NGF Årsmøte 20 September 2016 i Oslo. Sven Peter Näsholm, Steven J. Gibbons, Tormod Kværna.

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1 Observing the Sudden Stratospheric Warming in early March 2016 using data recordings of ocean-generated infrasound ducted through the stratosphere and back to ground NGF Årsmøte 20 September 2016 i Oslo Sven Peter Näsholm, Steven J. Gibbons, Tormod Kværna peter@norsar.no, steven@norsar.no, tormod@norsar.no

2 Sudden Stratospheric Warmings, SSWs Warm in the stratosphere after a few weeks / a month wait Cold on the surface 2 France (Vaux-de-Cernay) a few weeks after the January 2013 stratospheric warming

3 Sudden Stratospheric Warmings Rapid change in the stratospheric wind and temperature. 40 increase! Polar cap westerlies are slowed down or reversed rapidly; often within a few days Typically midwinter Pre-cursor to colder winter temperatures in Europe by a couple of weeks or months Example: cold winter of 2013 Normal winter condition Better & quicker SSW detection Potential to improve robustness of longterm weather & climate forecasts 3 Disturbed stratospheric jet (winds can even be reversed)

4 Prologue Middle atmosphere Stratosphere: ~ [15 50] km & ( ~ [40 80] km: «ignorosphere» ) Mesosphere: ~ [50 90] km Middle atmosphere dynamics influence the troposphere below. Coupling mechanisms: e.g. gravity waves & planetary waves Surface climate influenced by the middle atmosphere Middle atmosphere temperature & wind data sparse in space & time compared to lower altitudes Impaired accuracy of stratospheric representation in numerical climate & weather forecast Problematic to include mesospheric altitudes Improve climate modelling & long-range weather forecast with better knowledge of the middle atmosphere dynamics & linking to the troposphere Increasing the amount of past middle atmosphere data points Enhanced assessment of e.g. wind trends Wind: critical because of a lack of direct measurements Temperature, pressure, density better understood / modelled 4

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6 Atmospheric infrasound Inaudible & above acoustic cut-off f [3.3mHz, 20 Hz] Atmospheric acoustic attenuation ~ ω 2 low frequencies travel 100s or even 1000s of km Instrumentation to some extent sensitive to gravity waves below buoyancy: f 2.9 mhz Wave only probes where it propagates! Atmospheric ducting and refraction: Snell s law Wind & temperature c eff c 0 w n Winds event source as source event! Not equivalent 6

7 Infrasound sources Sprites Polar Low Pressures 7

8 ARCI IS37 NRSI 8

9 March 2016: Evidence for a Sudden Stratospheric Warming inferred from infrasound data recorded at IS37 in Bardufoss 9

10 Microbaroms from colliding counter-propagating ocean waves wind direction influences ducting Stratospheric wind influence: IS37 Strong easterlies enhance ducting from the east Strong westerlies enhance ducting from the west Continuous monitoring directions of microbarom detections 10 Information on stratospheric wind variability

11 March : SSW indication in NORSAR infrasound data in Bardufoss Because we suddenly started seeing microbaroms originating from the Pacific instead of from the Atlantic IS37 An SSW modifying the stratospheric infrasound propgation channel Microbaroms from colliding counter-propagating ocean waves 11

12 Pacific February 19 March 6 (from north-east) IS37 Atlantic (from west) Microbaroms from colliding counter-propagating ocean waves 12

13 Direction to source from IS37 in Bardufoss: 13

14 Other SSW indications Retrospect ECMWF modelling Gerd Baumgarten, IAP Kuhlungsborn: 14 At ALOMAR (Andøya) we saw the lowest and warmest stratopause of this winter just two days ago»

15 15 Retrospect circulation modelling at ~36 km altitude

16 16 More data