Ozone time series and trends

Various groups compute trends in different ways.

One goal of the workshop is to be able to compare time series and trends from different groups.

Therefore we are requesting that participants compute trends for common time periods in a common manner, to facilitate intercomparison of results. This is not mandatory, but is highly desirable.

This does not preclude participants presenting trends computed in other ways for other time periods (e.g., their entire record).

Recommendations for trend intercomparison.

• The template is a guide, to be followed as much as possible for the trend intercomparison.

• Comparing trends is only one aspect of the « Tropospheric O3 Changes » issue.

• Key points are:

• to show the entire time-series in ppb, as there is often non-linear behavior

• to analyse trends

• to check the regional consistency within different datasets.

General recommendations:

Please calculate all trends as the slope of the linear regression line and give the corresponding 95% confidence interval for the trend (2σ) and r2 for the fit.

Also give the intercept (with a confidence limit) for a selected reference year (e.g. 2000) or give the average mixing ratio for the record.

ALL trends (including seasonal trends) should be calculated based on monthly mean anomalies (i.e. deseasonalized trends) and reported in ppb/year +/- 2σ.

Specific recommendations for surface stations :Monthly means are calculated using original data resolution

(e.g. hourly means). Monthly mean is considered valid if less than 33% of points

are missing.

Specific recommendations for vertical profiles :

1.Monthly means should be reported for the following vertical layers:

• A: surface layer (ground-1 km)• B: lower free troposphere (1-3 km)• C: mid free troposphere (3-8 km)• D: upper troposphere (8 km - tropopause) : • E: UTLS

2.Or use vertical resolution of ~1 km from ground to the tropopause

3.Or if you use some other vertical grid, it would be helpful to report trends on the recommended altitude ranges.

Recommended time intervals

• Three time periods should be investigated if your data covers these periods:

1990-2009, 1990-1999 and 2000-2009.

1980-2009

• If these are not available, just use the data range you have e.g, 1995-2008 for MOZAIC

• Compute trends for 1995-2008 if you wish to compare to MOZAIC trends.

Data presentations talks (no more than 10 slides)

• Description of station/data set : 1 slide as suggested below (#7 or #9 for either surface or vertical profile station)

• Display of entire time series (in ppb) and highlight of special features. 1 slide

• Display of time series anomalies (in ppb) over 1990-2009 and/or 1990-1999 and/or 2000-2009 if possible and include a linear fit with indications on slope/2σ/r2 and intercept or average concentration over the record. (max 3 slides)

• Display of summary tables : 1 slide as suggested below (#8 or #10 for either surface or vertical profile station)

• Discussion points (1 slide).• Comparison with neighboring sites and/or alternative

statistical approaches. (max. 2 slides)• Summary and open issues. 1 slide

General information about surface station:

1) The station :Name, Latitude, Longitude, Altitude,

Surrounding (possible sources of precursors/ anthropogenic impact), Systematic changes in environment

2) Instrument (general performance/calibration)

3) Data set:Period:

% of missing points:

Particularities (e.g. years of the general tendency change)

From monthly mean anomalies based on all available data

From night data only (11 p.m. – 4 a.m. local time)

From day data only (11 a.m.- 4p.m. local time)

1990-2009

1990-1999

2000-2009

Annual trends

Seasonal trends (for day and night values)

DJF MAM JJA SON

1990-2009

1990-1999

2000-2009

« Night / Day » can be replaced by « Baseline / Non-Baseline » or « Regional / Local » influence 

General information about the vertical profile station:

1) The station:Name, Latitude, Longitude, launch altitude,Launch time and frequencysurrounding (possible sources of precursors/ anthropogenic impact), systematic changes in environment

2) Instrument (general performance/calibration)3) Data set:

PeriodBig data gapsParticularities (e.g. years of the general tendency change)

From monthly mean anomalies (in ppb) based on all available data

A B C D E

1990-2009

1990-1999

2000-2009

Annual trends for the five altitude layers (or whatever is convenient with your dataset)

Seasonal trends

DJF MAM JJA SON

1990-2009

1990-1999

2000-2009

A, B, C, D, E altitude levels can be replaced by plots of profile trends

Model evaluation talks (no more than 12 slides – focus on reanalysis simulations)

• Description of model and simulation set-up : 1 slide• General characterization of simulation results (e.g. maps or

“Stevenson-plot” (multi-panel regional averages): 1 slide• Up to 4 slides with time series comparisons for surface sites. Use

monthly mean anomalies as the data people; individual stations or regional averages: all graphs should have time axes 1990-2009 and/or 1990-1999 and/or 2000-2009 and include a linear fit with indications on slope/2σ/r2 and intercept or average concentration over the record.

• Up to 4 slides to analyze modeled vertical profiles versus MOZAIC and/or sondes. For MOZAIC use 1995-1999 and 2000-2008, for sondes 1990-1999 and 2000-2008. Show time series at standard pressure levels (850, 500, 250 hPa) plus summary slide for trend (ppbv/year) versus altitude.

• Discussion points (1 slide)• Summary and open issues: 1slide