Photometric variability of Uranus and Neptune, 1950–2004

Lockwood, G. W.; Jerzykiewicz, M.

doi:10.1016/j.icarus.2005.09.009

Cited by 37 publications

(48 citation statements)

References 33 publications

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“…Unlike Uranus, with its unusual inclination and negligible internal heat source (e.g., Pearl and Conrath, 1991), Neptune's weather layer exhibits rapidly varying cloud activity, zonal banding, dark ovals and sporadic orographic clouds. Furthermore, the extent of this meteorological activity and the planet's global visible albedo appear to vary with time (Lockwood and Jerzykiewicz, 2006;Hammel and Lockwood, 2007). In this study we attempt to connect this cloud-level activity to changes in Neptune's thermal structure and atmospheric chemistry between Voyager observations (1989) and ground-based observations close to Neptune's 2005 summer solstice.…”

Section: Introductionmentioning

confidence: 99%

Neptune at summer solstice: Zonal mean temperatures from ground-based observations, 2003–2007

Fletcher

Pater²,

Orton

et al. 2014

Icarus

108

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• ). 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 C 2 H 6 abundances are extremely sensitive to the details of the 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-H 2 conditions) and warm air sinking at the equator and poles (super-equilibrium para-H 2 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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Section: Introductionmentioning

confidence: 99%

Neptune at summer solstice: Zonal mean temperatures from ground-based observations, 2003–2007

Fletcher

Pater²,

Orton

et al. 2014

Icarus

108

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“…In August 2014, a large bright polar‐cap‐like feature was identified in Uranus's northern pole from Keck telescope images (de Pater et al, ), whose progressive formation over 2013 was observed by amateur telescopes (see PVOL database, Hueso et al, ). Based on long‐term records of Uranus brightness variations before the 2007 equinox (Hammel & Lockwood, ; Lockwood & Jerzykiewicz, ), it was thought that the polar cap could be a seasonal formation or redistribution of aerosols (de Pater et al, ; Sromovsky et al, ).…”

Section: Introductionmentioning

confidence: 99%

Uranus's Northern Polar Cap in 2014

Toledo

Irwin

Teanby

et al. 2018

Geophysical Research Letters

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In October and November 2014, spectra covering the 1.436 to 1.863‐μm wavelength range from the SINFONI Integral Field Unit Spectrometer on the Very Large Telescope showed the presence of a vast bright north polar cap on Uranus, extending northward from about 40°N and at all longitudes observed. The feature, first detected in August 2014 from Keck telescope images, has a morphology very similar to the southern polar cap that was seen to fade before the 2007 equinox. At strong methane‐absorbing wavelengths (for which only the high troposphere or stratosphere is sampled) the feature is not visible, indicating that it is not a stratospheric phenomenon. We show that the observed northern bright polar cap results mainly from a decrease in the tropospheric methane mixing ratio, rather than from a possible latitudinal variation of the optical properties or abundance of aerosol, implying an increase in polar downwelling near the tropopause level.

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“…comm.) and cover timescales of one to two years in longer cycles of ten to 30 years; such variability has been reported at least for Uranus and Neptune, with optical (B-band) peak-to-peak variations of about 25 and 7 mmag, respectively, over several decades (Lockwood & Jerzykiewicz 2006). Irregular and brusque variations caused by storms or structural changes in the planet's belts have also been observed in giant planets (e.g.…”

Section: Introductionmentioning

confidence: 73%

Long-termKs-band photometric monitoring of L dwarfs

Martí¹,

Osorio²

2014

A&A

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Context. Ultracool dwarfs ( < ∼ 2500 K) are known to display photometric variability in short timescales (hours to days), which has usually been related to rotation-modulated dust cloud patterns, or to unresolved companions. Aims. We perform photometric time-series analysis of a sample of ten early to mid-L dwarfs in the field over three years of Ks-band observations with the OMEGA 2000 infrared camera of the 3.5 m telescope on Calar Alto Observatory between January 2010 and December 2012. This study represents the first systematic long-term photometric monitoring of this kind of object to date. Methods. We perform Ks-band differential photometry of our targets (with typical errors of ±15−30 mmag at the 1σ level) by subtracting a reference flux from each photometric measurement. This reference flux is computed using three nearby, probably constant stars in the target's field-of-view. We then construct and visually inspect the light curves to search for variability, and use four different periodogram algorithms to look for possible periods in our photometric data. Results. Our targets do not display long-term variability over 1σ compared to other nearby stars of similar brightness, nor do the periodograms unveil any possible periodicity for these objects, with two exceptions: 2MASS J02411151-0326587 and G196-3B. In the case of 2MASS J02411151-0326587 (L0), our data suggest a tentative period of 307 ± 21 days, at 40% confidence level, which seems to be associated with peak-to-peak variability of 44 ± 10 mmag. This object may also display variability in timescales of years, as suggested by the comparison of our Ks-band photometry with 2MASS. For G196-3B (L3), we find peak-to-peak variations of 42 ± 10 mmag, with a possible photometric period of 442 ± 7 days, at 95% confidence level. This is roughly the double of the astrometric period reported by Zapatero Osorio et al. (2014, A&A, 568, A6). Given the significance of these results, further photometric data are required to confirm the long-term variability. Conclusions. Our results suggest that early-to mid-L dwarfs are fairly stable in the Ks-band within ±90 mmag at the 3σ level over months to years, which covers hundreds to tens of thousands of rotation cycles. Two out of ten targets show periodic photometric variability at 2.2 µm with peak-to-peak variations of about 40 mmag and tentative periods of ∼300 and ∼450 d.

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Photometric variability of Uranus and Neptune, 1950–2004

Cited by 37 publications

References 33 publications

Neptune at summer solstice: Zonal mean temperatures from ground-based observations, 2003–2007

Neptune at summer solstice: Zonal mean temperatures from ground-based observations, 2003–2007

Uranus's Northern Polar Cap in 2014

Long-termKs-band photometric monitoring of L dwarfs

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