Cloud ceiling analysis in the RTMA

1. Cloud ceiling analysis in the RTMA Yanqiu Zhu1, Geoff DiMego2, John Derber2, Manuel Pondeca1,Jim Purser1,Geoffrey Manikin2 1 IMSG and NOAA/NCEP/EMC, 2 NOAA/NCEP/EMC Camp Springs, Maryland, USA

2. Real-Time Mesoscale Analysis (RTMA) • Gridded Statistical Interpolation (GSI) 2DVAR analysis • Current analysis variables: surface pressure, 10m wind, 2m temperature and moisture, wind gust, visibility • Background fields generated by downscaling of RAP 1h forecasts • Terrain-following anisotropic background error covariance

3. New control variable: Cloud ceiling -- the lowest cloud base height where the total cloud cover exceeds 50% • Possible analysis approaches: • 1: analyze cloud ceiling directly as a 2D variable • 2: diagnose the ceiling field from the analyses of total cloud cover and lowest cloud base height The cloud ceiling is created by masking out those points in the lowest cloud base height field where the analyzed total cloud cover is less than 50%

4. Cloud observations used for the analyses of total cloud cover and lowest cloud base height • Direct Obs: • total cloud cover (TOCC) • height of base of lowest cloud seen (HBLCS) and cloud ceiling (VSSO) • Quasi-obs derived from • cloud amount (CLAM) • Ftotal = 1-(1-f1)(1-f2)…(1-fn) where fi is different layer cloud amount • cloud base height (HOCB) • present weather (PRWE) • Data Types: • 180 SFCSHP – Surface marine • 181 ADPSFC – Surface land (Synoptic, METAR) with reported station pressure • 183 ADPSFC, SFCSHP – with missing station pressure • 187 ADPSFC – Surface land (METAR) with missing station pressure • GOES cloud retrieval product

5. Data quality control • Standard duplicate and missing data check and gross check • Different qcmark indicators are specified for direct obs and quasi_obs • Quality control is also performed using the combination of all of the data info for cloud amount and cloud height, excluding obs with conflicting info (qcmark=15) An example: Total cloud cover obs number at 00Z March 9, 2012

6. Total cloud cover data : 00Z March 9, 2012 IQC OBS

7. Current Status Total cloud cover analysis: • codes are ready for a month-long run for the preparation of fine-tuning Lowest cloud base height (lcbas) analysis: • The variable lcbas is tested as the analysis variable • log10(lcbas) is tested as the analysis variable • The effect of variable correlation length is examined

8. Total Cloud Cover

9. Lowest Cloud Base Height CV(LOGlcbas)

10. Variable Correlation Length (Hayden and Purser, 1995)

11. Analysis Increment of Lowest Cloud Base Height Analysis variable: lcbas Convergence of minimization is slightly better with log10(lcbas) Analysis incr. fields are very similar Analysis variable: log10(lcbas)

12. Cloud Ceiling Analysis First guess Analysis Analysis variable: Log10(lcbas), Roption=.true.

13. Conclusions and future work • The total cloud cover and the lowest cloud base height are the latest two new analysis variables tested in the RTMA in an effort to provide cloud ceiling analysis along with visibility analysis. • Investigation was performed on the choice of the analysis variable for the lowest cloud base height, and the impact of the variable correlation length was also examined. • A month-long run will be conducted to tune the parameters for the analyses, such as the terrain tied features and land/water interface. • Consistency between the total cloud amount and the lowest cloud base height will be examined.

14. Additional slide

15. Lowest Cloud Base Height CV(lcbas)