Detecting Labrador Sea Water formation from space: DETECTING LSW FROM SPACE

In situ monitoring of deep water formation in the Labrador Sea is severely hampered by the harsh winter conditions in this area. Furthermore, the ongoing monitoring programs do not cover the entire Labrador Sea and are often summer observations. The network of satellite altimeters does not suffer from these limitations and could therefore give valuable additional information. Altimeters can in theory detect deep water formation, because the water column becomes denser during convection and therefore the sea surface becomes lower. This signal is small compared to variability in sea surface height induced by other sources, but when properly filtered and appropriately averaged in time and space, all four winters with Labrador Sea Water formation or renewal in the 1994–2009 period (1994, 1995, 2000, and 2008) have a clear large negative anomaly. The magnitude of this anomaly compares favorably with the range predicted by theory and in situ data analysis. Out of 16 winters, only one winter (2006) would be falsely identified as a deep convection winter based on its sea surface height anomaly signal, while the method did not miss a single deep convection winter. For most deep‒water‒formation winters even the spatial structure of the mixed layer depth distribution can be inferred.