RADCOR for US Sondes Dr. Bradley Ballish NCEP/NCO/PMB 10 March 2011

2 Outline Introduction Other temperature data types Aircraft and radiosonde temperature biases Comparison of sonde temperature with GPSRO data Model climate impact from warm aircraft temperatures Suggestions

3 Introduction Radiosonde temperatures are both important as input to analyses at NWP centers and for verification of forecasts Radiosonde temperatures are also important to compare with satellite radiances Radiosonde temperatures are also important in climate studies to show trends in the Earth’s climatic temperatures Since these temperatures are affected by solar and infrared radiation, radiation corrections (RADCOR) are applied to the temperatures, which is a difficult problem Since NWP centers use temperatures from other data types, that also have biases that are difficult to assess, scientists need as much information as possible to optimally use these data

4 Other Temperature Data Types Aircraft temperature measurements are quite different than those of sondes and are discussed in the next two slides Various types of satellite radiance data are used to estimate atmospheric temperatures and require complex modeling, statistics and comparison with NWP models for bias corrections New GPS Radio Occultation (GPSRO) temperature data are used to produce accurate temperature profiles with far less complexity than satellite radiances, but their data coverage is not currently that good and there are problems related to moisture in the lower troposphere

5 Aircraft and Radiosonde Temperature Biases Ballish and Kumar( BAMS Nov 2008) showed that aircraft temperatures average warmer than those of radiosondes, with biases depending on aircraft types –The next slide shows these bias differences are large in the US area around jet-level in November 2008, which is probably similar now –NCEP is planning to make aircraft and temperature bias corrections since these biases differences may be affecting forecasts

6 Aircraft vs Sonde GSI Draws to Temps between mb # Aircraft >> # Sondes, thus warm aircraft data overwhelms the GSI/GFS system Aircraft Tdiff (obs-ges) Aircraft Tdiff (obs-anl)SOND Tdiff (obs-anl) SOND Tdiff (obs-ges) Temperature differences in tenths of a degree C

7 Comparison of Sonde Temperatures with GPSRO Data NESDIS’s Bomin Sun and Anthony Reale (AMS annual meeting, January 2011) show that the new US sondes (US Sippican Mark IIA) temperatures are colder than collocated COSMIC GPSRO data, see the following two slides The NWS upper air group has started flying some sondes with improved use of balloon ascent rates in the radiation correction which will reduce the cold bias of these US sondes

8 Solar angle categories This sonde type shows a much colder bias than other sonde types, see next slide

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10 Model Climate Impact from Warm Aircraft Temperatures The next slide courtesy of Dick Dee of ECMWF shows the increase in the number of aircraft reports versus time at ECMWF The temperature bias of the ECMWF analysis and background seem to be affected by the large increase in the number of aircraft temperatures coupled with their warm biases along with other factors This is one example of where NWP models can be affected by biased observations, which complicates bias corrections for other temperature types as well as altering model climate trends

11 Model Climate Bias Impact From Warm Aircraft Temperatures Global-mean departures of analysis (blue) and background (red) from radiosonde temperatures (K) at 200hPa, and number of obs/day (x10 -4, green) Global-mean departures of analysis (blue) and background (red) from aircraft temperatures (K) at 200hPa, and number of obs/day (x10 -4, green)

12 Suggestions The new RRS software appears to have an improved RADCOR that likely reduces the bias differences with GPSRO data as shown on slide 8 If we can show by tables or even better by graphics similar to slide 8 on how the old and new RADCOR of US sondes varies with pressure for select solar angles, and possible balloon ascent rates, this would be very useful for NWP and climate studies It would be useful to have a website showing dates when US sites switch to the new software