were 0.12 and 0.09. Conversely, CALIOP AODs (0 to 8 km) for the high Arctic showed a slight decrease from 2010-2011 to 2011-2012 (0.04 vs 0.03)
Retrievals of ice-water content from an airborne elastic lidar in tropical convective clouds
Ice water content (IWC) is one of the critical parameters in determining the cloud radiative impact. In this work lidar-based IWC retrievals obtained in tropical mesoscale convective systems are evaluated in the context of an extensive in-situ and remote sensing instrumentation suite. Based on a test case of May 27, 2015 lidar-derived IWC values at 50 m above the aircraft were on average within 25% of the in-situ IWC measurements obtained using an isokinetic probe
Retrievals of ice-water content from an airborne elastic lidar in tropical convective clouds
Ice water content (IWC) is one of the critical parameters in determining the cloud radiative impact. In this work lidar-based IWC retrievals obtained in tropical mesoscale convective systems are evaluated in the context of an extensive in-situ and remote sensing instrumentation suite. Based on a test case of May 27, 2015 lidar-derived IWC values at 50 m above the aircraft were on average within 25% of the in-situ IWC measurements obtained using an isokinetic probe
Interpretative synergy of starphotometry and lidar measurements at two High-Arctic stations during Polar Winter of 2010-11.
Synchronized Starphotometry and Lidar measurements in the High Arctic
The sunphotometry-lidar synergy has proven to be effective for the characterization of aerosol events in the High Arctic. Sunphotometry measurements, however, are limited to the day-time periods. Starphotometry, based on the extinction of bright-star radiation, can mitigate the lack of aerosol optical depth (AOD) measurements during the Polar Night. In this work we present several examples of the coincident starphotometry-lidar measurements at Eureka, Canada (79Ā°59'N, 85Ā°56'W) obtained in Feb-Mar 2011. We show a correlation between fine (sub-micron) and coarse (super-micron) mode AOD dynamics from starphotometry and the backscatter profiles and depolarization ratio values from the lidar data