ATMOSPHERIC SCIENCE: Really High Clouds

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Science  13 Apr 2001:
Vol. 292, Issue 5515, pp. 171b
DOI: 10.1126/science.292.5515.171b

Most clouds in Earth's atmosphere are found in the relatively dense and moist troposphere, but some, such as the polar clouds that are implicated in ozone destruction, form in higher (stratospheric) regions. Earth's highest clouds, which form in the mesosphere above the poles at altitudes of 82 to 86 kilometers, have been increasing in brightness and geographic extent during the past four decades, and these changes may be linked to anthropogenic emissions of carbon dioxide and methane.

Gardner et al. report measurements of the temperature, iron density, and altitude of polar mesospheric clouds (PMCs) from an aircraft campaign using iron Boltzmann temperature lidar (lidar is similar to radar, but uses laser light instead of microwaves). The observed midsummer temperature profiles are consistent with model predictions, but in the austral fall, the observations deviate from the model. Over the South Pole, PMCs were 2 to 3 kilometers higher than over the North Pole, which may be due to differences in the temperature profile or to stronger upwelling over Antarctica. These data are crucial for validating climate models and predicting how the upper atmosphere will respond to climate change. — JU

Geophys. Res. Lett. 28, 1199 (2001).

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