J. F. Li

Comparisons of satellites liquid water estimates to ECMWF and GMAO analyses, 20th century IPCC AR4 climate simulations, and GCM simulations

[1] To assess the fidelity of general circulation models (GCMs) in simulating cloud liquid water, liquid water path (LWP) retrievals from several satellites with passive sensors and the vertically-resolved liquid water content (LWC) from the CloudSat are used. Comparisons are made with ECMWF and MERRA analyses, GCM simulations utilized in the IPCC 4th Assessment, and three GCM simulations. There is considerable disagreement amongst the LWP estimates and amongst the modeled values. The LWP from GCMs are much larger than the observed estimates and the two analyses. The largest values in the CloudSat LWP occur over the boundary-layer stratocumulus regions; this feature is not as evident in the analyses or models. Better agreement is found between the two analyses and CloudSat LWP when cases with surface precipitation are excluded. The upward vertical extent of LWC from the GCMs and analyses is greater than CloudSat estimates. The issues of representing LWC and precipitation consistently between satellite-derived and model values are discussed. Citation: Li, J.-L. F., D. Waliser, C. Woods, J. Teixeira, J. Bacmeister, J. Chern, B.-W. Shen, A. Tompkins,

Evaluation of CMIP3 and CMIP5 Wind Stress Climatology Using Satellite Measurements and Atmospheric Reanalysis Products

AbstractWind stress measurements from the Quick Scatterometer (QuikSCAT) satellite and two atmospheric reanalysis products are used to evaluate the annual mean and seasonal cycle of wind stress simulated by phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5). The ensemble CMIP3 and CMIP5 wind stresses are very similar to each other. Generally speaking, there is no significant improvement of CMIP5 over CMIP3. The CMIP ensemble–average zonal wind stress has eastward biases at midlatitude westerly wind regions (30°–50°N and 30°–50°S, with CMIP being too strong by as much as 55%), westward biases in subtropical–tropical easterly wind regions (15°–25°N and 15°–25°S), and westward biases at high-latitude regions (poleward of 55°S and 55°N). These biases correspond to too strong anticyclonic (cyclonic) wind stress curl over the subtropical (subpolar) ocean gyres, which would strengthen these gyres and influence oceanic meridional heat transport. In the equatorial zone, significant biase...

Global climate response to anthropogenic aerosol indirect effects: Present day and year 2100

Aerosol indirect effects (AIE) are a principal source of uncertainty in future climate predictions. The present study investigates the equilibrium response of the climate system to present-day and future AIE using the general circulation model (GCM), Goddard Institute for Space Studies (GISS) III. A diagnostic formulation correlating cloud droplet number concentration (N_c) with concentrations of aerosol soluble ions is developed as a basis for the calculation. Explicit dependence on N_c is introduced in the treatments of liquid-phase stratiform clouds in GISS III. The model is able to reproduce the general patterns of present-day cloud frequency, droplet size, and radiative balance observed by CloudSat, Moderate Resolution Imaging Spectroradiometer, and Earth Radiation Budget Experiment. For perturbations of N_c from preindustrial to present day, a net AIE forcing of −1.67 W m^(−2) is estimated, with a global mean surface cooling of 1.12 K, precipitation reduction of 3.36%, a southward shift of the Intertropical Convergence Zone, and a hydrological sensitivity of +3.00% K^(−1). For estimated perturbations of N_c from present day to year 2100, a net AIE forcing of −0.58 W m^(−2), a surface cooling of 0.47 K, and a decrease in precipitation of 1.7% are predicted. Sensitivity calculations show that the assumption of a background minimum N_c value has more significant effects on AIE forcing in the future than on that in present day. When AIE-related processes are included in the GCM, a decrease in stratiform precipitation is predicted over future greenhouse gas (GHG)-induced warming scenario, as opposed to the predicted increase when only GHG and aerosol direct effects are considered.