Rapporteur on Radiosonde Compatibility. (Original Report by John Elms) CIMO ET on Upper Air System Comparisons – Geneva 17-20 March 2003 Agenda Item 4 Rapporteur on Radiosonde Compatibility. (Original Report by John Elms) Tim Oakley + John Nash Met Office, Exeter, UK

GLOBAL RADIOSONDE NETWORK. At the beginning of 2002 there were 824 upper-air stations world-wide with at least one sounding reported on the GTS in the year.

Testing nearest to adequate Testing out of date or inadequate RF95

Some monitoring results Vaisala measurements are mostly consistent to ± 20m at 100 hPa ( equivalent to about ± 0.3 K in mean layer temperature from the surface to 100 hPa. Vaisala RS80 measurements in the USA show discrepancies relative to the rest of the world, which become pronounced above 100 hPa.

Differences between VIZ/Sippican measurements The spread of VIZ B temperature measurements between 100 and 30 hPa is similar to Vaisala as processed in the US. No adjustment for solar heating has been applied to measurements issued on the GTS The MkII and VIZ B measurements were clearly not equivalent in operation, with the MKII reading higher by about 40m, equivalent to a mean layer temperature difference of more than 1 K between 100 and 30 hPa.

New generation radiosondes in the US New radiosondes with new sensors are expected to be introduced soon to the US network Expert team is asked to consider what should be done to ensure that the use of radiosondes should be compatible on a global scale and not limited by national software limitations, or changes to sensor design, whether announced or unannounced by manufacturers.

Russian monitoring The Russian systems depend on correct functioning of the secondary radar, so there are some stations where this is not functioning correctly and large systematic biases are found at 100 hPa. A new secondary radar has been designed. The expert team is requested to consider a test to demonstrate that this new radar is capable of replacing the current tracking systems without degradation to measurement quality.

Results from Asia The following four slides summarise monitoring for China, India and Japan When performance is examined in detail some questions remain for all the systems. How can the WMO comparison programme aid resolution of problems in India, new system development in China and explanation of detailed monitoring anomalies in Japan?

Chinese Radiation Correction Scheme changed in 2000

New radiosonde at Beijing from 2002 At what stage should the new Chinese radiosonde be evaluated?

Anomalies in Japanese monitoring In Japan the systematic biases against the ECMWF first guess vary during the year, but this is not linked to the cycle of solar elevation in daytime measurements. In addition the systematic bias between 30 and 100 hPa drifted by about 40 m between 1998 and 2001. Was this a result of instability in the model fields or a problem with the radiosonde? How should issues of this type be addressed in future? Should some insitu test be conducted in Japan?