Comparison of methodologies for SO 2 and Ash identification using observations from IASI

Transcription

1 Comparison of methodologies for SO 2 and Ash identification using observations from IASI Maria Athanassiadou, Peter N Francis, Stephan Havemann, Elisa Carboni EGU, 15 Apr., 2015

2 This talk is about... IASI in Volcanic Ash and SO 2 detection Ash identification ² Kelut Feb., 2014 ² Active stratovolcano, East Java Indonesia ² Notorious for violent and deadly eruptions ² Present some results from comparing various methods using one instrument Methodology & Tools for monitoring SO 2 ² Kelut SO 2 plume(s) ² Bárðarbunga Oct., 2014 ² Satellite instruments & IASI in particular ² Plume height ² Basic concepts of Spectroscopy Summary & future plans

3 Kelut, February 2014 Erupted at ~1600 UTC on 13 Feb., 2014 Short lived ash event, SO 2 went on for days Mushroom ash plume at 17:30 UTC (VIIRS,Suomi NPP) Ash plume ~ 17 km, CALIOP on CALIPSO at 18:10 UTC Ash fall ~250 km away 100 km N Airport closures and disruption, impacts on agriculture, infrastructure and casualties.

4 Ash detection Pete Francis & Mike Cooke Sat. Appl., Met Office 2 Channel BT difference 14 Feb., UTC BT10.8 BT12.0 < 2K Split-window imager channels GEO vs LEO MTSAT 0400 UTC MODIS/TERRA 0335 UTC

5 Ash spectrum IASI Karagulian et al, 2010 Ganagle et al, 2010 Ash identification: Concentration Composition Particle size IASI spectrum : V-shape µm 10.8 µm Region_B < 0 ash < 0 cloud Exact shape and slopes depends on Type of eruption Composition Various approaches exploit either side of V min Region_A > 0 ash < 0 cloud

6 Name Ash Kelut: 14 Feb., 2014 IASI channels Ash iden,fica,on criterion Spectral posi,on Reference In Region A In Region B Ash_K1 BT(1072) BT(1215) < 0 Region_B Karagulian et al, 2010 Ash_K2 BT(982) BT(817.75) < 0 Region_A Karagulian et al, 2010 Ash_K1a BT(1072) BT(1216) < 0 Region_B Karagulian et al 2010 modified Ash_C BT(1168) BT(1231.5) < 0 Region_B Clarisse et al, 2010 Ash_R BT(926) BT(833.25) < 0 Region_A Prata 1989 Ash_M BT(982) BT(833.25)< 0 Region_A Present Work Methods in same spectral region give similar results Differences between regions substantial Amount of ash (BT diff) Horizontal extent Potential implications for ash quantification Further work needed

7 Clouds & ash True colour image from AQUA - MODIS Cloud from IASI at the same time as ash BT at 10.8 µm à 926 cm -1 Very good agreement between IASIcloud and MODIS Differences in the area where MODIS shows a layer of ash overlaying a thin layer of cloud Same area where methods in Region_B identify a more extended ash plume than methods using channels in Region_A In this case methods in Region_A underestimate both the extend and concentrations of the ash

8 IASI Clear Sky Spectrum & SO 2 bands TOA Radiance in the Infrared cm -1 Clear Sky LBL calculations for different atmospheres using the Met Office HT_FRTC, (Havemann-Taylor Fast Radiative Transfer Code). Shown for typical atmospheres: Tropical, Subarctic Summer, Subarctic Winter SO 2 absorption bands ν 1 =[ ] cm - 1, centred at 1151 cm - 1 ν 3 =[ ] cm - 1 centred at 1361 cm - 1 ν 1 +ν 3 =[ ] cm - 1 centred at 2499 cm - 1 Clear Sky differences depending on the atmospheric conditions SO 2 identification, Clarisse et al cm -1 and cm -1 for SO 2 absorption in the stronger ν 3 band cm -1 and cm -1, outside the band, for the baseline Maximise signal, minimise noise

9 Spectra IASI in ν 3 absorption band Plume Clear Sky SubArctic Inject SO 2 volcanic plume Different heights Different amounts of SO 2 Different atmospheres HT-FRTC LBL calculations Tropical Shown for 2 typical atmospheres: DBT = BT(SO 2 plume) - BT(ClearSky) DBT depends on both the height and amount because density of SO 2 is a function of P, T SO 2 plume identified in DBT at frequencies from Clarisse et al, 2008 shown in dashed lines

