05.08.2005 - 1 -

COSMO General MeetingZürich, 20 - 23 Sept 2005 1christoph.schraff@dwd.de

Martin Lange and Christoph Schraffmartin.lange@dwd.de

christoph.schraff@dwd.de

Latest Results on Variational Soil Moisture Initialisation

05.08.2005 - 2 -

COSMO General MeetingZürich, 20 - 23 Sept 2005 2christoph.schraff@dwd.de

model setup

• LM version 3.15• ELDAS configurations, 2-layer soil model• continuous assimilation cycle, 00-UTC forecasts

parameters setup related to soil moisture initialisation (SMA) for 4 experiments

variables in cost function precipitation fields used to update (for which prediction should soil moisture from one day to

next be improved by design) (evaporation always from

model)

‘SMA-T2m’ T2m precipitation of model forecast

‘SMA-T2m+Rh2m’ T2m + RH2m precipitation of model forecast

‘SMA-T2m+Rubel prec.’ T2m observed (‘Rubel’) precipitation

‘SMA-T2m+Rh2m+Rubel’ T2m + RH2m observed (‘Rubel’) precipitation

‘no SMA’ - -

ELDAS experiments for May – December 2000

05.08.2005 - 3 -

COSMO General MeetingZürich, 20 - 23 Sept 2005 3christoph.schraff@dwd.de

time series of running monthly mean

model increments

ELDAS domain average of soil moisture increments in bottom layer

SMA increments

evaporation > precipitation in summer SMA increments have more variability

top-layer mean increments are much smaller (not shown)

05.08.2005 - 4 -

COSMO General MeetingZürich, 20 - 23 Sept 2005 4christoph.schraff@dwd.de

time series of running monthly mean

model increments

root mean square over ELDAS domain of bottom-layer soil moisture increments

SMA increments

SMA increments >> model increments,

further increased if RH2m in cost function

05.08.2005 - 5 -

COSMO General MeetingZürich, 20 - 23 Sept 2005 5christoph.schraff@dwd.de

time series of running monthly mean

model increments

root mean square over ELDAS domain of top-layer soil moisture increments

SMA increments

( model increments smaller if

observed precipitation used )

SMA increments < model increments,

yet increased if RH2m in cost function

05.08.2005 - 6 -

COSMO General MeetingZürich, 20 - 23 Sept 2005 6christoph.schraff@dwd.de

time series of running monthly mean

bias

T2m forecasts for 12 and 15 UTC (ELDAS domain and time average for 00-UTC LM runs)

r m s e

SMA reduces bias in warm season SMA reduces rmse by ≥10% in warm season,

use of RH2m slightly beneficialuse of observed precip slightly beneficial

05.08.2005 - 7 -

COSMO General MeetingZürich, 20 - 23 Sept 2005 7christoph.schraff@dwd.de

time series of running monthly mean

bias

RH2m forecasts for 12 and 15 UTC (ELDAS domain and time average for 00-UTC LM runs)

r m s e

use of RH2m reduces bias in May - July SMA reduces rmse by 10 – 30 %,

use of RH2m beneficialuse of observed precip beneficial

05.08.2005 - 8 -

COSMO General MeetingZürich, 20 - 23 Sept 2005 8christoph.schraff@dwd.de

time series of running monthly mean

frequency bias

6- to 30-hour precipitation forecasts (ELDAS domain average for 00-UTC LM runs)

5 mm threshold

SMA strongly reduced bias, increases TSS by about 5 – 10 %

use of RH2m : neutral impactuse of observed precip : beneficial

TSS

05.08.2005 - 9 -

COSMO General MeetingZürich, 20 - 23 Sept 2005 9christoph.schraff@dwd.de

Conclusions

• current implementation of soil moisture initialisation is strongly beneficial for prediction of daytime T2m and RH2m, and also beneficial for precipitation forecasts

• inclusion of RH2m in addition to T2m in cost function further improves predicted RH2m

• use of observed precipitation to update soil moisture in time further improved prediction of daytime RH2m and of precipitation

• best results with both modifications

Further Plan

• investigation to replace the variationally derived relationship between 2-m temperature (+ 2-m humidity) and soil moisture by a parameterized regression.

this would render obsolete the extra model forecast integrations required in the current SMI implementation

Note

• the soil moisture initialisation adapted to the multi-layer soil model is running in the pre-operational LME suite