Global climate models help unravel the complex response of our planet to changing conditions, but progress can stall when observations and simulated results disagree. Fortunately, advances in both computing power and satellite imaging have brought opportunities to upgrade the analysis.

The Earth-orbiting CALIPSO and CloudSat satellites, launched in 2006, provide scientists with valuable data on the seasonal distribution of large and small ice crystals.

"CALIPSO and CloudSat are separated by less than a minute, allowing reliable collocation between the CALIPSO-mounted CALIOP LIDAR and the CloudSat-mounted Cloud-Profiling Radar," said Jui-Lin (Frank) Li of NASA’s Jet Propulsion Laboratory.

However, until recently the extent to which researchers could incorporate these ice crystal size data into their simulations was limited.

"The physics [of ice clouds] is tough – older models calculate snowfall, but it’s hard to do this well if you don’t have powerful computers," said Li. "It’s only with the new satellite measurements and the ability to run more advanced models that we could determine that crystal size plays such an important role."

Li and his colleagues isolated the influence of falling snow radiative effects by modifying current models and running comparisons. Test cases included the latest phase of the Coupled Model Intercomparison Project (CMIP5), which features a range of global climate simulations.

"CMIP5 models agree with data on Antarctic sea ice in lots of places – that’s the good news," Li told environmentalresearchweb. "But many of them also put ice in the wrong place or at the wrong time of the year. We show that in CESM1 [Community Earth System Model 1], including falling snow radiation fixes these disagreements in part."

The researchers focused on the interplay between the Sun’s radiation and falling snow on the level of sea ice cover in the Southern Ocean. It’s important to represent this interaction accurately as ice-sheet melt impacts sea-level rise. Sea ice cover also affects energy flows, reflecting radiation from the Sun and restricting heat and moisture exchange between the ocean and atmosphere.

Li and colleagues published their study in Environmental Research Letters (ERL) .

Related links

Related stories