Regional re-analysis without regional data - PowerPoint Presentation

Slide1

Regional re-analysis without regional data

VON STORCH HansInstitute of Coastal Research, Helmholtz Zentrum Geesthacht, Germanywith material of李德磊IOCAS, Qingdao

26

September 2016

– LASG, IAP, BeijingSlide2

VON STORCH Hans

Climate researcher (in the field since 1971)Coastal climate (storms, storm surges, waves; North and Baltic Sea, North Atlantic, Yellow Sea); statistical analysisDirector emeritus of the Institute of Coastal Research of the Helmholtz Zentrum

Geesthacht, GermanyProfessor at Universität Hamburg

Guest professor at

中国

海洋大学Slide3

Overview

Spectral nudging approach for constraining regional modelling- Improved representation of medium scale variability- Constructing a homogeneous regional re-analysis.Improved representation in coastal regions:- variability at medium scales.- sub-synoptic phenomena (e.g., polar lows)- forcing fields for impact models (ocean waves, storm surges)The regional reanalysis CoastDat

for governmental agencies, commercial companies and the public/media Slide4

Climate

and downscaling

The genesis of „regional“ climate my be conceptualized (only at

midlatitudes

?) as R = f(L,

Φ

s

) with L = larger scale climate, R = smaller scale climate,

Φ

s

= physiographic detail at smaller scale (mountains, cities, coastlines etc.).

Climate models generate numbers for all scales, beginning at the grid resolution. The smallest of these scales are heavily disturbed because of an insufficient representation of the small-scale physiography but also because of the abrupt truncation at the grid resolution.

The largest scales in global re-analysis may be in many cases considered as well an

d

homogeneously described. The smallest scales are considered less realistic and subject to

inhomogeneities

(sensitive to changes of observational local data availability).Slide5

Skillfully

represented scalesInsufficiently represented scalesGrid point resolutionMaximumresolution

Skillfully represented scales

Insufficiently

represented

scales

Grid point

resolution

Maximumresolution

Added

value

Global Analysis

Regional

Analysis

Con-straining

Downscaling using R = f(L,

Φ

s

) processes the reliably and homogeneously described large scales L. The constraining may be implemented by spectral nudging into a regional or even global dynamical model.

(

von Storch, H., H.

Langenberg

and F.

Feser

, 2000: A spectral nudging technique for dynamical downscaling purposes.

Mon.

Wea

. Rev.

128: 3664-3673)Slide6

Regional re-analysiswithout regional data.

exploiting the presence of a “downscaling” situation L > Rand the availability of long, homogeneous re-analysis of “large-scale” dynamics L.Added value is in R, i.e. in the regional detail, which results from L and the regional physiographic detail (such as coastlines, mountains)Done for - Europe (including hydrodynamic of marginal seas; COASTDAT)- China (Yellow Sea region, see 李德磊),- Central Siberia and Southern Atlantic,- nd recently

the Globe.Slide7

Improved presentation of

in coastal regionsERA-I-driven multidecadal simulation with RCM CCLM over the Bohai Sea and the Yellow Sea region (李德磊, 2015)Grid resolution: 0.06oMaterial by 李德磊 Slide8

Model setups

and datasets

Long-term simulation

COSMO-CLM (CCLM):

1979.01-2013.12,

spectral

nudging

Forcing dataset

ERA-Interim (1979 – 2013,

~

80km,

6

hourly

)

Physical

Para-

meterization

Tiedtke

convection

scheme

and

Charnock-formula

for

RL

Resolution

Spatial

: 0.0625° (~7 km),

40

vertical

layers

,

hourly

output

GridRotated coordinate system168 x 190

Land Station Data67 land surface stations, 3-hourly (HadISD)Marine StationData7 stations, including 3 offshore stations and 4 coastal stations (NCDC and KMA)Satellite DataQuikSCAT L2B in 12.5 km swath data (QSCAT, 1999.12- 2009.11)Slide9

Is there an added value?

9

Added value (positive BSS) in coastal areas for wind speed > 3 m/s

BSS:

[-

1, 1

]

BSS =1, Perfect model

BSS > 0,

added value (improvement)

BSS < 0,

no

added value

is

error variance between the regional model data

and QSCAT;

is

error

variance between the reference

data ERA-I and QSCAT.

