A Characterization
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A Characterization of Atmospheric Blocking. Huw C. Davies & Mischa Croci-Maspoli Institute for Atmospheric and Climate Science, ETH Zurich, Switzerland & MeteoSwiss, Zurich, Switzerlan d. OUTLINE. I Spatial Structure - Basis for the characterization II Temporal Features

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Huw c davies mischa croci maspoli institute for atmospheric and climate science

A Characterization

of

Atmospheric Blocking

Huw C. Davies

& Mischa Croci-Maspoli

Institute for Atmospheric and Climate Science,

ETH Zurich, Switzerland

& MeteoSwiss, Zurich, Switzerland


Huw c davies mischa croci maspoli institute for atmospheric and climate science

OUTLINE

I Spatial Structure

- Basis for the characterization

II Temporal Features

- Credibility of the characterization

III Dynamics

- Utility of the characterization

.

via consideration of :-

block origin & resilience,

quasi-stationarity & formation

IV Relationship with other Phenomena


Huw c davies mischa croci maspoli institute for atmospheric and climate science

I:

Spatial Structure

Conventional Perspective

  • Notable features:

  • .

  • surface anticyclone, with

  • ridge aloft & local easterly flow

  • elevated tropopause &

  • jet bifurcation

Tropopause

SLP anomaly & 500hPa pattern

Latitudinal cross-section of height anomaly


Huw c davies mischa croci maspoli institute for atmospheric and climate science

I :

Spatial Structure

An Alternative Characterization

  • Block also evident as :

  • .

  • a negative PV anomaly

  • on upper-level isentropes

- anomaly located beneath

an elevated tropopause

PV=2

latitude [°N]

- contiguous anomalies present at surface and upper-level


Huw c davies mischa croci maspoli institute for atmospheric and climate science

I :

Spatial Structure

Essence of Characterization

ABLOCK constitutes

.

“a LENS of low PV located beneath an elevated tropopause”.

Develop an "identification and tracking" tool that can catalogue

every block (sic. negative PV lens) in terms of its:

- amplitude, location, structure, movement and duration.


Huw c davies mischa croci maspoli institute for atmospheric and climate science

II: Temporal

Features

Some Salient Features

  • A Block / PV Lens

  • occurs in preferred geographical regions,

  • persists for supra-synoptic time scales, and

  • during its mature phase does NOT undergo significant :

  • .

  • - change of shape

  • despite being subject to large-scale deformation (sic. a structurally resilient system)

  • .

  • - translation

  • despite its location within band of zonal mean westerlies (sic. a quasi-stationary system)


Huw c davies mischa croci maspoli institute for atmospheric and climate science

II: Temporal

Features

Credibility of Characterization

(B) Synoptic

Simultaneity

1

2

3

4

5

6

7

8

9

10

  • Lens Climatology

  • Comparable !

T&M

P&H

13%

10%

5%

1%

DJF

TIME

(days)

476 events -> 3.5 per month


Huw c davies mischa croci maspoli institute for atmospheric and climate science

Essence of

a Block

Quasi-stationarity


Huw c davies mischa croci maspoli institute for atmospheric and climate science

III: Dynamics

Questions

Questions prompted by “Lens” characterization of a Block:

  • Origin of the ‘Lens’ (i.e. the negative PV anomaly) ?

  • (B) Dynamics of system’s structuralresilience ?

  • (C) Dynamics of the system’s quasi-stationary ?

  • Establishment of the overall PV pattern ?

  • (- i.e. of the lens plus contiguous features)


Huw c davies mischa croci maspoli institute for atmospheric and climate science

III: Dynamics

(A) Origin of Lens

  • NOTE: Two possible sources for anomalously low PV near tropopause :

  • - advection from low latitudes

  • -convection (- diabatic cross-isentropic flow) from the low troposphere.

ASSESS relative contribution by

- examining backward trajectories from the ‘Lens’

Indication that two major sources contribute to the ‘Lens’

- tropopause-level air from far-upstream, and

- low level moist air-stream ascending after passing over warm SST anomaly


Huw c davies mischa croci maspoli institute for atmospheric and climate science

III: Dynamics

(A) Origin of Lens

QUERY :

Is the LENS formation influenced by ascent of the coherent moist airstream ?

NUMERICAL EXPERIMENT :

Modify nature of airstream by changing the positive upstream anomalies

in SST and land surface temperature

TWO INFERENCES

-Block formation sensitive to upstream surface conditions,

-THE ULTIMATE TEST of a model’s cloud dynamics and microphysics

is the delivery of ‘correct’ PV distribution aloft.

