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Diurnal Variations in Southern Great Plain during IHOP -- data and NCAR/CAM

Diurnal Variations in Southern Great Plain during IHOP -- data and NCAR/CAM. Junhong (June) Wang Dave Parsons, Julie Caron and Jim Hack NCAR ATD and CGD. Acknowledgement: Kate Young (NCAR/ATD) and Aiguo Dai (NCAR/CGD). Thanks NCAR Water Cycle Initiative Support. Outline.

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Diurnal Variations in Southern Great Plain during IHOP -- data and NCAR/CAM

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  1. Diurnal Variations in Southern Great Plain during IHOP -- data and NCAR/CAM Junhong (June) Wang Dave Parsons, Julie Caron and Jim Hack NCAR ATD and CGD Acknowledgement: Kate Young (NCAR/ATD) and Aiguo Dai (NCAR/CGD) Thanks NCAR Water Cycle Initiative Support

  2. Outline • Document and understand diurnal variations in SGP using IHOP data • Two modes: LLJ v.s. non-LLJ • Diurnal variations and differences between two modes • Understand humidity variations • Understand nocturnal precipitation maximum in SGP • Compare with CAM simulations

  3. Why study diurnal cycle? • The diurnal cycle is one of the most obvious and reliable signals of the climate. • Most physical processes (such convection and radiation) are non-linear and can not be simulated adequately using daily mean values. • The diurnal cycle can be used as an excellent test bed for evaluating model physics because of its large amplitude and short time scale. • Some earlier GCMs did not even include the diurnal cycle to save computer time. • There is a lack of data with high resolution for studying the diurnal cycle on the global scale. Courtesy of Aiguo Dai (NCAR/CGD)

  4. ARM Data • IHOP: 20-day (May 26 to June 14, 2002) 3-hrly data at five stations • 3-hrly ARM radiosonde data during IOPs (315 soundings from 1996-2000)

  5. Observations:Twenty days of wind speed profiles: two modes

  6. Temperature and MR in two modes T MR

  7. Diurnal cycle at surface

  8. Diurnal Cycle of LLJ and non-LLJ cases: Winds Whiteman et al. (1997)

  9. U wind anomaly Day Night solenoidal circulation

  10. Temperature: Anomaly

  11. Sonde Mixing Ratio: Anomaly

  12. NCAR Atmospheric Technology Division Comparisons of diurnal variations in WV profiles Radiosonde (Dai et al. 2002) JJA MWPR JJA

  13. horizontal advection (g/kg/day) Data from objective variational analysis of the ARM IOP data (Zhang et al. 2000) Omaga (mb/day) Vertical advection (g/kg/day) 11/17 23.5

  14. Nocturnal precipitation maximum • Why? • Eastward propagation of mountain-generated systems from the previous afternoon (Riley et al. 1987, Carbone et al. 2002) • Large-scale convergence as a result of solar-driven diurnal and semidiurnal cycles of surface pressures (Dai et al. 1999) • … From Dai et al. (1999)

  15. CAPE/CIN: mean • Larger CAPE for LLJ throughout the diurnal cycle • Maximum CAPE but minimum CIN in the afternoon for LLJ • The 2nd small maximum at ~0.5 km around early morning

  16. Qualitative behavior and simple scaling arguments suggest a possible link between the diurnal cycles in stability and rainfall. From Dave Parsons

  17. CAPE/CIN from large scale advection and from surface flux forcing (Zhang et al. 2003) Tropospheric forcing CAPE PBL forcing Convective Non-Convective

  18. Links to nocturnal precipitation maximum • Future work: • Analysis of more data, • Rain v.s. non-rain days? • MWRP data? • Large-scale circulation data?

  19. Model and Runs • Community Atmospheric Model (CAM) Version 3.0 • Model run • with climatological SSTs • - hourly output • - over an IHOP season (May, June) • - 1 realization (so far) • - hourly data averaged to 3-hourly for consistency with obs • - results shown are for T42 resolution • - T85 (150km) and T170 (75km) explorations • - Ensembles, as opposed to single realizations

  20. Winds from the Climate Model

  21. Data V anomaly LLJ CAM ~4 hours early for the peak of LLJ

  22. Data U anomaly LLJ CAM

  23. Data CAM T anomaly LLJ

  24. Data CAM Q anomaly LLJ

  25. Conclusions • The 20-day, 3-hrly radiosonde data at five stations during IHOP show that the atmosphere is in two modes, LLJ v.s. non-LLJ. The atmosphere is warmer, humid, and more unstable for LLJ days than non-LLJ days. • Southerly LLJ exists throughout the night and reaches the maximum wind speed at 500-600 m AGL around 2 am CST. The height of the maximum wind speed does not change a lot during night. • The phase of diurnal cycles of temperature, CAPE/CIN and MR in BL is similar for LLJ and non-LLJ cases, but the magnitude is larger for LLJ case. The diurnal cycle of MR in the free troposphere is different for two cases. • The diurnal cycle of CAPE/CIN shows that the most favorable condition for convections occurs at the late afternoon, so can’t explain the nocturnal precipitation maximum. Different processes contributing to diurnal cycle of stability will be examined separately. The limited data show that rain often follows the end of LLJ events. • Preliminary results show good agreements between CAM and data in wind and T, but humidity. More analysis and comparisons with model need to be done. How to use rich weather-driven field experiment data for climate research and improving climate model! “Get the right answers for the right reasons”

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