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 – ψ(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 – ψ(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 – ψ(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 – ψ(t) Days on July 1996 [mm/hr] [%] Precipitation Rate at surface – p(t)

Regression method: t = -10 hour Relative Humidity (RH) at surface – ψ(t) Days on July 1996 [mm/hr] [%] Precipitation Rate at surface – p(t)

Regression method: t = +10 hour Relative Humidity (RH) at surface – ψ(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