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TRANSCRIPT
Convec'on-‐permi-ng modelling the diurnal cycle and gravity waves in the
mari'me con'nent – what can we learn from YMC?
Todd Lane
School of Earth Sciences, The University of Melbourne ARC Centre of Excellence for Climate System Science (ARCCSS)
Collaborators: Claire Vincent (U. Melb., ARCCSS), Muhammad Hassim (CCRS Singapore), Wojciech Grabowski (NCAR), Matt Wheeler (BoM), Alain Protat (BoM), Robyn Schofield (U. Melb).
YMC Workshop
24-26 November 2015, Jakarta
Peatman et al. (2014, QJRMS)
November-April Diurnal Cycle (LT) of Precipitation from TRMM
[3B42HQ, 1998-2012]
21:00
06:00
Motivation, Focus, Science Questions • What controls the formation of the offshore early-morning precipitation
maximum? • Many classes of models overemphasise the precipitation over land and do
not properly represent the offshore maxima. • Discussions in Houze et al. (1981); Mapes et al. (2003); Love et al. (2011),
Hassim et al. (2015), Vincent and Lane (2015) particularly relevant. • What role do diurnally-forced gravity waves play?
• Equatorward of 30° the sea/land-breeze system is intertwined with propagating inertia-gravity waves (Rotunno 1983)
• How does the diurnal cycle of maritime continent precipitation vary with the passage of the MJO?
• Recent work (Peatman et al. 2014) has shown that the amplitude of the diurnal cycle of precipitation over land is maximized immediately before the arrival of the MJO.
Two recent papers focusing on New Guinea: Hassim, M. E. E., Lane, T. P., and Grabowski, W. W.: The diurnal cycle of rainfall over New Guinea in convection-permitting WRF simulations, Atmos. Chem. Phys. Discuss., 15, 18327-18363, doi:10.5194/acpd-15-18327-2015, 2015. Vincent, C.L., and Lane, T.P., 2015: Evolution of the diurnal precipitation cycle with the passage of a Madden-Julian Oscillation event through the Maritime Continent. Mon. Wea. Rev., under review.
WRF Results – 4 km domain (nested within 12 km – within ERA-I)
JANUARY 2010 wind perpendicular to New Guinea & Rain
MJO
Lea
d-up
M
JO A
ctiv
e M
JO F
ollo
w-o
n
Tow
ards
Coa
st
Away
from
Coa
st
coas
t • Gravity wave induced wind perturbations extend up to 800 km offshore
• Structure agrees with linear theory - though deeper vertical wavelengths due to importance of convective heating/cooling
• More far-offshore rainfall during lead-up and active phases of MJO.
• Related to mid-level moisture
• Evidence of modulation of far-offshore rainfall by gravity waves
• Esp. in lead-up and active phases
Time (LST)
COAST
400 km OFFSHORE
JAN 2010
Per
t Win
d (m
/s)
Per
t Win
d (m
/s)
Rai
n ra
te (m
m/h
r)
Rai
n ra
te (m
m/h
r)
Wind anomalies (shaded)
Potential temperature anomalies 4 LST 16 LST
WRF Simulations – Multiple DJF periods Domain 1: 12 km Domain 2: 4 km
Initialised and boundaries forced with ERA-Interim
RMM 8/1
RMM 4/5 (active)
(suppressed)
TRMM – diurnal composite WRF – diurnal composite
RMM MJO Phase 4
RMM MJO Phase 1
Christmas Island Jakarta Airport
RMM Phase 1
RMM Phase 4
Difference in timing (hours) of peak rainfall in TRMM versus WRF (-ve = WRF leads)
Outstanding ques'ons..
Why do convec+on-‐permi1ng models over-‐emphasize convec+on over land? (or do they?) How realis+c are the offshore propaga+ng wave pa>erns in terms of their amplitude and ver+cal structure (and hence phase speed)?
If land-‐based convec+on is too strong, does that cause the waves to be too strong? How important is stra+form precipita+on in controlling waves / offshore propaga+on? Model simula+ons are producing similar waves throughout all MJO phases though with some varia+on in amplitude – implies available moisture is key to offshore systems – is this true?
What is the ver+cal structure of the sea/land-‐breeze system near the coast and how does this interact with the coastal convec+on?
Ship Location
Soundings (High-res in time)
Surface observations
Soundings (High-res in time)