Upper atmosphere cooling over the past 33 years

Abstract

Theoretical models and observations have suggested that the increasing greenhouse gas concentration in the troposphere causes the upper atmosphere to cool and contract. However, our understanding of the long-term trends in the upper atmosphere is still quite incomplete, due to a limited amount of available and well-calibrated data. The European Incoherent Scatter radar has gathered data in the polar ionosphere above Tromsø for over 33 years. Using this long-term data set, we have estimated the first significant trends of ion temperature at altitudes between 200 and 450 km. The estimated trends indicate a cooling of 10-15 K/decade near the F region peak (220-380 km altitude), whereas above 400 km the trend is nearly zero or even warming. The height profiles of the observed trends are close to those predicted by recent atmospheric general circulation models. Our results are the first quantitative confirmation of the simulations and of the qualitative expectations.

Long-term variations of the upper atmosphere parameters on Rome ionosonde observations and their interpretation

“…This gives cooling rate of ∼(3-4) K/decade analyzing a period of 30-40 years. This is close to an exospheric temperature trend of À1 to À2 K/decade estimated from satellite drag observations (Emmert, 2015) and much smaller than Tex trends inferred from ground-based ISR measurements: À18 K/ decade for noontime exospheric temperature at Millstone Hill (Oliver et al, 2014), À60 K/decade at 350 km for daytime hours at Saint Santin/Nancay (Donaldson et al, 2010), À10 to À15 K/decade at F 2 -layer heights for day-time hours at Tromso (Ogawa et al, 2014), and À20 K/decade at 350 km for daytime hours at Millstone Hill (Zhang & Holt, 2013). A recent analysis by Zhang et al (2016) of Sondrestrom and Chatanika/ Poker Flat ISR observations has shown that the high latitude long-term trend results are compared to those from the Millstone Hill mid-latitude dataset.…”

Neutral atmosphere temperature trends and variability at 90 km, 70 °N, 19 °E, 2003–2014

“…However, for years with higher F10.7 values the tendency of increasing fit residuals is less distinct. Ogawa et al (2014) find a non-linear relationship between upper-atmospheric temperatures and solar activity using EISCAT UHF (ultra-high frequency) radar ob- servations from 200 to 450 km altitude over Tromsø, even though it must be noted that the altitude range they look at differs from ours.…”

Altitude and solar activity dependence of 1967–2005 thermospheric density trends derived from orbital drag

“…Exospheric temperature trends estimates derived from ground‐based incoherent scatter radar (ISR) measurements have been much larger than the orbit‐derived estimates given in Table . The most recent estimates from Millstone Hill (43°N, 72°W), Saint Santin (47°N, 2°E), and Tromsø (70°N, 19°E) are, respectively, −18 K/decade [ Oliver et al ., ], −30 K/decade [ Donaldson et al ., ], and −10 to −15 K/decade [ Ogawa et al ., ]. Oliver et al .…”