Verifiying

ECMWF Analysis

Control

Simulation


Huw c davies mischa croci maspoli institute for atmospheric and climate science

III: Dynamics

(B) Resilience

How does a “PV-Lens” retain its coherent structure ?

(i) PV-lens in a horizontal uniformly sheared flow


Huw c davies mischa croci maspoli institute for atmospheric and climate science

III: Dynamics

(C) Quasi-stationarity

  • What keeps a PV Lens quasi-stationary ?

(i) PV-lens in a horizontal uniformly sheared westerly flow


Huw c davies mischa croci maspoli institute for atmospheric and climate science

III: Dynamics

(C) Quasi-stationarity

IMPLICATION: STATIONARITY requires a richer anomalous PV pattern

- isolated LENS does not suffice

High PV

Low PV

Consider the typical instantaneous

PV distribution on an isentropic surface

crossing the tropopause.

North

High PV

Low PV


Huw c davies mischa croci maspoli institute for atmospheric and climate science

Dynamics

An Example of a Block with a di-polar PV configuration


Huw c davies mischa croci maspoli institute for atmospheric and climate science

(C) Quasi-stationary: Schematic of possible

alternative configurations

III: Dynamics

High PV

Low PV


Huw c davies mischa croci maspoli institute for atmospheric and climate science

(C) Alternative quasi-stationary configurations

III: Dynamics

An Example of a Block with a tri-polar PV configuration


Huw c davies mischa croci maspoli institute for atmospheric and climate science

III: Dynamics

(D) Establishment of overall PV-pattern

BREAKING WAVE(s) SCENARIOS

  • TYPE C TYPE A

High PV

Low PV

High PV

Low PV

High PV

Low PV

High PV

Low PV

High PV

Low PV


Huw c davies mischa croci maspoli institute for atmospheric and climate science

III: Dynamics

(D) Establishment of overall PV-pattern

BREAKING WAVE(s) SCENARIOS

High PV

Low PV

High PV

Low PV


Huw c davies mischa croci maspoli institute for atmospheric and climate science

III: Dynamics

(D) Establishment of overall PV-pattern

EXAMPLE OF A BLOCK FORMATION

Breaking wave

(TYPE A)

..

Secluded Lens

Breaking wave

(TYPE C)

PVU

PV on 320K


Huw c davies mischa croci maspoli institute for atmospheric and climate science

III: Dynamics

(D) Establishment of overall PV-pattern

HOVEMOELLER COMPOSITE (centred on Block)

Meridional Velocity from Day-6 to DAY+6

  • ATLANTIC PACIFIC


Huw c davies mischa croci maspoli institute for atmospheric and climate science

III: Dynamics

(D) Establishment of overall PV-pattern

COMPOSITE OF BREAKING WAVES

  • ATLANTIC

  • PACIFIC

  • TYPE A

  • TYPE C


Huw c davies mischa croci maspoli institute for atmospheric and climate science

IV: Related

Phenomena

Forcing, Patterns of Climate Variability (PCV)

and BLOCKS

CONVENTIONAL CAUSAL CHAIN

Forcing PCV Character ofWeather Systems

AN ALTERNATIVE CAUSAL CHAIN

Forcing Weather Systems

PCV


Huw c davies mischa croci maspoli institute for atmospheric and climate science

IV: Related

Phenomena

Forcing, Sudden Stratospheric Warmings

and BLOCKS

Troposphere - Stratosphere Linkage

Baldwin and Dunkerton 2001


Huw c davies mischa croci maspoli institute for atmospheric and climate science

IV: Related

Phenomena

Sudden Stratospheric Warming & BLOCKS


Huw c davies mischa croci maspoli institute for atmospheric and climate science

IV: Related

Phenomena

Sudden Stratospheric Warmings & BLOCKS

SSW

rules OK !! ?

A. Scaife

Blocks

rule OK !! ?

Evolution of mean zonal wind at 600N between 1000 and 0.1 hPa


Huw c davies mischa croci maspoli institute for atmospheric and climate science

IV: Related

Phenomena

PCV, the NAO and BLOCKS

Normalized time-traces of

the Atlantic Blocking Frequency and the NAO - index

for the three winter months

Blocking

Frequency

NAO-

r = -0.65


Huw c davies mischa croci maspoli institute for atmospheric and climate science

IV: Related

Phenomena

The NAO & BLOCKS

Evolution of NAO index during a blocking event

total tracks

random

random

short tracks (< 10 days)

short duration (< 10 days)

long tracks (> 10 days)

long duration (> 10 days)

random

random


Huw c davies mischa croci maspoli institute for atmospheric and climate science

SOME POSSIBLE INFERENCES

What is

a

BLOCK ??

Requisite for representation

of

BLOCKS in models


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