Noctilucent clouds observed from the UK and Denmark – trends and variations over 43 years
The combined UK/Denmark record of noctilucent cloud (NLC) observations over the period 1964–2006 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 signific...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2008-05-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/26/1243/2008/angeo-26-1243-2008.pdf |
| _version_ | 1819206796756123648 |
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| author | S. Kirkwood P. Dalin A. Réchou |
| author_facet | S. Kirkwood P. Dalin A. Réchou |
| author_sort | S. Kirkwood |
| collection | DOAJ |
| description | The combined UK/Denmark record of noctilucent cloud (NLC) observations over
the period 1964–2006 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 solar-cycle 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. |
| first_indexed | 2024-12-23T05:13:18Z |
| format | Article |
| id | doaj.art-03f0b9a18272479a8f3339a3d3aa9201 |
| institution | Directory Open Access Journal |
| issn | 0992-7689 1432-0576 |
| language | English |
| last_indexed | 2024-12-23T05:13:18Z |
| publishDate | 2008-05-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Annales Geophysicae |
| spelling | doaj.art-03f0b9a18272479a8f3339a3d3aa92012022-12-21T17:58:54ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05762008-05-01261243125410.5194/angeo-26-1243-2008Noctilucent clouds observed from the UK and Denmark – trends and variations over 43 yearsS. Kirkwood0P. Dalin1A. Réchou2Swedish Institute of Space Physics, Box 812, 98128 Kiruna, SwedenSwedish Institute of Space Physics, Box 812, 98128 Kiruna, SwedenLaboratoire de l'Atmosphère et des Cyclones, Université de la Réunion – Faculté des Sciences et Technologies, BP 7151 – 15 avenue René Cassin – 97715 ST DENIS Messag Cedex 9, Ile de la Réunion, FranceThe combined UK/Denmark record of noctilucent cloud (NLC) observations over the period 1964–2006 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 solar-cycle 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.https://www.ann-geophys.net/26/1243/2008/angeo-26-1243-2008.pdf |
| spellingShingle | S. Kirkwood P. Dalin A. Réchou Noctilucent clouds observed from the UK and Denmark – trends and variations over 43 years Annales Geophysicae |
| title | Noctilucent clouds observed from the UK and Denmark – trends and variations over 43 years |
| title_full | Noctilucent clouds observed from the UK and Denmark – trends and variations over 43 years |
| title_fullStr | Noctilucent clouds observed from the UK and Denmark – trends and variations over 43 years |
| title_full_unstemmed | Noctilucent clouds observed from the UK and Denmark – trends and variations over 43 years |
| title_short | Noctilucent clouds observed from the UK and Denmark – trends and variations over 43 years |
| title_sort | noctilucent clouds observed from the uk and denmark ndash trends and variations over 43 years |
| url | https://www.ann-geophys.net/26/1243/2008/angeo-26-1243-2008.pdf |
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