ALTOS

Perennial sea ice in the Arctic has declined by more than 20% since the mid-1970s, raising concerns that a threshold in the ice-albedo feedback may have been crossed. Recent studies suggest that the observed Arctic sea-ice retreats, as depicted by the summer ice edge, are correlated closely to an upward trend in the downwelling, long-wave radiative flux in the Arctic. Increasing downwelling long-wave flux appears to be driven mostly by increases in clouds and precipitable water vapor, thus establishing the need to better understand the contribution of clouds in this important feedback process.

The Arctic Lower Troposphere Observed Structure (ALTOS) campaign* will conduct regular in situ cloud and aerosol measurements of the Arctic lower troposphere (lower 2 km) at Oliktok Point on the North Slope of Alaska. The principle observing system is a tethered balloon system (TBS) equipped with state-of-the art atmospheric state, cloud microphysics, and aerosol sampling devices. The TBS is supplemented with surface based remote sensing instrumentation characterizing the radiative component of the clouds energy budget as well as the cloud profile. These profiles through the cloudy atmosphere are needed to address several key questions:

I. What is the distribution of microphysical properties of low-level Arctic clouds, and how do these vary with environmental conditions?

II. What is the horizontal variability in microphysical properties in layered clouds, and what are the factors that determine this horizontal variability?

III. How do gravity waves interact with and impact cloud layers?

IV. What is the relationship between micro- and macroscopic cloud properties and the thermodynamic environment in which they occur?

V. How well do ARM microphysical retrievals capture the statistical distributions of cloud properties?

VI. Can we make a definitive conclusion about ice shattering effects on microphysical measurements from the low-aspiration balloon measurements?

ALTOS will provide a comprehensive and extensive description of the cloudy atmosphere over a large range of Arctic atmospheric conditions. This unique data set of in situ cloud microphysics, aerosol and radiative measurements will foremost provide a thorough test for parameterizations of Arctic cloud processes, and secondary, the set of cloud property retrieval algorithms developed by the ARM and other national programs. In the context of the atmospheric state measurements, these cloud observations will provide a unique opportunity to study the interplay between wave structures in the stable atmosphere and cloud properties.

*NOTE: An unfortunate incident in the early stages of ALTOS (October 2010) has resulted in the campaign being terminated. During one of the tethered balloon's initial flights, its primary and secondary tethers broke, and the instrument payload landed in the ocean where it could not be safely retrieved. If replacement instruments can be obtained in the next few months, there is a possibility the campaign could restart in the spring.

Timeline