Influence of the polar vortex on Arctic column-averaged dry-air mixing ratios of atmospheric methane

Transcription

1 Influence of the polar vortex on Arctic column-averaged dry-air mixing ratios of atmospheric methane Leif Backman, Tuula Aalto Climate Research, Finnish Meteorological Institute Rigel Kivi, Pauli Heikkinen Arctic Research Centre, Finnish Meteorological Institute Juha Hatakka, Tuomas Laurila Atmospheric Composition Research, Finnish Meteorological Institute Huilin Chen Center for Isotope Research, University of Groningen Cooperative Institute for Research in Environmental Sciences, University of Colorado GRUAN ICM-9, June, Helsinki, Finland

2 Motivation Column-averaged dry-air mixing ratio: XCH 4 = CH 4,column / dry air column = CH 4,column * / O 2, column Motivation: Significant seasonal changes in the stratospheric profile of methane in the Arctic due to the polar vortex Better understanding of the data Ground truth of satellite instruments Identify & understand possible data quality issues Use of data in inverse models or for model validation Tropospheric column averaged mixing ratio, XCH 4,tropo Results possibly useful in satellite retrievals 2

3 Methane profile hν: Dominant loss > 65 km Stratospheric loss: ~8% of total sink -r = [CH 4 ]*(k OH [OH] + k O1D [O 1 D] + k Cl [Cl] + J CH4 ) O 1 D: More important than OH > 50 km Equal to OH ~30 km OH: Major stratospheric loss XCH 4 Cl: 20% in the mid and upper stratosphere [OH], [Cl], soil Tropopause 3

4 Polar vortex definition Polar vortex edge is defined by the largest gradient in the potential vorticity field on equivalent latitudes Nash et al., JGR, K level ECMWF ERA-Interim reanalysis 4

5 Polar vortex definition The onset and breakup dates of the polar vortex is determined from the wind speed along the vortex edge 5

6 Climatological polar vortex Arctic FTS stations The location of the potential measurement stations overlaid with the average number of days that the polar vortex resides above the location during winter days 6

7 Climatological polar vortex Arctic FTS stations days 7

8 Climatological polar vortex Number of days with polar vortex conditions on average during February May (late vortex) + solar zenith angle < 82 Sodankylä: ~32 days Eureka: ~19 days days 8

9 Sodankylä XCH 4 (TCCON) Outside vortex Inside vortex October January (early vortex) Inside vortex February May (late vortex) 9

10 Kiruna XCH 4 (NDACC) Outside vortex Inside vortex October January (early vortex) Inside vortex February May (late vortex) 10

11 Sodankylä XCH 4 April 15 May 31, 2014 Top panel: potential vorticity K (9 levs) PVU Bottom panel: Sodankylä XCH 4 11

12 Sodankylä XCH 4 AirCore on May 8, 2014 PVU 12

13 Climatological XCH 4 at Sodankylä 13

14 Climatological XCH 4 at Sodankylä Early polar vortex Late polar vortex Outside polar vortex 14

15 XCH 4 vs. solar zenith angle March 2014 Inside polar vortex Outside polar vortex 15

16 Stratospheric profiles Stratospheric CH 4 and HF profiles HALOE (version 19) ACE-FTS (version 3.6) Sorted according to Outside polar vortex April September, Summer extra tropics October March, Winter surf zone Inside polar vortex October January, Early vortex February May, Late vortex Equivalent latitudes Used to derive tropospheric XCH 4 Tracer-tracer correlation, CH 4 vs. HF Climatological profiles 16

17 HALOE data coverage Early polar vortex Late polar vortex Summer extratropics Winter surf zone 17

18 ACE-FTS data coverage Early polar vortex Late polar vortex Summer extratropics Winter surf zone 18

19 Climatological profiles of CH 4 Inside polar vortex Outside polar vortex HALOE March ACE-FTS March 19

20 Stratospheric CH 4 and HF ACE-FTS June 2012 CH 4 HF 20

21 XHF as proxy for tropopause height Early polar vortex Late polar vortex Outside polar vortex WMO definition (Reichler et al. Determining the tropopause height from gridded data, GRL, 2003.) 21

22 XCH 4 vs. XHF at Sodankylä Early polar vortex Late polar vortex Outside polar vortex 22

23 Tropospheric XCH 4 HF present only in the stratosphere Linear correlation between [HF] and [CH 4 ] in the stratosphere [CH 4 ] = a + b * [HF] Tropospheric XCH 4 XCH 4,tropo = * (CH 4,column - b * HF column ) / O 2,column XCH 4,tropo = XCH 4 - b * XHF 23 e.g. Washenfelder et al. Tropospheric methane retrieved from ground based near-ir solar absorption spectra, GRL, 2003.

24 Tracer-tracer correlation CH 4 vs. HF θ (K) 24

25 Time series of slopes CH 4 vs. HF + HALOE ACE-FTS 25

26 Sodankylä XCH 4 and XCH 4,tropo & Pallas CH 4 (flask) 26

27 Climatological XCH 4,tropo at Sodankylä All data Outside vortex Early vortex Late vortex 27

28 Summary The polar vortex has a significant effect on the Arctic XCH 4 A significant portion of the springtime data is influenced Minimum in the XHC 4 climatology: All data April; Outside vortex May Possible data quality issues for data inside polar vortex Prior profile Satellite data of CH 4 and HF used to derive tropospheric XCH 4 Minimum in the XHC 4, tropo climatology in June Next steps Interannual variability in stratospheric profiles Effect of tropopause height Analysis extended to other Arctic stations in addition to Sodankylä Updated prior profiles & selection based on equivalent latitude 28

29 Thank you for your attention!