Cloud droplet spectral dispersion and the indirect aerosol effect: Comparison of two treatments in a GCM, Geophys

[1] Two parameterizations of cloud droplet spectral dispersion and their impact on the indirect aerosol effect are compared in a global climate model. The earlier scheme specifies b, the ratio of droplet effective radius to volumemean radius, in terms of N, the cloud droplet number concentration. The new scheme specifies b in terms of mean droplet mass (L/N), where L is liquid water content, to account for the effect of variations in L. For low to moderate N, the new scheme gives a stronger increase of b with increasing N than the old scheme. In a present-climate simulation, the new scheme shows a stronger gradient between remote regions (small b) and polluted/continental regions (large b). The new scheme also offsets the first indirect aerosol forcing (DF) more strongly: DF = À0.65 W

Precipitation changes in a GCM resulting from the indirect effects of anthropogenic aerosols

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94948/1/grl13844.pd

Have Australian rainfall and cloudiness increased due to the remote effects of Asian anthropogenic aerosols?

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94749/1/jgrd13340.pd

Projected effects of declining anthropogenic aerosols on the southern annular mode

Declining emissions of anthropogenic aerosols have been shown to contribute to global warming in climate projections from the Coupled Model Intercomparison Project Phase 5 (CMIP5). This study considers the response of the southern annular mode (SAM) in austral summer to declining aerosols in simulations forced by Representative Concentration Pathway 4.5 (RCP4.5) using CSIRO-Mk3.6, a CMIP5-generation model. A ten-member ensemble forced by RCP4.5 for the period 2006–2100 is compared with another experiment, which is identical except that emissions of anthropogenic aerosols are held fixed at their 2005 values. With fixed aerosol emissions, the model simulates a negative (but statistically insignificant) ensemble-mean SAM trend in austral summer, suggesting that the effects of recovering stratospheric ozone slightly outweigh the effects of increasing long-lived greenhouse gases (GHGs). In contrast, the standard RCP4.5 experiment (including additional warming due to declining aerosols) simulates a positive ensemble-mean SAM trend, and the difference between the two trends is significant at 5%. The response of Southern Hemisphere zonal-mean atmospheric circulation and temperature to declining aerosols resembles the response to increasing GHGs; this suggests that the positive SAM trend due to declining aerosols may be driven by mechanisms that are similar to those that cause the positive SAM trend in response to increasing GHGs

A simple pan-evaporation model for analysis of climate simulations: Evaluation over Australia

We show that a simple model of pan evaporation ("PenPan") can be used to analyze monthly mean output from a global climate model (GCM). PenPan is based on a modified version of Penman's potential evapotranspiration equation. Very good agreement is obtained with observed annual pan evaporation for Australian sites when PenPan is forced by surface observations of radiation, wind speed, humidity and air temperature. When PenPan is forced with monthly mean output from the CSIRO GCM, the results are still satisfactory, but pan evaporation is overestimated over southern Australia, primarily due to excessive surface solar radiation simulated by the GCM. The results suggest that PenPan will be a valuable tool for reconciling observed panevaporation trends with climate-model simulations

On the attribution of changing pan evaporation

Evaporative demand, measured by pan evaporation, has declined in many regions over the last several decades. It is important to understand why. Here we use a generic physical model based on mass and energy balances to attribute pan evaporation changes t

Precipitation changes in a GCM resulting from the indirect effects of anthropogenic aerosols

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94948/1/grl13844.pd