| 03 Mar 2026
Correction of the Observatoire Haute Provence electrochemical concentration cell (ECC) ozonesonde 1991–2023 data record
Abstract. The Observatoire Haute Provence (OHP) station is one of the few long-term measuring stations for vertical ozone profiles in southern Europe. Since 1991, vertical ozone distribution has been monitored by the OHP weekly electrochemical concentration cell (ECC) ozonesonde. In this study, we have corrected the ECC datasets for the period 2002–2007. The correction of the ECC has been carried out using comparisons with other ozone-measuring instrument at the same station, stratospheric lidar, and with collocated satellite observations of the ozone vertical profile by Microwave Limb Sounder (MLS). Median ozone concentration of the ECC for the period 2002–2007 was -3.4 % lower than that of the stratospheric lidar and MLS. The ECC internal pump temperature showed a sudden drop of 16 K at 25 km for the period 2002–2007 compared to the period 1991–2001. Considering the long-term trends of the ECC current and stratospheric lidar ozone concentration at 25 km as well as the ECC pump speed trend, we show that the observed ECC pump temperature between 2002 and 2007 is too low by –10 K at 25 km. The ECC pump temperature for the period 2002–2007 has been corrected accordingly by 0 K at 0 km and 10 K at 30 km and the bias at 25 km with the stratospheric lidar and MLS have been reduced to -0.5 %.
Review of “Correction of the Observatoire Haute Provence electrochemical concentration cell (ECC) ozonesonde 1991-2023 data record” by Okamoto et al.
Summary and General Comments:
The authors summarize ECC ozonesonde measurements collected at the OHP station beginning in 1991, including a period of anomalously low ECC pump temperatures from January 2001 to July 2007. In the absence of any other changes, erroneously low ECC pump temperatures will cause measured ozone values to be too low. However, the authors were unable to find an explanation for the low pump temperatures, and state that no changes to the ozonesonde preparation were made during January 2001 to July 2007 to cause them.
The ECC pump temperature adjustment and subsequent recalculation of the ozone values are performed using near-coincident OHP lidar stratospheric ozone as a reference. Using the OHP ozone lidar data to adjust the pump temperature and resulting ECC ozone measurements has the unfortunate consequence of losing the independence of the ECC ozone measurements during this period.
I am not aware of similar pump temperature behaviors at any other En-Sci ozonesonde station during this period, so I strongly encourage the authors to expand discussion that rules out potential causes and seek to find an explanation for this anomalous behavior. For example, are the ECC pump motor current and ECC battery voltage recorded for this time period? Was the pump thermistor instead taped to the side of the Styrofoam box instead of the pump block during this period? Also, it was discovered a few years ago that the ozone calculation scripts in Vaisala’s MW41 software had a bug that reported incorrect ECC pump temperatures, causing erroneous ECC ozone measurements. Could a software issue potentially explain this?
I also wonder about the validity of a linear correction to the pump temperature. Have the authors evaluated the corrected ECC ozone measurements other than in the stratosphere and total column? Also, it is not explained how the total column is derived from the ECCs – I presume an above-burst satellite climatology is used.
The authors should consider changing 1991-2023 to 2001-2007 in the title, since those are the only dates where the ECC measurements are adjusted.
Recommendation:
The paper is concise, well-written, and only requires a few minor technical corrections. However, before acceptance I strongly encourage the authors to expand the discussion on the potential origins of the anomalously low ECC pump temperatures from 2001-2007, and the validity of the linear pump temperature correction.
Line-by-Line and Technical Comments: