Hydroxyl airglow temperatures above Davis Station, Antarctica

290 Pages·2014·47.43 MB·English

Hydroxyl Airglow Temperatures
above Davis Station, Antarctica
2-ok- ---
W. John R. French. B.Sc (Hons) - J..
Submitted in fulfilment of the
requirements
for the Degree of
DOCTOR OF PHILOSOPHY
in the
UNIVERSITY OF TASMANIA
and the
AUSTRALIAN ANTARCTIC DIVISION
September, 2001
THE
UNINERSiTY
OF TASMNIA
LE3P,UZY
Declaration
This thesis contains no material which has been accepted for a degree or diploma by
the University of Tasmania or any other tertiary institution, and, to the best of the
author's knowledge and belief, it contains no material previously published or written
by another person, except where due reference is made in the text.
W. John R. French
18-Sep-01
Authority of Access
I consent to this thesis being made available for loan and limited copying in
accordance with the Copyright Act 1968.
pi-- -,
W. John. R. French
18-Sep-01
Hydroxyl Airglow Temperatures above Davis Station, Antarctica
Abstract
The hydroxyl airglow (6-2) band has been monitored above Davis station, Antarctica
(68.6°S, 78.0°E) by means of a Czerny-Turner spectrometer since 1990. This thesis
is an investigation of the long-term trends and variability in OH(6-2) rotational-
temperatures over an 11 year time span.
Tropospheric warming, due to increased greenhouse gases concentrations over the
last 150 years, is expected to be associated with enhanced cooling in the stratosphere
and mesosphere. Modelling studies indicate a maximum cooling response in the high
latitude mesosphere. Some reported observations suggest that pronounced cooling,
(up to 7 K/clecade) in excess of model predictions, has already taken place.
Hydroxyl airglow emissions originate near 87 km. The layer is ideally located to
monitor mesopause region temperatures by ground based spectroscopic means. The
Davis OH(6-2) database contains 8 years of observations that span 1990 to 2000;
over 126,000 spectra, which yield 1310 nightly averages. Observations are limited by
day length at Davis. Night-time observations are possible between day-of-year 45
(14-Feb) and 300 (27-Oct).
Analysis techniques are developed to optimise the rotational temperature
determinations for the P1(2), P1(4) and P1(5) ratio's in this band for climate change
studies. Precise calibration of the instrument spectral response is important for long-
term trend assessment. Inter-year spectral response variation of less than 0.3% has
been achieved. Temperature errors associated with the response calibration amount
to 1.5 K for earlier years and less than 0.3 K since 1996.
A detailed investigation of auroral and OH satellite line emissions, solar Fraunhofer
and water vapour absorption across the OH(6-2) region (X837.5-851.5 nm) is
undertaken. These features can modify the apparent intensity of the P-branch lines.
P1(3) is rejected from further analysis due to un-thermalised contributions from the
OH(5-1)P1(12) lines. A correction is applied to account for the Q1(5) contribution
under P1(2). N2 1PG and N Meinel auroral emissions and solar Fraunhofer
absorption are accounted for by appropriate selection of the backgrounds for each
line. Water vapour absorption is not found to be significant. Correction factors are
also applied to account for the difference in A-doubling between the P-branch lines.
These are derived from frequency-stabilised laser determinations of the instrument
bandwidth (which is 0.15nm). Errors associated with each correction are assessed.
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Hydroxyl Airglow Temperatures above Davis Station, Antarctica
Serendipitously, auroral emissions due to atmospheric Argon are identified for the
first time in this investigation. Two argon lines (at k840.82 nm and k842.46 nm,
between P1(2) and P1(3)) are apparent during intense auroral activity but do not
influence the rotational temperatures at the resolution of the Davis instrument.
As a scanning instrument is used, a 'sampling' error is also associated with the time
taken to acquire each spectrum due to possible intensity variations. A mean trend of
—1.1 K due to an average intensity decrease across the night, with a 7 K standard
deviation is found from coincident photometer observations. As a result of the
investigation of background features, acquisition times were reduced from the order
of 1 hour (in 1990) to 7.3 minutes (from the end of 1996) by scanning only selected
P-branch lines and background regions, which reduces the standard deviation.
Furthermore, an analysis technique for time interpolation of sampled branch lines
and backgrounds between spectra is developed, which removes the trend component.
Three sets of published transitions probabilities yield a 12 K range in the absolute
temperature derived. An experimental investigation of OH(6-2) Qi/Pi and RI/Pi
emission intensity ratios, for rotational states up to j'=4.5, is undertaken to determine
which set is most suitable for application to the OH(6-2) band.
Selection criteria are established to reject spectra that do not yield consistent
temperatures for each of the three possible ratios, suffer low signal-to-noise, or are
contaminated by strong aurora, scattered moonlight or changing cloud conditions.
