Jae-Jin Kim 1 , Do-Yong Kim 1 , Bok- Haeng Heo 2 , and Jae- Kwang Won 2

1. TECO 2012, Brussels Belgium Assessment of Environmental Impact for AWS Observation Data Using a Computational Fluid Dynamics Model Jae-Jin Kim1, Do-Yong Kim1, Bok-Haeng Heo2, and Jae-Kwang Won2 1Pukyong National University 2Korean Meteorological Administration

2. Background ▪ Korean Meteorological Administration (KMA) enacted a law on ‘Weather Observation Standardization (WOS)’ in 2006. ▪ Currently, conducting WOS project for 26 observational organs& 3,469 observational facilities. ▪ For scientific/objective evaluation & management, KMA conducted a planning project on ‘Weather Observational Environment Simulator (WOES)’ in 2010. ▪ This study has been performed from 2011, following up the WOES project.

3. ▪ Evaluation for 14 AWSs/ASOSs in 2011 Kangneong ASOS 105 Kangnam AWS 400 N. Kangneong ASOS 104 Yangcheon AWS 405 Pyoungteak AWS 551 Seogu AWS 846 Deagu ASOS 143 GochanggunASOS 251 GochangASOS 174 Juam ASOS 256 Dongreagu AWS 940 Jeju ASOS 184 Suncheon ASOS 174

4. ▪ 15 ASOSs in 2012 - focusing on wind and direct solar radiation urban Chuncheon ASOS Seoul ASOS Icheon ASOS rural Deakwanryoung ASOS standard Deajeon ASOS Chupungryoung ASOS Uljin ASOS Gumi ASOS Jeonju ASOS Namwon ASOS Ulsan ASOS Busan ASOS Kwangju ASOS Boseong AWS Gosan ASOS

5. Meteorological Model • urban flow/dispersion - extremely complex - highly nonlinear • resolution • terrain following, sigma - building (obstacle) shape • 3D, nonhydrostatic, • nonrotating, Boussinesq • k-eturbulence closure • sheme Computational Fluid Dynamics (CFD) model

6. ▪ Target Areas 1) Kangnam AWS – located in a highly congested area (urban) 2) Gochang ASOS – transferred on May 15, 2007 – conducted as a standard observatory 3) Seoul ASOS – class 1 for surface wind, class 4 for direct radiation

7. ▪ 16 different inflow directions for AWSs & ASOSs ▪ wind data at AWS/ASOS are compared with inflow S NW NNE NNW WSW WNW NE ENE N W E SSE SW SE SSW ESE AWS

8. Results and Discussion ▪ Kangnam AWS 4 Higher than AWS AWS ▪ located in a highly congested area ▪ building complexes in the north, east, and west directions ▪ park in the south direction

9. ▪ Inflow vs AWS the same as inflow [wind speed] [wind direction] the ESE (112.5°) and NW (315°) cases

10. ▪ wind speed ratio to inflow for east-south-east (112.5°) - larger decrease in wind speed but no change in wind direction acceleration deceleration inflow ▪ flow acceleration in the upwind region due to ‘channeling effect’ ▪ flow deceleration in the downwind region due to ‘building drag’

11. ▪ wind vector for north-west (315°) - largest decrease in wind speed and large change in wind direction (m) inflow

12. ▪ Reproducing AWS wind data using a WRF-CFD model [period: Apr. 03 – Apr. 09, 2008] AWS WRF WRF-CFD wind direction wind speed RMSE ▪ WRF = 3.11 m s-1 ▪ WRF-CFD = 1.35 m s-1 (43%) time (hr) ▪ wind direction – very strong dependency on WRF ▪ wind speed – more realistic reproducing of AWS data than WRF

13. ▪ Gochang ASOS – a standard observatory (2007. 05.) 4 4 before transfer • conducted to May 14, 2007 • apartment complex (12 stories) in the • north and northeast, small buildings in • the west • low mountain from south to north in the • east after transfer • conducted from May 15, 2007 • no higher building around • ASOS built in flat terrain and • higher than around

14. ▪ Inflow vs AWS [wind speed] [wind direction] before after

15. ② 고창군 ASOS(ASOS 251) → 고창 ASOS(ASOS 172) ▪ wind vector for north (360°) before transfer - larger decrease in wind speed and no change in wind direction inflow (m) ASOS

16. ▪ wind speed ratio for south (180°) after transfer - no change in wind direction but ~25 % decrease in wind speed (%) inflow ▪ ASOS in the deceleration zone induced by far upwind buildings ▪ mostly (96%) equivalent to inflow

17. ▪ wind speed ratio averaged for 16 after before ▪ well representing background wind after transfer ▪ worthy of a standard observatory (surface wind)

18. ▪ Seoul ASOS 4 ASOS ▪ ‘class 1 & 4’ for wind & DR from a survey using HemiView & NAOBS data ▪ no higher building than the observation filed except for one building in the northwest (5 m) and an observatory building (5 m) ▪ open from southeast to northwest  satisfying the obstacle restriction of the ‘class 1’ standard

19. ▪ Inflow vs AWS [wind speed] [wind direction] Inflow speed no building ▪ slight change in wind direction but relatively large decrease in wind speed ▪ even in the cases of no building higher in the upwind region (from SE to NW)

20. ▪ wind vector and wind speed ratio for southwest (225°) inflow ▪ ASOS in deceleration zone behind the mountain in the south west ▪ resultantly ~45% decrease despite no higher building in the upwind region

21. ▪ Model for direct radiation & sunshine duration - using solar angle and buildings for special application to urban areas KASI Model 8:00 AM S E E S E S N W N N W W 5:00 PM ▪ validated against data from Korea Astronomy & Space Science Institute (KASI) ▪ the same solar locations

22. ▪ Application to Seoul ASOS - no cloud day in winter (Dec. 6, 2008) - shadow is long enough to investigate the obstacle’s interference KASI & Model (no topo nor building) latitude longitude height 17:13 07:32

23. ▪ ASOS vs Model - topography + buildings - ASOS: hourly averaged (1 – full sunshine, 0 – no sunshine) direct radiation 1.0 0.0 07 08 09 10 11 12 13 14 15 16 17 18 time ASOS model – 1 min model – 1 hour average Slight difference results from model (building) resolution c.f.) KASI sunrise – 07:32 sunset – 17:13 Sunrise – 07:52, Sunset – 16:58  Interference of topography and buildings

24. ▪ Interference by buildings VS no interference by buildings interference by buildings 17:13 ▪ Late sunrise is caused by topography but early sunset is caused by buildings ▪ Shade (less than 30%, satisfied for class 4) by far upwind buildings not by the observatory building or building in the northwest

25. previous survey study model result ·class 1 for surface wind? - yes, for just the SE ~ NW cases · class 4 for direct radiation - based on buildings just around the observatory ·large decrease in wind speed even for the SE ~ NW cases  sufficient for class 1? · satisfying class 4 but caused by far upwind buildings ▪ Survey study vs Model results discrepancy resulted from considering only the obstacles near observatories  More detail information is required, including obstacle’s orientation, far upwind area information, site elevation/location, and so on.

26. Summary and Conclusion ▪ Evaluating the observational environment for AWSs & ASOSs focusing on surface wind and direct radiation ▪ Systematic & quantitative analysis KN – larger decrease in wind speed due to buildings – WRF-CFD improved the RMSE GC – well representing background wind as a standard observatory after transfer SU – discrepancy between the previous survey and this studies, implying more systematic and detailed method required for classification ▪ CFD model can be used for evaluation & classification of AWS and/or ASOS

27. This study was supported by the national meteorological observation-standardization project of Korean Meteorological Administration