Modified Brier Skill Score: BSS (

Winterfeldt

et al. 2011)

Areas with added value are larger for strong wind speed (right) than for wind speed > 3 m/s (left)

BSS (CCLM, ref: ERA-I,

obs:QSCAT

> 3 m/s)

BSS (CCLM, ref: ERA-I,

obs:QSCAT

> 10.8 m/s)

IEO

S

EOSlide10

Comparison of CCLM/ERA-I and in-situ data:

offshore station (IEO)No improvement of CCLM wind speed (left) relative to ERA-I wind speed (right) at offshore station IEOCCLMERA-I

qq

-plotSlide11

11

Comparison of CCLM/ERA-I and in-situ data : coastal station (SEO)CCLM wind speed (left) is in better agreement with observations than ERA-I wind speed (right) at coastal station SEOCCLMERA-I

qq-plotSlide12

Climatological mean of annual extreme surface wind speed (99%-

iles) 12Similar distribution pattern, more spatial variability and detail in CCLM wind field

CCLM: lower values over mountainous areas and larger values over some water areas

CCLM: better in agreement with observations

(m/s)Slide13

NCEP-driven multidecadal simulation with RCM CLM over North Pacific

(陈飞 et al., 2012, 2013, 2014)Grid resolution: about 0.4oEmploying spectral nudging (wind above 850 hPa, for scales > 800 km)Simulation of sub-synoptic phenomenaPolar lows in the Northern North PacificGenerating additional regional dynamical detailSlide14

North Pacific Polar Low

on

7 March 1977

NOAA-5 infrared satellite image at 09:58UTC 7th March 1977

North Pacific Polar Lows

(

陈

飞

et al.,

2012, 2013 and 2014)Slide15

Annual

frequency of past polar lows in the North Pacific

陈

飞

et al., 2013

Number of detected Polar Lows in the North

Pacific per

Polar Low season

(PLS; October

to April

). The trend

from 62 PLSs, from 1948/1949

to 2009/2010

,

amounts to 0.17 cases/year

.Slide16

Improved representation of

forcing fields for impact models NCEP-driven multidecadal simulation with RCM REMO in EuropeGrid resolution: 0.5 oEmploying spectral nudging (wind above 850 hPa, for scales > 800 km)1948-2010 simulationWind and air pressure used to drive hydrodynamical models for describing currents and sea level Wind used to drive models of the statistics of surface waves (ocean waves) in coastal seas (North Sea).Slide17

Red: buoy,

yellow: radar,

blue: wave model run with REMO winds

wave direction

significant wave height

[days]

[days]

Gerd Gayer, pers.

comm

., 2001Slide18

Annual mean winter high waters Cuxhaven

red – reconstruction

, black – observations

Interannual variability of mean water levels

(Weisse and Plüß 2006)Slide19

The

CoastDat-effort at the Institute for Coastal Research@HZG

Long-term, high-resolution

reconstructions

(60 years) of

present

and recent developments of weather related phenomena in coastal regions as well as scenarios of future developments (100 years)

Northeast Atlantic and northern Europe.

Assessment of changes in storms, ocean waves, storm surges, currents and regional transport of anthropogenic substances.

Applications

many authorities with responsibilities for different aspects of the German coasts

economic applications by engineering companies (off-shore wind potentials and risks) and shipbuilding company

Public information

www.coastdat.de

Integration area used in HZG reconstruction and regional scenariosSlide20

Wave Energy Flux [kW/m]

Currents Power [W/m

2

]

Some applications of

Ship design

Navigational safety

Offshore wind

Interpretation of measurements

Oils spill risk and chronic oil

pollution

Ocean energy

Scenarios of storm surge conditions

Scenarios of future wave conditions

Weisse, pers.

c

omm

.Slide21

Conclusion …

Dynamical downscaling (R = f(L,Φs)) works … - Large scales are hardly affected but smaller scales are more realistically described in heterogeneous regions (coasts, mountains)Downscaling allows the generation of homogeneous data sets i.e., a regional re-analysis

with uniform quality (across time). Added value in describing medium scale phenomena – such as wind

storms

Added value in generating regional impact variables,

such as

wind for storm surges and ocean waves.Several such regional re-analysis

has been done, among them for the region of the Bo Hai and the Huang Hai on a 7-km grid by 李德

磊.