The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Patrick G. J. Irwin - One of the best experts on this subject based on the ideXlab platform.
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neptune at Summer Solstice zonal mean temperatures from ground based observations 2003 2007
Icarus, 2014Co-Authors: Leigh N. Fletcher, Imkede De Pater, Glenn S. Orton, Michael L. Sitko, Heidi Hammel, Patrick G. J. IrwinAbstract:Imaging and spectroscopy of Neptune’s thermal infrared emission from Keck/LWS (2003), Gemini-N/MICHELLE (2005); VLT/VISIR (2006) and Gemini-S/TReCS (2007) is used to assess seasonal changes in Neptune’s zonal mean temperatures between Voyager-2 observations (1989, heliocentric longitude Ls=236°Ls=236°) and southern Summer Solstice (2005, Ls=270°Ls=270°). Our aim was to analyse imaging and spectroscopy from multiple different sources using a single self-consistent radiative-transfer model to assess the magnitude of seasonal variability. Globally-averaged stratospheric temperatures measured from methane emission tend towards a quasi-isothermal structure (158–164 K) above the 0.1-mbar level, and are found to be consistent with spacecraft observations of AKARI. This remarkable consistency, despite very different observing conditions, suggests that stratospheric temporal variability, if present, is <±5 K at 1 mbar and <±3 K at 0.1 mbar during this Solstice period. Conversely, ethane emission is highly variable, with abundance determinations varying by more than a factor of two (from 500 to 1200 ppb at 1 mbar). The retrieved C2H6 abundances are extremely sensitive to the details of the T(p)T(p) derivation, although the underlying cause of the variable ethane emission remains unidentified. Stratospheric temperatures and ethane are found to be latitudinally uniform away from the south pole (assuming a latitudinally-uniform distribution of stratospheric methane), with no large seasonal hemispheric asymmetries evident at Solstice. At low and mid-latitudes, comparisons of synthetic Voyager-era images with Solstice-era observations suggest that tropospheric zonal temperatures are unchanged since the Voyager 2 encounter, with cool mid-latitudes and a warm equator and pole. A re-analysis of Voyager/IRIS 25–50 μm mapping of tropospheric temperatures and para-hydrogen disequilibrium (a tracer for vertical motions) suggests a symmetric meridional circulation with cold air rising at mid-latitudes (sub-equilibrium para-H2 conditions) and warm air sinking at the equator and poles (super-equilibrium para-H2 conditions). The most significant atmospheric changes have occurred at high southern latitudes, where zonal temperatures retrieved from 2003 images suggest a polar enhancement of 7–8 K above the tropopause, and an increase of 5–6 K throughout the 70–90°S region between 0.1 and 200 mbar. Such a large perturbation, if present in 1989, would have been detectable by Voyager/IRIS in a single scan despite its long-wavelength sensitivity, and we conclude that Neptune’s south polar cyclonic vortex increased in strength significantly from Voyager to Solstice.
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Neptune at Summer Solstice: Zonal mean temperatures from ground-based observations, 2003–2007
Icarus, 2014Co-Authors: Leigh N. Fletcher, Imkede De Pater, Glenn S. Orton, Heidi B. Hammel, Michael L. Sitko, Patrick G. J. IrwinAbstract:Imaging and spectroscopy of Neptune’s thermal infrared emission from Keck/LWS (2003), Gemini-N/MICHELLE (2005); VLT/VISIR (2006) and Gemini-S/TReCS (2007) is used to assess seasonal changes in Neptune’s zonal mean temperatures between Voyager-2 observations (1989, heliocentric longitude Ls=236°Ls=236°) and southern Summer Solstice (2005, Ls=270°Ls=270°). Our aim was to analyse imaging and spectroscopy from multiple different sources using a single self-consistent radiative-transfer model to assess the magnitude of seasonal variability. Globally-averaged stratospheric temperatures measured from methane emission tend towards a quasi-isothermal structure (158–164 K) above the 0.1-mbar level, and are found to be consistent with spacecraft observations of AKARI. This remarkable consistency, despite very different observing conditions, suggests that stratospheric temporal variability, if present, is
John E. Frederick - One of the best experts on this subject based on the ideXlab platform.
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Photosynthetically active sunlight at high southern latitudes.
