Regional analysis of multi- year aerosol indirect effects Dr. Thomas Jones University of Alabama in Huntsville January 13, th Annual AMS Conference, Phoenix, AZ Special Symposium on Aerosol–Cloud–Climate Interactions: 4.4

Aerosol Indirect Effects Aerosol interact with atmospheric and cloud properties in many ways Aerosol interact with atmospheric and cloud properties in many ways First (Twomey 1977) First (Twomey 1977) more aerosols increase # of CCN thereby reducing droplet size more aerosols increase # of CCN thereby reducing droplet size Second (Albrecht 1989) Second (Albrecht 1989) Reduced droplet size leads to delay in onset of C&C reducing precipitation efficiency and increasing cloud lifetime Reduced droplet size leads to delay in onset of C&C reducing precipitation efficiency and increasing cloud lifetime Semi-direct (Ackerman et al. 2000) Semi-direct (Ackerman et al. 2000) Absorbing aerosols (dust or black carbon) can warm key atmospheric layers affecting stability and likelihood of cloud formation Absorbing aerosols (dust or black carbon) can warm key atmospheric layers affecting stability and likelihood of cloud formation Convective (Andreae et al. 2004) Convective (Andreae et al. 2004) Reduction in stratiform precipitation efficiency can lead to an increase in convective precipitation. Reduction in stratiform precipitation efficiency can lead to an increase in convective precipitation.

Importance of aerosol type & surrounding conditions Certain types of aerosols affect cloud properties differently Certain types of aerosols affect cloud properties differently Sulfates and sea salt make excellent CCN Sulfates and sea salt make excellent CCN Dust aerosols are less effective CCN and also have the offsetting effect of absorbing rather than reflecting solar radiation Dust aerosols are less effective CCN and also have the offsetting effect of absorbing rather than reflecting solar radiation Atmospheric conditions Atmospheric conditions If sufficient moisture and synoptic forcing are not sufficient for cloud formation, then aerosol indirect effects would not be observed If sufficient moisture and synoptic forcing are not sufficient for cloud formation, then aerosol indirect effects would not be observed Thus, increasing AOT may not necessarily lead to larger values of AIE… Thus, increasing AOT may not necessarily lead to larger values of AIE…

Regional analysis of AIE Goals: Goals: Calculate AIE for several regions around the globe, each containing unique aerosol and atmospheric conditions Calculate AIE for several regions around the globe, each containing unique aerosol and atmospheric conditions Separate total AOT into (primarily) anthropogenic and dust components to analyze the relative indirect effects for both aerosol types Separate total AOT into (primarily) anthropogenic and dust components to analyze the relative indirect effects for both aerosol types Apply to a multi-year data set to study the effects of changing aerosol and atmospheric conditions on AIE Apply to a multi-year data set to study the effects of changing aerosol and atmospheric conditions on AIE Using case study examples, determine if aerosol and cloud layers are located at the appropriate levels to explain observed effects Using case study examples, determine if aerosol and cloud layers are located at the appropriate levels to explain observed effects For example, for the first AIE to be occurring, then aerosols and clouds should be in the same atmospheric layer For example, for the first AIE to be occurring, then aerosols and clouds should be in the same atmospheric layer

Data Aerosol and cloud properties are obtained from the CERES-SSF product over several regions Aerosol and cloud properties are obtained from the CERES-SSF product over several regions Contains collection 4 AOT Contains collection 4 AOT Cloud parameters derived using the Minnis et al. (2003) algorithm Cloud parameters derived using the Minnis et al. (2003) algorithm We only use liquid-water cloud information We only use liquid-water cloud information Atmospheric conditions are obtained from the NCEP Re-analysis product Atmospheric conditions are obtained from the NCEP Re-analysis product Temperature, moisture, and vertical velocity at a 2.5°x2.5° resolution Temperature, moisture, and vertical velocity at a 2.5°x2.5° resolution Both products are combined into a monthly averaged dataset between Mar and Dec Both products are combined into a monthly averaged dataset between Mar and Dec Only Terra results are shown, but data from Aqua produces similar results Only Terra results are shown, but data from Aqua produces similar results

Regions Arabian Sea: (Mix of dust and anthropogenic aerosols) Arabian Sea: (Mix of dust and anthropogenic aerosols) Bay of Bengal: (Primarily anthropogenic) Bay of Bengal: (Primarily anthropogenic) Eastern Atlantic: (Dust aerosols) Eastern Atlantic: (Dust aerosols) Dust Mix AN

Methodology Compare time-series and correlation statistics between AOT and cloud properties to determine if expected relationships exist. Compare time-series and correlation statistics between AOT and cloud properties to determine if expected relationships exist. Anthropogenic and dust AOT separated using a modified version of the Kaufman method. (Large uncertainties, but does give qualitative feel for differences) Anthropogenic and dust AOT separated using a modified version of the Kaufman method. (Large uncertainties, but does give qualitative feel for differences) Calculate aerosol direct and indirect effects at top of atmosphere using a modified form of method outlined by Quaas et al. (2008) Calculate aerosol direct and indirect effects at top of atmosphere using a modified form of method outlined by Quaas et al. (2008) We use a different diurnal averaging scheme and have modified the anthropogenic equations to derive dust effects as well We use a different diurnal averaging scheme and have modified the anthropogenic equations to derive dust effects as well Only AIE values from first indirect effect are calculated Only AIE values from first indirect effect are calculated

Arabian Sea AOT - R c Correlation < 0.0 High COT Summer AIE

Arabian Sea Aerosol concentrations and types change dramatically as a function of season Aerosol concentrations and types change dramatically as a function of season High AOT (0.6) associated with dust in the summer, lower AOT (0.2) associated with anthropogenic aerosols in the winter. High AOT (0.6) associated with dust in the summer, lower AOT (0.2) associated with anthropogenic aerosols in the winter. Correlation between AOT and R c is most negative during summer (-0.3) Correlation between AOT and R c is most negative during summer (-0.3) Indicative of first AIE Indicative of first AIE Increase in COT at this time consistent with this Increase in COT at this time consistent with this Both dust and anthropogenic AIE have similar magnitudes (peak values of -1.5 Wm -2 ) Both dust and anthropogenic AIE have similar magnitudes (peak values of -1.5 Wm -2 ) Direct effect from anthropogenic aerosols greatest in winter, when AIE is negligible. Direct effect from anthropogenic aerosols greatest in winter, when AIE is negligible.

