Category: Ocean and climate news

High winds, flooding and landslides from heavy rains with Typhoon Bopha have caused close to 300 deaths in the southern Philippines. Jason-2 has flown over the typhoon path and has observed it.

This image of Super Typhoon Bopha was taken by the astronaut Kevin Ford from the International Space Station on Sunday Dec. 2, when winds reached up to 135 miles per hour (60m/s). Cedits NASA (source <link http: www.nasa.gov multimedia imagegallery image_feature_2402.html>www.nasa.gov/multimedia/imagegallery/image_feature_2402.html) Altimeters have been designed to observe the sea level variability. Although the probability to fly over such a phenomenon is low, sometimes the satellite happens to observe ocean variability in the case of strong cyclones. In the case of Bopha, Jason-2 overflew the Typhoon twice: on November 28 and December 4.

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Path of Typhoon Bopha with its intensity overlaid on the two passes of Jason-2: pass 99 of cycle 162 which overflew the Typhoon on November 28 with a time difference of 1 hour 40 and pass 12 of cycle 163 on December 4 with a time difference of 2 hours.

The nominal measurements of the altimetry Sea Surface Height in case of extreme low pressure events are impacted by heavy rain and strong wind speed. <link http: www.mdpi.com _blank external-link-new-window>Carrère et al., 2009: "Observing and Studying Etreme Low Pressure Events with Altimetry", have developed specific altimeter and radiometer treatments taking advantage of the dual-frequency capabilities of altimeters in order to recompute Sea Level Anomaly (SLA) during those particular conditions. The satellite hasn't overflown the Typhoon when the winds where the strongest (before hitting the coast), nevertheless, observations could be made along the path and the methodology could be applied. On November 28, although Bopha was classified as a tropcial storm, we observed a sea level elevation on the recomputed SLA of about 30 cm along the track, compared to the normal oceanic variability (see figure below).

	Recomputed Sea Level Anomaly (SLA) in meters as described in Carrère et al., 2009 for pass 99 of cycle 162 of Jason-2 on November 28 when Bopha was classified as a tropical storm.

In the case of the second observation on December 4 (TYPHOON-2), it was not possible to recompute SLA because it was too close to the coast. But we observed recomputed wind speed up to 30m/s (figure below). Note that the direct observation of very low pressure systems by radar altimeters begin to be investigated. Some work has been performed and the results provided here are a first estimation of what can be done. Indeed, they are still affected by errors because we are close to the limit of instruments and models capabilities.

Wind speed in m/s from Quilfen et al., 2006, (Altimeter dual-frequency observations of surface winds, waves and rain rate in tropical cyclone Isabel.) for pass 12 of cycle 163 Jason-2 when the Typhoon is classified as TYPHOON-3 on December 4. Credits CNES/IFREMER/CLS.	<media 13129="" -="" download=""> </media>

Further information:

• Applications: <link http: www.aviso.oceanobs.com en applications atmosphere-wind-and-waves hurricanes.html _blank external-link-new-window>Hurricanes
• Unisys weather Service: <link http: weather.unisys.com hurricane _blank external-link-new-window>weather.unisys.com/hurricane
• Nasa earth observatory: <link http: earthobservatory.nasa.gov naturalhazards _blank external-link-new-window>earthobservatory.nasa.gov/NaturalHazards
• <link http: www.mdpi.com _blank external-link-new-window>Carrère et al., 2009: "Observing and Studying Etreme Low Pressure Events with Altimetry"
• <link http: www.agu.org journals abs external-link-new-window>Quilfen, Y.; Tournadre, J.; Chapron, B. Altimeter dual-frequency observations of surface winds, waves and rain rate in tropical cyclone Isabel. J. Geophys. Res. 2006, 111, C01004.