Photochemistry and photobiology, 2005Co-Authors: John E. Frederick, Yixiang LiaoAbstract:Abstract A network of scanning spectroradiometers has acquired a multiyear database of visible solar irradiance, covering wavelengths from 400 to 600 nm, at four sites in the high-latitude Southern Hemisphere, from 55°S to 90°S. Monthly irradiations computed from the hourly measurements reveal the character of the seasonal cycle and illustrate the role of cloudiness as functions of latitude. Near Summer Solstice, the combined influences of solar elevation and the duration of daylight would produce a monthly irradiation with little latitude dependence under clear skies. However, the attenuation associated with local cloudiness varies geographically, with the greatest effect at the most northern locations, Ushuaia, Argentina and Palmer Station on the Antarctic Peninsula. Near Summer Solstice, the South Pole experiences the largest monthly irradiation of the sites studied, where relatively clear skies contribute to this result. Scaling factors derived from radiative-transfer calculations combined with the me...
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Prolonged enhancement in surface ultraviolet radiation during the Antarctic spring of 1990
Geophysical Research Letters, 1991Co-Authors: John E. Frederick, Amy D. AlbertsAbstract:Measurements of the ultraviolet solar spectral irradiance from the earth's surface at Palmer Station, Antarctica, latitude 64.8 degrees South, show behavior in the spring of 1990 which differs from that observed during the seasonal ozone depletions of the previous two years. As the Austral spring progresses, the sun rises in the sky, and the duration of daylight increases up to the Summer Solstice on December 21. This is naturally accompanied by increasing ultraviolet irradiances irrespective of the behavior of column ozone. If, as in 1988, the ozone depletion is confined to October and early November, the irradiances at local noon may remain at or below values characteristic of an unperturbed Summer Solstice. However, in 1990 enhanced irradiances persisted well into December. The largest values observed at a wavelength of 306.5 nm were approximately double those expected at Summer Solstice with an unperturbed ozone amount.
Bettina Meyer - One of the best experts on this subject based on the ideXlab platform.
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Widely rhythmic transcriptome in Calanus finmarchicus during the high Arctic Summer Solstice period
iScience, 2020Co-Authors: Laura Payton, Lukas Hüppe, Céline Noirot, Claire Hoede, David C. Wilcockson, Elizaveta Ershova, Sophie Valière, Bettina MeyerAbstract:Summary Solar light/dark cycles and seasonal photoperiods underpin daily and annual rhythms of life on Earth. Yet, the Arctic is characterized by several months of permanent illumination (“midnight sun”). To determine the persistence of 24h rhythms during the midnight sun, we investigated transcriptomic dynamics in the copepod Calanus finmarchicus during the Summer Solstice period in the Arctic, with the lowest diel oscillation and the highest altitude of the sun's position. Here we reveal that in these extreme photic conditions, a widely rhythmic daily transcriptome exists, showing that very weak solar cues are sufficient to entrain organisms. Furthermore, at extremely high latitudes and under sea-ice, gene oscillations become re-organized to include
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daily transcriptomes of the copepod calanus finmarchicus during the Summer Solstice at high arctic latitudes
Scientific Data, 2020Co-Authors: Laura Payton, Lukas Hüppe, Céline Noirot, Claire Hoede, David C. Wilcockson, Elizaveta Ershova, Sophie Valière, Bettina MeyerAbstract:The zooplankter Calanus finmarchicus is a member of the so-called “Calanus Complex”, a group of copepods that constitutes a key element of the Arctic polar marine ecosystem, providing a crucial link between primary production and higher trophic levels. Climate change induces the shift of C. finmarchicus to higher latitudes with currently unknown impacts on its endogenous timing. Here we generated a daily transcriptome of C. finmarchicus at two high Arctic stations, during the more extreme time of Midnight Sun, the Summer Solstice. While the southern station (74.5 °N) was sea ice-free, the northern one (82.5 °N) was sea ice-covered. The mRNAs of the 42 samples have been sequenced with an average of 126 ± 5 million reads (mean ± SE) per sample, and aligned to the reference transcriptome. We detail the quality assessment of the datasets and the complete annotation procedure, providing the possibility to investigate daily gene expression of this ecologically important species at high Arctic latitudes, and to compare gene expression according to latitude and sea ice-coverage. Machine-accessible metadata file describing the reported data: https://doi.org/10.6084/m9.figshare.13008035
Amy D. Alberts - One of the best experts on this subject based on the ideXlab platform.
