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ACE Comparisons
Kaley Walker, Ashley Jones, Chris Boone, Chris Sioris, Felicia Kolonjari, Sean McLeod, Peter Bernath and Tom McElroy
MOHAVE-2009 #2 Workshop - Bern, Switzerland - 20 October 2010
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Talk Overview
• Recap of ACE satellite and measurement technique
• ACE occultation measurements during MOHAVE
• Comparisons with:
– MIPAS and MLS
– STROZ and ALVICE
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ACE on SCISAT-1
Launch date: August 12, 2003Orbit: 74° inclination at 650 kmMeasurement mode: solar occultation
ACE-FTS: • FTIR spectrometer, 2-13 microns at
0.02 cm-1 resolution• 2-channel visible/NIR imager, 0.525
and 1.02 micronsMAESTRO:• dual UV / visible / NIR grating
spectrophotometer, 285 to 1030 nm at ~1-2 nm resolution
Pointing: suntracker in ACE-FTS
Atmospheric Chemistry Experiment (ACE) Satellite Mission:
Mission to measure atmospheric composition: profiles of trace gas species, cloud and aerosol extinction and temperature/pressure
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Technique: Solar Occultation
Advantages: • Radiance of sun gives higher signal-to-noise than emission• Limb view gives longer path length ~500 km (lower
detection limits) than nadir• “Self-calibrating” so excellent long-term accuracy and
precision
Disadvantages: • Modest global coverage• Samples only free troposphere
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Occultation sequence
Sunset 2245
12 Jan. 2004 9:50:23 UTC
Lat: 67°S
Lon: 168°W
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ACE Latitude Coverage 2005/2006
Orbit allows repeat of measurement locations each year
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Beta Angle of Measurement
• Beta is the angle between the orbit plane of the satellite and the Earth-Sun vector
• The larger the beta angle the longer the occultation measurement and thus more frequent altitude sampling
Diagram shows beta angle as viewed from Sun
Low beta
High beta
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ACE Measurements for MOHAVE
• Seven ACE occultations were measured near TMF during the MOHAVE-2009 campaign
• All are “Opportunity Science” observations - beta angle > 60°
– With higher beta angle, occultations are longer and cover larger ground tracks
• Plot shows ground-tracks of ACE occultations from 0 to 150 km in altitude (stretch over 10 º lat.!)
• Label location of occultation using 30 km point (geometric)
TMF
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ACE Occultations
Occultation Date and Time (UTC) Latitude Longitude Beta angle Distance
ss33239 2009-10-15 00:44:19.07 20.34 -107.79 60.77 1842.0
ss33254 2009-10-16 01:12:01.27 29.72 -116.71 61.93 528.7
ss33269 2009-10-17 01:39:46.81 39.19 -126.22 62.79 926.3
ss33283 2009-10-18 00:29:36.56 47.57 -111.75 63.34 1546.1
sr33350 2009-10-22 13:55:54.92 45.65 -111.14 62.08 1368.8
sr33351 2009-10-22 15:33:46.02 45.02 -135.84 62.02 1942.4
sr33365 2009-10-23 14:23:40.13 36.10 -121.23 60.97 372.1
• ACE Measurement times, locations and distances from TMF– Distance from TMF (34.4 N, 117.7 W) to location of ACE 30 km tangent altitude
(as calculated geometrically) – Have profiles for all occultations from ACE-FTS and for two from MAESTRO
(ss33239 and ss33254)
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ACE-FTS data processing
• Raw data to atmospheric transmission spectra (Level 0 to 1) – Interferograms transmitted to Earth are Fourier
transformed and transmission spectra are calculated using exo-atmospheric spectra
• Spectra to atmospheric profiles (Level 1 to 2) – Temperature and pressure profiles are determined from
global (non-linear least-squares) fit of CO2 transitions – relative line intensities give temperature and absolute line intensities give pressure
– Then concentration profiles of atmospheric species are retrieved using microwindow approach
– ACE-MAESTRO retrievals also use ACE-FTS pressure and temperature profiles
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ACE Water Vapour
• ACE-FTS profiles (version 2.2 + O3, N2O5 & HDO updates):
– Cloud tops to ~90 km depending on abundance
– ~3-4 km vertical resolution from FTS field of view
– H2O MWs
• v2.2: ~60 from 950-975 cm-1 and 1360-2000 cm-1
• v3.0: ~40 from 935-945 cm-1 and 1195-1945 cm-1
• MAESTRO profiles:
– H2O - research product - not part of current v1.2 distribution
– Cloud tops to tropopause is best region for retrievals
– ~1 km vertical from MAESTRO
– Spectral range: 926 - 969.7 nm
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ACE H2O Validation
M. Carleer et al., ACPD, 8, 4499-4559 (2008), still in revision
• Comparisons with SAGE II, HALOE, POAM III, MIPAS and SMR
– ACE-FTS v2.2 fitting errors generally better than 5% from 7 to 70 km and increasing above
– In all comparisons except for POAM III, ACE-FTS typically biased high on order of 3-10 % from 15 to 70 km
– Approximately constant wet bias of 0.4 ppmv for ACE-FTS versus SMR from 50 to 90 km
– Largest differences for ACE-FTS at lowest altitudes - MAESTRO results seem better in upper troposphere
• Vertical resolution effect?
