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The Analysis of Ozone Dependence on Synoptic Weather Patterns

7 th Annual CMAS Conference, October 6th , 2008. The Analysis of Ozone Dependence on Synoptic Weather Patterns. Fong (Fantine) Ngan and DaeWon Byun IMAQS, Department of Earth Sciences, University of Houston. Contents. Introduction Methodology Cluster Characteristics

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The Analysis of Ozone Dependence on Synoptic Weather Patterns

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  1. 7th Annual CMAS Conference, October 6th , 2008 The Analysis of Ozone Dependence on Synoptic Weather Patterns Fong (Fantine) Ngan and DaeWon Byun IMAQS, Department of Earth Sciences, University of Houston

  2. Contents Introduction Methodology Cluster Characteristics Clusters .vs. Ozone Episodes Clusters .vs. CMAQ Forecasting Summary and Future Work

  3. Introduction • Houston/Galveston area is a unique environment for O3 development. • (Various emissions + complex geophysical characteristics) • Banta et al. (2005), Darby (2005) – Met. factors are a key on determining the production, dilution and transport of O3. • Muller & Jackson (1985), Eder et al. (1995), Davis et al. (1998) – The development of O3 levels depends greatly on meteorological conditions which affect photochemical reaction and transport of O3 precursors. • Appel et al. (2007) – model biases in O3 prediction vary based on the meteorological conditions. Synoptic flow patterns have been classified during 2005/2006 TexAQS-II. Understanding the dependence of O3 on meteorology How high O3 events are associated with certain weather scenarios Evaluating AQF results according to the weather clusters

  4. PCA (fortran programs) Average linkage SAS (commercial software) Convergent K-means Methodology • The study period encompassed 5-month ozone season (May-September) recorded in 2005 and 2006; 5 days were excluded since they were influenced strongly by Hurricanes. (total 301 days) • The meteorological grid data (100*100 in 12-km resolution) from UH-RDAS (NAM + objective analysis) was used for the cluster analysis. • The weather conditions were categorized using a two-stage (average linkage then convergent k-means) clustering approach based on the 850 mb wind fields (U & V components of wind) at 12 UTC. 850mb U/V from UH-RDAS Principle Component Analysis: reduce size of dataset 12-km domain 8 PCs (80%)

  5. Weather Clusters (composite maps on 850 mb) C2: E, 56 days (19%) C3: clam, 69 days (23%) C1: SE/S, 93 days (30%) C5: SW, 40 days (13%) C6: strong SW, 2 days (1%) C4: N, 41 days (14%)

  6. C4 Mean hourly dew point depression associated with clusters ClusterCharacteristics C2, C3 CAMS sites & cluster average of T and T-TD C4 (northerly): Lowest min T and driest C1 & C5 (southerly): Relative lower T and more humid C6 (warm section): highest T and most humid C1, C5, C6 Mean hourly temperature associated with clusters C6 C4

  7. Mean hourly wind SPD associated with clusters ClusterCharacteristics C6 • CAMS sites & cluster average of wind speed & O3 conc. • Good correlation of cluster wind speed & O3 conc. • Lower wind, higher O3 Higher O3 level group: C2 (easterly) – 65 ppb C3 (clam condition) – 61 ppb C4 (northerly) – 56 ppb Peak happens at 14 CST Lower O3 level group: C1 (southerly) – 35 ppb C5 (southwesterly) – 40 ppb Lowest O3 level: C6 (strong SW) – 20 ppb C1 C5 C2, C3, C4 Mean hourly ozone associated with clusters C2, C3, C4 C5 C1 C6

  8. Data Source and Ozone Episodes Both met. and chemical data are from CAMS sites (TCEQ). Around 45 sites are available in HGA (region 12) during the study period. CAMS sites map Criteria for defining O3 Episodes: 8 hr average O3 >= 85 ppb 92 ozone events Criteria for defining rainy days: precip. recorded during 10 – 16 CST 98 rainy days

  9. Black bars: number days White bars: number of O3 days Percentages: ratio of O3 days and total days in clusters C2, C3 & C4: good for O3 development. Why C2, C3 & C4 don’t get O3 events on some days? Rainy day, clouds & relatively strong wind 11.86% C1 & C5: not good for O3 development. Why C1 & C5 get O3 events on certain days? System passes through quickly, light wind 58.33% 47.22% 58.82% 17.39% 0%

  10. Cluster Characteristics during TexAQS-II intensive period O3 events occurred in C2, C3 & C4 Precip. Prevents O3 events Active frontal passage Before front – C5 Cool air reached – C4 After front – C3 Sub-tropical high was dominant No C4 was identified

  11. C2 Location of O3 peak Observed O3 (CAMS sites, 8-hr average) on event days have been sorted. The three sites with the highest values were marked on the maps. The circle color indicates how many times were marked at that CAMS site. O3 peak is subjected to the flow pattern. C2: SW of downtown C3: wide spread over the city C4: S of Harris County C3 C4 Harris Brazoria

  12. Clusters .vs. CMAQ Forecasting (O3) C2 Mean max 8hr O3 for clusters: UH-AQF (F1, shaded) CAMS OBS (circle) C3 Figures are generated by Dr. HyunCheol Kim

  13. Clusters .vs. CMAQ Forecasting (O3) Mean max 8hr O3 for clusters: UH-AQF (F1, shaded), CAMS OBS (circle) C4 Mean max O3 for cluster 4 in AQF further south than CAMS observations by Dr. HyunCheol Kim

  14. C4 case: September 13, 2006 Weather condition: Mostly clear to partly cloudy Light northerly winds all day Weak sea breeze in late afternoon Max T 93F at IAH Front passed through HGA It is classified as cluster 4. SFC weather map at 06z 9/13 SFC weather map at 12z 9/13 SFC weather map at 18z 9/13

  15. Snap shot of O3 & wind on 9/13UH-AQF (shaded) & CAMS (circle) 06 CST O3 level started to build up at noon. Too strong northerly (northeasterly) wind in the morning pushed pollutants southward (or southwestward). O3 peak ended up in Brazoria. Figures are from UH-AQF web display 12 CST 18 CST

  16. Snap shot of model & observed wind on 9/13UH-AQF (shaded) & CAMS (circle) Over-prediction of wind speed in the morning 08 CST Figures are from UH-AQF web display

  17. Time Series of O3 on 9/13 forecasting at CAMS site C1 & C619 Red: AQF O3 Blue: observed O3 Located in Houston downtown Under-prediction of O3 Located south of Houston Good estimation of O3 Figures are from UH-AQF web display

  18. Summary & Future Work • Include more years for weather pattern classification (2007 & 2008) • Develop secondary factor base on weather pattern for O3 forecasting Synoptic weather patterns in HGA during summer 2005/2006 were classified into 6 clusters. C1, C5 & C6 (southerly): lower mean hourly O3, higher average wind speed. C2 (easterly), C3 (stagnant condition) and C4 (northerly) have larger contributions on high O3 events. Precip., clouds and strong wind prevent O3 development in these clusters. August 2006: dominated by southerly flow (C1 & C5), less O3 events September 2006: frequent frontal passage (C4), more O3 events (C2 & C3) In cluster 4 (northerly), CMAQ forecasting of O3 peak was placed south of the city due to over-prediction of wind speed in the morning.

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