WISHE mechanism cou ld not dr ive PL intensification – LH and SH fluxes during hole life-time period < 80 W/m2

30.09 00:00 01.10 00:00H

eat

flu

x, W

/m2

4.2 Latent & sensible heat fluxes

Polar lows (hereafter PL) are intensive high latitude maritime vortices usually characterized by high wind velocity (more 15 m/s) and precipitation (up to 40 mm/h), which could be dangerous for sea operations’ implementation [4]. Increased interest in natural recourses extraction and marine traffic in Arctic region in case of continuing global warming cause the necessity of high-quality PL forecasting. Lack of observational data and wide variety of PL types in different geographical and atmospheric conditions causes the absence of the concept of PL.This investigation is aimed at evaluation the role of various mechanisms in the dynamics of a particular real case of polar low development using mesoscale numerical simulations data. Quality of modelling was estimated by comparing model wind and water vapor fields with that received from satellite data. Two numerical experiments were conducted – with microphysics parameterization and without it - to assess the role of CISK mechanism. In order to divide low- and upper-level forcing in PL dynamics we used attribution concept applied to quasi-geostrophic omega equation ensured that QG theory could be used for this PL case.

Case: Mesocyclone in Kara sea, 29 – 30 September 2008Model: Weather Research and Forecasting model (WRF ARW) [1]Resources: Supercomputer “Lomonosov”, MSU [2]Initial and boundary conditions data: ERA-Interim reanalisys(European Centre of Medium-range Weather Forecast) Observational data: satellite cloud fields of MODIS (AQUA), data from microwave radiometer

AMSR-E (AQUA) for wind speed on 10 meters level and integrated atmospheric water vapor [3], wind speed and direction (QuickSCAT scatterometer)

Numerical simulation setup:Mesh spacing: 5 km (225*210 grid points) and 50 vertical levels Parameterizations and schemes:џ Community atmospheric model for long/shortwave radiation, џ Mellor-Jamada- Janjich for PBL turbulence, џ Monin-Obukhov for surface layer, џ Noah of 4 soil levels for surface scheme, џ microphysics processes by Goddard center and convection resolved directly.

Upper and low level forcing could be divided by using height attribution concept applying for quasi-geostrophic omega equation:

As we reduce it to the Helmholtz-formed operator

Does quasi-geostrophic theory could be used with mesoscale phenomenon? Three-dimensional spatial correlation between Ertel PV and Ertel PV in quasigeostrophic assumption = 0.46-0.59. Without gravitation waves over land surface correlation is 0.69-0.82.

Total potential votriсity advection (PVU/s)

QG

Pot

enti

al

vor

tiсi

ty (

PV

U)

an

d t

emp

era

ture

(K

)

4.5.2 Upper-level forcing and quasigeostrophic theory

Mean

seale

vel

pre

ssu

re (

hP

a)

Tem

pera

ture

(°C

) W

ind

sp

eed

an

d d

irect

ion

Tem

pera

ture

(°C

)

at

4 k

m h

eig

ht

4.3 Baroclinic instability

Low-level baroclinic instability wasn't a trigger for PL development: dT/dy ~ 1°C/100km and no cold outbreaks. Shallow baroclinic zone appeared in mid-troposphere due to upper level induced isentropic curvature.

Potential temperature rises with height in each profile point – no conditions for convective PLs

Avera

ge B

run

t-V

ais

ala

frequ

en

cy, s-

1

Pote

nti

al

tem

pera

ture

, K

4.1 Convective instability

Latent heat release (or other heat source) in middle troposphere p r o d u c e s « + » P V anomaly below and «-» anomaly above it [5].

CISK plays a significant role in PL intensification: in “wet” experiment cyclone intensity parameters are in 7-20% lager, than that for “dry” one.

drywet

wet dry

Win

d s

pee

d o

n 1

0 m

, m

/s

Pot

enti

al

vor

tici

ty o

n 8

50 h

Pa (

fill

ed)

on 3

00 h

Pa (

red

cou

nte

r)

4.4 Conditional instability of second kind

Upper (400 hPa) and low(850 hPa) level potential vorticity anomalies.

