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Assimilation of Vorcore Balloons

Assimilation of Vorcore Balloons. Andrew Tangborn June 2008. History and Purpose of Lagrangian Balloon Experiments. Observe wind, temperature and pressure along a quasi-Lagrangian path. Can stay aloft for as long as 4 months. Studies of polar vortex and equatorial winds.

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Assimilation of Vorcore Balloons

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  1. Assimilation of Vorcore Balloons Andrew Tangborn June 2008

  2. History and Purpose of Lagrangian Balloon Experiments • Observe wind, temperature and pressure along a quasi-Lagrangian path. • Can stay aloft for as long as 4 months. • Studies of polar vortex and equatorial winds. • Move along constant density surfaces Experiment Dates • 1971-72 Antarctic (Eole) • 1998 Equator • 2001 Arctic • 2002 Arctic • 2005-2006 Antarctic (Vorcore) • 2009 Antarctic (Concordiasi)

  3. Vorcore campaign 2005 • Vorcore is an experiment to study the Antarctic polar vortex from it’s peak to breakup (Sept – Jan) using long lived drifting balloons. • PI – Francois Vial , LMD, Paris. Motivation for Present Study • Can polar vortex winds be improved using a relatively dense network of in situ measurements? • What is the impact of improvements to polar winds on ozone assimilation and forecasts?

  4. Characteristic Balloon Trajectories Balloon 1 Balloon 2 Balloon 27 Green trajectory represents last 7 days Oct 28, 2005 – Feb 1, 2006 Sept 5 – 11, 2005 Sept 6 – Dec 6, 2005

  5. Pressure Levels • 2005-06 experiments at 50 and 70 mb • 1971-72 experiments at 200 mb Example: Balloon 2 from Vorcore campaign. D D D D D D . . . . . . Gradual loss of altitude lifetime of each balloon

  6. Data Processing/superobbing • Observations are superobbed to reduce data density. • Balloon 2 is removed from for use as outside data set. Observations on Sept 15, 2005 3 balloons Observations on Oct 15, 2005 9 balloons

  7. Impact of Assimilation on Stratospheric Winds • Compare stratospheric wind field analyses and forecasts with and without assimilating derived winds from the Vorcore balloons. • What causes the sudden increase in wind forecast errors around Nov 5? • Assimilation of the derived Vorcore winds eliminates this increase in forecast errors.

  8. RMS of O-F and O-A for balloon wind observations. Oct. 6, 2005, start of vortex breakdown Sept 5, 2005

  9. Impact on MODIS Wind O-Fsfor 200<p<300 hPa RMS Difference

  10. Zonal wind fields during vortex break down Nov. 1, 2005 Nov. 11, 2005 Zonal winds show the Antarctic vortex centered close to the pole on Nov. 1. On Nov. 11, the the flow has become very asymmetric, with a zonal wind reversal over Antarctica. This indicates that the vortex breakdown process is underway.

  11. Conclusions and Future Work • The relatively small number of high quality in-situ wind observations that follow the wind fields can provide a substantial improvement to Antarctic wind forecasts once the vortex breakdown has begun. • Future work will include combining the new wind forecasts with ozone assimilation to determine the impact of the balloon assimilation on ozone forecats. • We also plan to assimilate the Lagrangian balloon positions rather than the derived wind product with the goal of further improvements in wind forecast accuracy (in collaboration with Kayo Ide).

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