Nightly averages are determined from spectra that pass all criteria. Annual variations
are characterised by an extended warm (206 ± 4 K) winter period, with a gradual
decline (-0.04 K/day) over the interval DOY 106-258 and including episodic 10-20
day (planetary scale) variations of amplitude up to 30 K. Equinoctial transitions from
cold summer temperatures show a sharp rise in autumn (1.2 K/day; DOY 49-80) and
a more gradual spring decline (-0.65 K/day; DOY 275-296). The autumn transition
occurs earlier, and the spring transition later than either CIRA86 or MSISE-90 model
predictions. The midwinter local minimum in MSISE-90 is also not supported.
Mean winter temperatures calculated from the daily averages for each year are
consistent with a positive solar cycle association of 0.066 K/solar-flux-unit,
considerably lower than most values reported in the literature. Multivariate analysis
supports a long term cooling trend of the order of 0.5 K/year in the winter average
temperatures over Davis.
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Hydroxyl Airglow Temperatures above Davis Station, Antarctica
Acknowledgements
There are many people I wish to sincerely thank for their contribution to this work.
I particularly thank Dr. Gary Burns, Principal Research Scientist at the Australian
Antarctic Division for his highly enthusiastic supervision. Always helpful, always
with new ideas and directions, a meticulous attention to detail and a tenacious desire
to wring every last shred of information out of every photon collected. I have
enjoyed being associated with Gary on various projects for thirteen years.
I was fortunate to also have Dr. Pene Greet as co-supervisor. Pene was principal
investigator on the hydroxyl airglow project during most of my association with it. I
greatly appreciate Pene's guidance and encouragement and her review and many
constructive comments on this thesis.
Prof. Bob Lowe of the University of Western Ontario has openly and enthusiastically
shared his wealth of knowledge on many OH matters with our group. His association
has established a strong bond of collaboration between UWO and AAD that
promises an exciting future. I thank him for his kindness, interest and insightful
answers to many questions.
I joined the hydroxyl airglow project in late 1994 and enrolled in this degree part-
time with the Institute of Antarctic and Southern Ocean Studies (IASOS) at the
University of Tasmania. Prof. Garth Paltridge has kindly acted as my administrative
supervisor at IASOS during my candidature. I am grateful to the University for
HECS scholarship support during this degree.
I have been very fortunate to be able to complete this thesis while being employed
full-time with the Atmospheric and Space Physics Group (ASP) at the Australian
Antarctic Division. I am largely indebted to Dr. Ray Morris for this opportunity, who
has steered the helm of ASP for over seven years. I would also like to thank Keith
Finlayson, Damian Murphy, Andrew Klekociuk, John Innis, Pelham Williams and
David Rasch for their friendship, valued opinions and assistance over the years. It
has been a pleasure working with these people at ASP.
Two unforgettable years have been spent as ASP optical physicist at Davis station,
Antarctica during the course of this project. I sincerely thank the extraordinary men
and women of the Australian National Antarctic Research Expeditions (ANARE)
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Hydroxyl Airglow Temperatures above Davis Station, Antarctica
1995 and 1998 for their hard work, hard play, humour and company in the
experience of a lifetime.
During these years I have had the distinct pleasure of working with ASP electronics
engineers Lloyd Symons and Andrew Bish. Both demonstrated exceptional technical
ability in support of ASP experiments and equipment. I appreciate their talent,
enthusiasm and friendship.
I also wish to thank those dedicated ASP physicists who have contributed to the OH
project at Davis; Pelham Williams (1984,1987,1990,1994), Keith Finlayson (1996),
Pene Greet (1997), Frances Phillips (1999) and George Klich (2000). It is their
careful operation and calibration of the scanning spectrometer and other instruments
over the years that have made this project possible. Their efforts are also embodied in
this thesis.
I am indebted to Mr Errol Atkinson of the National Measurement Laboratory (NML)
in Sydney, Australia for many repeated and painstaking calibrations of our low
brightness sources for instrument calibration.
I thank my parents, Reg and Llyween for their continued interest and support of all
my endeavours. Finally, to my wife, Karen and my son, Matthew I owe special
thanks. They have been my inspiration. I have had the unique privilege of spending
both years at Davis with Karen. It was her observation of a noctilucent cloud in Feb-
98 that has led to a renewed interest in southern hemisphere NLC's. Behind the
scenes, while writing this thesis, we were married, moved into a new house, Matthew
was born, we spent 31/2 months as lighthouse caretakers on a remote southern
Tasmanian island and Karen finished her teaching degree. I thank them for some
wonderful times and for keeping life in perspective
John French.
