Predictability and dynamical processes

Heini Wernli

Institute for Atmosphere and Climate ScienceETH Zurich

HIW Workshop, Karlsruhe18 March 2013

Key points

(i)the dynamics of high-impact weather is often complex and closely related to basic/fundamental research questions,

(ii)relevant processes range from large-scale to microscale; from Rossby wave dynamics to deep convection, cloud microphysics and turbulence,

(iii) occasionally, forecast uncertainties are still large for various of these processes and their interaction,

(iv) field experiments, together with dedicated modeling/diagnostic research activities, are important for bringing the community together to work jointly on important issues,

(v)important pillars of a future HIW project should be (a) collaboration between universities, research institutes, and weather services, and (b) research projects like, e.g., DIAMET and PANDOWAE.

High-impact wet snowfallPoor forecasts for wet snowfall event in NW Germany in Nov 2005

- transition from rain to wet snow poorly predicted by ECMWF and COSMO models

- issue of correctly predicting position of surface cyclone

Frick and Wernli 2012 (WaF)

Sting jets: high-impact winds in cyclonesComplex dynamical & physical processes on various scales

Clark et al. 2005 (QJ)

Sting jet within cyclone Friedhelm(8 Dec 2011), observed during the DIAMET field experiment

- Frontal structure of cyclone- Conditional symmetric instability?- Sublimation of ice particles?- Stability of BL and vertical momentum transport

Heavy precipitation events: Stability vs. transport

Role of conditional instability (CAPE) and horizontal moisture flux varies for different events

Nuissier et al. 2008 (QJ)

Heavy precipitation events and long-range moisture transportFlooding event in Bernese Oberland in October 2011

- plume of moisture extending from the tropics to central Europe (cf. atmospheric river, tropical moisture export)

- link to ET of Philipp

from Nicolas Piaget

Relevance of synoptic systems for precipitation extremes% of HPE associated with cyclone or WCBHPE defined as >99 percentile in ERA-Interim dataset

Pfahl et al., in preparation

Case study of major forecast bust

5-day ECMWF forecast from 12 UTC 13 Jan 2005

SLP average over C. Europe

analysis 1003 hPa

deterministic fc 1024 hPa

EPS 1012 – 1037 hPa !!

what happened meteorologically?

Case study of major forecast bust

ana +3.5

fc +3.5

ana +5

fc +5

T850 and SLP

Case study of major forecast bust

ana +3.5

fc +3.5

ana +5

fc +5

R1T1

T1R1

R1R1

PV on 320 K

T1

T1

generation of a positive PV anomaly(downstream trough)

WCB amplified upper-level ridge downstream troughWCB triggers / enhances downstream Rossby wave activity

+

-

-

Hypothesis: errors in WCBs amplify downstream

Warm conveyor beltsMicrophysical processes diagnosed in COSMO simulation

Joos and Wernli 2012 (QJ)

T-NAWDEX-Falcon: IOP3 (19/20 Oct 2012)In-situ observations in warm conveyor belts

from Maxi Böttcher

- TPCs are frequent and fairly long-lived (> week)- TPCs can trigger / amplify waves along jet- TPCs are associated with characteristic pattern of radiative and latent heating

Kew et al. 2010 (MWR)Cavallo & Hakim 2010 (MWR)

Tropopause polar cyclonesLong-lived mesoscale vortices associated with diabatic processes

radiative heating

latent heating

Croci Maspoli & Davies 2009 (MWR)

Longer time scales: cold winters & hot summersCold winter 2005/06 in Europe: five events of upstream blocking

blocking events

temper

ature

blocking

cold

influence from upstream weather systems

HIW-related research projects

T-PARC, DIAMET, PANDOWAE, Prevassemble, …

• strong (international) collaboration

• collaboration between weather services & universities

• linkage of observational & modeling research

• strengthen research with benefit for operational forecasting at universities

• education of next generation of “weather scientists”

key component of future WWRP HIW Project

Scientific challenges for future HIW project

Scale-interactions of dynamical and physical processes including large-scale, mesoscale & microscale

Non-linear processes & thresholds

Upscale and downscale forecast error propagation

Interaction of atmospheric water cycle and dynamics

Interaction of cloud microphysics and dynamics

Specific model evaluation for HIW events

Quantify benefit from convection-permitting models for HIW

Link communities from nowcasting to (sub)seasonal prediction