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Prolonged enhancement in surface ultraviolet radiation during the Antarctic spring of 1990
Geophysical Research Letters, 1991Co-Authors: John E. Frederick, Amy D. AlbertsAbstract:Measurements of the ultraviolet solar spectral irradiance from the earth's surface at Palmer Station, Antarctica, latitude 64.8 degrees South, show behavior in the spring of 1990 which differs from that observed during the seasonal ozone depletions of the previous two years. As the Austral spring progresses, the sun rises in the sky, and the duration of daylight increases up to the Summer Solstice on December 21. This is naturally accompanied by increasing ultraviolet irradiances irrespective of the behavior of column ozone. If, as in 1988, the ozone depletion is confined to October and early November, the irradiances at local noon may remain at or below values characteristic of an unperturbed Summer Solstice. However, in 1990 enhanced irradiances persisted well into December. The largest values observed at a wavelength of 306.5 nm were approximately double those expected at Summer Solstice with an unperturbed ozone amount.
Leigh N. Fletcher - One of the best experts on this subject based on the ideXlab platform.
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neptune at Summer Solstice zonal mean temperatures from ground based observations 2003 2007
Icarus, 2014Co-Authors: Leigh N. Fletcher, Imkede De Pater, Glenn S. Orton, Michael L. Sitko, Heidi Hammel, Patrick G. J. IrwinAbstract:Imaging and spectroscopy of Neptune’s thermal infrared emission from Keck/LWS (2003), Gemini-N/MICHELLE (2005); VLT/VISIR (2006) and Gemini-S/TReCS (2007) is used to assess seasonal changes in Neptune’s zonal mean temperatures between Voyager-2 observations (1989, heliocentric longitude Ls=236°Ls=236°) and southern Summer Solstice (2005, Ls=270°Ls=270°). Our aim was to analyse imaging and spectroscopy from multiple different sources using a single self-consistent radiative-transfer model to assess the magnitude of seasonal variability. Globally-averaged stratospheric temperatures measured from methane emission tend towards a quasi-isothermal structure (158–164 K) above the 0.1-mbar level, and are found to be consistent with spacecraft observations of AKARI. This remarkable consistency, despite very different observing conditions, suggests that stratospheric temporal variability, if present, is <±5 K at 1 mbar and <±3 K at 0.1 mbar during this Solstice period. Conversely, ethane emission is highly variable, with abundance determinations varying by more than a factor of two (from 500 to 1200 ppb at 1 mbar). The retrieved C2H6 abundances are extremely sensitive to the details of the T(p)T(p) derivation, although the underlying cause of the variable ethane emission remains unidentified. Stratospheric temperatures and ethane are found to be latitudinally uniform away from the south pole (assuming a latitudinally-uniform distribution of stratospheric methane), with no large seasonal hemispheric asymmetries evident at Solstice. At low and mid-latitudes, comparisons of synthetic Voyager-era images with Solstice-era observations suggest that tropospheric zonal temperatures are unchanged since the Voyager 2 encounter, with cool mid-latitudes and a warm equator and pole. A re-analysis of Voyager/IRIS 25–50 μm mapping of tropospheric temperatures and para-hydrogen disequilibrium (a tracer for vertical motions) suggests a symmetric meridional circulation with cold air rising at mid-latitudes (sub-equilibrium para-H2 conditions) and warm air sinking at the equator and poles (super-equilibrium para-H2 conditions). The most significant atmospheric changes have occurred at high southern latitudes, where zonal temperatures retrieved from 2003 images suggest a polar enhancement of 7–8 K above the tropopause, and an increase of 5–6 K throughout the 70–90°S region between 0.1 and 200 mbar. Such a large perturbation, if present in 1989, would have been detectable by Voyager/IRIS in a single scan despite its long-wavelength sensitivity, and we conclude that Neptune’s south polar cyclonic vortex increased in strength significantly from Voyager to Solstice.
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Neptune at Summer Solstice: Zonal mean temperatures from ground-based observations, 2003–2007
Icarus, 2014Co-Authors: Leigh N. Fletcher, Imkede De Pater, Glenn S. Orton, Heidi B. Hammel, Michael L. Sitko, Patrick G. J. IrwinAbstract:Imaging and spectroscopy of Neptune’s thermal infrared emission from Keck/LWS (2003), Gemini-N/MICHELLE (2005); VLT/VISIR (2006) and Gemini-S/TReCS (2007) is used to assess seasonal changes in Neptune’s zonal mean temperatures between Voyager-2 observations (1989, heliocentric longitude Ls=236°Ls=236°) and southern Summer Solstice (2005, Ls=270°Ls=270°). Our aim was to analyse imaging and spectroscopy from multiple different sources using a single self-consistent radiative-transfer model to assess the magnitude of seasonal variability. Globally-averaged stratospheric temperatures measured from methane emission tend towards a quasi-isothermal structure (158–164 K) above the 0.1-mbar level, and are found to be consistent with spacecraft observations of AKARI. This remarkable consistency, despite very different observing conditions, suggests that stratospheric temporal variability, if present, is
