A secular change in noctilucent cloud occurrence

Gadsden, M.

doi:10.1016/0021-9169(90)90091-z

Cited by 95 publications

(60 citation statements)

References 7 publications

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“…Fogle and Haurwitz, 1974;Thomas et al, 1989;Gadsden, 1990Gadsden, , 1998Gadsden, , 2002Kirkwood and Stebel, 2003;Romejko et al, 2003;. Traditionally this occurrence rate has been expressed by the number of nights per summer season in which NLC were observed visually from the ground.…”

Section: Decadal Variations Of Nlc Occurrence Ratementioning

confidence: 99%

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Noctilucent clouds and the mesospheric water vapour: the past decade

et al. 2004

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Abstract. The topic of this paper is the sensitivity of the brightness of noctilucent clouds (NLC) on the ambient water vapour mixing ratio f(H 2 O). Firstly, we use state-of-the-art models of NLC layer formation to predict NLC brightness changes in response to changes in the 80 km mixing ratio f(H 2 O) for the two cases of ground-based 532 nm lidar observations at 69 • N and for hemispheric satellite SBUV observations at 252 nm wavelength. In this study, we include a re-evaluation of the sensitivity of NLC brightness to changes in solar Lyman α flux. Secondly, we review observations of episodic changes in f(H 2 O) and those in NLC brightness, the former being available since 1992, the latter since 1979. To this review, we add a new series of observations of f(H 2 O), performed in the Arctic summer at the ALOMAR observatory. The episodic change exhibited by the Arctic summer means of f(H 2 O) turns out to be quite different from all those derived from annual means of f(H 2 O). The latter indicate that since 1996 a significant reduction of annually averaged upper mesospheric water vapour has occurred at low, mid, and high latitudes. These decreases of f(H 2 O) have been observed over the same time period in which a slow increase of SBUV NLC albedo has occurred. From this scenario and additional arguments we conclude that the cause for the observed long-term increase in NLC albedo remains to be identified. We close with comments on the very different character of decadal variations in NLC brightness and occurrence rate.

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Section: Decadal Variations Of Nlc Occurrence Ratementioning

confidence: 99%

“…The observed increase of A might well be caused by a rather gradual temperature decrease of the summer Arctic mesopause region, which is, however, so small, that it is still not directly measurable. An early discussion of this topic was given by Gadsden (1990).…”

Section: Unexpected Stability Of the Arctic Summer Mesospherementioning

confidence: 99%

Noctilucent clouds and the mesospheric water vapour: the past decade

et al. 2004

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“…This error bar does not include a contribution from the uncertainty of the altitude range over which we need to distribute the "evaporated" water vapor in order to obtain non-NLC conditions. [Gadsden, 1990]. The strengths of lidar-observed NLC events were defined by von Cossart et al [ 1997] by their maximum backscatter ratio R,,•x at 532 run.…”

Section: Data Processing and Analysismentioning

confidence: 99%

Size distributions of NLC particles as determined from 3‐color observations of NLC by ground‐based lidar

Cossart

Fiedler

Zahn

1999

Geophysical Research Letters

193

188

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Abstract. From June to August 1998 the ALOMAR Rayleigh/Mie/ Raman lidar, located at 69øN and 16øE in Northem Norway, repeatedly observed noctilucent clouds (NLCs) overhead the lidar. Due to a recent upgrade in detector technology, the lidar was able to obtain 151 hours of NLC observations, simultaneously at 355, 532, and 1064 nm. For the 11 strongest NLC events, we have calculated size distributions for the NLC particles from the b•kscatter ratios measured at the 3 wavelengths and using the assumptions of spherical ice particles with a monomodal lognormal size distribution. For all events evaluated at the layer maxima, we obtain well-defined median radii rmea, width parameters a, and particle number densities N•_c for the NLC particle distributions. Mean values for 10 out of the 11 events are r,,,ea = 51 nm, a = 1.42, and NNLc = 82 crn -3.

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“…However, the different approaches arrived to controversial conclusions on the subject which suggest either continuously increasing NLC numbers over Western Europe (Gadsden 1990(Gadsden , 1998 and PMC activity for sub-polar and polar latitudes (DeLand et al 2006(DeLand et al , 2007Shettle et al 2009) or zero-trends derived from ground-based observations (Romejko et al 2002(Romejko et al , 2003Dalin et al 2006;Kirkwood et al 2008;Dubietis et al 2010). The main reasons for these differences are attributed to different analyzed variables, different time intervals and latitude range used for the analysis and inhomogeneity of the datasets (Dalin et al 2006;Kirkwood et al 2008).…”

Section: Introductionmentioning

confidence: 99%

Noctilucent clouds observed from the ground: sensitivity to mesospheric parameters and long-term time series

et al. 2014

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Long-term systematic observations of noctilucent clouds in the regions of Moscow (Russia), Vilnius (Lithuania), and La Ronge (Canada) are considered. Variables, describing the seasonal activity of noctilucent clouds, are discussed. It is shown that there are no statistically significant trends within time intervals of several recent decades. This result is compared to other known findings on trends in mesospheric clouds. Based on the data of the modern ground-based noctilucent cloud observing network in the northern hemisphere and simultaneous satellite data on mesospheric temperature and humidity, we estimate sensitivity of noctilucent clouds to the relative humidity of the upper mesosphere. Such an approach allows us to discuss possible changes of the upper-mesospheric relative humidity, which are consistent with a zero secular trend in noctilucent cloud activity.

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A secular change in noctilucent cloud occurrence

Cited by 95 publications

References 7 publications

Noctilucent clouds and the mesospheric water vapour: the past decade

Noctilucent clouds and the mesospheric water vapour: the past decade

Size distributions of NLC particles as determined from 3‐color observations of NLC by ground‐based lidar

Noctilucent clouds observed from the ground: sensitivity to mesospheric parameters and long-term time series

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