Reanalysis

A blend of many observations + a physics model, run to produce a complete, gap-free, consistent record of the atmosphere or ocean (e.g. MERRA-2).

Why it matters

Observations have gaps (clouds, orbit gaps, instrument downtime). Reanalysis fills them with model physics so you get a value everywhere, every hour — but it’s part model, not pure measurement.

Where you’ll meet it

• MERRA-2 is NASA’s flagship atmospheric reanalysis — it stitches decades of satellite observations into hourly, gap-free fields of wind, temperature, humidity, and aerosols.
• It’s distributed through the GES DISC data center, so you reach it the same way as other NASA products: an Earthdata login and an OPeNDAP or download endpoint.
• When you need a value at a spot a satellite never directly measured (a cloudy day, a polar gap), reanalysis is the layer that fills it — useful context, but remember it’s part model.

In plain terms

Like a detective reconstructing a complete timeline from partial witness accounts plus knowledge of how events must unfold — coherent, but inferred where evidence is thin.