Transport of mesospheric H<sub>2</sub>O during and after the stratospheric sudden warming of January 2010: observation and simulation

Abstract

Abstract. The transportable ground based microwave radiometer MIAWARA-C monitored the upper stratospheric and lower mesospheric (USLM) water vapor distribution over Sodankylä, Finland (67.4 • N, 26.6 • E) from January to June 2010. At the end of January, approximately 2 weeks after MIAWARA-C's start of operation in Finland, a stratospheric sudden warming (SSW) disturbed the circulation of the middle atmosphere. Shortly after the onset of the SSW water vapor rapidly increased at pressures between 1 and 0.01 hPa. Backward trajectory calculations show that this strong increase is due to the breakdown of the polar vortex and meridional advection of subtropical air to the Arctic USLM region. In addition, mesospheric upwelling in the course of the SSW led to an increase in observed water vapor between 0.1 and 0.03 hPa.After the SSW MIAWARA-C observed a decrease in mesospheric water vapor volume mixing ratio (VMR) due to the subsidence of H 2 O poor air masses in the polar region. Backward trajectory analysis and the zonal mean water vapor distribution from the Microwave Limb Sounder on the Aura satellite (Aura/MLS) indicate the occurrence of two regimes of circulation from 50 • N to the North Pole:(1) regime of enhanced meridional mixing throughout February and (2) regime of an eastward circulation in the USLM region reestablished between early March and the equinox.

Observations of middle atmospheric H<sub>2</sub>O and O<sub>3</sub> during the 2010 major sudden stratospheric warming by a network of microwave radiometers

“…This subsidence was also observed in the stratosphere at around 3 hPa just before the SSW. A detailed study on this particular observation of mesospheric subsidence can be found in Straub et al (2012). On 20 February, relatively low stratospheric H 2 O was observed between 10 and 3 hPa for approximately 5 days, coinciding with the shift of the vortex away from Sodankylä.…”

“…Middle atmospheric water vapor was also used as tracer for calculating the descent rate of polar mesospheric air during winter (e.g. Siskind et al, 2007;Orsolini et al, 2010;Lahoz et al, 2011;Straub et al, 2012). Manney et al (2008a and2008b) and Orsolini et al (2010) showed that after the major SSWs of 2004, 2006 and 2009, the stratopause and the eastward wind jet reformed at approximately 75 km altitude.…”

Assessing the ability to derive rates of polar middle-atmospheric descent using trace gas measurements from remote sensors

“…2 (2011) and Straub et al (2012), for the general shape of the trajectory and in that the parcels do not originate above approximately 100 km. The parcels at 80 • N arrive from higher altitudes due to a stronger vertical component of the circulation compared to 67 • N. Conversely, the horizontal component of the circulation is stronger at 67 • N and the parcels arriving there originate from lower latitudes compared to those arriving at 80 • N. The magnitude of the TEM wind is larger for the higher altitudes, as is also shown in Smith et al (2011), and the air parcels that arrive above 66 km altitude originate in the summer hemisphere.…”

“…It is important to note that an average over altitude can mask the higher descent rates that are found in the mesosphere. For example, Straub et al (2012) show a descent rate of −325 m day −1 from averaged modelled wind profiles, between 0.6 (∼ 52 km) and 0.06 hPa (∼ 68 km), whereas the individual wind profiles often show descent rates larger than −1000 m day −1 at 0.06 hPa.…”

“…Water vapour (H 2 O) is used to infer vertical motion (e.g. Straub et al, 2012) but a varying vertical gradient limits the altitudes at which it can be used (Lee et al, 2011). Nassar et al (2005) used nitrous oxide (N 2 O), CH 4 , and H 2 O to infer rates of vertical motion in the upper stratosphere and lower mesosphere, and Bailey et al (2014) used a combination of NO, H 2 O, and CH 4 to derive profiles of vertical motion in the middle atmosphere.…”