State of Environment

Indicator 14 - Midwinter atmospheric temperature at altitude 87km

Index: Description | Data | Custodian evaluation | Related resources | Parameters

Description

Indicator Definition
Midwinter atmospheric temperatures at ~87km above Davis station, Antarctica,
are determined from hydroxyl airglow emissions. The temperature reported is
determined over the interval, day-of-year (DOY) 106 to DOY 258.


Responsible organisation

Australian Antarctic Division ( Australia )

Custodians

Theme area

Atmosphere

Indicator type

Condition

Criteria the indicator satisfies

The following 12 out of 15 criteria

1. Serve as a robust indicator of environmental change
2. Reflect a fundamental or highly-valued aspect of the environment or an important environmental issue
3. Be either national in scope or applicable to regional environmental issues of national significance
4. Provide an early warning of potential problems
5. Be capable of being monitored to provide statistically verifiable and reproducible data that shows trends over time and, preferably, apply to a broad range of environmental regions
6. Be scientifically credible
7. Be easy to understand
9. Be cost-effective
10. Have relevance to policy and management needs
11. Contribute to monitoring of progress towards implementing commitments in nationally important environmental policies
13. Contribute to the fulfillment of reporting obligations under international agreements
15. Where possible and appropriate, be consistent and comparable with other countries´┐Ż and state and territory indicators

For details of indicators, see the State of Environment Bibliography entries 16336 and 16337

Date input

Yearly measurements

Monitoring location

Rationale For Indicator Selection
Over the last century the concentration of greenhouse gases has risen in the
atmosphere. Greenhouse gases result in warming of the lower atmosphere but
enhanced cooling of the upper atmosphere. Enhanced cooling rates of the upper
atmosphere may provide a more readily measurable indicator of 'global
warming'.


Midwinter hydroxyl layer temperatures, give a proxy temperature for an
altitude of ~87km (just below the coldest region of the atmosphere in winter).
Associated with anthropogenic greenhouse gas increases, this tenuous region of
the atmosphere is expected to cool, with the magnitude of the cooling being
significantly larger than the warming at ground level. When properly measured
and interpreted, this may be the atmospheric region where variations in trends
associated with anthropogenic climate change can be most rapidly and
conclusively determined.


Hydroxyl airglow is emitted from an ~8km wide layer, centred at ~87 km.


Design and Strategy For Indicator Monitoring Program
Spatial Scale: Point value at Davis station, Antarctica


Frequency: Winter averages


Measurement Technique: Hydroxyly airglow rotational temperatures are
determined by the standard technique involvinging the ratios of the
intensity of hydroxyl airglow line emissions. The difficulties
encountered and methods adopted at Davis are detailed in Greet et al.,
1998. Refinement to the absolute temperatures determined by this
technique have been published by French et al., 2000.


Research Issues
The values continue to be refined, though their relative difference between
years is well quantified (see error estimates). The potential exists for
determining some values at earlier epochs if instrumental uncertainties can
be better quantified. This work is underway.


Data

Timespan
1990 to 2008
Number of data points
16

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Custodian evaluation

15 Apr 2002

The yearly winter temperature data at ~87 km above Davis have been evaluated to determine a solar cycle (11 year, natural cyclic trend evaluted as K per sfu [=solar flux unit. Multiply by 120 to express this value as K per average solar cycle) and a linear long-term trend. [1990, 1995-2000]: solar cycle: 0.067 +/- (std. error) 0.009 K per sfu [=~8 K per solar cycle]. lower 95% confidence limit value: 0.045 K per sfu. upper 95% confidence level value: 0.090 K per sfu. linear trend: -0.47 +/- (std error) 0.13 K per annum. lower 95% confidence limit value: -0.81 K per annum. upper 95% confidence limit value: -0.13 K per annum. That looks like 'cooling is weakly significant'. I would not be prepared to support these results from the present data because an assumption of the multiple-regression analysis used to derive the values listed is that the temperature from each year is known to the same accuracy. However, the 1990 datum is the least reliable datum, but it presently dominates the trend estimate. It is necessary to wait until we reach the minimum of the present solar cycle (~5 years) to be confident that uncertainties in the 1990 datum are not the source of the excessive cooling. The significance of the 1990 datum can be gauged by removing it from the analysis. [1995-2000]: solar cycle: 0.049 +/- (std. error) 0.009 K per sfu. [=~6 K per solar cycle] lower 95% confidence limit value: 0.018 K per sfu. upper 95% confidence level value: 0.080 K per sfu. linear trend: -0.003 +/- (std error) 0.28 K per annum. lower 95% confidence limit value: -0.78 K per annum. upper 95% confidence limit value: +0.77 K per annum. No significant cooling or warming trend is apparent from the most reliable, recent 6 years of data.