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ACE Data Used for Comparisons
• Using newest versions of ACE-FTS (v3.0) and MAESTRO (research) profiles (available in MOHAVE database)
• ACE-FTS: now all seven occultations have processed
– Challenges with large number of measurements in each occultation (because of high beta angle)
– For highest beta, analyse every other measurement to deal with large amount of data (sr33350, ss33283, ss33254)
– For slightly lower high beta, every measurement is analysed but small distance between them (< 1.5 km) can cause oscillations to occur (ss33269 and ss33365)
• ACE-MAESTRO: two occultations available (ss33239 and ss33254)
– Limited by number of spectra processed with new L1 code
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MAESTRO versus ACE-FTS
ss33254, 2009-10-16 01:12UTC; (29.72N, 116.71W); beta 61.93; 528.7 km
ACE-FTS gives fitting errors while MAESTRO calculates uncertainty for each altitude
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MAESTRO versus ACE-FTS
ss33239, 2009-10-15 00:44UTC; (20.34N, 107.79W); beta 60.77; 1842.0 km
Large error given for this value!
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Comparison Details
• Starting with each ACE occultation, search for coincidences within:– 6 hours and 500 km for MLS (~same resolution)– 6 hours and 700 km for MIPAS (~same resolution)– 6 hours and 500 km for lidars (STROZ, ALVICE)
• Employed smoothing technique to make vertical resolution of measurements comparable
• Created 3 km wide weighting functions at ACE-FTS observation altitudes and convolved these with the individual lidar profiles - used in v2.2 validation!
• Focus only on water vapour for these comparisons...
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ACE-FTS vs. MIPAS
sr33365; 2009-10-23 14:23UTC; (36.10N, 121.23W); beta 60.97; 372.1 km
Example of oscillationsin profiles
1 ACE-FTS versus 3 MIPAS profiles
See average comparisons in Gabi’s MIPAS talk!
Non-LTE effects for MIPAS above 50 km
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ACE-FTS versus MLS
sr33351; 2009-10-22 15:33UTC; (45.02 N, 135.84W); beta 62.02; 1942.4 km
Example of minimal oscillationsin profiles
1 ACE-FTS vs. 6 MLS profiles
Consistent with ACE-MLS v2.2 comparisons±5% with no bias
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ACE-FTS versus STROZ
ss33254, 2009-10-16 01:12UTC; (29.72N, 116.71W); beta 61.93; 528.7 km
Using 1 hour integ. STROZ
Within (just) 6 hours!
Smoothing generally makes profiles more comparable.
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ACE-FTS versus STROZ
ss33254, 2009-10-16 01:12UTC; (29.72N, 116.71W); beta 61.93; 528.7 km
Using 1 hour integ. STROZ
Focusing on UTLS part of profile
Challenge of comparing limb and vertical profiles!
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ACE-FTS versus STROZ
ss33254, 2009-10-16 01:12UTC; (29.72N, 116.71W); beta 61.93; 528.7 km
Using 1 hour integ. STROZ
Now within ~3 hours
UTLS more comparable when closer in time.
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ACE-FTS versus ALVICE
ss33254, 2009-10-16 01:12UTC; (29.72N, 116.71W); beta 61.93; 528.7 km
Using 1 hour integ. ALVICE within ~3 hours
See larger differences than with STROZ
Would be useful to look at T, O3
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Summary
• Seven occultations were measured within 2000 km of TMF
– ACE-FTS v3.0 and new MAESTRO profiles available from archive
• All “Opportunity Science” Observations
– Challenging to process because of high beta angle
• Limited opportunities for statistical comparisons (unlike MIPAS, MLS)
– So, how do we best to use ACE in MOHAVE comparisons?
Funding for ACE provided by:
• Canadian Space Agency (CSA)
• Natural Sciences and Engineering Research Council of Canada (NSERC)
• Environment Canada
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ACE-FTS versus HALOE v19
• 36 coincidences within 2 hours and 500 km; most northern polar summer occultations
• Hygropause at same altitude but more rapid increase in H2O at lower altitudes for POAM III
C. Randall (in ACE H2O validation paper)