Impact of the Assimilation of CHMAP Refractivity Profile on Environment Canada Global Forecasts.

1. Impact of the Assimilation of CHMAP Refractivity Profile on Environment Canada Global Forecasts. Aparicio, J. M., and G. Deblonde, 2008: Mon. Wea. Rev., 136, 257–275.

2. Introduction O: Observation F: Forecast fields A: Analysis fields (O-F) VS. (O-A) The ratio occultation technique: 利用低軌衛星(LEO)接收到GPS資料，來決定射線的彎角(Bending angle)，再計算出大氣折射指數的分佈。

3. 水汽分壓 乾空氣分壓 Methodology • Assimilation system The assimilation system：EC (Environment Canada) system with 3DVAR. The forecasting system: GEM (EC’s Global Environmental Multiscale model). • Ratio occultation • Formulation of refractivity

4. The observation operator: 1. Array (h,Nobs) 2. We can get those data (Ps, T, and q and the Height) form each grid of model level and get the p: 3. To account for the presence of vertical correlation : The world Geodetic System 1984 World Geodetic Model Get the (h, Nmodel ) at each model level The distance of GPSRO data < 1Km O: Observation F: Forecast fields E: Assumed observation error

5. Observation error and quality control • Description of the experiments FRAC= vertical weighting

6. Evaluation of forecast performance • GPSRO evaluation of 6-h forecasts. Ref: reference cycle GPSRO: assimilation GPSRO data

7. AMSU evaluation of 6 h forecasts T↑ T↑ The brightness temperature of AMSU-A channels 9 and 10 (weighting function) The statistics of (O-F)/F for AMSU observations in the GPS experiment vs. the reference

8. Radiosonde evaluation of 6 h forecasts The globally averaged result for the skill of the 6-h forecast of temperature is a small but positive improvement about 0.5%–1% in both summer and winter experiments. The radiosonde (RS) temperatures at the mandatory pressure levels, the ratio of STD in the experiment where GPSRO are assimilated vs. the reference.

9. RS temperature observations in the GPS experiment vs. the reference. RS dewpoint depression observations, in the GPS experiment vs. the reference.

10. Longer-range forecast Anomaly correlation (each experiment’s forecasts against its own analysis) of the temperature field, as a function of the forecast range, for the Southern Hemisphere in the winter experiment. The reference experiment is represented with the dark line (WinterRef), whereas the GPSRO experiment is the light gray line (WinterGPS).

11. Anomaly correlation (each experiment’s forecasts against its own analysis) of the temperature field, as a function of the forecast range, for the Southern Hemisphere in the summer experiment. The reference experiment is represented with the dark line (SummerRef), whereas the GPSRO experiment is the light gray line (SummerGPS).

12. Discussion and Conclusions GPSRO: 改善南半球和北極區平流層的預報約30%。 AMSU: 改善南半球平流層預報約30%(winter case)，但是其他地區改善有限。 Radiosonde: 溫度大致有改善，但是濕度改善效果不佳。 相同: 1. 赤道低對流層地區改善不明顯，這是因為赤道地區水汽集中，應利用不 同的QC方式。 2. 南半球平流層的預報都是增加，表示GPSRO資料可以補足此層資料 不足的情況。 Longer-range forecast: 加入GPSRO Data後夏天個案和冬天個案的預報分數都有 明顯改善(南半球)，越長時間預報改善越明顯。

13. μr Bouguer’s formula a θ ro rp Abel transform and Abel inversion α is bending angle μ is refractivity index θ is the zenithal angle a is the impact parameter x is the μr and μ(rp) rp=a

14. Le Ĺe α μ P,T,E Assimilation of refractivity data a. Forward operator (Smith and Weintraub 1953) P is the total atmospheric pressure T is the atmospheric temperature Pv is the partial pressure of water vapor Note: N is directly interpolated form model levels to the local of observations by assuming an exponential behavior of μ