Wesley Berg, Tristan L’Ecuyer, and Sue van den HeeverWesley Berg, Tristan L’Ecuyer, and Sue van den Heever

Department of Atmospheric ScienceDepartment of Atmospheric ScienceColorado State UniversityColorado State University

Evaluating the impact of aerosols on the onset and microphysical properties of rainfall off the coast of China

Differences in TRMM Rainfall DetectionFebruary 1, 2000

Impact of Aerosols on Rainfall Detection?

TMI-PR Rain Detection Differences SPRINTARS Sulfate AOD

Calipso 532 nm Attenuated Backscatter

Aerosol Layer(~3-5 km)

Coincident TRMM/CloudSat Case3 April 2007

Coincident TRMM/CloudSat Case3 April 2007

Rain Rate Histograms3 April 2007

Differences in Radar SensitivityTRMM PR (13.8 GHz) vs. CloudSat (94 GHz)

Simulated Near-Surface ZCloud

Refle

ctiv

ity

(dBZ

)Drizzle Cloud

LWC (gm-3) Rainrate (mm h-1)

MDS = 18 dBZ

MDS = -28 dBZPR

CPR

1 6 10 15 0.1 1 10 100

Coincident TRMM/CloudSat Case3 April 2007

Cloud Resolving Model SimulationsCSU RAMS

3-D Cloud Structure Transect of Cloud Liquid Water

Cloud Resolving Model SimulationsEffect of Variations in Sulfate Aerosol Optical Depth

Cloud Water Path Rain Water Path

Total Water Path

Cloud Resolving Model SimulationsEffect of Variations in Sulfate Aerosol Optical Depth

Accumulated Precipitation

Ratio of Cloud Water Path to Total Water Path

Probability of Precipitation versus Liquid Water Path

Summary

• Differences in rain fraction between PR and TMI off the coast of China point to a modification of cloud microphysical properties by aerosols.

– Magnitude is substantial (i.e. the frequency of occurrence leads to large differences in the total rain (up to ~50% or 2 mm/day) locally.

• Results from 3 April 2007 Case and “Idealized” CRM Simulations– Consistency in rain area between TMI and CloudSat indicate the presence of large-

scale light rain and/or drizzle below the PR detection threshold (~17 dBZ)– High AOD CRM simulation has substantially more cloud water and the onset of rain is

delayed.– This is consistent with the observations as higher cloud water paths may lead to an

overestimate of the rain rate by TMI/CloudSat and possible underestimate by the PR as a result of smaller drops initially. In addition, the delay in the development of rain drops may be a factor leading to the underestimate of the rain area by PR.

• Results from Statistical Analysis (Global ocean analysis from 2007)– Probability of precipitation decreases significantly in high sulfate aerosol environment.– Aerosol effect is evident in both stable and unstable environments.– Results are consistent using either SPRINTARS sulfate AOD or MODIS aerosol index.

Primary Objective: To provide, from space, the first global survey of cloud profiles and cloud physical properties, with seasonal and geographical variations needed to evaluate the way clouds are parameterized in global models, thereby contributing to weather predictions, climate and the cloud-climate feedback problem.

The CloudSat Mission

• Nadir pointing, 94 GHz radar• 3.3s pulse 500m vertical res.• 1.4 km horizontal res.• Sensitivity ~ -28 dBZ• Dynamic Range: 80 dB• Antenna Diameter: 1.85 m• Mass: 250 kg• Power: 322 W

500m

~1.4 km

The Cloud Profiling Radar

TRMM SensorsPrecipitation radar (PR):

13.8 GHz4.3 km footprint0.25 km vertical res.215 km swath

Microwave radiometer (TMI):10.7, 19.3, 21.3, 37.085.5 GHz (dual polarizedexcept for 21.3 V-only)10x7 km FOV at 37 GHz760 km swath

Visible/infrared radiometer (VIRS):0.63, 1.61, 3.75, 10.8, and 12 :at 2.2 km resolution

Lightning Imaging Sensor (LIS )

Cloud & Earth Radiant Energy System (CERES)

Nov. 1997 launch, 35° inclination; 402 kmNov. 1997 launch, 35° inclination; 402 km

Tropical Rainfall Measuring Mission Tropical Rainfall Measuring Mission (TRMM)(TRMM)