A soft solid surface on Titan as revealed by the Huygens Surface Science Package.

The surface of Saturn's largest satellite--Titan--is largely obscured by an optically thick atmospheric haze, and so its nature has been the subject of considerable speculation and discussion. The Huygens probe entered Titan's atmosphere on 14 January 2005 and descended to the surface using a parachute system. Here we report measurements made just above and on the surface of Titan by the Huygens Surface Science Package. Acoustic sounding over the last 90 m above the surface reveals a relatively smooth, but not completely flat, surface surrounding the landing site. Penetrometry and accelerometry measurements during the probe impact event reveal that the surface was neither hard (like solid ice) nor very compressible (like a blanket of fluffy aerosol); rather, the Huygens probe landed on a relatively soft solid surface whose properties are analogous to wet clay, lightly packed snow and wet or dry sand. The probe settled gradually by a few millimetres after landing.

Measurements of the offshore wave climate around the British Isles by satellite altimeter.

Satellite altimetry gives a new perspective on ocean wave climate. Measurements around the British Isles show a strong seasonality, with exceptionally large average wave heights to the west and north of the British Isles in the winter. Furthermore, the interannual variability of winter wave climate is very high. Most of this variability can be described by a strong linear dependence on the North Atlantic Oscillation (NAO) index. This relationship may largely explain observations of increasing wave heights in the northeastern Atlantic and northern North Sea during the latter decades of the 20th century, coincident with a long-term rise in the NAO.

Rossby waves: synergy in action.

Rossby waves are an important phenomenon, linking processes in the west of ocean basins with forcing that occurred earlier in the east. We show evidence for such features in satellite-derived datasets of sea-surface height, temperature and ocean colour, using a section of the south Indian Ocean as an example. We discuss the possible mechanisms for an effect on chlorophyll, and we investigate this by comparing the ocean colour signal with the other datasets. In this region, the primary mechanism for a Rossby-wave signal in ocean colour appears to be meridional advection of water across a strong chlorophyll gradient. However, this cannot fully explain the observations in the westernmost basin.