The nature of rain events in summer vs. winter at the SGP ARM Facility MPO 581 Class Project Emily Riley, Siwon Song, & Brian Mapes Background ARM Atmospheric Radiation Measurements Several Sites (facilities) funded by DOE Background ARM Atmospheric Radiation Measurements SGP-Southern Great Plains Data Climate Modeling Best Estimate (CMBE) Data 1996 2009 Data averaged over one hour time intervals Data Climate Modeling Best Estimate (CMBE) Data 1996 2009 Data averaged over one hour time intervals * Cloud fraction profiles * Total, high, middle, and low clouds * Liquid water path and precipitable water vapor * Surface radiative fluxes * TOA radiative fluxes * Soundings * NWP analysis data * Surface sensible and latent heat fluxes * Surface precipitation * Surface temperature, relative humidity, and horizontal winds Methods Composite Weighted Composite Regression July 1996 RH and Precipitation Relative Humidity (RH) at surface (t) Days on July 1996 [mm/hr] [%] Precipitation Rate at surface p(t) : Rain Event non-weighted composite method non-weighted composite t lag = [-7*24, 7*24] hours N = total number of selected rain events non-weighted composite -7 days+7 days Relative Humidity (RH) at surface (t) Days on July 1996 [mm/hr] [%] Precipitation Rate at surface p(t) -7 days+7 days-7 days+7 days-7 days+7 days-7 days+7 days-7 days+7 days : Rain Event Weighted composite method weighted composite t lag = [-7*24, 7*24] hours N = total number of selected rain events Non-weighting Weighted composite -7 days+7 days Relative Humidity (RH) at surface (t) Days on July 1996 [mm/hr] [%] Precipitation Rate at surface p(t) -7 days+7 days-7 days+7 days-7 days+7 days-7 days+7 days-7 days+7 days : Rain Event Composite vs. Weighted Composite mm/hr Regression method Regression Coefficient t = whole time series t lag = [-7*24, 7*24] hours Regression method: t = 0 hour Relative Humidity (RH) at surface (t) Days on July 1996 [mm/hr] [%] Precipitation Rate at surface p(t) Regression method: t = -10 hour Relative Humidity (RH) at surface (t) Days on July 1996 [mm/hr] [%] Precipitation Rate at surface p(t) Regression method: t = +10 hour Relative Humidity (RH) at surface (t) Days on July 1996 [mm/hr] [%] Precipitation Rate at surface p(t) Comparison: Regression vs. weighted composite Regression Coefficient Weighted composite t = whole time series t lag = [-7*24, 7*24] hours N = total number of selected rain events Weighted Composite vs. Regression % RH on precipitation Weighted Composite vs. Regression SAME, except for units % RH on precipitation Relative Humidity Perturbation Weighted [%] Regression [%/(mm/hr)] Non-weighted [%] Time for some results. Oklahoma JJA vs. DJF precipitation Cumulative Fraction of Rain Events JJA DJF DJF - ~45% time not raining JJA - ~32% time not raining Cumulative Fraction of Rain Events JJA DJF DJF - ~45% time not raining JJA - ~32% time not raining 5 ~20% rain events > 5 mm/hr Cumulative Fraction of Rain Events JJA DJF DJF - ~45% time not raining JJA - ~32% time not raining 5 ~5% rain events > 5 mm/hr Summer vs. Winter Precipitation Summer vs. Winter Temperature Strong Diurnal Cycle Weak Diurnal Cycle Summer vs. Winter Temperature Strong Diurnal Cycle Weak Diurnal Cycle Frontal Precip Afternoon Convection Seasonal: Temperature perturbation [K] DJF: Winter JJA: Summer Summer vs. Winter Surface Pressure Summer vs. Winter Relative Humidity Seasonal: Relative Humidity perturbation [%] DJF: Winter JJA: Summer Seasonal: Relative Humidity perturbation [%] DJF: Winter JJA: Summer Summer vs. Winter LWP Summer vs. Winter Cloud Fraction Seasonal: All Cloud Fraction perturbation [%] DJF: Winter JJA: Summer Summer vs. Winter Cloud Top Height Seasonal: Omega perturbation [Pa/s] DJF: Winter JJA: Summer Summary Summer (JJA): More rain events Heavier, but shorter rain events Stronger diurnal cycle Higher cloud tops Winter (DJF): Tilted vertical structure for RH and Cloud Fraction THOUGH, hourly time composites might reveal tilted structure in summer
