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© Crown copyright Page 1 Cloud-resolving simulations of the tropics and the tropical tropopause layer Glenn Shutts June 13 2006
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Page 1 Crown copyright Cloud-resolving simulations of the tropics and the tropical tropopause layer Glenn Shutts June 13 2006.

Jan 19, 2018

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Page 3© Crown copyright Balanced geostrophic wind in and around the lens NEQ jetstream
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Page 1: Page 1 Crown copyright Cloud-resolving simulations of the tropics and the tropical tropopause layer Glenn Shutts June 13 2006.

© Crown copyright Page 1

Cloud-resolving simulations of the tropics and the tropical tropopause layer

Glenn Shutts June 13 2006

Page 2: Page 1 Crown copyright Cloud-resolving simulations of the tropics and the tropical tropopause layer Glenn Shutts June 13 2006.

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Convective mass flux – “pumping up the lens”

Homogeneous intrusion solution of Gill(1981) adapted for equatorial beta-plane i.e. f = y

cold

EQ N

Zero PV region embedded in background linear meridional PV variation

The large-scale perspective

cold

jet

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Balanced geostrophic wind in and around the lens

NEQ

jetstream

1

2

3 13

8

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‘big domain simulations of tropical convection

Need CRM domain size > 2000 km (c/)1/2 ~ 1000 km

Need horizontal gridlengths ~ 1 or 2 km

Uniform resolution too computationally demanding for long runs anisotropic grid

Explicit time stepping t ~ 5 sec; run length > 15 days !

3-phase cloud microphysics scheme

Smagorinsky-Lilly turbulence closure

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Met Office Cloud-resolving mode (LEM) configurations

Acknowledgment: ECMWF for computer support/resources

Equatorial beta-plane with SST variation, imposed tropospheric cooling (1.5 K/day) and ‘Trade Wind forcing function’ to drive surface easterlies

1. 96 x 7680 x 30 km dx= 1km dy= 1 km Lat. range +/- 35 degs

2. 3840 x 7680 x 30 km dx= 2 km dy= 40 km Lat. range +/- 35 degs

3. 7680 x 7680 x 30 km. dx= 2km dy=10 km. Lat. range +/- 35 degs

4. 40000 x 5120 x 30 km dx=2.44 km dy= 40 km Lat. range +/- 23 degs

Domain dimensions and grids used:35 N

35 S1 2 3

4

Domain shapes

Grid-box shapes

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Cooling profile used in simulations

-1.5 0K/day

20 km

15 km

10 km

30 km

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Anisotropic grid run

dx= 1 km dy=40 km

Domain :

3840 km

7680 km

35 N

35 S

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Hovmuller diagram of rainfall rate averaged from 10 S to 10 N

14 m/s

-13 m/s

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U field in vertical sections along the Equator at 6-hourly intervals

Red is westerly

Blue is easterly

-25 < u < 28 m/s

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Wave structure at the equator

Fourier decompose u,v and T in the x-direction at all height and at 15 minute intervals

plot the amplitude and phase for each zonal wavenumber as a function of time and height

e.g. u= A(z,t) cos[2kx/Lx + (z,t)] A(z,t) is the amplitude; (z,t) is the phase

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Time-height plot of the amplitude of wavenumber 1 for u field (wavelength=3840 km)

0 (white) < amp(u) < 15 m/s (black)

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Time-height plot of the phase of wavenumber 1for u field (wavelength= 3840 km)

Kelvin wave phase slope

Period ~ 69 hours0 360 degrees

Black grey white

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Time-height plot of the amplitude of wavenumber 1 for v field (wavelength=3840 km)

0 (white) < amp(v) < 11 m/s (black)

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Time-height plot of the phase of wavenumber 1 for v (wavelength= 3840 km)

Period ~ 33 hours

n=2 equatorially-trapped inertia-gravity wave

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Phase of wavenumber 2 in potential temperature field (wavelength= 1920 km)

Boomerang-shaped phase lines

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‘boomerang structure’ – Wheeler et al (2000)

T’ contours

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Phase of wavenumber 5 in u field

n=1 equatorially-trapped inertia-gravity wave

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Time-height section of u at a point on the equator

Time 0 15.4

days

Z (km)

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u perturbation from radiosonde data taken during the ARM Nauru99 field experiment (Boehm and Verlinde,2000)

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‘circum-equatorial ’ simulation of tropical atmosphere

horizontal domain extent = 40,000 km

gridlengths dx=2.44 km dy=40 km

Meridional extent: 23 S 23 N

11 day simulation from uniform easterly (5 m/s)

initial dry atmosphere

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u in a N-S slice through the domain

23 S 23 NEQ

30 km

12 km

narrow jetstream due to meridional SST

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U field in longitude/height section along equator at day 10

40,000 km

z

30 km

Red= 25 m/s Blue= -25 m/s

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Potential temperature perturbation + ice mixing ratioalong equator on day 11

30 km

0 40,000 kmSuperimposed ice cloud

amplitude in stratosphere ~ 10 K

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From Boehm and Verlinde (2000) time-height section of temp. perturbation and cirrus

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Ice mixing ratio at z= 13.9 km

5120 km

8550 km

Sub-domain view

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Ice mixing ratio at z= 16.8 km

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Ice mixing ratio at z=17.6 km

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Correlation of log(qi) and ’ at z= 13.9 km

log(q I )

x (longitude)0 40,000 km

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Horizontally-averaged ice mixing ratio profile

30 km

20 km

10 km

0 4 x 10-5Ice mixing ratio (kg/kg)

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Horizontally-averaged temperature profile

30 km

20 km

10 km

150 200 250 300

T (K)

Too cold !

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Summary

convective mass flux terminating near 12 km drives ascent and adiabatic cooling in the TTL

- ‘inflating the lens’

‘Big domain’ simulations of tropical convection using anisotropic grids are a useful intermediate solution to the problem of insufficient computer power

squall lines are organized by Kelvin waves propagating eastward at 14 m/s.

Observed ‘boomerang-shaped’ wave systems are found in the simulations

Model cirrus tends to occur in cold phase of convectively-coupled wave system