© University of Reading REACT4C Meeting November 2012 WP1 UPDATE Emma Irvine, Keith Shine, Brian Hoskins 1

Outline Weather types –Persistence of weather types –Weather types for extended winter and summer seasons Trajectory analysis of ice-supersaturated regions –Lifetime –Origin –Characteristics (temperature and moisture)

Preferred transitions between weather types WEATHER TYPE TOMORROW WEATHER TYPE TODAY Evidence of persistence (the most probable transition is no change) No transitions between types 1 and 3 or 2 and 4. They are opposites in terms of their projection onto EA and NAO patterns, e.g. 2 is +NAO and 4 is –NAO.

Persistence of Winter Weather Types For a given day, the likelihood that all of the next day(s) are also the same type, as a percentage of the number of days of that weather type

Weather Type Classification Original classifications based on DJF and JJA time periods Extending to NDJFM, JJAS Timeseries of daily weather type available, – being used outside REACT4C by U. Schumann and K. Graf (DLR) Winter period extension gives same weather types: Types using NDJFM Types using DJF

Trajectory Analysis T+0T-48 h T+48 h Forward trajectory Backward Trajectory Trajectories released on a 1x1 degree grid, over North Atlantic from 3 pressure levels: 200 hPa, 250 hPa, 300 hPa Trajectories initialised every 12 h for 3 winters and 3 summers Lagrangian trajectory code (Methven, 1997) run on ERA-Interim data Outputs: lat, lon, pressure, q, PV, theta, derive Rhi.

Trajectory Analysis Lifetime of ice- supersaturated air Origin of ice- supersaturated air T+0T-48 h T+48 h Total 249,874 trajectories with ice-supersaturation (so far just winter) Of these, 62.6% start in the troposphere, 37.4% in stratosphere

Lifetime of ice-supersaturated air Total lifetime = median lifetime * frequency Percentage of ISSRs with lifetime at least 24 h: 5% (tropospheric ISSRs) 23% (stratospheric ISSRs) ALL ISS points Tropospheric ISS Stratospheric ISS

Density plot showing preferred locations of ice-supersaturation Four regions: UK, mid-Atlantic, NW Atlantic and Greenland.

Trajectories of air which become ice-supersaturated over the UK For ISS trajectories with lifetime at least 24 h, starting in the troposphere Air that becomes ice-supersaturated over the UK comes from SW and moves NE.

Trajectories of air which become ice-supersaturated in different regions Results only shown for a particular region and level where > 90 trajectories 300 hPa 250 hPa 200hPa

Properties of long-lived ISSRs forming in different geographical locations RegionT (K)q (g/kg) MeanStdev.MeanStdev. ALL UK Mid Atlantic NW Atlantic Greenland

Summary Weather Types –Weather types can persist for days –Similar weather types are obtained by a classification based on an extended winter season –Weather types being used outside of REACT4C project by Ulrich Schumann and Kaspar Graf Trajectory analysis –Trajectory analysis yields lifetime, origin and characteristics of ice-supersaturated air. –Ice-supersaturated air has different temperature and moisture characteristics based on the origin of the air. –Will extend this work to look at summer.