30.09 02:00 01.10 00:00

Pot

enti

al

vor

tiсi

ty (

PV

U)

an

d t

emp

eratu

re (

K)

How does upper anomaly intensify lower one? Average advection ~0

Pot

enti

al

vor

tiсi

ty (

PV

U)

an

d t

emp

era

ture

(K

)

We can estimate contribution of upper-level forcing by calculating influence function (Green’s function) from omega-equation. Solution of omega-equation in infinite domain looks like:

, where G is Green’s function:

Poten

tial v

ortiсity (P

VU

) an

d tem

pera

ture (K

)

Green’s function

1. Abstract

2. Data & Methods

3. Model vs observations

5. ConclusionsMany aspects of one particular PL were explored. The role of different mechanisms was estimated – neither baroclinic and convective instabilities nor WISHE mechanism triggered and intensified this PL development. Big CISK contribution to the PL increasing is noticeably visible from low-level PV anomaly intensification in “wet” experiment – it rises from 1 to 4,5 PVU during PL lifetime. Wind speeds and absolute vorticity decreases up to 2-3 units in “dry” experiment. The possibility of applying the quasi geostrophic theory to the mesoscale phenomena was shown with 0.93 correlation. Green function was calculated.

[1] – Skamarock, W. C., J. B. Klemp, J. Dudhia, D. O. Gill, D. M. Barker, W. Wang, and J. G. Powers, 2008: A description of the Advanced Research WRF Version 3. NCAR Tech Notes-468+STR.[2] – V. Sadovnichy, A. Tikhonravov, Vl. Voevodin, and V. Opanasenko "Lomonosov": Supercomputing at Moscow State University. In Contemporary High Performance Computing: From Petascale toward Exascale (Chapman & Hall/CRC Computational Science), pp.283-307, Boca Raton, USA, CRC Press, 2013.[3] – Zabolotskikh, E. V., L. M. Mitnik, and B. Chapron (2013), New approach for severe marine weather study using satellite passive microwave sensing, Geophys. Res. Lett., 40, 3347–3350, doi:10.1002/grl.50664.[4] – Polar lows, J. Turner, E.A. Rasmussen, 612, Cambridge University press, Cambridge, 2003.[5] – Hoskins, B. J., McIntyre, M. E. and Robertson, A. W. (1985), On the use and significance of isentropic potential vorticity maps. Q.J.R. Meteorol. Soc., 111: 877–946. doi: 10.1002/qj.49711147002[6] – Deveson, a. C. L., Browning, K. a., & Hewson, T. D. (2002). A classification of {FASTEX} cyclones using a height-attributable quasi-geostrophic vertical-motion diagnostic. Quarterly Journal of the Royal Meteorological Society, 128, 93–117. doi:10.1256/00359000260498806[7] – Clough, S., Davitt, C., & Thorpe, A. (1996). Attribution concepts applied to the omega equation. Quarterly Journal of the Royal Meteorological Society, 122, 1943–1962. doi:10.1256/smsqj.53609

This study was supported by RFBR grant 14-05-00959 «Characteristics of mesoscale atmospheric circulation in the Arctic and their impact on atmospheric – ocean energy exchange»

References & Anknowledgments

Numerical simulation study of polar lows in Russian Arctic:dynamical characteristics

Verezemskaya Polina(1), Stepanenko Victor(1), Baranuk Anastasia(2)1 – Lomonosov Moscow State University (aves.indemicas@gmail.com), 2 – V.I. Il’ichev Pacific Oceanology Institute FEB RAS

4. Testing polar low development concepts

4.5.1 Potential vorticity anomalies

00:00 08:00 16:00 22:00

T, °CP, hPaV, m/s

WRFfields

AMSR-Eor

MODISfields

wind speed, 10 m cloudiness water wapor

WRF integration domain