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

Background ▪ Korean Meteorological Administration (KMA) enacted a law on ‘Weather Observation Standardization (WOS)’ in ▪ 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 ▪ This study has been performed from 2011, following up the WOES project.

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

▪ 15 ASOSs in focusing on wind and direct solar radiation Seoul ASOS Deajeon ASOS Busan ASOS Kwangju ASOS Chupungryoung ASOS Ulsan ASOS Boseon g AWS Jeonju ASOS Chuncheo n ASOS Icheon ASOS Namwon ASOS Gumi ASOS Gosan ASOS Gosan ASOS Deakwanryoun g ASOS Uljin ASOS urban rural standard

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

▪ 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

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

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

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

wind speed ratioarea fraction ~ 20( ~ 1.18 m s -1 )11.51 ~ 40( ~ 2.37 m s -1 )10.39 ~ 60( ~ 3.55 m s -1 )15.44 ~ 80( ~ 4.73 m s -1 )19.56 ~ 100( ~ 5.92 m s -1 )18.13 ~ 120( ~ 7.10 m s -1 )23.30 ~ 140( ~ 8.28 m s -1 )1.67 ~ 160( ~ 9.46 m s -1 )0.01 ~ 180( ~10.65 m s -1 )0.00 ~ 200( ~11.83 m s -1 )0.00 ▪ wind speed ratio to inflow for east-south-east (112.5 °) - larger decrease in wind speed but no change in wind direction ▪ flow acceleration in the upwind region due to ‘channeling effect’ ▪ flow deceleration in the downwind region due to ‘building drag’ acceleration deceleration inflow

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

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

before transfer - conducted to May 14, 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, no higher building around - ASOS built in flat terrain and higher than around ▪ Gochang ASOS – a standard observatory ( )

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

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 (m) ASOS inflow

(%) wind speed ratioarea fraction ~ 20( ~ 1.18 m s -1 )0.89 ~ 40( ~ 2.37 m s -1 )0.17 ~ 60( ~ 3.55 m s -1 )0.28 ~ 80( ~ 4.73 m s -1 )2.94 ~ 100( ~ 5.92 m s -1 )59.3 ~ 120( ~ 7.10 m s -1 )36.43 ~ 140( ~ 8.28 m s -1 )0.00 ~ 160( ~ 9.46 m s -1 )0.00 ~ 180( ~10.65 m s -1 )0.00 ~ 200( ~11.83 m s -1 )0.00 ▪ wind speed ratio for south (180°) after transfer - no change in wind direction but ~25 % decrease in wind speed ▪ ASOS in the deceleration zone induced by far upwind buildings ▪ mostly (96%) equivalent to inflow inflow

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

▪ Seoul 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 ASOS

▪ 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) [wind speed] [wind direction] Inflow speed no building ▪ Inflow vs AWS

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

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

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

08:0009:0010:0011:0012:0013:0014:0015:0016:0017:0018:00 ASOS model(a vg) time direct radiation ASOSmodel – 1 minmodel – 1 hour average Sunrise – 07:52, Sunset – 16:58  Interference of topography and buildings ▪ ASOS vs Model - topography + buildings - ASOS: hourly averaged (1 – full sunshine, 0 – no sunshine) Slight difference results from model (building) resolution c.f.) KASI sunrise – 07:32 sunset – 17:13

▪ Interference by buildings VS 08:0009:0010:0011:0012:0013:0014:0015:0016:0017:0018:00 with buildings without buildings ▪ 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 17:13no interference by buildingsinterference by buildings

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

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

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