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

Page 2© Crown copyright Convective mass flux – “pumping up the lens” Homogeneous intrusion solution of Gill(1981) adapted for equatorial beta-plane i.e. f =  y cold EQN Zero PV region embedded in background linear meridional PV variation The large-scale perspective  cold jet

Page 3© Crown copyright Balanced geostrophic wind in and around the lens NEQ jetstream

Page 4© Crown copyright ‘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

Page 5© Crown copyright 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 x 7680 x 30 km dx= 1km dy= 1 km Lat. range +/- 35 degs x 7680 x 30 km dx= 2 km dy= 40 km Lat. range +/- 35 degs x 7680 x 30 km. dx= 2km dy=10 km. Lat. range +/- 35 degs x 5120 x 30 km dx=2.44 km dy= 40 km Lat. range +/- 23 degs Domain dimensions and grids used: 35 N 35 S Domain shapes Grid-box shapes

Page 6© Crown copyright Cooling profile used in simulations K/day 20 km 15 km 10 km 30 km

Page 7© Crown copyright Anisotropic grid run  dx= 1 km dy=40 km Domain : 3840 km 7680 km 35 N 35 S

Page 8© Crown copyright Hovmuller diagram of rainfall rate averaged from 10 S to 10 N 14 m/s -13 m/s

Page 9© Crown copyright U field in vertical sections along the Equator at 6-hourly intervals Red is westerly Blue is easterly -25 < u < 28 m/s

Page 10© Crown copyright 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[2  kx/L x +  (z,t)]  A(z,t) is the amplitude;  (z,t) is the phase

Page 11© Crown copyright Time-height plot of the amplitude of wavenumber 1 for u field (wavelength=3840 km) 0 (white) < amp(u) < 15 m/s (black)

Page 12© Crown copyright Time-height plot of the phase of wavenumber 1 for u field (wavelength= 3840 km) Kelvin wave phase slope Period ~ 69 hours 0360 degrees Black grey white

Page 13© Crown copyright Time-height plot of the amplitude of wavenumber 1 for v field (wavelength=3840 km) 0 (white) < amp(v) < 11 m/s (black)

Page 14© Crown copyright Time-height plot of the phase of wavenumber 1 for v (wavelength= 3840 km) Period ~ 33 hours n=2 equatorially-trapped inertia-gravity wave

Page 15© Crown copyright Phase of wavenumber 2 in potential temperature field (wavelength= 1920 km) Boomerang- shaped phase lines

Page 16© Crown copyright ‘boomerang structure’ – Wheeler et al (2000) T’ contours

Page 17© Crown copyright Phase of wavenumber 5 in u field n=1 equatorially-trapped inertia-gravity wave

Page 18© Crown copyright Time-height section of u at a point on the equator Time days Z (km)

Page 19© Crown copyright u perturbation from radiosonde data taken during the ARM Nauru99 field experiment (Boehm and Verlinde,2000)

Page 20© Crown copyright ‘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

Page 21© Crown copyright u in a N-S slice through the domain 23 S23 N EQ 30 km 12 km narrow jetstream due to meridional SST

Page 22© Crown copyright 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

Page 23© Crown copyright Potential temperature perturbation + ice mixing ratio along equator on day km 0 40,000 km Superimposed ice cloud  amplitude in stratosphere ~ 10 K

Page 24© Crown copyright From Boehm and Verlinde (2000) time-height section of temp. perturbation and cirrus

Page 25© Crown copyright Ice mixing ratio at z= 13.9 km 5120 km 8550 km Sub-domain view

Page 26© Crown copyright Ice mixing ratio at z= 16.8 km

Page 27© Crown copyright Ice mixing ratio at z=17.6 km

Page 28© Crown copyright Correlation of log(q i ) and  ’ at z= 13.9 km log(q I )  ’  x (longitude) 0 40,000 km

Page 29© Crown copyright Horizontally-averaged ice mixing ratio profile 30 km 20 km 10 km 04 x Ice mixing ratio (kg/kg)

Page 30© Crown copyright Horizontally-averaged temperature profile 30 km 20 km 10 km T (K) Too cold !

Page 31© Crown copyright 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