Cloud Heights Measured by MISR: Time Series, Teleconnections and the TBO

The Multiangle Imaging SpectroRadiometer (MISR) on the Terra satellite has been remotely sensing the geometric heights of cloud-tops using stereo pattern-matching techniques since data collection started in March 2000. Individual cloud heights are retrieved with an accuracy of a few hundred meters, and have been validated against more precise lidar measurements. Operationally, cloud heights are retrieved on horizontal squares of dimension 1.1 km over swath widths of about 300 km, pole to pole, providing sun-synchronous global coverage from 233 orbital paths, repeating every 14 days. The large number of independent measurements yields a sampling uncertainty in the global, annual mean of only ±8 m. This is lower than any other present satellite, and is sufficient to detect interannual and regional variations in cloud heights that are of interest to climate studies.

The climate data record of cloud-top heights from MISR has been reprocessed to provide a homogeneous time series that is now over 18 years duration. The global record is still too short to show any significant trend, but there are significant annual departures from the mean, reaching up to 60 m, that are associated with La Niña and El Niño events.

Regional height anomalies show even greater values, with annual height anomalies of over 2 km for the Central Pacific and the Maritime Continent. These regions oscillate out of phase with each other, showing a quasi-biennial oscillation that is likely related to the Tropospheric Biennial Oscillation. The difference in height anomaly between the Maritime Continent and the Central Pacific provides an index that is virtually synonymous with the SOI.

When the correlations between regional height anomalies are mapped, clear patterns of teleconnections emerge. These link cloud-top height behavior globally, possibly through variations in dynamical modes that alter jet stream patterns. So far, it seems that two different modes in the teleconnection patterns are evident, associated respectively with El Niño and La Niña phases. These different modes appear to affect some regions more than others. Anomalies over the Indian Ocean, for example, are positively correlated with those in the South Pacific Convergence Zone during the La Niña mode, and negatively correlated during the El Niño mode.

The detail contained in MISR’s remotely sensed cloud-top heights appears to be useful not only for global climate studies, but potentially also for extended range meteorological predictions.