Interactive nature of climate change and aerosol forcing.

The effect of changing cloud cover on climate, based on cloud-aerosol interactions, is one of the major unknowns for climate forcing and climate sensitivity. It has two components: (1) the impact of aerosols on clouds and climate due to in situ interactions (i.e., rapid response) and (2) the effect of aerosols on the cloud feedback that arises as climate changes-climate feedback response. We examine both effects utilizing the NASA Goddard Institute for Space Studies ModelE2 to assess the indirect effect, with both mass-based and microphysical aerosol schemes, in transient twentieth century simulations. We separate the rapid response and climate feedback effects by making simulations with a coupled version of the model as well as one with no sea surface temperature or sea ice response ("atmosphere-only" simulations). We show that the indirect effect of aerosols on temperature is altered by the climate feedbacks following the ocean response, and this change differs depending upon which aerosol model is employed. Overall, the effective radiative forcing (ERF) for the "direct effect" of aerosol-radiation interaction (ERFari) ranges between -0.2 and -0.6 W m-2 for atmosphere-only experiments, while the total effective radiative forcing, including[C0]the indirect effect (ERFari+aci) varies between about -0.4 and -1.1 W m-2 for atmosphere-only simulations; both ranges are in agreement with those given in Intergovernmental Panel on Climate Change (2013). Including the full feedback of the climate system lowers these ranges to -0.2 to -0.5 W m-2 for ERFari and -0.3 to -0.74 W m-2 for ERFari+aci. With both aerosol schemes, the climate change feedbacks have reduced the global average indirect radiative effect of atmospheric aerosols relative to what the emission changes would have produced, at least partially due to its effect on tropical upper tropospheric clouds.

Rapid and extensive surface changes near Titan's equator: evidence of April showers.

Although there is evidence that liquids have flowed on the surface at Titan's equator in the past, to date, liquids have only been confirmed on the surface at polar latitudes, and the vast expanses of dunes that dominate Titan's equatorial regions require a predominantly arid climate. We report the detection by Cassini's Imaging Science Subsystem of a large low-latitude cloud system early in Titan's northern spring and extensive surface changes (spanning more than 500,000 square kilometers) in the wake of this storm. The changes are most consistent with widespread methane rainfall reaching the surface, which suggests that the dry channels observed at Titan's low latitudes are carved by seasonal precipitation.

Cassini Imaging Science: initial results on Saturn's rings and small satellites.

Images acquired of Saturn's rings and small moons by the Cassini Imaging Science Subsystem (ISS) during the first 9 months of Cassini operations at Saturn have produced many new findings. These include new saturnian moons; refined orbits of new and previously known moons; narrow diffuse rings in the F-ring region and embedded in gaps within the main rings; exceptionally fine-scale ring structure in moderate- to high-optical depth regions; new estimates for the masses of ring-region moons, as well as ring particle properties in the Cassini division, derived from the analysis of linear density waves; ring particle albedos in select ring regions; and never-before-seen phenomena within the rings.

Cassini Imaging Science: initial results on Phoebe and Iapetus.

The Cassini Imaging Science Subsystem acquired high-resolution imaging data on the outer Saturnian moon, Phoebe, during Cassini's close flyby on 11 June 2004 and on Iapetus during a flyby on 31 December 2004. Phoebe has a heavily cratered and ancient surface, shows evidence of ice near the surface, has distinct layering of different materials, and has a mean density that is indicative of an ice-rock mixture. Iapetus's dark leading side (Cassini Regio) is ancient, heavily cratered terrain bisected by an equatorial ridge system that reaches 20 kilometers relief. Local albedo variations within and bordering Cassini Regio suggest mass wasting of ballistically deposited material, the origin of which remains unknown.

Cassini Imaging Science: initial results on Saturn's atmosphere.

The Cassini Imaging Science Subsystem (ISS) began observing Saturn in early February 2004. From analysis of cloud motions through early October 2004, we report vertical wind shear in Saturn's equatorial jet and a maximum wind speed of approximately 375 meters per second, a value that differs from both Hubble Space Telescope and Voyager values. We also report a particularly active narrow southern mid-latitude region in which dark ovals are observed both to merge with each other and to arise from the eruptions of large, bright storms. Bright storm eruptions are correlated with Saturn's electrostatic discharges, which are thought to originate from lightning.

Uncertainties in carbon dioxide radiative forcing in atmospheric general circulation models.

Global warming caused by an increase in the concentrations of greenhouse gases, is the direct result of greenhouse gas-induced radiative forcing. When a doubling of atmospheric carbon dioxide is considered, this forcing differed substantially among 15 atmospheric general circulation models. Although there are several potential causes, the largest contributor was the carbon dioxide radiation parameterizations of the models.

Cloud images from the pioneer venus orbiter.

Ultraviolet images of Venus over a 3-month period show marked evolution of the planetary scale features in the cloud patterns. The dark horizontal Y feature recurs quasi-periodically, at intervals of about 4 days, but it has also been absent for periods of several weeks. Bow-shaped features observed in Pioneer Venus images are farther upstream from the subsolar point than those in Mariner 10 images.