Task B Determination of the O4 profiles and O4 VCDs

In this document, my procedure for the extraction of the O4 profiles and O4 VCDs is described. Other people might follow this procedure or make their own choices.

O4 profiles and O4 VCDs are used for the conversion of the measured O4 (D)SCDs into (D) AMFs. The O4 profiles are also used as input in the radiative transfer simulations.

B1 Extraction of O4 profiles:

The O4 profiles are calculated from the temperature and pressure profiles (task A). First the oxygen concentration is derived from the air concentration by multiplication with 0.21. Also the mixing ratio of water vapor on the air concentration is calculated from the relative humidity and temperature. Close to the surface, mixing ratio of water vapor is up to > 2%. There the effect on the O4 concentrtion is up to >4%. However, for the total O4 VCD the effect of water vapor is rather small (~ 1%). Thus the water vapor profile might be usually ignored for O4 profiles and O4 VCDs.

The temperature and pressure profiles (determined in task A) are provided in the zip file: Extracted_T_and_p_profiles.7z. This file contains the following files:

Temperature

/ Pressure
T_1806_8_11h.txt
T_1806_11_14h.txt
T_1806_14_19h.txt
T_0807_4_7h.txt
T_0807_7_11h.txt
T_0807_11_19h.txt / p_1806_8_11h.txt
p_1806_11_14h.txt
p_1806_14_19h.txt
p_0807_4_7h.txt
p_0807_7_11h.txt
p_0807_11_19h.txt

(the first column is the height in km; the second columns the temperature and pressure in K or hPa, respectively)

Note that the height grid of these files starts at zero (which represents 150 m altitude in reality), because in our radiative transfer simulations an altitude of 0km represents the location of the MAX-DOAS instrument.

The average relative humidity for the three periods on both days is taken from the in situ measurements at Mainz Mombach:

18.06., 08:00 – 11:00: 52%

18.06., 11:00 – 14:00: 38%

18.06., 14:00 – 19:00: 30%

08.07., 04:00 – 07:00: 66%

08.07., 07:00 – 11:00: 45%

08.07., 11:00 – 19:00: 36%

Water vapor mixing ratio 18.06.2013 / Water vapor mixing ratio 08.07.2013

Fig. B1 Mixing ratio of water vapor calculated for the three periods on both days derived from the temperature profiles by assuming a constant relative humidity.

O4 profiles

18.06.2013 / 08.07.2013

Fig. B2 O4 profiles (expressed as the square of the oxygen (O2) concentration) for the three periods on both days.

The O4 profiles are provided in the zip file: Task_B_O4_VCD.7z

It contins the following files:

O4_1806_8_11h.txt

O4_1806_11_14h.txt

O4_1806_14_19h.txt

O4_0807_4_7h.txt

O4_0807_7_11h.txt

O4_0807_11_19h.txt

(the first column is the height in km, the second column the squared O2 concentration in molecules²/cm6)

Note that the height grid of these files starts at zero (which represents 150 m altitude in reality), because in our radiative transfer simulations an altitude of 0km represents the location of the MAX-DOAS instrument.

From the derived O4 profiles the O4 VCD is calculated. The O4 profiles (squared oxygen concentration) are integrated from 150m to 30km (the vertical resolution is 20m). The obtained O4 VCDs are shown in the table below.

Table B1 O4 VCD for the three time periods of both days

Date, time / O4 VCD [1043molec²/cm5]
18.06., 08:00 – 11:00 / 1.228
18.06., 11:00 – 14:00 / 1.232
18.06., 14:00 – 19:00 / 1.233
08.07., 04:00 – 07:00 / 1.278
08.07., 07:00 – 11:00 / 1.281
08.07., 11:00 – 19:00 / 1.282

B2 Simplified claculations for the whole time period May to August 2013

(This section is not part of Task B, but might be of interest)

In addition to the above calculations (based on the ECMWF temperature profiles) also a simpler method for the determination of the O4 VCD was applied using surface pressure and temperature (in situe measurements at Mainz Mombach at 12:00) and assuming a constant lapse rate of 0.65K/100m. The results are compared to the results from above in the table below. The results of both methods agree within 3%.

Table B2 Comparison of the O4 VCD [1043molec²/cm5] for the different time periods of both days based on ECMWF profiles (see above) or on surface pressure and temperature data.

Date, time / T surface / P surface / O4 VCD (ECMWF) [1043molec²/cm5] / O4 VCD (in situ) [1043molec²/cm5]
18.06., 08:00 – 11:00 / 27 / 1017 / 1.228 / 1.234
18.06., 11:00 – 14:00 / 32 / 1017 / 1.232 / 1.209
18.06., 14:00 – 19:00 / 35 / 1017 / 1.233 / 1.193
08.07., 04:00 – 07:00 / 17 / 1030 / 1.278 / 1.316
08.07., 07:00 – 11:00 / 24 / 1030 / 1.281 / 1.282
08.07., 11:00 – 19:00 / 29 / 1030 / 1.282 / 1.256

The O4 VCs were calculated for a period of 3 months from the in situ temperature and pressure profiles. The O4 VCDs varied by about 13% over that time period (see Fig. B3).

Fig. B3 Time series of O4 VCDs for May to August 2013.

The following figures display the calculated O4 VCDs shown in Fig. B3 as function of the corresponding surface temperture and pressure (at 12:00). It is found that the surface temperature is the dominant parameter to describe the variability of the O4 VCD. Also shown (magenta lines) are the respective dependencies on temperature and pressure for fixed pressures (p=1018 hPa) or temperature (T= 293K). These lines well describe the overall dependencies.

Fig. B4 Dependence of the O4 VCD on surface temperature for all days in the period May to August 2013. The red line indicates the temperature dependence for a fixed surface pressure of 1018 hPa).

Fig. B5 Dependence of the O4 VCD on surface pressure for all days in the period May to August 2013. The red line indicates the temperature dependence for a fixed surface temperature of 293K).