How can we understand the Antarctic atmosphere?

Transcription

1 How can we understand the Antarctic atmosphere? John Storey, Michael Ashley, Jon Lawrence, Colin Bonner & Daniel Luong-Van Image: John Storey

2 Outline Why Antarctica? The free atmosphere The Stable Boundary Layer Why Antarctica is different The Antarctic Olympics SCAR AAA Image: Patrik Kaufmann

3 Outline Why Antarctica? The free atmosphere The Stable Boundary Layer Why Antarctica is different The Antarctic Olympics SCAR AAA Image: Patrik Kaufmann

4 Why Antarctica? Image quality twice as good as at temperate sites Photometric precision twice as good Infrared sky times darker Long periods of uninterrupted darkness Big science with small telescope Unique opportunity for widefield, high precision astronomy Image: Camillo Calvaresi

5 Not just cold, but clear and calm.

6 Contour map of Antarctica South Pole Dome F Dome A Dome C USGS image

7 Outline Why Antarctica? The free atmosphere The Stable Boundary Layer Why Antarctica is different The Antarctic Olympics SCAR AAA Image: Patrik Kaufmann

8 MASS Multi-Aperture Scintillation Sensor Sensitive measurement of the vertical distribution of turbulence A collaboration between CTIO, JPL and UNSW Deployed to Dome C November 2003 Image: Andrei Tokovinin

9 Image: Jon Lawrence Image: Andrei Tokovinin

10 Turbulence Atmospheric characteristics: Cerro Paranal, Dome C (>30 m) 100 r 0 coherence length CP 13 cm, DC 41 cm Coherence Length (m)! 0 isoplanatic (coherence) angle CP 2.5 arcsec, DC 5.4 arcsec Isoplanatic Angle (arcsec)! 0 coherence time CP 3.4 ms, DC 7.0 ms Coherence time (ms) Source: Lawrence et al 2008

11 At Dome C, the turbulence at 16 km is always less than in Chile, and so astrometry is better and scintillation is less Kenyon et al 2006

12 What it claims to measure: Turbulence profile What it actually measures: Fluctuations in curvature of wavefront at several scales up to ~10 cm, after wave has passed through atmosphere Advantages: Gives coarse turbulence profile Insensitive to near-ground turbulence Disadvantages: MASS Insensitive to near-ground turbulence Complicated data reduction

13 DIMM: Differential Image-Motion Monitor The transverse (" t2 ) and longitudinal (" l2 ) variances of the difference between the positions of the spots gives two estimates of the seeing #. Images and data from Aristidi et al (LUAN group)

14 DIMM at South Pole Image: UNSW Group, 2001

15 Seeing Data, South Pole ADIMM winter 2001/2: median seeing 1.8 arcsec (Travouillon et al, 2003) HDIMM summer 1998: median seeing 1.5 arcsec (Lowenstein et al, 1998) But the weather at the South Pole is not always perfect...

16 Seeing Data, Dome C 0.09 arcseconds (February) 0.14 arcseconds (October) Seeing from ground level, measured with DIMM by Eric Aristidi (LUAN) in 2006

17 DIMM What it claims to measure: Seeing What it actually measures: Average slope of wavefront across a distance of ~30 cm, after wave has passed through atmosphere Advantages: Samples whole atmosphere Disadvantages: Samples whole atmosphere

18 Images: Karim Agabi (LUAN) Balloon microthermals

19 Image: Anna Moore

20 What it claims to measure: Turbulence profile What it actually measures: In situ differential fluctuations in $T of two sensors separated by scales of ~100 cm, throughout atmosphere Advantages: Gives detailed turbulence profile Almost direct measurement of C N 2 Disadvantages: Expensive, therefore infrequent time sampling Balloon wake? Balloon microthermals Sensor response time

21 What they claim to measure: Turbulence profile What they actually measure: Correlation between scintillation patterns/wavefront slopes from two stars Advantages: Better height resolution than MASS Generalised SCIDAR can measure down to ground Realistic measurement Disadvantages: SCIDAR and SLODAR Requires large telescope Expensive instrument

22 Outline Why Antarctica? The free atmosphere The Stable Boundary Layer Why Antarctica is different The Antarctic Olympics SCAR AAA Image: Patrik Kaufmann

23 Data: AAD/CHINARE AWS

24 Estimates of the boundary layer thickness at Dome C < 30 m Lawrence et al 2004, SODAR > 20 m Agabi et al 2006, DIMM 36 ± 19 m Agabi et al 2006, Balloon µthermal 27 m median Swain & Gallee 2006, modelling ~20 m Aristidi et al 2008, DIMM

