Evaluation of the use of radiosonde humidity data to predict the occurrence of persistent contrails

Abstract

Regular visual observations of persistent contrails over Reading, UK, have been used to evaluate radiosonde measurements of temperature and humidity defining cold ice-supersaturated atmospheric regions which are assumed to be a necessary condition for persistent condensation trails (contrails) to form. Results show a good correlation between observations and predictions using data from Larkhill, 63 km from Reading. A statistical analysis of this result and the forecasts using data from four additional UK radiosonde stations are presented. The horizontal extent of supersaturated layers could be inferred from this to be several hundred kilometres. The necessity of bias corrections to radiosonde humidity measurements is discussed and an analysis of measured ice-supersaturated atmospheric layers in the troposphere is presented. It is found that ice supersaturation is more likely to occur in winter than in summer, with frequencies of 17.3% and 9.4%, respectively, which is mostly due to the layers being thicker in winter than in summer. The most probable height for them to occur is about 10 km.

Numerical simulations of contrail-to-cirrus transition – Part 2: Impact of initial ice crystal number, radiation, stratification, secondary nucleation and layer depth

“…Although the average depth of ice supersaturated layers seems to exceed 500m (Spichtinger et al, 2003;Treffeisen et al, 2007;Rädel and Shine, 2007), the statistical distribution of the layer depths peaks at smaller values in all these studies and very thick ISSRs occur rarely. Hence, fallstreaks from contrails should rarely be as strong as in our simulations which generally assumed an ISSR layer depth of more than one km.…”

A contrail cirrus prediction model

“…The decision of whether a contrail forms or not along a given flight is a relatively simple task because it can be explained thermodynamically once the meteorological and aircraft parameters are sufficiently known (Schumann, 1996;Rädel and Shine, 2007). Weather and flight track data have been used to identify contrail forming flight tracks and follow their advection (Duda et al, 2004;Atlas et al, 2006;Duda et al, 2009).…”

“…Since a few years, the ECMWF model allows for supersaturation in clear air which has been demonstrated useful for this purpose (Tompkins et al, 2007;Rädel and Shine, 2007;Haywood et al, 2009;Lamquin et al, 2009Lamquin et al, , 2012. The model assumes that ice forms in a fraction of a grid cell when the supersaturation reaches the limit for homogeneous ice nucleation (Koop et al, 2000), typically of the order 150 %.…”

“…In case of very low temperatures, short-lived contrails may form from the emitted water vapor even in totally dry air. Contrails are sometimes observed in slightly subsaturated air masses (Schröder et al, 2000;Rädel and Shine, 2007;Krämer et al, 2009;Voigt et al, 2010). At least at low temperatures, it may take up to an hour until the ice formed initially from emitted water is sublimated, see Appendix A6.…”

Technical Note: 30 years of HIRS data of upper tropospheric humidity

“…As the weighting kernels of HIRS channel 12 are sensitive to a deep atmospheric layer roughly between 300 and 500 hPa, UTH has to be interpreted as a kind of mean relative humidity over that layer, and UTH i > 100 % only arises when most of this thick layer is supersaturated which occurs only rarely; only few percent of ice supersaturated layers reach a depth of 3 km and more (cf. thickness statistics in Spichtinger et al, 2003a;Treffeisen et al, 2007;Rädel and Shine, 2007;Dickson et al, 2010). Jackson and Bates (2001) determined their regression coefficients for the HIRS version 2 (HIRS/2) instrument on NOAA-7, but the recent intercalibration of HIRS channels was based on HIRS/4 on METOP-A.…”