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Homogenization of water vapour data from RS-80 and RS-90 radiosondes

Homogenization of water vapour data from RS-80 and RS-90 radiosondes . Barbara Brzóska, Adam Jaczewski and Zenobia Litynska Institute of Meteorology and Water Management Centre of Aerology. Humidity correction methods for RS-80 radiosonde.

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Homogenization of water vapour data from RS-80 and RS-90 radiosondes

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  1. Homogenization of water vapour data from RS-80 and RS-90 radiosondes Barbara Brzóska, Adam Jaczewski and Zenobia Litynska Institute of Meteorology and Water Management Centre of Aerology

  2. Humidity correction methods for RS-80 radiosonde For correction of RS-80's humidity series, five methods have been used, available at literature. The correction equations are results of comparison of measurements from different sensors or of laboratory measurements. Sources of correction factors used: • Simultaneous RH measurements from RS80-A and frostpoint hygrometers at NOAA, Boulder (cooperation with Vaisala): SPARC Assessment of Upper Tropospheric and Stratospheric Water Vapour, 2000: (SPARC Boulder) Miloshevich, L. M. et al., 2000: “Characterization and correction of relative humidity measurements from Vaisala RS80-A radiosondes at cold temperatures”: (Colorado)

  3. Humidity correction methods for RS-80 radiosonde (cont’d) • Laboratory measurements conducted at Vaisala: SPARC Assessment of Upper Tropospheric and Stratospheric Water Vapour, 2000: (SPARC Vaisala) and (SPARC Vaisala2) • Data collected during TOGA COARE experiment (1992/1993): Wang et al., 2002: “Corrections of humidity measurement errors from the Vaisala RS80 radiosonde - Application to TOGA COARE Data” (Colorado2)

  4. The dependence of most of correction factors on temperature is similar. Only one correction factor depend also on actual humidity (Colorado2), and also values of that correction factor are smallest for that method, at very low temperatures.

  5. Humidity series for Legionowo 12 UT, 1992-2003 uncorrected corrected (Sparc Vaisala) corrected (Colorado) corrected (Sparc Boulder) corrected (Sparc Vaisala2) corrected (Colorado2) Humidity series show that all correction methods overestimate humidity values at higher heights. But, it seems that the Colorado2 method is best one.

  6. Humidity series for Legionowo 00 UT, 1993-2003 uncorrected corrected (Sparc Vaisala) corrected (Colorado) corrected (Sparc Boulder) corrected (Sparc Vaisala2) corrected (Colorado2) Humidity series show that all correction methods overestimate humidity values at higher heights. But, it seems that the Colorado2 method is best one.

  7. 12 UT 00 UT RS-80 RS-90 uncorrected uncorrected corrected (Colorado2) corrected (Colorado2) Colorado2 correction ‘repairs’ smaller values of humidity, detected by RS-80 radiosonde in comparison to RS-90.

  8. How to check if that correction ‘works’ well? We have looked at the time series at given heights, the humidity tendencies, and have compared them with temperature tendencies.

  9. temperature humidity uncorrected humidity corrected (Colorado2)

  10. To the height of 3 km all tendencies are positive. At the height of 3.5 km, temperature tendency begin to be negative. At height about 5 km, the humidity tendencies of corrected series begin to be negative, what is inconsistent with the negative temperature tendencies.

  11. temperature humidity uncorrected humidity corrected (Colorado2)

  12. Humidity tendency for uncorrected series increases with height, and, as the result, at the layer 9.5-10.5 km, tendency of corrected series appears positive. It is because of shifting of plots to higher values. At the height of 11 km is negative again.

  13. Conclusions • Colorado2 correction seems to be the best one for our series correction purposes • To the heights of 3.5 km humidity tendencies for corrected and uncorrected series are comparable • Humidity tendencies for uncorrected series are positive but • For the heights above 5 km, the tendencies of corrected series begin to be negative, what is inconsistent with the negative temperature tendencies • It seems, that the corrections for these heights with very low temperatures, are not reliable • Humidity measurements from RS-80 radiosonde show smaller amplitudes for both, corrected and uncorrected series, than for the RS-90, what can be clearly seen at the heights above 9.5 km

  14. Conclusions (cont’d) • At the first view, the corrections shift only the humidity values to bigger ones, but do not correct the amplitudes • The question is if it is enough, even as the first step of correction? • Another question is, what is the reason for the humidity sensors behavior: greater RS-90’s sensitivity and/or sensor heating mechanism? • Is it possible at all, to simulate the greater RS-90’s sensitivity to RS-80 humidity sensor? • It seems that the homogenization needs other correction methods, taking into account ‘amplitude correction’, especially in the stratosphere • It is still unclear, what are the ‘reliable’ humidity tendencies in the stratosphere?

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