Extremely cold cloud top temperatures

November 22nd, 2008 |
MTSAT-1R IR imagesMTSAT-1R 10.8 µm IR images

Hat-tip to blog reader Boris Konon for sending us this in an email:

Noted a large area of extremely cold cloud tops on a thunderstorm complex over northern Australia 17-23z 11/22.  So cold it went off our IR color table scale we use here at WSI for MTSAT!

MTSAT-1R 10.8 µm IR images (above) did indeed show an area of convection that exhibited an unusually large canopy of cloud top temperatures colder than -80º C (light purple color enhancement) on 22 November 2008. The coldest IR brightness temperature seen with this particular thunderstorm complex was 174.78º K (-98.37º C), just off the northern coast of Australia at 20:30 UTC.

A comparison of MTSAT-1R visible and IR images at 20:30 UTC (below) showed that there were a number of overshooting tops within the area of cold cloud top temperatures, as the convective system was beginning to move offshore across the Gulf of Carpenteria. This squall line was responsible for producing 25-50 mm of rainfall (BOM rainfall analysis) and wind gusts to 96 km/h (52 knots) at Bradshaw and 68 km/h (37 knots) at Gove (thanks to Jeff Callaghan, Australian Bureau of Meteorlogy for that information!).

MTSAT-1R visible and IR images

MTSAT-1R visible and IR images

A closer view using 1-km resolution NOAA-15 10.8 µm IR data (below) revealed a bit more detail in the cloud top temperature structure around 19:56 UTC. Unfortunately, the image was marred by a large number of “noise” pixels — but the coldest reliable cloud top temperature seen on this AVHRR IR image was 170.2 K (-102.95º C), located within the farthest southeast cold pixel cluster (IR brightness temperatures colder than -100º C are enhanced in the yellow to brown colors at the end of the scale). If this cloud top temperature is accurate, it rivals what is believed to be the coldest cloud top temperature value noted in the literature: -102º C in Ebert and Holland, 1992.

NOAA-15 AVHRR 10.8 µm IR image

NOAA-15 AVHRR 10.8 µm IR image

Rawinsonde data from Darwin Airport at 00:00 UTC on 23 November 2008 (below) indicates that the tropopause was at a very high altitude (around 100 hPa, approximately 16.0 km). Such a high and cold tropopause is not unusal  in the tropics — especially in that particular region, as studies have shown that the average tropopause level is quite high and quite cold over the western tropical Pacific Ocean.

Darwin, Australia rawinsonde report

Darwin, Australia rawinsonde report