11-Sep-2001
Contents ... iv
Hydroxyl Airglow Temperatures above Davis Station, Antarctica
Table of Contents
1. INTRODUCTION AND REVIEW 1
1.1. Climate Change 1
1.2. Modelling Trends 4
1.3. Monitoring Trends 10
2. HYDROXYL AIRGLOW 21
2.1. Historical Observations 21
2.2. Instrumental Techniques S 22
2.2.1. Spectrometers 23
2.2.2. Photometers 23
2.2.3. Camera Systems 24
2.2.4. Fourier transform spectrometers 24
2.2.5. Fabry-Perot Spectrometers 25
2.3. Molecular Spectroscopy 26
2.3.1. Translational Energy 27
2.3.2. Electronic Energy 27
2.3.3. Vibrational energy 31
2.3.4. Rotational energy 32
2.3.5. Nuclear Orientation 33
2.3.6. OH Vibrational and Rotational Constants 33
2.3.7. Transitions between states 34
2.3.8. Transition probability 36
2.3.9. Rotational temperature 37
2.4. OH Photochemistry 41
2.4.1. Hydrogen-Ozone reaction 41
2.4.2. 02* hypothesis 42
2.4.3. Perhydroxyl mechanism 43
2.4.4. Collisional Quenching by N2 and 02 45
2.4.5. Atomic Oxygen production and loss 48
2.4.6. Production of Hydrogen 49
2.5. Altitude Profile 50
Contents ... v
Hydroxyl Airglow Temperatures above Davis Station, Antarctica
3. INSTRUMENTATION, CALIBRATIONS AND DATA 53
3.1. Optical Instruments at Davis. 53
3.2. The Davis Scanning Spectrometer 57
3.2.1. Overview 57
3.2.2. System Components. 58
3.3. Diffraction Characteristics 66
3.3.1. The Grating Equation 67
3.3.2. Angular and Linear Dispersion 69
3.3.3. Resolution and Resolving Power 71
3.3.4. Throughput and Etendue 73
3.3.5. Blazing and Woods Anomalies 74
3.3.6. Ghosts 75
3.4. Instrument Function Calibrations 77
3.4.1. Intrinsic Width Method 77
3.4.2. Empirical Fit Method 77
3.4.3. Slit Rotation Method 78
3.4.4. A-doubling correction factors 80
3.5. Low Brightness Source Calibration Lamps 83
3.5.1. Primary Tungsten-Filament Lamps 83
3.5.2. Secondary Calibration Lamp 84
3.5.3. McEwen Portable Low Brightness Source 85
3.5.4. Eather Low Brightness Source 87
3.5.5. Annual NML Calibrations: Comparisons, Problems and Tests 89
3.6. Instrument Response Calibrations at Davis 111
3.6.1. Retrospective Calibrations 111
3.6.2. Response to the Eather Source - RE96 00 112
3.6.3. Response to the Secondary Calibration Lamp - RQ yR(X) 114
3.6.4. Inter-year Comparisons of RE(?.) 115
3.6.5. Errors in Line Ratios 117
3.6.6. Absolute Instrument Response. 118
3.7. Data Sets and Scan Parameters 119
3.7.1. Data formats 119
3.7.2. Data Catalogue 120
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Hydroxyl Airglow Temperatures above Davis Station, Antarctica
4. ROTATIONAL TEMPERATURE ANALYSIS 123
4.1. Data selected for analysis development 123
4.2. Identification of weak spectral features 125
4.2.1. Satellite lines 126
4.2.2. Auroral Emissions 127
4.2.3. P1 branch line contamination 130
4.2.4. Atmospheric Absorption 131
4.2.5. Solar Fraunhofer Absorption 133
4.3. Analysis Procedures 133
4.3.1. Aims and Previous Work 133
4.3.2. Spike Corrections 136
4.3.3. Offset Correction 136
4.3.4. Dark Count Measurement and Estimations 140
4.3.5. Response Corrections 142
4.3.6. Backgrounds 143
4.3.7. Auroral Correction 143
4.3.8. Optimised Width 145
4.3.9. A-doubling factors 146
4.3.10. Q1(5) correction 146
4.3.11. Transition Probability Sets 146
4.4. Temperature and Uncertainty Results 147
4.4.1. Principle Data Set 147
4.4.2. Sampling Errors 149
4.4.3. Error in the average temperature 150
4.4.4. Comparison of temperatures from each ratio 151
4.4.5. Expanded Data set 151
4.4.6. Seasonal Variations 152
4.4.7. Diurnal Variations 154
4.5. Discussion 155
4.5.1. P1 branch line influences 155
4.5.2. Argon Aurora 156
4.5.3. Reducing temperature uncertainties 159
4.6. Conclusions 160
Contents ... vii