NASA’s Polarized Submillimeter Ice-Cloud Radiometer (PolSIR): Observing the Diurnal Cycle of Ice Clouds in the Tropics and Sub-Tropics

In May 2023 NASA has selected PolSIR as the latest addition to its Earth Venture Instrument class missions (EVI-6). PolSIR addresses key research priorities related to uncertainties in our current understanding in high clouds and cloud feedbacks as formulated in NASA’s latest Decadal Survey and in the latest Intergovernmental Panel on Climate Change (IPCC) Assessment. In this context, PolSIR will address the following objectives:

• Constrain the seasonally influenced diurnal cycle amplitude, form, and timing of the ice water path (IWP) and particle diameter in tropical and sub-tropical ice clouds,
• Determine the diurnal variability of ice clouds in the convective outflow areas and understand relation to deep convection,
• Determine the relationship between shortwave and longwave radiative fluxes and the diurnal variability of ice clouds,
• Enable improvement of climate models by providing novel observations of the diurnal cycle of ice clouds, ultimately leading to improved climate modeling skills and increased fidelity of climate forecasts in support of critical decision-making.

The PolSIR mission consists of two 16U CubeSats, each equipped with a cross-track scanning polarized submillimeter radiometer near 325 and 684 GHz. The two PolSIR satellites fly in separate, 52-degree inclination, non-sun-synchronous orbits, to measure the diurnal variation of cloud ice and its microphysical properties on a monthly basis in the tropics and sub-tropics.

The mission is PI-led by Vanderbilt University. NASA Goddard provides the project management team that builds the two instruments, while science operations are conducted by the Space Science and Engineering Center at the University of Wisconsin. The two spacecraft will be built by Blue Canyon Technologies. Launch of the two satellites is currently anticipated for late 2026/early 2027.

In this presentation we will give an overview on the science to be addressed by PolSIR and on the current project status.