Abstract

During winter 2015/2016 the Arctic stratosphere was characterized by extraordinarily low temperatures in connection with the occurrence of extensive polar stratospheric clouds. From mid of December 2015 until mid of March 2016 the German research aircraft HALO (High Altitude and Long–Range Research Aircraft) was deployed to probe the lowermost stratosphere in the Arctic region within the POLSTRACC (Polar Stratosphere in a Changing Climate) mission. More than twenty flights have been conducted out of Kiruna/Sweden and Oberpfaffenhofen/Germany, covering the whole winter period. Besides total reactive nitrogen (NOy), observations of nitrous oxide, nitric acid, ozone and water were used for this study. Total reactive nitrogen and its partitioning between gas- and particle phase are key parameters for understanding processes controlling the ozone budget in the polar winter stratosphere. The redistribution of total reactive nitrogen was evaluated by using tracer–tracer correlations. In January air masses with extensive nitrification were encountered at altitudes between 12 and 15 km. The excess NOy amounted up to about 6 ppb. During several flights, along with gas–phase nitrification, indications for extensive occurrence of nitric acid containing particles at flight altitude were found. These observations support the assumption of sedimentation and subsequent evaporation of nitric acid containing particles leading to redistribution of total reactive nitrogen. Remnants of nitrified air masses have been observed until mid of March. Between end of February and mid of March also de-nitrified air masses have been observed in connection with high potential temperatures. Using tracer–tracer correlations, missing total reactive nitrogen was estimated to amount up to 6 ppb. This indicates the downward transport of air masses that have been denitrified during the earlier winter phase. Observations within POLSTRACC, at the bottom of the vortex, reflect heterogeneous processes from the overlying Arctic winter stratosphere. The comparison of the observations with CLaMS model simulations confirm and complete the picture arising from the present measurements. The simulations confirm, that the ensemble of all observations is representative for the vortex–wide vertical NOy-redistribution.

Highlights

  • Since the mid–1980s, observations in the Antarctic and later in the Arctic region have revealed unprecedented ozone loss in the polar stratosphere with beginning of the spring season (e.g. Farman et al, 1985; Müller et al, 1996; Waibel et al, 1999; Sinnhuber et al, 2000)

  • 30 nitrification, indications for extensive occurrence of nitric acid containing particles at flight altitude were found. These observations support the assumption of sedimentation and subsequent evaporation of nitric acid containing particles leading to redistribution of total reactive nitrogen

  • During the course of the extremely cold winter 2015/2016 aircraft–based measurements with the German research aircraft High Altitude and Long Range Research Aircraft (HALO) have been performed in the lowermost stratosphere of the Arctic region within the POLSTRACC mission

Read more

Summary

20 Abstract

During winter 2015/2016 the Arctic stratosphere was characterized by extraordinarily low temperatures in connection with the occurrence of extensive polar stratospheric clouds. Besides total reactive nitrogen (NOy), observations of nitrous oxide, nitric acid, ozone and water were used for this study. Total reactive nitrogen and its partitioning between gas- and particle phase are key parameters for understanding processes controlling the ozone budget in the polar winter stratosphere. 30 nitrification, indications for extensive occurrence of nitric acid containing particles at flight altitude were found. These observations support the assumption of sedimentation and subsequent evaporation of nitric acid containing particles leading to redistribution of total reactive nitrogen. Between end of February and mid of March de–nitrified air masses have been observed in connection with high potential temperatures. The simulations confirm, that the ensemble of all observations is representative for the vortex–wide vertical NOy–redistribution

Introduction
Instruments and Methods
Nitrous oxide
Nitric acid
Tracer–tracer correlations
Early winter phase
Mid–Winter Phase
Observations of Particulate Nitrate
Findings
680 5 Summary
Full Text
Paper version not known

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call