Intensive observations over the Kuroshio Extension front

in the Baiu season

Yoshimi Kawai (JAMSTEC)& Y. Tachibana, T. Miyama, A. Manda, S. Iizuka, M. Yoshioka,

H. Nakamura10:05-10:25, 5 Aug. 2013

Frontal Scale Air-Sea Interaction Workshop

Unique Observations in Our Project1) Three-vessel simultaneous observations across

the KE front in the Baiu/Meiyu Season of 2012

2) Intensive observations across the Subarctic front in April 2013

3) Aircraft-vessel simultaneous observations across the KE front in July 2013

Why three vessels?• We need to clearly separate spatial distribution

across the front from temporal variations

Why Baiu/Meiyu season?• Relatively calm (if not, we have to escape!)

• Response of low clouds on the SST front• Is the atmospheric response on SST really weak in

summer?

Simultaneous observations (2-6 July)

Seisui-maru

Wakataka-maru

Tansei-maru

Microwave OISST by RSS

Tansei-maru

Wakataka-maru

Seisui-maru

Radiosonde diagram

Every 2 hours

4hr

• Calm condition throughout the observation period• It rained on 2 and 4 July

L

L

Surface wind speed

Surface Air Temp. (SAT)

Meridional wind speed

northerly

southerly

Latent heat flux and distance from the SST front

South North

11:00-15:00, 2 July (JST) 03:00-07:00, 3 July (JST)

Cloud base height 03:00-15:00, 3 July

Color: Relative humidity (%)Dot: cloud base height

L

15:00-19:00, 2 July (JST)

Tanimoto et al. (2009)

Model experimentsControl

Smoothed SST

JCOPE2SST

Obs.

Smoothed JCOPE2

JCOPE2: 3D-VAR ocean reanalysis, 1/12º (by Dr. Miyazawa, JAMSTEC)

on 3 July 2012

NOAA OISST v.2 Observation

JMA MGDSST JCOPE2 Reanalysis

143ºE SST

WRF, nestingBy Dr. Manda

IPRC-RAMBy Dr. Miyama

Cloud Liquid Water in CTL

Red dot: observed cloud base height

SST Smoothed

SST smoothed → cloud height lowered south of the front

Smoothed – Control 　IPRC-RAMBy Dr. Miyama

WRF, nestingBy Dr. Manda

Cloud Liquid Water

Reference height = 400m

Mean PVT during 0300-1900 on 3 July

ps ps’

Δp =

p s’-p s

0.3 hPa

pref = pref

Summary• We successfully observed fine structure of SST, air

temperature, and cloud base height across the KE front• Turbulent heat flux showed clear meridional contrast, the

maximum around 50 km away from the front.• Slope structure of cloud base height was observed • Regional models successfully simulated the slope

structure of cloud base height across the front• Smoothed SST lowered cloud base height on the southern

side, and reduced the gradient of cloud base• Direct effect of the front was limited within about 500 m

height • Contribution of the differential heating to SLP was about

0.3 hPa in this case

For future studies• Does the horizontal difference in SLP of a few tenths

hPa significantly affect synoptic-scale phenomena? • Can we capture evidence of the deep heating

(Minobe et al., 2010) over the Kuroshio/KE by in situ observations?

• Is the existing OI (or 3D-Var) SST enough for simulating frontal-scale atmospheric phenomena?

• Model results depends on types of SST and lateral boundary condition