Noctilucent clouds

Fogle, Benson; Haurwitz, B.

doi:10.1007/bf00173768

Cited by 107 publications

(60 citation statements)

References 6 publications

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“…A decadal variation in NLC numbers has been noted many times, including in NLC datasets from other locations and other epochs (see e.g. Simmons and MacIntosh, 1983;Fogle and Haurwitz, 1966;Gadsden, 1998;Romejko et al, 2003). Some indirect relation with the Sun's ∼10 year activity cycle has usually been suggested, and this is represented by the solar 10.7 cm radio flux in Fig.…”

Section: Quasi-decadal Variationmentioning

confidence: 84%

“…They are seen from the ground, by the naked eye, as silvergrey patterns against the twilight sky, lit up from below by the sun below the horizon. As described in the review by Fogle and Haurwitz (1966), the earliest well documented reports of NLC are from 1884, when many observers were watching the twilight sky to see the dramatic results of the dust thrown into the atmosphere by the eruption of Krakatoa in the previous year. However, NLC-like features in a painting by W. Dyce in 1836 or 1837, showing a twilight scene from Edinburgh in Scotland (56 • N), may point to earlier observations (Gadsden, 2002a), before the special nature of these clouds was recognized in the late 19th century.…”

Section: Introductionmentioning

confidence: 99%

“…These are expertly summarized by Fogle and Haurwitz (1966) and by Gadsden and Schröder (1989). No attempt is made to make a complete review of NLC science in this short report, only the most important characteristics are mentioned, which are of relevance for the present study, which concerns possible trends over the last 43 years.…”

Section: Introductionmentioning

confidence: 99%

“…It is also clear from the historical record that NLC occurrence rates have varied by large factors from year to year, during the late 19th and early 20th centuries, long before anthropogenic inputs are likely to have had any effect (Fogle and Haurwitz, 1966). These natural fluctuations also need to be better documented and understood.…”

Section: Introductionmentioning

confidence: 99%

“…Fogle and Haurwitz, 1966;Paton, 1971;Simmons and McIntosh, 1983), so that statistical studies to look for changes in occurrence rates must be based on observations made throughout from the same geographical region, restricted in both latitude and longitude. The third important NLC characteristic is that there is a strong daily variation.…”

Section: Introductionmentioning

confidence: 99%

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Noctilucent clouds observed from the UK and Denmark – trends and variations over 43 years

2008

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Abstract. The combined UK/Denmark record of noctilucent cloud (NLC) observations over the period is analysed. This data set is based on visual observations by professional and voluntary observers, with around 40 observers each year contributing reports. Evidence is found for a significantly longer NLC season, a greater frequency of bright NLC, and a decreased sensitivity to 5-day planetary waves, from 1973-1982, compared to the rest of the time interval. This coincides with a period when the length of the summer season in the stratosphere was also longer (defined by zonal winds at 60 • N, 30 hPa). At NLC heights, lower mean temperatures, and/or higher water vapour and/or smaller planetary wave amplitudes could explain these results. The time series of number of NLC nights each year shows a quasi-decadal variation with good anti-correlation with the 10.7 cm solar flux, with a lag of 13-17 months. Using multi-parameter linear fitting, it is found that the solarcycle and the length of summer in the stratosphere together can explain ∼40% of the year-to-year variation in NLC numbers. However, no statistically confidant long-term trend in moderate or bright NLC is found. For NLC displays of moderate or greater intensity, the multi-parameter fit gives a trend of ∼0.08 nights (0.35%) per year with a statistical probability of 28% that it is zero, or as high as 0.16 nights (0.7%) per year. There is a significant increasing trend in the number of reports of faint or very faint NLC which is inconsistent with other observations and may be due changes in observing practices.

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Section: Quasi-decadal Variationmentioning

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Noctilucent clouds observed from the UK and Denmark – trends and variations over 43 years

2008

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Horizontal winds derived from the polar mesospheric cloud images as observed by the CIPS instrument on the AIM satellite

et al. 2015

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A cloud pattern matching technique is applied to polar mesospheric cloud (PMC) images taken by the Cloud Imaging and Particle Size instrument (CIPS) to infer the wind velocities in the mesopause region. CIPS measurements are analyzed to detect patterns that repeat from one orbit to the next but are displaced in location; the displacement provides a measure of the wind velocity. Pattern matching is achieved by resampling the CIPS data to longitude and latitude grids with the grid-box size forced at~5 km in both directions. The correlated patterns are searched within a geographic region referred to as a "frame" of 500 km in longitude × 400 km in latitude. The histograms of the derived velocities indicate that easterly winds prevail, with a mean zonal wind of À20 to À15 m/s. Mean meridional winds are overall small, but in late summer the histogram indicated a poleward wind of~20-30 m/s. The variability of CIPS cloud albedo on consecutive orbits is also examined at fixed geolocations. The statistical results suggest that~86% of pairs underwent mean cloud albedo variation of < 50% on consecutive orbits, suggesting a moderate change. It is also found that the correlation of the cloud structures between two consecutive orbits at a fixed location is generally poor. These findings suggest that cloud patterns are subject to wind advection, but the cloud patches are more extended in size than the movement that occurs. Cloud voids are found to be more likely to remain at the same geolocations.

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Investigating Gravity Waves in Polar Mesospheric Clouds Using Tomographic Reconstructions of AIM Satellite Imagery

et al. 2018

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This research presents the first application of tomographic techniques for investigating gravity wave structures in polar mesospheric clouds (PMCs) imaged by the Cloud Imaging and Particle Size instrument on the NASA AIM satellite. Albedo data comprising consecutive PMC scenes were used to tomographically reconstruct a 3‐D layer using the Partially Constrained Algebraic Reconstruction Technique algorithm and a previously developed “fanning” technique. For this pilot study, a large region (760 × 148 km) of the PMC layer (altitude ~83 km) was sampled with a ~2 km horizontal resolution, and an intensity weighted centroid technique was developed to create novel 2‐D surface maps, characterizing the individual gravity waves as well as their altitude variability. Spectral analysis of seven selected wave events observed during the Northern Hemisphere 2007 PMC season exhibited dominant horizontal wavelengths of ~60–90 km, consistent with previous studies. These tomographic analyses have enabled a broad range of new investigations. For example, a clear spatial anticorrelation was observed between the PMC albedo and wave‐induced altitude changes, with higher‐albedo structures aligning well with wave troughs, while low‐intensity regions aligned with wave crests. This result appears to be consistent with current theories of PMC development in the mesopause region. This new tomographic imaging technique also provides valuable wave amplitude information enabling further mesospheric gravity wave investigations, including quantitative analysis of their hemispheric and interannual characteristics and variations.

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Noctilucent clouds

Cited by 107 publications

References 6 publications

Noctilucent clouds observed from the UK and Denmark – trends and variations over 43 years

Noctilucent clouds observed from the UK and Denmark – trends and variations over 43 years

Horizontal winds derived from the polar mesospheric cloud images as observed by the CIPS instrument on the AIM satellite

Investigating Gravity Waves in Polar Mesospheric Clouds Using Tomographic Reconstructions of AIM Satellite Imagery

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