Total ozone series in Arosa, Switzerland


The total ozone series of Arosa (Switzerland, 46.8N/9.68E 1820 masl) is the longest in the world. The measurements began in 1926 by F. W. P. Götz and were continued by G. Perl and then H. U. Dütsch from the Federal Institute of Technology from Zürich (ETHZ). Since 1988, Meteo Schweiz (formerly Swiss Meteorological Institute) is responsible for operational measurements at Arosa (LKO).


Fig.1 Total ozone yearly means at Arosa since 1926

Total ozone is presently measured by four instruments at Arosa to obtain redundancy for reliable trend determination. International comparisons of the instruments are regularly performed to guarantee the quality of the data. This series is very valuable to assess the ozone \ depletion in the northern mid-latitudal. It is at the basis of the following current research projects: Responsible of the "Troposphere chemistry and long-term ozone trend analysis"-group at the Institute for Atmospheric and Climate Science at ETHZ (IACETH): Johannes Staehelin.

Further information:

General information on total ozone

The atmospheric ozone shield prevents harmful solar short-wave ultraviolet (UV) radiation in the UV-B range (wavelength between 285 and 320 nm) from reaching the earth's surface.
Since the beginning of the 70s the destruction of the stratospheric ozone layer by anthropogenic activities was discussed in science and public. The most dramatic effect of this destruction can be observed over Antarctica during the southern hemisphere spring: the so called ozone hole. However, a significant decrease of the ozone shield was also found over mid latitudes.
Presently it is proven that manmade chemicals such as Chlorofluorormethanes (CFCs) and Halons (containing Bromine) are destroying the stratospheric ozone.
The largest proportion of ozone in the atmospheric column resides in the stratosphere (around 90%) with a maximum at about 23 Km above sea level in the mid-latitudal. Only approximately 10% of the atmospheric ozone is located in the troposphere (0-10 Km high).
The tropospheric ozone was found to increase in the northern hemisphere since the end of the 50s. Tropospheric (surface) ozone increased, for example, by a factor two between the end of the 50ís and 1990 at Arosa. This increase is related to anthropogenic emissions such as nitrogen oxides and hydrocarbons (photochemical reactions). However, this increase can not compensate for the ozone decrease in the stratosphere.
The largest proportion of ozone in the atmospheric column resides in the stratosphere (around 90%) with a maximum at about 23 Km above sea level in the mid-latitudal. Only approximately 10% of the atmospheric ozone is located in the troposphere (0-10 Km high).
The tropospheric ozone was found to increase in the northern hemisphere since the end of the 50s. Tropospheric (surface) ozone increased, for example, by a factor two between the end of the 50ís and 1990 at Arosa. This increase is related to anthropogenic emissions such as nitrogen oxides and hydrocarbons (photochemical reactions). However, this increase can not compensate for the ozone decrease in the stratosphere.

Total ozone measurements at Arosa




Fig. 2 Total ozone daily means 1997

The daily averages of the total ozone amount at Arosa (see Fig. 2 for 1997) show a seasonal variation with larger values in spring and lower in fall and a large day-to-day variability. The systematic seasonal variation is due to the general circulation in the stratosphere. The day-to-day variation is related to the meteorological conditions.
The total ozone amount is given in Dobson units (DU). 1 DU = 10-3 atm-cm.300 DU = 1 layer of 3 mm if the whole ozone column is taken at the sea level with standard conditions.
The ozone depletion occurs primarily in spring and in winter (Fig. 3).


Fig. 3 Total ozone seasonal means at Arosa since 1926

Recent Research Results

Anthropogenic and Dynamic Contributions to Ozone Trends of the Swiss Total Ozone Umkehr and Balloon Sounding Series.

PhD work of Andrea K. Weiss
published at GCA-Verlag (2000)
Dissertation ETH No 13635, ISBN 3-934389-88-0

In the PhD work of Andrea Weiss, which is funded by the Global Watch program of SMI, the dynamic contribution to long-term stratospheric ozone trends is quantified. Winter (January to March) total ozone trends of the period from 1970 to 1998 are reduced from -(3.2±0.6) to -(2.4±05) percent per decade when taking into account the natural variability originating from the North Atlantic Oscillation (NAO). NAO is defined as the pressure gradient between Greenland and the Azores and describes the zonality of the flow in the North Atlantic region. On multi-annual time scale European winter climate is strongly linked to NAO.
The statistical analysis is based on the Arosa homogenized total ozone series starting 1926  which is measured  with Dobson spectrophotometry. The linear regression model includes as explanatory variables the NAO-index, the solar cycle (F 10.7 solar flux), the Quasi-biennial Oscillation (QBO) and a data set describing the influence of violent volcanic eruptions (optical depth). Similar results were obtained by replacing NAO by the tropopause pressure because of its control by NAO. Total ozone trends of February and March means of the series of Reykjavik, Iceland increase from statistically insignificant to (-2.7 ±1.0) percent per decade when including tropopause pressure as explanatory variable. We also conclude that the longitudinal variability at northern mid-latitude of total ozone trends in the satellite measurements of TOMS instruments (Total Ozone Mapping Spectrometers) is strongly linked to NAO. Tropopause pressure (NAO) strongly influences the ozone profiles in particular at the tropopause and in the lowest part of the stratosphere and therefore influences profile ozone trends. This effect is studied in the analysis of the homogenized long-term Swiss ozone balloon record (performed by Brewer Mast sensors).  Check the NAO-influence page and the Umkehr page for more research results.

Dynamical causes for deviations of ozone profiles in Switzerland

PhD work of Gisela Koch
march 2000 until march 2003
E-Mail: gisela@iac.umnw.ethz.ch - Homepage

Vertical ozone profiles in northern mid-latitudes show large variability and are strongly influenced by dynamical processes and the associated atmospheric transport.
In this study we want to specify the dynamical contributions to this variability and link ozone deviations with the origin of air masses. Ozone profiles have been measured 3 times a week by MeteoSwiss at Payerne, Switzerland (46.80N, 6.95E, 490 a.s.l.) since autumn 1968. The high resolution ozone profiles are sensored by a Brewer-Mast sonde. A correction factor scales the soundings to match the total ozone values measured at Arosa, Switzerland. Ozone deviations are calculated with respect to the 30-year monthly means in units of standard deviations in the lower and middle stratosphere. The vertical range comprises the region of the climatological ozone maximum. 10-day backward trajectory calculations were performed for each of the ozone profiles between 1977 and 2000 with on 16 isentropic surfaces between 340K and 700K which correspond to pressure levels between about 300hPa and 20hPa. These calculations are based on wind fields from the NCEP reanalysis data set.
Conclusions
* Between 460K and 560K: in the 1990s ozone values in winter are smaller than expected by the fit to 1980s' values and can not be explained dynamically in terms of varying origin.
* Between 340K and 440K: No trend in ozone at these altitudes. Variability can be dynamically explained by the changing frequencies of transport form polar vs. subtropical regions.

Long Term trends of Total Ozone in the Northern Midlatitudes in Relationship with a large Set of Atmospheric Parameters

PhD work of Jörg A. Mäder
november 2000 until november 2003 (PhD available as pdf in german)
E-Mail: maeder@iac.umnw.ethz.ch - Homepage

coming soon

Data available on the internet

The annual and monthly mean values of the total ozone amount at Arosa are available on the internet via ftp. They are based on the daily averages of the homogenized series of Arosa.
For questions, please send a mail to Jörg Mäder

Bibliography

research themes IACETH Last update: Februar 2008