Convective indexes calculated from HIRLAM output St.Petersburg The Russian State Hydrometeorological University Faculty of Meteorology Meteorological Forecasting Department Kanukhina Anna

Aims: to estimate possible use of convective indexes calculated on HIRLAM outputs for forecasting of place, beginning time and type of mesoscale convective phenomena

Initial data are HIRLAM analysis and forecast files : - air temperature at surface and heights at various periods; - dew point temperature at surface and heights at various periods; - wind parameters at surface and heights at various periods; - surface pressure tendencies; - specific humidity at surface and heights at various periods;

3 types of indexes: diagnostic - atmospheric preparedness for convection development (Г, С, MOCON); index having triggering function (  ); indexes estimating possible type of arising phenomena (CAPE,HEI);

atmosphere statical stability index Г Ге = Г =

moisture convergence MOCON= r – specific humidity, kg/kg ; V – wind speed at 10 m, m/s ;

generalized index indicating possibility of convective disturbance formation С Г =

convective instability indicator (Falkovich’s index) χ  =

EHI energy helicity index EHI =CAPE*H Н – relative wind helicity; CAPE convective available potential energy: CAP  =

Studied cases divided into 3 groups 1 group: days with thunderstorms and showers; indexes indicate high possibility of these weather phenomena; 2 group: days without any convective phenomena but indexes shows existing possibility of phenomena arising( atmospheric instability); 3 group: days associated with thunderstorms and showers; atmosphere is stable according to indexes consideration;

Used data HIRLAM forecast; HIRLAM analysis; sounding data; surface observations (synoptic charts OSCAR, registered thunderstorm charts from FMI site

Studied cases

UTC

Indexes profiles for Kardla, Estonia

MOCON, 1/s for Kardla (Estonia) on UTC analyse fc=12 fc=24

MOCON and χ scattering graph for 6 h forecast (on base of analisys on :00 UTC and forecast :00 UTC)

С and Γ scattering graph for 6 h forecast (on base of analisys on :00 UTC and forecast :00 UTC)

CAPE and HEI scattering graph for 6 h forecast (on base of analisys on :00 UTC and forecast :00 UTC)

UTC

MOCON, CAPE analysis on UTC

Thunderstorms chat on (

СAPE and MOCON scattering graph for 24 h forecast (on base of analisys on :00 UTC and forecast :00 )

С and Γ scattering graph for 24 h forecast (on base of analisys on :00 UTC and forecast :00 )

Indexes’ correlation coefficients (forecast and analysis) Ряд 1 –С Ряд 2 – Γ Ряд 3 – χ Ряд 4 – СAPE Ряд 5 – MOCON Ряд 6 – HEI

Conclusions -χ values defined by forecasts have essential distinctions with calculations from analysis and χ can not be used for atmospheric state estimation when forecasting at period more than 6h. -The same could be said for HEI. -CAPE and MOCON may be used forecasting at period no more than 12h. -С and Γ forecasts are close to real situation even at 24h forecast period particularly for C values.