By Steven Goddard
There have been a number of inaccurate claims made by commentors about Navy PIPS2 ice thickness maps. These claims have been along the lines of :
- PIPS isn’t used by the Navy any more, because it isn’t accurate enough
- PIPS maps over-represent ice because they don’t see areas of open water
- PIPS maps don’t take into account ice concentration. They consider the ice to be 100% concentrated
- PIPS is just a model. It isn’t an accurate representation of the ice.
04/06/2010 – Pamela Posey
The Polar Ice Prediction System (PIPS 2.0) is the current U.S. Navy’s operational ice forecasting system.
PIPS 2.0 forecasts ice conditions in the northern hemisphere with a horizontal grid resolution ranging from 17-33 km depending on the grid location. The system couples the Hibler ice model to the Cox ocean model and exchanges information by interfacing the top level of the ocean model with the ice model. Ice concentration fields derived from the Special Sensor Microwave/Imager (SSM/I) are assimilated into the PIPS 2.0 system along the ice edge. The system produces a 120-hour forecast of ice fields which are sent to the National Ice Center (NIC) to be used in their daily ice forecasts.
The model-derived ice thickness field and the ocean surface temperature field are then adjusted to be consistent with the concentration data.
These models are required to go through rigorous validation studies to prove their capability to produce accurate short term variability. Data assimilation plays a major role in the accuracy of these forecasts. Once operational, continuous quality control and evaluation of the products may be used to upgrade the system and improve forecast accuracy.
The video below for June 10, 2010 shows that PIPS maps accurately reproduce current ice conditions. It overlays the UIUC ice concentration map on the PIPS map.
Map sources :
As you can see, areas of open water are shown as open water, and areas of low concentration also have lower thicknesses. The incorrect claims repeated over and over and over again by FUDsters just don’t hold any water.
PIPS2 is not perfect. Here is what the Navy says :
A recent study by a group of scientists from the NIC and NOAA (Van Woert et al., 2001), showed that although the PIPS 2.0 forecasts (48-hour) were better than persistence on average, there were still substantial biases in its prediction of the growth and decay of sea ice in the marginal ice zone. PIPS 2.0 often over-pre- dicts the amount of ice in the Barents Sea and therefore often places the ice edge too far south. In contrast, PIPS 2.0 often under-predicts the ice extent in the Labrador Sea and Hudson Bay.
This doesn’t affect my calculations, because I am only measuring regions which normally contain significant amounts of late summer ice. Also, my comparisons are relative year over year comparisons. The absolute values of ice thickness are not important to my conclusions.
Conclusion : PIPS2 maps is the best available and are used by the US Navy. They are quite accurate and they do account for ice concentration. No doubt, some commentors will continue to ignore the facts, and post instead what suits their agenda.