25 All that s needed is a small tower! Image: Robert Hammerschlag et al, 2006 Image: Andrew McGrath, 2008

26 Boundary layer height ~18 m ~21 m ~27 m Swain and Gallee, 2006

27 Image: Tony Travouillon Tower microthermals

28 Image: Geanpiero Venturi

29 What it claims to measure: Turbulence profile from ground level to top of tower What it actually measures: $T fluctuation profile from ground level to top of tower Advantages: Gives detailed turbulence profile Almost direct measurement of C N 2 Disadvantages: Finite height of tower Sensors accumulate ice Local effect of tower Tower microthermals

30 SHABAR (Lunar Shadow-Band Radiometer) Image: Anna Moore

31 What it claims to measure: Turbulence profile from ground level to ~100 m What it actually measures: Correlation between scintillation noise seen by detectors over spatial scales of ~2 m Advantages: Amazingly simple Disadvantages: Immature technology SHABAR Only works when moon is available

32 SODAR: Acoustic Radar SODAR Image: Geanpiero Venturi

33 Colin built a really good one, called Snodar. Measure boundary layer turbulence at ~1 m resolution Solve intensity calibration problem Simple, cheap, robust, winterisable Colin s talk is at 1715 hrs on Tuesday. Images: Colin Bonner

34 What it claims to measure: Turbulence profile from ground level to ~1km What it actually measures: Turbulence profile from ground level to ~1km Advantages: Actually does measure turbulence profile Accurate height data Good height resolution Disadvantages: Acoustic radar Finite range Very difficult to calibrate turbulence intensity Kind of noisy and anti-social

35 Outline Why Antarctica? The free atmosphere The Stable Boundary Layer Why Antarctica is different The Antarctic Olympics SCAR AAA Image: Patrik Kaufmann

36 Why Antarctica is different The temperature inversion is huge (often 5ºC/metre) The Stable Boundary Layer is thin (~ 25 metres) As a result, the Stable Boundary Layer is stable The relative humidity is % Therefore there can be little vertical mixing Therefore the turbulence cannot possibly be threedimensional, and cannot be Kolmogorov. Image: Guillaume Dargaud

37 Outline Why Antarctica? The free atmosphere The Stable Boundary Layer Why Antarctica is different The Antarctic Olympics SCAR AAA Image: Patrik Kaufmann

38 The Antarctic Olympics! South Pole! Dome A! Dome C! Dome F Competing for gold in:! Free-atmosphere turbulence! Surface layer thickness! Wind speed! Cloud cover and sky brightness

39 South Pole Big engineering projects are possible in Antarctica Image: South Image: Pole Andrew Telescope Mcgrath

40 Dome C: the gold medal winner? Image: John Storey

41 PILOT vision overview 2.5 metre optical/infrared telescope Dual role: pathfinder and unique science International project Sited at Concordia Station, Dome C, Antarctica Image: Andrew McGrath

42 PILOT must be in a an airconditioned dome because of the high relative humididty CFD simulation of PILOT airflow by LEAP Pty Ltd

43 The PILOT Conceptual Design Study The PILOT Phase A study is part of an initiative of the Australian Government being conducted as part of the National Collaborative Research Infrastructure Strategy. Image: John Storey

44 Image: Andrew Mcgrath

45 Dome F REMTECH PA-1 Naruhisa Takato, Fumihiro Uraguchi (Subaru Telescope), Hideaki Motoyama, Kotaro Fukui (NIPR)

46 Image: Li Yuansheng Dome A

47 Dome A in 2011 Image: CHINARE

48 PLATO is a collaboration between China, Australia, USA and UK. Image: CCAA

49 PLATO at Dome A! Dome A: Jan 2008 Image AACC

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51 PLATO at Dome A

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53 PLATO site testing! Turbulence (Snodar, DASLE) " Boundary layer height, distribution and variability! Sky emission (Gattini SBC) " Visible sky background versus sun/moon elevation, auroral spectral intensity and distribution,! Sky transmission (Pre-HEAT) " Transparency and noise in long wave (submillimetre) windows! Cloud (Gattini ASC) " Cloud cover statistics and distribution! Science (CSTAR) " Optical transients: variable stars, transits, microlensing, GRB, etc

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56 PLATO website Image: CCAA

57 Image: PLATO

58 Image: PLATO

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60 Image: PLATO

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62 Image: PLATO

63 Image: PLATO

64 Image: PLATO

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68 Image: PLATO

69 Outline Why Antarctica? The free atmosphere The Stable Boundary Layer Why Antarctica is different The Antarctic Olympics SCAR AAA Image: Patrik Kaufmann

70 Astronomy & Astrophysics from Antarctica a new SCAR Scientific Research Program Image: David A. Hardy

71 Scientific Committee on Antarctic Research Astronomy & Astrophysics from Antarctica (AAA) Proposal to establish the AAA Scientific Research Programme VERSION: 18 June 2008 Expected Duration: Estimated SCAR funding: $US60,000

72 Thank you! Image: John Storey