(LDS3) Effects of geomagnetic storms in the lower thermosphere and mesosphere (Final Report)

Convener:
Larisa P. Goncharenko (lpg@haystack.mit.edu)

2004 Monday 28 June 0400-0600 PM

The workshop was intended as opportunity to review recent progress and outline future efforts in our understanding of effects of geomagnetic storms in the lower thermosphere and mesosphere. The workshop concentrated on changes in neutral winds, temperature and composition below ~150 km.

Speakers and topics:

• J. Emmert, Storm-induced disturbance winds in the lower thermosphere: Recent experimental results and future challenges
• T. Fuller-Rowell, What do physical models predict for storm-time changes in the dynamics of the lower thermosphere
• G. Lu et al., The Global Ionospheric and Magnetospheric Response to the October 2003 Geomagnetic Storm: Observations and Initial TIME-GCM Results (presented by M. Hagan)
• R. Niciejewsky, Neutral wind measurements from orbit of the MLT altitude range during recent geomag- netic storms
• Q. Wu, TIDI neutral wind results during recent storm events
• L. Goncharenko, Studies of storm-time variations in lower thermosphere dynamics with Millstone Hill IS radar
• L. Paxton, Storm time dynamics from GUVI studies
• M. Ruohoniemi, Mesospheric winds from SuperDARN radar

The presented work reveals general agreement between predicted and observed storm-related perturbations. The current understanding of the processes can be summarized as follows:

• Storm effects penetrate down to at least 100 km at all latitudes.
• A major source of mid and high latitude disturbance wind is expanded/enhanced ionospheric convection. It drives:
  • Zonal wind - eastward in the dawn sector, westward in the dusk sector
  • Meridional wind - equatorward in the dawn sector, poleward in the dusk sector (due to Pedersen effect and ion drag)
• Direction of meridional wind depends on superposition of many forces (pressure gradients, ion drag, Coriolis) and can be highly variable
• Average disturbance winds maximize near 130-150 km, and diminish sharply below 120 km.
• During very large storms, wind magnitudes in the lower thermosphere at mid-latitudes can increase by as much as 700 m/s.
• Response / saturation times are 0-9 / 12-24 hours, and do not change much with height above 110-120 km.

Special attention at the workshop was given to October-November 2003 Superstorms, with following highlights:

• TIDI detected ~50 m/s eastward disturbance wind at 90-110 km at southern high latitudes and eastward wind shift from post-noon to pre-noon at low latitudes
• GUVI observed deep depletions in O/N2 penetrating to 0-15 deg lat with areas of increase in O/N2
• Millstone Hill ISR observed increase in E-region ion temperature up to 1000-1300 K (factor of 2-3) and increase in electron density up to 2.5-5 1011 m-3 (> factor of 5)
• TIMEGCM (G. Lu, M. Hagan) and TIMEGCM/ASPEN (G. Crowley) model runs have been generated.

The workshop participants identified several future challenges:

• To collect more data, especially in the night-time lower thermosphere, which is not provided by current experimental techniques
• To verify data reduction, assumptions and techniques for cases of major storms
• To separate storm-related disturbances from day-to-day variability (in both observations and models)

Finally, workshop included discussion of types of data available currently and in the future. It was noted that data provided by the instruments on the TIMED satellite have an important role for our understanding of storm-related changes in the MLT region. Among ground-based instruments, observations from the AMISR system and mesospheric winds from SuperDARN radars present a new and exciting data resource.