Arabian Sea cont… However, atmospheric conditions also play an important role However, atmospheric conditions also play an important role Humidity and upward vertical motion maximized in summer, creating conditions more favorable for cloud formation. Humidity and upward vertical motion maximized in summer, creating conditions more favorable for cloud formation. Strong upward vertical motion appears to overcome any semi-direct effects due to dust absorption. Strong upward vertical motion appears to overcome any semi-direct effects due to dust absorption. Indirect effects are not observed in winter, when conditions are less favorable for cloud formation Indirect effects are not observed in winter, when conditions are less favorable for cloud formation Despite high anthropogenic AOT content and anthropogenic DRE Despite high anthropogenic AOT content and anthropogenic DRE

Arabian Sea Case Study

Bay of Bengal AOT - R c Correlation > 0.0 AIE ~ 0 Wm -2

Bay of Bengal Seasonal variations in AOT less than observed in Arabian Sea, anthropogenic aerosol dominate aerosol type Seasonal variations in AOT less than observed in Arabian Sea, anthropogenic aerosol dominate aerosol type Some influx of dust aerosols in summer Some influx of dust aerosols in summer Cloud fraction, COT, and cloud height are all maximized in summer, but the correlation between R c and AOT is not consistently negative during this time. Cloud fraction, COT, and cloud height are all maximized in summer, but the correlation between R c and AOT is not consistently negative during this time. Of interest is that CTP in this region are ~30 hPa higher than in the Arabian Sea Of interest is that CTP in this region are ~30 hPa higher than in the Arabian Sea Despite favorable conditions for cloud formation in summer, only weak AIE was observed. Despite favorable conditions for cloud formation in summer, only weak AIE was observed. Based on some case study examples, it appears the discontinuity between aerosol and cloud layers may play a part in this result Based on some case study examples, it appears the discontinuity between aerosol and cloud layers may play a part in this result

North Atlantic Correlation

North Atlantic Dust from Saharan Desert accounts for much of the AOT. Dust from Saharan Desert accounts for much of the AOT. AOT maximized in summer (0.7) when transport from the desert is greatest AOT maximized in summer (0.7) when transport from the desert is greatest Dust transported higher into atmosphere than in other regions (5 km and above) Dust transported higher into atmosphere than in other regions (5 km and above) COT increases at the same time with the northward movement of the ITCZ COT increases at the same time with the northward movement of the ITCZ Corresponds with maximum in atmospheric humidity Corresponds with maximum in atmospheric humidity But mean vertical velocity never indicates large scale uplift But mean vertical velocity never indicates large scale uplift A seasonal cycle in AIE was observed, but… A seasonal cycle in AIE was observed, but… AOT - R c correlation only near 0 in summer, not negative AOT - R c correlation only near 0 in summer, not negative AIE radiative effects of only -1.0 Wm -2 in summer, none in winter AIE radiative effects of only -1.0 Wm -2 in summer, none in winter Recall that dust aerosols absorb solar radiation and can warm certain layers of the atmosphere Recall that dust aerosols absorb solar radiation and can warm certain layers of the atmosphere Increase stability and reduce favorability of environment towards cloud formation, but cloud fraction remains approximately constant Increase stability and reduce favorability of environment towards cloud formation, but cloud fraction remains approximately constant First AIE is likely occurring, but is being offset by semi- direct effects from the presence of absorbing aerosols First AIE is likely occurring, but is being offset by semi- direct effects from the presence of absorbing aerosols

Importance of vertical motion Upward vertical motion is greatest in the Arabian Sea Upward vertical motion is greatest in the Arabian Sea Region most favorable for cloud formation Region most favorable for cloud formation In turn is the region with the largest AIE values In turn is the region with the largest AIE values (compared to Bay of Bengal and the eastern North Atlantic (compared to Bay of Bengal and the eastern North Atlantic Up Down

Vertical Distribution Example

Conclusions Aerosol indirect effects are more likely to be observed when atmospheric conditions are more favorable for cloud development. Aerosol indirect effects are more likely to be observed when atmospheric conditions are more favorable for cloud development. No clouds, no AIE! No clouds, no AIE! Relative vertical distributions of aerosol and cloud layers is also very important Relative vertical distributions of aerosol and cloud layers is also very important If aerosols are not in the same layer as clouds, then first AIE is not likely to occur. If aerosols are not in the same layer as clouds, then first AIE is not likely to occur. Important application for CALIPSO & CloudSat data Important application for CALIPSO & CloudSat data Semi direct effects of absorbing aerosols can offset those of the aerosols acting as CCN Semi direct effects of absorbing aerosols can offset those of the aerosols acting as CCN When dust AOT is very high such as in North Atlantic When dust AOT is very high such as in North Atlantic

Questions I know, at lot to digest in 12 minutes…I’m writing a paper with all the details I know, at lot to digest in 12 minutes…I’m writing a paper with all the details Dr. Sundar Christopher Dr. Sundar Christopher Dr. Johannes Quaas Dr. Johannes Quaas LARC (CERES-SSF data) LARC (CERES-SSF data) Acknowledgments:

Future work