Long-term variations of the oxygen red 630 nm line nightglow intensity

The long-term data set of total nightglow intensity of the oxygen red 630.0~nm line observed at Abastumani (41.8°N, 42.8°E) between 1957–1993 is investigated. The long-term trend and characteristic variations in solar radiation during an 11 year cycle of the red-line intensity are different after astronomical twilight (premidnight) and at midnight. The amplitude of deviation of the red-line intensity from its mean value at solar maximum and (or) minimum phase is greatest after astronomical twilight and decreases toward midnight. The long-term trend of these variations changes from its value about 0.74 R/year premidnight to its minimum negative value of about –1.92 R/year at and after midnight. This behavior of the long-term trend is considered as a possible result of an increase in electron density below the peak height (hmF2) of the ionospheric F2 layer and lowering of the height hmF2 after midnight predicted by the TIME-GCM model on the assumption of an increase in density of greenhouse gases in the lower atmosphere. The third-order regression equation (with different solar activity indices) is considered to be convenient for describing long-term variations in the mean annual red-line intensity.PACS Nos.: 94.10.Rk, 94.20.Ji, 92.60.Vb

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Different long-term trends of the oxygen red 630.0 nm line nightglow intensity as the result of lowering the ionosphere F2 layer

Annales Geophysicae ◽

10.5194/angeo-26-2069-2008 ◽

2008 ◽

Vol 26 (8) ◽

pp. 2069-2080 ◽

Cited By ~ 5

Author(s):

N. B. Gudadze ◽

G. G. Didebulidze ◽

L. N. Lomidze ◽

G. Sh. Javakhishvili ◽

M. A. Marsagishvili ◽

...

Keyword(s):

Electron Density ◽

Line Intensity ◽

Peak Height ◽

Height Distribution ◽

Theoretical Simulation ◽

Type Layer ◽

Long Term Trends ◽

The Mean ◽

Long Term Trend

Abstract. Long-term observations of total nightglow intensity of the atomic oxygen red 630.0 nm line at Abastumani (41.75° N, 42.82° E) in 1957–1993 and measurements of the ionosphere F2 layer parameters from the Tbilisi ionosphere station (41.65° N, 44.75° E) in 1963–1986 have been analyzed. It is shown that a decrease in the long-term trend of the mean annual red 630.0 nm line intensity from the pre-midnight value (+0.770±1.045 R/year) to its minimum negative value (−1.080±0.670 R/year) at the midnight/after midnight is a possible result of the observed lowering of the peak height of the ionosphere F2 layer electron density hmF2 (−0.455±0.343 km/year). A theoretical simulation is carried out using a simple Chapman-type layer (damping in time) for the height distribution of the F2 layer electron density. The estimated values of the lowering in the hmF2, the increase in the red line intensity at pre-midnight and its decrease at midnight/after midnight are close to their observational ones, when a negative trend in the total neutral density of the upper atmosphere and an increase in the mean northward wind (or its possible consequence – a decrease in the southward one) are assumed.

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Long-term trend and variability of atmospheric PM<sub>10</sub> concentration in the Po Valley

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-4895-2014 ◽

2014 ◽

Vol 14 (10) ◽

pp. 4895-4907 ◽

Cited By ~ 39

Author(s):

A. Bigi ◽

G. Ghermandi

Keyword(s):

Weekend Effect ◽

Wilcoxon Test ◽

Particulate Emissions ◽

Gaseous Emissions ◽

Atmospheric Pollutant ◽

Data Set ◽

Term Trend ◽

Po Valley ◽

Long Term Trend

Abstract. The limits to atmospheric pollutant concentration set by the European Commission provide a challenging target for the municipalities in the Po Valley, because of the characteristic climatic conditions and high population density of this region. In order to assess climatology and trends in the concentration of atmospheric particles in the Po Valley, a data set of PM10 data from 41 sites across the Po Valley have been analysed, including both traffic and background sites (either urban, suburban or rural). Of these 41 sites, 18 with 10 yr or longer record have been analysed for long-term trend in deseasonalized monthly means, in annual quantiles and in monthly frequency distribution. A widespread significant decreasing trend has been observed at most sites, up to a few percent per year, by a generalized least squares and Theil–Sen method. All 41 sites have been tested for significant weekly periodicity by Kruskal–Wallis test for mean anomalies and by Wilcoxon test for weekend effect magnitude. A significant weekly periodicity has been observed for most PM10 series, particularly in summer and ascribed mainly to anthropic particulate emissions. A cluster analysis has been applied in order to highlight stations sharing similar pollution conditions over the reference period. Five clusters have been found, two encompassing the metropolitan areas of Turin and Milan and their respective nearby sites and the other three clusters gathering northeast, northwest and central Po Valley sites respectively. Finally, the observed trends in atmospheric PM10 have been compared to trends in provincial emissions of particulates and PM precursors, and analysed along with data on vehicular fleet age, composition and fuel sales. A significant basin-wide drop in emissions occurred for gaseous pollutants, contrarily to emissions of PM10 and PM2.5, whose drop was low and restricted to a few provinces. It is not clear whether the decrease for only gaseous emissions is sufficient to explain the observed drop in atmospheric PM10, or if the low drop in particulate emissions is indeed due to the uncertainty in the emission inventory data for this species.

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Long-term Trend Comparison of Planetary Boundary Layer Height in Observations and CMIP6 models over China

Journal of Climate ◽

10.1175/jcli-d-20-1000.1 ◽

2021 ◽

pp. 1-64

Author(s):

Man Yue ◽

Minghuai Wang ◽

Jianping Guo ◽

Haipeng Zhang ◽

Xinyi Dong ◽

...

Keyword(s):

Boundary Layer ◽

Heat Flux ◽

Planetary Boundary Layer ◽

Climate Models ◽

Radiative Effect ◽

Term Trend ◽

Cloud Radiative Effect ◽

Long Term Trend ◽

Long Term Variations

AbstractThe planetary boundary layer (PBL) plays an essential role in climate and air quality simulations. Nevertheless, large uncertainties remain in understanding the drivers for long-term trend of PBL height (PBLH) and its simulation. Here we combinate the radiosonde data and reanalysis datasets to analyze PBLH long-term trends over China, and to further explore the performance of CMIP6 climate models in simulating these trends. Results show that the observed long-term “positive to negative” trend shift of PBLH is related to the variation in the surface upward sensible heat flux (SHFLX), and the SHFLX is further controlled by the synergistic effect of low cloud cover (LCC) and soil moisture (SM) changes. Variabilities in LCC and SM directly influence the energy balance via surface net downward shortwave flux (SWF) and the latent heat flux (LHFLX), respectively. The CMIP6 climate models, however, cannot reproduce the observed PBLH long-term trend shift over China. The CMIP6 results illustrate an overwhelming continuous downward PBLH trend during the 1979–2014 period, which is largely caused by the poor capability in simulating long-term variations of cloud radiative effect. Our results reveal that the long-term cloud radiative effect simulation is critical for CMIP6 models in reproducing the long-term trend of PBLH. This study highlights the importance of processes associated with LCC and SM in modulating PBLH long-term variations and calls attentions to improve these processes in climate models in order to improve the PBLH long-term trend simulations.

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