Decadal variability in mid-atmosphere temperature derived from continuous lidar observations

Abstract

Nine Rayleigh scattering-based lidars, some of which are affiliated with the Network for the Detection of Atmospheric Composition Change (NDACC) and the Atmospheric Remote Sensing in Stratosphere and mesosphere (ARISE) for monitoring stratospheric ozone, have been routinely observing temperature profile variations in the middle atmosphere for many years with excellent vertical resolution (around one kilometer). These observatories are located at various points around the globe from north to south: ALOMAR in Norway, Kühlungsborn in Mecklenburg-Western Pomerania Germany, Hohenpeissenberg in Bavaria Germany, Haute-Provence in southern France, Purple Crow in the Canadian London Ontario, Table Mountain in California, Mauna Loa in Hawaii, Maido on Reunion Island, Coral in Tierra del Fuego Argentina . These unique datasets have made it possible to update the climatology and seasonal variations of middle atmosphere temperatures between 30 and 80 km at several latitudes with significantly long databases that could be compared with numerical models. The behavior is similar at all sites, with a marked annual variation in the stratosphere of up to 6K, little variation around the stratopause ($\approx$ 2K) and a continuously increasing seasonal variation in the mesosphere of up to 16 K for some sites. These seasonal cycles are halved in tropical sites. The QBO (Quasi-Biennial Oscillation) is clearly visible in the temperature series and causes variations that can exceed 1 K. The temporal extent of the series, spanning several 11-year solar cycles, made it possible to extract variations associated with changes in solar activity on the vertical temperature profile, showing signatures of up to 4 K. In summer at mid and low latitudes, the signature is weak and around 1 K, in line with the expected photochemical effects. In winter, the response at mid-latitudes confirms previous observations of a negative effect. At higher latitudes, even larger signatures are observed, confirming the effect of feedback in the atmospheric response. This analysis also allowed us to update the quantification of decadal trends in the middle atmosphere, which show differences depending on latitude. These fluctuations become significant when the series are longer than one solar cycle. Observations at mid and low latitudes confirm the significant detection of a cooling ranging from about 1 K/decade in the upper stratosphere and increasing in the mesosphere to several K/decade. At mid latitudes, the three sites show good agreement, but in tropical/subtropical regions, greater variability is observed. In particular, in the mesosphere, observations obtained over Reunion Island in the tropical region in the southern hemisphere show cooling of up to 5 K/decade in the mesosphere, significantly greater than at other sites. Polar lidar data show that in these regions the trend is towards warming, with values remaining around 2K/decade, mainly in the mesosphere however the variability is large and the sampling larger in winter.