Latitude‐dependent long‐term variations in polar mesospheric clouds from SBUV version 3 PMC data

Abstract

[1] Previous studies have suggested that there should be secular trends in polar mesospheric cloud (PMC) occurrence frequency and brightness on decadal timescales and that those trends would be strongest at the lowest latitudes of the PMC existence region. We have analyzed the 27-year PMC data set created from Solar Backscatter Ultraviolet (SBUV, SBUV/2) satellite instruments for long-term variations in albedo using three latitude bands (50°-64°, 64°-74°, 74°-82°). The improved version 3 data set includes revisions to the PMC detection algorithm to produce more consistent results in all measurement conditions. A detailed error analysis yields an approximate uncertainty of 1-2% for seasonally averaged 252-nm albedo values. Adjustments for local time variations in PMC brightness between different satellite data sets were derived to ensure accurate trend calculations. Multiple linear regression fits show that albedo variations are anticorrelated with solar activity in all latitude bands, with a stronger response at high latitudes. The albedo increase from solar maximum to solar minimum ranges from +2% at 50°-64°S to +17% at 74°-82°N. Secular trends in albedo are positive, with long-term changes over 27 years ranging from +12% to +20% depending on hemisphere and latitude. The derived long-term trend in PMC albedo at 50°-64°is smaller than that of higher latitudes. This result contradicts previous suggestions that PMC brightness changes might be most rapid at low latitudes. The albedo response to solar variations is larger in the Northern Hemisphere, while long-term trends are approximately the same in both hemispheres.Citation: DeLand, M. T., E. P. Shettle, G. E. Thomas, and J. J. Olivero (2007), Latitude-dependent long-term variations in polar mesospheric clouds from SBUV version 3 PMC data,

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

“…Since we find no corresponding trend in the length of the season, nor trends in the number of moderate or bright displays, nor is any trend discernible in the sensitivity to planetary waves, we must consider whether this is an artefact of observing practices rather than a geophysical effect. We can also consider that the trends, 0.2 or 0.4 nights/year would correspond to 48% or 57% increases over 27 years, which is much higher than reported for the PMC albedo trend by DeLand et al (2007). All these factors give reason to doubt the geophysical significance of the increase in reported faint NLC which may instead be due to increasing skill on the part of the observers in identifying faint NLC.…”

“…DeLand et al (2003DeLand et al ( , 2007 have made detailed analyses of PMC albedo for the period . Since the satellite data do not cover earlier years than 1979, there is no possibility to compare our present observation of different characteristics in the decade 1973-1982 compared to earlier or later decades.…”

“…Also Shettle et al (2002), found an increase in the numbers of the brightest PMC between 1983 and 1996, using satellite observations. In the most comprehensive analysis of satellite data so far, DeLand et al (2007) found a 17% increase in northern hemisphere PMC albedo for the period 1979-2006. In contrast, recent analysis of ground-based NLC observations from Moscow (1962Moscow ( -2005 and Denmark (1983Denmark ( -2005 has found no evidence for statistically significant increases in occurrence frequency or brightness (Dalin et al, 2006).…”

“…The LT variation is a problem for the studies based on satellite data, where the LT of the observations changes over the years, particularly when a series of different satellites is used. DeLand et al (2007) have attempted to make corrections for the LT variations but the latter are not well determined by the available measurements, so that any correction applied has some uncertainty.…”

Polar mesosphere summer echo strength in relation to solar variability and geomagnetic activity during 1997–2009

“…Thus possible long-term trends in NLC derived using both ground-based and satelliteborne measurements attract great interest and discussion in the literature (e.g. DeLand et al, 2003DeLand et al, , 2007Kirkwood et al, 2008;Shettle et al, 2009). PMSE are readily measured by VHF radars and have been monitored on a continuous basis since the 1990s.…”