Operational water-vapour products at EUMETSAT, latest evaluation in pre-convective situations and future plans

EUMETSAT generates operational water-vapour and temperature ‘all-sky’ products from the infrared (IASI) and microwave (AMSU, MHS) sounders onboard EPS/Metop satellites (EUMETSAT Polar System). The atmospheric profiles are available to the regional users within 15 to 30 minutes from sensing, via EUMETSAT EARS-IASI L2 service¹.

The potential for the prediction and monitoring of severe storms of such satellite–based thermodynamic profiles -and their derived nowcasting-relevant parameters, e.g. CAPE- complementary to numerical forecasts has been established in dedicated severe storm test beds² and nowcasting studies³. The operational baseline of the future sounding missions –IASI-NG and MTG-IRS- directly builds on the experience made with IASI, implementing the same machine-learning all-sky retrieval approach, namely the piece-wise linear regression (PWLR)⁴.

It is essential to characterise and document the precision of the satellite products in particular in severe weather precursor conditions. The quality of the satellite sounding products is routinely assessed against radiosondes for validation and long-term monitoring purposes⁵. Unfortunately, the satellite overpass times rarely match the in situ measurements from the synoptic sondes. The 3h difference tolerated in building the validation match-ups (satellite-sonde) can incur large collocation uncertainties especially in the boundary layer. This and the fact that radiosonde sites are relatively scarce, makes it difficult to evaluate the satellite products in pre-convective situations with large statistical significance.

To circumvent this and evaluate satellite products specifically in pre-convective environments, we studied the potential of routine in situ measurements acquired from commercial airlines. These are coordinated under WMO auspices in the AMDAR (Aircraft Meteorological Data Relay) programme. The AMDAR data have the decisive advantage of higher spatio-temporal density than radiosondes, which ensures numerous and more representative collocations to satellite products.

We present here the preliminary results, confirming that satellite sounders are capable of quantifying atmospheric instability. These results also tend to quantitatively identify a dry bias in unstable situations, which was previously suspected, while confirming the relative robustness and accuracy of temperature soundings in the free and lower troposhere. The next generation of EUMETSAT imagers, e.g. MTG-FCI and EPS-SG/METimage, will operate channels around 0.9 µm. This near-infrared channel has unique sensitivity to atmospheric moisture in the boundary layer while infrared sounders have their maximum sensitivity in the mid-troposphere. We will also present the status and plans to retrieve atmospheric humidity from the optical imagers (TCWV first, and then study in the boundary layer) and their complementarity with passive sounders, which will provide key information for storm prediction.

 

¹ https://www.eumetsat.int/ears-iasi

² https://www.eumetsat.int/severe-storm-forecasting-lab

³ https://www.eumetsat.int/hyperspectral-instability-monitoring-using-iasi

⁴ https://www.eumetsat.int/IASI-PWLR

⁵ https://www.eumetsat.int/iasi-level-2-geophysical-products-monitoring-reports