10 Bárðarbunga eruption Sept., 2104 Mar., August: small fissure eruption in Holuhraun 31 August: Lava eruption on a 1.5 km long fissure September pattern: Plumes drift mainly in an E, ENE direction consistent with MSLP anomaly of the Icelandic low Exceptions September: 5-6 Sep., & Sep., where the plume drifts S over the UK October pattern: Strong MSLP anomaly between Iceland and UK. Low pressure systems sweeping across from the west. Plumes approach UK in dry intrusion behind a frontal system. Atmospheric conditions in October favour plume identification with IASI 12:45 UTC August 31, 2014, (MODIS) Composite of natural colour & IR night view from Sep. 1. ALI on EO-1 satellite. 5 Sep., :50 LT 19-21/10: SO 2 plume identified on IASI, part of it reaching UK

11 Bárðarbunga, October Oct., 1053 UTC 21 Oct., 0729 UTC 20 Oct., 1257 UTC 20 Oct., 2123 UTC 19 Oct., 2144 UTC Credit to: Nigel Atkinson, SA

12 Bárðarbunga plume height 19 Oct., 2144 UTC Matching: ² ² Back trajectories (NAME & UM) from various heights above Wales (*), N. Ireland (*) & Barents Sea (*), released on 21 Oct. IASI TOA DBT 20 Oct., 1257 UTC 20 Oct., 2123 UTC Notation example: W on 20 Oct. ² ² W6: starting point i.e., Wales at 6 km on 21 Oct. 7634: plume height (m) on 20 Oct 1257 UTC

13 Bárðarbunga plume 21 October 2014 N-Plume Two-part plume Different Heights Different Concentrations N-Plume High troposphere, low stratosphere (6-10 km) DU S-Plume Low to mid troposphere (1 4.5 km) 5-10 DU Evolution consistent with cyclone development flow pattern Depending on time of emissions: Plume is caught up in the upwards flow associated with the head of the low, turns anti- then cyclonically as it rises to high levels Later emissions either stay in vicinity or decent in the dry intrusion flow behind the front. S-Plume

14 Typical vs Real (UM) Atmospheric Profiles Influence on DBT & concentrations Meteorological profiles used as input to HT-FRTC

15 DBT(Plume-ClearSky) Sensitivity to choice of reference spectrum Radiances from same reference atmosphere: BT(Plume) - BT(ClearSky) < 0 Assumed reference atmosphere: BT(Plume) - BT(ClearSky) =? Depends on differences between the actual and reference profiles of: ² ² Tsfc, T(z), H 2 O(z), SO 2 (z) Errors can be larger than the signal Plume in actual Midlatitude winter Using same reference Plume in actual Subarctic winter

16 Bárðarbunga Carboni et al., code

17 Summary & Future plans Challenges associated with volcanic plumes Satellites provide the best global observational platform Combine information - available tools à constrain uncertainty Advantages & disadvantages of various instruments / methodologies GOME-2 & IASI on MetOp satellites (same time, complementary information) GEOs & LEOs (global, high temporal coverage & high spectral information) Need to understand & quantify differences in plume detection Better estimation of concentrations confidence in results Provide better input to modelling and forecaster tools Sensitivity to reference spectrum Explore more IASI spectrum for ash Work in progress Develop SO 2 detection system Independent assessment of plume height Putting SO 2 into our RTTOV

18 Extra Slides

19 Typical patterns - September GOME-2 SACS website

20 Exceptions - September 4-6 September September

21 Typical patterns - October GOME-2 SACS website

22 MSLP anomaly (HadSLP2r data) SEPTEMBER OCTOBER

23 Bardarbunga, October 2014 GOME-2 (from sacs.aeronomie.be) Reduction in UV/Vis capability with receding daylight GOME-2 (from sacs.aeronomie.be)

24 Bardarbunga, 21 October 2014 Cloud from BT at 10.8 µm Agrees with water vapour image Consistent with dry intrusion behind the frontal system

25 Bárðarbunga Carboni et al., code