Interhemispheric Coupling Study by Observations and Modelling (ICSOM)

Observation Strategy

Plan of observations and simulations

The first research target of ICSOM is the interhemispheric coupling initiated from a sudden stratospheric warming (SSW) in the Arctic. Statistics indicate that SSWs, extreme events in the stratosphere, occur in winter twice every three years in the Arctic on average. Roughly speaking, the prediction of an SSW is possible five days before the onset. Observations will be necessary over at least ten successive days starting three days before the SSW onset, which allows for the time lag of the Antarctic atmospheric response to the Arctic SSW. Even in the case of no SSW during the observation window, simultaneous observations will still be beneficial: If another extreme event of vortex intensification (VI) is predicted, we will perform coordinated observations in a similar way. If normal conditions of the polar vortex are expected, we will perform continuous observations over about seven days to obtain reference data which can be compared with future successful SSW observations. Simultaneous observations for the troposphere and lower stratosphere in addition to mesospheric observations will also be important so as to distinguish the modulation of gravity wave characteristics by the SSW from that originating from the gravity wave source variation. Measurements and analysis of the state of potential modulators of gravity wave activity, such as planetary waves and tides, Quasi-Biennial Oscillation (QBO) and Semi-Annual Oscillation (SAO) will also be made.

Complementary observations utilizing MF and meteor radars, lidars, imagers, interferometers and radiosondes will also be performed. High resolution satellite observations covering the whole stratosphere are included for the analysis as well.

Simulation of high-resolution general circulation models covering the MST region will be made using super computers. Initial conditions for the model simulation will be made based on global analysis data covering the mesosphere such as MERRA. Regional models or models having a stretched grid configuration will also be used for simulations with finer resolutions. Mechanistic model studies will also be made to deepen our understanding of inherent mechanisms suggested by these observation and high-resolution model studies.

The announcement of observation start time according to the SSW onset prediction

The PANSY radar group will look at following prediction sites:

Two types of announcements will be sent.

A daily report on northern hemisphere stratospheric condition which will be sent to members who wish to receive: This report will be sent by Yoshihiro Tomikawa at NIPR (PANSY group, every day. Please let us (Kaoru Sato and Yoshihiro Tomikawa) know if you want to receive the daily reports.

Announcements regarding the observation start time which will be sent to all members: The first one is to inform an estimated observation start time when the SSW onset is predicted. This announcement will be sent soon after the SSW onset prediction is made. The second one is to inform the observation start time and end time. This announcement will be sent one day before the predicted SSW onset date. These announcements will be sent by Kaoru Sato at U Tokyo (PANSY group,