COMPARISON OF BREWER AND DOBSON TOTAL OZONE
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. COMPARISON OF BREWER AND DOBSON TOTAL OZONE COMPARISON OF BREWER AND DOBSON TOTAL OZONE Brewer and Dobson spectrophotometers are widely used for Total Ozone monitoring. In Arosa (Switzerland, 46.8N/9.68E 1820 m a.s.l.) there are two semi-automatic Dobson systems and three automatic Brewer systems, which measure total ozone continuously and quasi - simultaneously. The co-location of these two instruments allows a direct comparison for QUALITY CONTROL and for STUDYING THE DIFFERENCES BETWEEN THE TWO TYPES OF SPECTROPHOTOMETERS. Data (1995-2004) from the two types of sun spectrophotometers (Dobson 62, 101 and Brewer 40, 72, 156) are compared two by two and analysed using the following statistical model: O 3 Br - O 3 D = C + + X T + O 3 Br ; O 3 D : Brewer and Dobson Total Ozone C: allows a zero mean difference μ: linear term proportional to the air mass [Thomason et al., 1983] X T : influence of temperature error Two distinct approaches for differences in temperature sensitivities of ozone wavelengths are considered: Approach 1 T eff : ozone effective temperature calculated from ozone and temperature sounding data from Payerne (200 km from Arosa). Approach 2 T p : simplified approach only using temperature at two altitudes (at 31 and 51 hPa given by the soundings of Payerne Aerological Station). Wave length [nm] Ozone cross section 300 310 320 330 340 5*10^-22 5*10^-21 5*10^-20 5*10^-19 O3 X-section temperature dependance 202 K 221 K 241 K 273 K 293 K A-pair C-pair D-pair DOBSON MS5 MS6 MS7 BREWER Reduction of seasonal differences by model (Fig. 3): Annual Average: The contribution to the difference from the effective temperature is significantly larger than that from μ (Fig. 4, center plot): Seasonal Variability: • The relative contribution to the difference from μ is larger in winter than in summer • Dependence on the magnitude of TOZ: – TOZ<290 DU: agreement between the 2 instruments is better, with improved agreement in summer than winter. –TOZ>290 DU: the influence of atmospheric parameters is reduced in winter. Approach 2 Less precise. Further analysis: Attempt to generalize transfer function using other instruments at Arosa. METHOD Fig 2. Model of the molecular ozone cross-section from the Global Ozone Monitoring Experiment (satellite UV- visible spectrophotometer) database. Quasi-simultaneous direct sun measurements from the two types of spectrophotometers yield small, but characteristic seasonal variation in the differences of Total Ozone (Fig. 1). Causes of differences might include: • Different wavelengths with different T sensitivities of ozone absorption (Fig. 2) • Different retrieval algorithms • Different fields of view • Differing influence of scattered light Fig 4. Residual distribution of Total Ozone when applying different explanatory variables. Contact: [email protected] Fig 3. Time series of the residuals for B40 and D101(AD) after the model has been applied to the total ozone difference. MEASUREMENTS RESULTS Approach 1 Barbara Scarnato 1) , Johannes Staehelin 1) , René Stübi 2) , Herbert Schill 2) 1) IAC/ETH, Zürich; Switzerland 2) MeteoSwiss, Aerological Station; Payerne Switzerland Dobson Brewer INTRODUCTION Difference of readings [DU] Density Fig 1. Time series for B40 and D101 (AD pair) and their difference. The coincidence criterion is 10 min.
description
Barbara Scarnato 1) , Johannes Staehelin 1) , René Stübi 2) , Herbert Schill 2) 1) IAC/ETH, Zürich; Switzerland 2) MeteoSwiss, Aerological Station; Payerne Switzerland. RESULTS Approach 1. INTRODUCTION. METHOD. Reduction of seasonal differences by model (Fig. 3): Annual Average : - PowerPoint PPT Presentation
Transcript of COMPARISON OF BREWER AND DOBSON TOTAL OZONE
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COMPARISON OF BREWER AND DOBSON TOTAL OZONECOMPARISON OF BREWER AND DOBSON TOTAL OZONE
Brewer and Dobson spectrophotometers are widely used for Total Ozone monitoring.
In Arosa (Switzerland, 46.8N/9.68E 1820 m a.s.l.) there are two semi-automatic Dobson systems and three automatic Brewer systems, which measure total ozone continuously and quasi - simultaneously. The co-location of these two instruments allows a direct comparison for QUALITY CONTROL and for STUDYING THE DIFFERENCES BETWEEN THE TWO TYPES OF SPECTROPHOTOMETERS.
Data (1995-2004) from the two types of sun spectrophotometers (Dobson 62, 101 and Brewer 40, 72, 156) are compared two by two and analysed using the following statistical model:
O3Br - O3
D = C + + XT +
O3 Br; O3 D: Brewer and Dobson Total Ozone C: allows a zero mean difference μ: linear term proportional to the air mass [Thomason et al., 1983]XT: influence of temperatureerror
Two distinct approaches for differences in temperature sensitivities of ozone wavelengths are considered:
Approach 1
Teff: ozone effective temperature calculated from ozone and temperature sounding data from Payerne (200 km from Arosa).
Approach 2
Tp: simplified approach only using temperature at two altitudes (at 31 and 51 hPa given by the soundings of Payerne Aerological Station).
Wave length [nm]
Ozon
e cr
oss s
ectio
n
300 310 320 330 340
5*10
^-22
5*10
^-21
5*10
^-20
5*10
^-19
O3 X-section temperature dependance
202 K221 K241 K273 K293 K
A-pairC-pair
D-pair
DOBSON
MS5
MS6
MS7
BREWER
Reduction of seasonal differences by model (Fig. 3):
Annual Average:
The contribution to the difference from the effective temperature is significantly larger than that from μ (Fig. 4, center plot):
Seasonal Variability:
• The relative contribution to the difference from μ is larger in winter than in summer• Dependence on the magnitude of TOZ:
– TOZ<290 DU: agreement between the 2 instruments is better, with improved agreement in summer than winter. –TOZ>290 DU: the influence of atmospheric parameters is reduced in winter.
Approach 2
Less precise.Further analysis: Attempt to generalize transfer function using other instruments at Arosa.
METHOD
Fig 2. Model of the molecular ozone cross-section from the Global Ozone Monitoring Experiment (satellite UV-visible spectrophotometer) database.
Quasi-simultaneous direct sun measurements from the two types of spectrophotometers yield small, but characteristic seasonal variation in the differences of Total Ozone (Fig. 1).
Causes of differences might include:
• Different wavelengths with different T sensitivities of ozone absorption (Fig. 2)
• Different retrieval algorithms
• Different fields of view
• Differing influence of scattered light
Fig 4. Residual distribution of Total Ozone when applying different explanatory variables.
Contact: [email protected]
Fig 3. Time series of the residuals for B40 and D101(AD) after the model has been applied to the total ozone difference.
MEASUREMENTS
RESULTSApproach 1
Barbara Scarnato1), Johannes Staehelin1), René Stübi 2), Herbert Schill 2)
1) IAC/ETH, Zürich; Switzerland 2) MeteoSwiss, Aerological Station; Payerne Switzerland
Dobson
Brewer
INTRODUCTION
Difference of readings [DU]
Den
sity
Fig 1. Time series for B40 and D101 (AD pair) and their difference. The coincidence criterion is 10 min.
