Low stratus (and fog) forecast for Central Europe introducing an empirical enhancement scheme for sub-inversion cloudiness Harald Seidl and Alexander Kann

EMS Ljubljana Low stratus (and fog) forecast for Central Europe introducing an empirical scheme for sub- inversion cloudiness Content  Problem of inversion initialization and forecast with Aladin  Introduction of sub-inversion (SK) cloudiness scheme  Evidence for significant improvements with SK  How to diagnose ground fog without (prognostic) cloud liquid water ?  Introduction of cloud liquid water, recent developments  Outlook

EMS Ljubljana Low stratus (and fog) forecast for Central Europe introducing an empirical scheme for sub- inversion cloudiness  Problem of inversion initialization and forecast with Aladin

EMS Ljubljana Low stratus (and fog) forecast for Central Europe introducing an empirical scheme for sub- inversion cloudiness Inversion forecast verification Inversion strengthInversion base height Inversion top height +hhMAEBIASMAEBIASMAEBIAS Modelled inversions systematically too low and too weak ALADIN model, Jan-Dec 1997

EMS Ljubljana Low stratus (and fog) forecast for Central Europe introducing an empirical scheme for sub- inversion cloudiness  Introduction of sub-inversion (SK) cloudiness scheme SK-1) Coherent levels of quasi-saturation must define a layer of thickness Ф exceeding a critical thickness value Ф c. SK-2) Coherent inversion of critical strength in terms of temperature difference > c must also exist in order to trigger Stratus diagnosis. SK-3) “Shift criterion”: quasi-saturation zone may not arbitrarily penetrate into inversion layer: Penetration depth δ may not exceed critical value: δ < δ c. Current settings are:  c =0.1, Ф c =2000 (m 2 /s 2 ), c =1.5K, and δ c =2000 (m 2 /s 2 ). (Ф c and δ c are in terms of geopotential)  Now if all three criteria are fulfilled at any gridpoint SK-scheme runs also its enhancement section (fig. 1b) at this certain grid point, in the following way:  Cloudiness for each level within low cloud etage is re-initialised to zero, and each quasi-saturated level as well as total low cloudiness is set to 1.0 (100 per cent).  This will trigger a strong response from radiation routine “ACRANEB” tending to intensify or at least keep the pre-existing inversion(s) through infrared flux divergence inducing cloud-top cooling and heating at lower levels.

EMS Ljubljana Low stratus (and fog) forecast for Central Europe introducing an empirical scheme for sub- inversion cloudiness

EMS Ljubljana Low stratus (and fog) forecast for Central Europe introducing an empirical scheme for sub- inversion cloudiness

EMS Ljubljana Low stratus (and fog) forecast for Central Europe introducing an empirical scheme for sub- inversion cloudiness Evidence for significant improvements with SK  Focus on case studies  Evaluation episodes (statistical scores)

EMS Ljubljana Low stratus (and fog) forecast for Central Europe introducing an empirical scheme for sub- inversion cloudiness

EMS Ljubljana Low stratus (and fog) forecast for Central Europe introducing an empirical scheme for sub- inversion cloudiness

EMS Ljubljana Low stratus (and fog) forecast for Central Europe introducing an empirical scheme for sub- inversion cloudiness  Diagnostic relationship in order to derive visibility categories (no cloud liquid water in the model) VisibilitySkrhcrit[%]Inrhcrit[%]Norhcrit[%]SFCinvCrit 350m K 600m K 1000m K 1500m K 3000m K COST722 – Model Intercomparison: How to diagnose ground fog without (prognostic) cloud liquid water ?

EMS Ljubljana Low stratus (and fog) forecast for Central Europe introducing an empirical scheme for sub- inversion cloudiness  IF SK-scheme has diagnosed lifted fog conditions, criterion rh(1) ≥ Skrhcrit is used.  OTHERWISE test for surface inversion strength ≥ SFCinvCrit.  IF the latter is TRUE, rh(1) ≥ Inrhcrit in order for visibility below threshold  IF NOT THEN rh(1) ≥ Norhcrit in order to remain under visibility threshold.

EMS Ljubljana Low stratus (and fog) forecast for Central Europe introducing an empirical scheme for sub- inversion cloudiness 3 months evaluation for Lindenberg/Germany (autumn 2005) → kind of reference for later model versions

EMS Ljubljana Low stratus (and fog) forecast for Central Europe introducing an empirical scheme for sub- inversion cloudiness Recent developments & Outlook  Tests with INCA analysis (&nowcasting) system to gain more accurate initial vertical state of the model atmosphere (esp. Lifted inversions !!) => not yet very successful (influence radius of observed soundings not large enough for the analysis)  Experiments with soil moisture initialization (preliminary results indicate improvements of cloudiness but rather of the Sc Cugen. type than the lifted stratus type; ground fog forecast however should improve !)  Aladin/AUT cycle29-30 with prognostic cloud water (Lopez scheme): precondition for fog simulation and forecast closer to natural physical processes

EMS Ljubljana Low stratus (and fog) forecast for Central Europe introducing an empirical scheme for sub- inversion cloudiness Progn. Liqu. Water & LOPEZ Traditional SK-scheme Extended SK- Scheme added Austrian LAEF methods (test suite) ETKFETmulti physicsbreeding

EMS Ljubljana Low stratus (and fog) forecast for Central Europe introducing an empirical scheme for sub- inversion cloudiness Tests with Aladin/AUT cy29 (+cloud water +SK)  Direct use of cloud liquid water at lowest model level → ground fog indicator  SK scheme still working  Benefits in comparison with reference run (no SK) seem to reduce → Calibration of SK, incorporation of cloud water into this sub-inversion scheme

EMS Ljubljana Low stratus (and fog) forecast for Central Europe introducing an empirical scheme for sub- inversion cloudiness

EMS Ljubljana Low stratus (and fog) forecast for Central Europe introducing an empirical scheme for sub- inversion cloudiness Some similarities, but still: A lot to improve !

EMS Ljubljana Thank you for your attention !