Initialization procedure

Two sources were used for initialization of species which were considered in the simulation. The first one are the measurements of the BONBON instru-ment on-board the TRIPLE gondola. It is a cryogenic whole air sampler (Schmidt et al., 1987). The whole air samples are collected cryogenically in evacuated and conditioned sample bottles cooled with liquid neon and are analyzed by gas chromatography using an electron capture detector. The vertical profiles of the most important CF C species, Halons, as well as SF₆, CH₄, and N₂O can be obtained using BONBON. The second initialization data source is the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS) (Russell et al., 1993). This instru-ment measures ozone and other species using the solar occultation technique.

It observes daily profiles at multiple longitudes along two latitude circles de-termined by the satellite’s orbit. HALOE observes 15 sunrise and 15 sunset profiles per day at lower latitudes; the latitude range was 29.83^◦N - 74.25^◦N in May and 61.07^◦N - 64.47^◦N in the end of June 2003.

The CLaMS simulation described here starts on 20 May 2003 (20 days before the flight date) and is performed on 13 isentropic levels (384.4, 409.8, 465.7, 502.8, 538.1, 576.1, 615.3, 667.9, 721., 779., 845.6, 881.9, and 913 K). This set of theta levels corresponds to the altitudes where BONBON has taken samples. The inorganic bromine was initialized with the help of the BONBON data. Total bromine was set to 18.4 ppt (see Text below).

For every point probed by BONBON a 20-days backward trajectory was calculated.

The initialization for ozone is taken from HALOE. Unfortunately HALOE measurements are quite sparse. That is why we tried two approaches for the initialization: a ”temporal initialization” and a ”spatial initialization”. For the temporal initialization the closest HALOE scan to the midnight of May 20 was chosen and its values were taken to initialize the model. There is a gap in HALOE data between May 12 and 21, though. Therefore the HALOE values from May 21 were used. For the spatial initialization all HALOE scans performed in May - June 2003 were examined to reveal the closest spatial ones of them for each Θ-level and their values were used for the initialization (Fig.5.6). Both initializations have their own profiles so we decided to carry out simulation runs for both in order to test the sensitivity of the model to different initializations. To initialize the chemically inert tracer CH₄ HALOE

Figure 5.6: The spatial and temporal initialization for the CLaMS run. The red diamonds mark the positions of air parcels on different theta levels on May 20, 2003 at 0:00 UTC which were then probed by TRIPLE on June 9, 2003. The green square shows the geolocation of the closest in time HALOE scan on May 21, 2003, at 20:17 UTC. The volume mixing ratios obtained during this scan were used as ”temporal” initialization. The blue squares mark HALOE scans performed in May-June 2003, which are closest to the locations of the TRIPLE measurements. These volume mixing ratios were taken as ”spatial” initialization.

data were used as well. The same principle as for ozone was applied.

The so called family concept is used in CLaMS. This means that certain chemical species are grouped together into chemical families. The intrafamily conversion rates are typically much faster than the net rate of change of a given family. The chemical families defined in CLaMS are O_x(= O₃ + O(¹D) + O(³P )), N O_x(N O + N O₂ + N O₃), ClO_x(= Cl + ClO + 2Cl₂O₂), and BrOx(= Br + BrO). For long model runs one can initialize just one family member with the sum of the entire family. This does not cause any error, because after a few steps the species are distributed within a family due to relatively fast chemistry.

From the N O_xfamily HALOE detects N O and N O₂ only. Their sum was taken as the initial value for N O₂, while N O was initialized as zero due to the short photochemical lifetime. As for O3 and CH4 there are two versions of initialization: the ”spatial” and the ”temporal” ones. H₂O and HCl were also initialized with the help of HALOE. All ”temporal” and ”spatial” initial profiles, as well as the HALOE profiles used for initialization are shown in Fig.5.7.

To initialize the bromine family a tracer correlation between Br_y and CH4 determined by Grooß et al. (2002) was used. This correlation was ascer-tained for spring conditions, so it can be used as a good approach for the late spring conditions. For this correlation, all measurements at mid-latitudes to high latitudes made by the ACATS (the Airborne Chromatograph for Atmo-spheric Trace Species) instrument on-board the American research aircraft ER-2 and by the cryogenic whole air sampler BONBON were analyzed. The correlation was found to be very tight. With the polynomial fit to these data

[Br_y, ppt] = 44.3 − 106.3[CH₄, ppm] + 155[CH₄, ppm]²−

− 92.83[CH₄, ppm]³+ 17.8[CH₄, ppm]⁴ (5.1) the CH₄ measured by BONBON on the balloon flight on 9 June 2003 was used to calculate the mixing ratio of total inorganic bromine Bry. The CH4

from BONBON and Br_y, as well as the correlation curve between CH₄ and Br_y from (5.1) are shown in Fig.5.8. The simulation was started in the nighttime. Taking the above mentioned family concept employed in CLaMS into consideration, BrON O₂ as the main night reservoir was initialized by Br_y, while the other bromine species (HBr, Br, HOBr, BrO, BrCl, and Br2) were initialized to zero.

The remaining chemical species are of less importance for the chemical simulations and were initialized using the corresponding Mainz 2-D photo-chemical model results (Gidel et al., 1983; Grooß , 1996).

To check the sensitivity of the model towards the partitioning within

Figure 5.7: O₃, CH₄, N O_x, H₂O, and HCl initializations on 20 May 2003 for 13 theta levels. There are 13 profiles for each species from the best spatially collocated HALOE scans (shown in grey). For every theta level the value from the closest corresponding profile is taken as the ”spatial” initialization.

The resulting spatial initialization profile is shown by red diamonds. The best temporally collocated HALOE profile is shown in green

Figure 5.8: The CH₄/Br_y correlation (left panel) and the initialization de-rived by means of this correlation and BONBON CH₄ observation (right panel).

the chlorine family and towards N O2 three additional initialization cases were created. The first one was the same as the standard case, but volume mixing ratios of chlorine nitrate ClON O₂ were halved and the mixing ratio of hydrochloric acid HCl was doubled. The second and third initialization cases were the same as the standard one as well, but volume mixing ratios of nitric oxide N O₂ were doubled in the second case and halved in the third case, respectively.