8 Nov 2002

Condition scale - 3
1 - the environment degraded to the point where rehabilitation is impossible
0 1 2 3 4 5 6 7
7 - the environment is pristine, in perfect condition, no anthropogenic influences
State of Knowledge scale - 2
1 - Poor
0 1 2 3 4 5 6 7
7 - Excellent

11 Sep 2003

The absolute value (and standard error) for 2002 are potentially seriously misleading if this value is used for trend estimates. Our spectral calibrations for 2002 were much more variable than for recent, previous years. We have tracked a source of this variability to the photomultiplier cooler which performed poorly (variably) during 2002. We estimate that individual nightly average temperatures may be in error in our present analysis by up to 4K. Normal errors from the spectral calibration amount to less than 0.5K. If we can commit time to investigating and correcting for this variation, we may be able to improve the accuracy of the 2002 value (...but will not be able to obtain the accuracy of previous or future years). It is essential to note that there is this degree of uncertainty in the present 2002 value.

Condition scale - 4 - fair condition
1 - the environment degraded to the point where rehabilitation is impossible
0 1 2 3 4 5 6 7
7 - the environment is pristine, in perfect condition, no anthropogenic influences
State of Knowledge scale - 4 - Fair
1 - Poor
0 1 2 3 4 5 6 7
7 - Excellent

For definitions of the Scale categories, consult the Explanation of the Status Categories

Related resources


Project 701 - Long-term monitoring of the mesopause region via hydroxyl emissions at Davis
Scientific Bibliography 17315 - French, W.J.R., G.B. Burns, K.Finlayson, P.A. Greet, R.P. Lowe and P.F.B. Williams. (2000) Hydroxyl (6-2) airglow emission intensity ratios for rotational temperature determination. Annales Geophysicae, 18: 1293-1303.
Scientific Bibliography 17316 - Golitsyn, G.S., A.I. Semenov, N.N. Shefov, L.M. Fishcova, E.V. Lysenko, S.P. Perov. (1996) Long-term temperature trend in the middle and upper atmosphere Geophysical Research Letters, 23(24):1741-1744.
Scientific Bibliography 17317 - Greet, P.A, W.J.R. French, G.B. Burns, P.F.B. Williams, R.P. Lowe and K. Finlayson. (1998) OH(6-2) spectra and rotation temperature measurements at Davis, Antarctica. Annales Geophysicae, 16:79-89.
SOE Indicator 1 - Monthly mean air temperatures at Australian Antarctic Stations
SOE Indicator 2 - Highest monthly air temperatures at Australian Antarctic Stations
SOE Indicator 3 - Lowest monthly air temperatures at Australian Antarctic Stations
SOE Indicator 4 - Monthly mean lower stratospheric temperatures above Australian Antarctic Stations
SOE Indicator 5 - Monthly mean mid-tropospheric temperatures above Australian Antarctic Stations
SOE Indicator 11 - Atmospheric concentrations of greenhouse gas species
SOE Indicator 12 - Noctilucent cloud observations at Davis
SOE Indicator 13 - Polar stratospheric cloud observations at Davis
SOE Indicator 15 - Stratopause region parameters for Davis

Parameters

The properties link can be used to view details of the parameters measured for this indicator.

Parameter Name Unit of measure Properties
Absolute temperature Kelvin Properties