![]() Microwave radiometers have an excellent temporal coverage, but their application is limited to the lower and middle troposphere (Westwater, 1978 HanĪnd Westwater, 1995 Solheim and Godwin, 1998) and altitudes above 20 km (Nedoluha et al., 1997 Deuber et al., 2004, 2005 KämpferĮt al., 2013), with somewhat limited vertical resolution. Lyman- α hygrometers (Kley and Stone, 1978 Weinstock et al., 1990 Khattatov et al., 1994 Hintsa et al., 1999 Zöger et al., 1999 KämpferĮt al., 2013), though being highly accurate, are rarely used in dense routine measurement programmes due to their elevated costs. Balloon-borne cryogenic frost-point hygrometers (CFHs Vömel et al., 2007b, 2016 Kämpfer et al., 2013 Hurst et al., 2016) and The sensors exhibit slow response and low sensitivity (Miloshevich et al., 2006 Vömel et al., 2007a Steinbrecht et al., 2008 KämpferĮt al., 2013). Greatly improved within the troposphere in recent years, but deficiencies exist in the very cold tropopause region and the lower stratosphere, where All the most commonly used sensors used for routine measurements have limitations. Instrumentation covering the entire free troposphere and the lower stratosphere has become more and more important during the past 2 decades Other locations (Solomon et al., 2010 Hegglin et al., 2014).ĭue to the role of water vapour as the most important greenhouse gas, the optimization of high-accuracy, range-resolved vertical sounding Negative that occurred around 2000 (Hurst et al., 2011), but the pronounced positive trend during the early phase since the late 1980s is not confirmed for In the lower stratosphere, the Boulder series shows a trend reversal from positive to Layer, where thermal radiation is trapped by water vapour anyway. However, they evaluate columnar quantities that are dominated by the moist boundary Other studies show at least regionally positive trends ![]() Particular in the upper troposphere, in contrast to the expectations from climate modelling. (National Centers for Environmental Prediction, last access: 20 January 2021) reanalysis data, in ![]() (2009) report negative trends for the period 1973 to 2007 at all free tropospheric altitudes in NCEP ![]() Water-vapour trends in the troposphere derived from observationsĪre discussed in literature. Also verticalĮxchange processes could change in a warmer climate (Trickl et al., 2010a, 2020a). However, this increase could be counteracted by additional cloud formation and precipitation. In a warmer climate, the atmosphere takes up more Kiehl and Trenberth, 1997 Schmidt et al., 2010 Lacis et al., 2013). Water vapour in the upper troposphere and lower stratosphere (UTLS) is the key factor controlling how much thermal infrared radiation escapes from theĪtmosphere into space (e.g. ![]()
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