On the impact of the SSO scheme in the COSMO model into the development of a deep cyclone in the Tirrenian sea

Case study: April 21 2009

Antonella Morgillo ARPA SIMC Bologna, Italy

General COSMO meeting: Offenbach 7-11 september 2009

Outline

Motivation:

Description of the case study:

Description of the experiments:

Results.

One of the most common error in the COSMO model forecast is the sistematically bias of the surface pressure (see e.g. Damrath et all 2007). The seasonal verification in Arpa – Simc shows the same behaviour in the MSLP forecast. It’s almost systematically biased (negative bias in winter and positive in spring, see e.g. ARPA-SIMC internal verification report).

The SSO scheme deals with the low level flow blocked by a sub-grid scale orography sufficiently high. For this type of blocked flow there is a separation at the mountain flanks, a part of the flow goes around the flanks and the other part goes over the mountains to force the gravity wave. So, the introduction of the SSO scheme ought to resolve, or at least, correct this uncorrected behaviour filling up the low pressure and weakening the high pressure. As shown by J.P Schulz in his paper (COSMO newsletters n° 9 – 2008) it seems to work well.

The Italian penisula is surrounded by the sea, by the Alps in the North and with the Appennine mountains in the middle . This case study describe which kind of effects the SSO scheme has on a deep cyclone spring up in a basin like the Tirrenian sea close to the Appennine mountain and the effect of the Appennine orography on his development.

synoptic map at surface april 21 00

UTC

A

A large area of low pressure in the low Tirrenian sea between the Sardinia island and the Calabria cost (south Italy) will cause precipitation along all the south Tirrenian costs. The following estward flux will bring precipitations along all the central Adriatic cost and along the Appennine mountain (between the Emilia-Romagna and the Abruzzo region). This situation will last for two days (from april 21 to 22).

synoptic map at surface april 22 00

UTC

IR satellite image at 00 UTC of april 21 - 2009.

COSMOI7 MSLP analysis

Operational COSMO model analysis for april 21 at 00 UTC (on the left), 22 april 00 UTC (on the right), and 23 april 00 UTC (on the bottom middle) Contouring every 2 hPa

1016

1008 1004

April 21 00 UTCApril 21 00 UTC April 22 00 UTCApril 22 00 UTC

April 23 00 UTC

Forecast 21/04/09 00 UTC FC+24

ANALISYS 22/04/09 00 UTC

10021004

The 24h forecast The 24h forecast was a little bit was a little bit deeper and shifted deeper and shifted toward the Calabria toward the Calabria costcost

28mm/24h

85 mm/24h

12mm/24h

38mm/24h

TP forecasted by the operational model on april 22 at 00 UTC

Total precipitation(mm/24h) observed at (some) synop stations

Total precipitation (mm/24h) observed on april 22 over the Emilia-Romagna region

Experimental set up.

Initial date: 21 april 2009 00 UTC; fc + 48 hours; Int2lm: version 1.8; COSMO: version 4.6; IC from 12h previous cosmo assimilation cycle (20 april 12 UTC fc+12); BC from IFS analyses.

sso = trueSSO scheme with 4 the additonal external parameter (standard deviation, anisotropy, slope and geographical orientation of sub-grid scale orography)

SSO

sso = false (default)Like the operational one; Ctrl

Parameter change in the namelist

Description of changeExperiments

CTRL SSO

Map of the mslp &Z500 at 00 UTC of 22 april (24 hours later the beginning of the run)

Mslp = blue-dot line Z500 black-solid line

SSO – CTRL: Z500 (on the left) and MSLP (on the right) at 22 april 00 UTC (fc +24)

SSO – CTRL: Z500 (on the left) and MSLP (on the right) at 23 april 00 UTC (fc +48)

TP forecast for CTRL april 22 00 UTC

TP forecast for SSO april 22 00 UTC

SSO – CTRL April 21 fc +24 SSO – CTRL April 21 fc +48

CTRL SSO

Map of the mslp&10m wind at 00 UTC of 22 april (24 hours later the beginning of the run)

SSO - CTRL april 22 april 00 UTC 10m wind

The difference tends towards the opposite direction of the wind flux to show a reduction on the wind speed.

Conclusions: The SSO scheme acts more efficiently on cyclone over land than

over sea, but for this single case study some conclusion can be drawn:

A small weakening of mslp in the maximum of the cyclone and a shift of the minimum towards South-Est nearest to the Calabria cost (in agreement with observations);

A reduction of “upstream” precipitation on the Appennine mountain in Emilia Romagna and on the Calabria cost (maybe mainly due to the SE shift of the minimum);

Weak reduction of the of 10m wind speed over orography (in particular over the Emilia – Romagna).

Thank you

A single case study is not enough to decide if the SSO scheme is

a gain or not for the italian region. If we want to get right

conclusions and a solid statistic we need more case study

and more investigation.

A single case study is not enough to decide if the SSO scheme is

a gain or not for the italian region. If we want to get right

conclusions and a solid statistic we need more case study

and more investigation.

Slide di supporto