basic characteristics of stratospheric predictability: results from 1-month ensemble hindcast...

Basic characteristics

of stratospheric predictability:

Results from 1-month ensemble hindcast

experiments for 1979-2009

Masakazu TaguchiAichi University of Education

Kariya, JAPAN

Despite potential importance, stratospheric PR

for days to months is relatively unexplored.

Ref.: Baldwin and Dunkerton (2001)

■Suggestion

Importance of stratosphere in extended weather forecasts

■Stratospheric PR for intraseasonal timescales

Relatively unexplored

⇒JMA 1-mo. ensemble HC data became available (thru MSJ).

Intro 　

We use data from JMA 1-mo. hindcast (HC)

experiments for 1979-2009.

JMA HC data　

Ref.: JMA （ 2010, 2011）

■System 　 JMA 1-mo. EP system of March 2011 version 　 Global model w/ TL159(Δx≈110km), L60 to 0.1hPa 　■Initial conditions 　 10th, 20th, last day of each month for 1979-2009 　 Perturbations in troposphere of NH and tropics　 1-month ensemble predictions with N=5 ■Boundary conditions Assume persistent SST anomalies

We use some basic quantities and measures

to examine stratospheric PR.

Quantities and measures

Ref.: None

■JRA-25/JCDAS reanalysis and HC data

AJRA, AHC,n, AHC,EM where A= [U], Z10, Z500

EM: ensemble mean, [ ]: zonal mean

■Measures to evaluate HC data for Z10 or Z500 (Φ≥20N)2 1/ 2

1 1

1 1SPREAD( ) { ( 10 ( ) 10 ( )) }

I N

n EMi n

t Z t Z tI N

2 1/ 2

1

1RMSE( ) { ( 10 ( ) 10 ( )) }

I

EM JRAi

t Z t Z tI

Root of spatial mean of error2 of EM from JRA

Spatial mean of spread at each gridpointi: index for space i = 1, 2, …, In: ensemble n =1, 2, …, N N = 5

Winter stratosphere has larger average and

variability in RMSE, with longer timescale.

RMSE

Normalized RMSE of Z, poleward of 20N. 10hPa

500hPa

Ref.: Black lines denote SD of interannual variability of JRA monthly Z for Φ≥20N.

PL Results for each yearMean wrt year

SD= 59.1

SD=362.5 SD= 63.6

SD= 33.7

No

rma

lize

d R

MS

E

PL is longer on average and has larger variability

at 10hPa (in winter) than at 500hPa.

PL

Ref.: PL is defined when RMSE exceeds 1xSD poleward of 20N. Bin widths differ between 10 and 500 hPa.

PDFs of PL (Predictable Limit)

10hPa

500hPa

Will be meaningless because RMSE

is very small.

15.8±6.4 15.1±4.1

MN±SD=5.5±1.1 4.1±0.7

Both average increase and variability

in RMSE Z10 become large around 15 days.

RMSE

Ref.: None.

Time variations of RMSE of Z10 (Φ 20N) ≧

INITIAL=0110

MN±1xSDof RMSE

RMSE for each year

SPREAD&RMSE of Z10 are positively

correlated, with 　 large skewness of RMSE

(clear outliers). SPREAD-RMSE

Ref.: This figure uses time means of SPREAD/RMSE for t=15±3 d, after 11/10-02/10.

Scatter plot between SPREAD and RMSE of Z10

Additional lines

Best-fit line

At 60N, 10hPa, Δ[U] ≥ +15 m/s Δ[U] ≤ -5 m/s Δ = EM of HC – JRA.

SPREAD (m)

RM

SE

(m

) R=+0.46

FREQ. (%) FREQ.

(%)

SPREAD&RMSE of Z500 are positively

correlated, with less marked outliers.

SPREAD-RMSE



At 60N, 10hPa, Δ[U] ≥ +5 m/s Δ[U] ≤ -5 m/s Δ = EM of HC – JRA.

SPREAD (m)

RM

SE

(m

) R=+0.41

Best-fit line

FREQ. (%) FREQ.

(%)

PDFs of RMSE and DISTANCE (to best-fit lines)

are more highly skewed at 10hPa.

RMSE and DISTANCE

Ref.: Distance is measured from each data point perpendicularly to the best-fit line.

PDFs of RMSE and DISTANCE at 10/500hPa

(Normalized) (Normalized)

10hPa

500hPa

10hPa

500hPa

Level Skew.

10hPa 2.3

500hPa 0.62

Level Skew.

10hPa 2.5

500hPa 0.64

In the following, we look at meteorological

conditions for a few outliers.

SPREAD-RMSE



SPREAD (m)

RM

SE

(m

)

1

23

(4)(5)

HC data (#1) completely miss

occurrence of vortex split MSSW in Jan., 2009.

#1 (INIT=20090110)

Ref.: Color shades denote Z10. Black contours denote anomalies of JRA from climatology, or error of HC EM from JRA.

SPREAD Z10 (m)

RM

SE

Z1

0 (

m)

INITIAL +1 wk +2 wks

HC JRA

Z10

JRA

HC

EM

1

(4) 2006(5) 1985

2009/01/10↓

HC data (#2) fail to reproduce horizontal vortex

structure in recovery after mSSW in ND, 2000.

#2 (INIT=20001130)


SPREAD Z10 (m)

RM

SE

Z1

0 (

m)


HC JRA

Z10

JRA

HC

EM

2

2000/11/30↓

HC data (#3) fail to reproduce horizontal vortex

structure during MSSW in January, 2003.

#3 (INIT=20030110)


SPREAD Z10 (m)

RM

SE

Z1

0 (

m)


HC JRA

Z10

JRA

HC

EM

3

2003/01/10↓

Using JMA HC data, this study reveals following

characteristics of stratospheric PR for NH winter.

Summary

Ref.: None

■SPREAD and RMSE

Larger average and variability

　⇒ Longer average (≈2 wks) and larger variability of PL

■SPREAD-RMSE (skill) relationship

◇Positive correlation

◇Large skewness in RMSE, or outliers from the relationship

Contributed by SSWs in onset and also recovery phases

　⇒ Suggest importance and difficulty of good SSW predictions

in extended weather forecasts

Back-ups

The climatological bias of HC data

from JRA reanalysis is generally small.

Bias

Ref.: Initial dates is 1210 or 0610, and t=34 d (last day of predictions). Dots denote 95% significance in two-tail test, i.e., HC clim differs from JRA clim.

Clim. bias of [U] (m/s) in mid-January/July

Winter stratosphere has large spread on

average.

Yr-to-yr (case-to-case) variability is also large. SPREAD

SPREAD of Z (m) poleward of 20N.

Ref.: Cyan lines denote results for each year. Blue lines denote the mean for all years.

10hPa

500hPa

HC data (#4) fail to reproduce the onset

of the MSSW in January, 2006.

#4 (20060110)


SPREAD Z10 (m)

RM

SE

Z1

0 (

m)


HC JRA

Z10

JRA

HC

EM

HC data (#5) mostly fail to reproduce the onset

of the MSSW in Dec./Jan., 1984/85.

#5 (19841220)


SPREAD Z10 (m)

RM

SE

Z1

0 (

m)


HC

JRA

Z10

JRA

HC

E

M

basic characteristics of stratospheric predictability: results from 1-month ensemble hindcast...

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