Why do GCMs have trouble with the MJO?

The Madden-Julian Oscillation West East 200 [hpa] 500 Cool & dry Cool & dry p 700 850 SST Lag Day +20 +15 +10 +5 0-5 -10-15 -20 ~20 days ~10 days ~10-15 days -25 Suppressed convection Convective and stratiform rainfall, stabilization Deepening cumulus heating & moistening, destabilization Figure from Jim Benedict

MJO Noisy, seasonally varying background Individual realizations vary widely Appears over the Indian Ocean Propagates eastward at about 5 to 10 m/s Large zonal scale, but more like a moving bump than a wave train Weakens or jumps over the Maritime Continent Re-emerges over the Western Pacific Fades out east of the Date Line

The MJO is an embarrassment. It was not even discovered until 1972. We still don t know what it is or how it works. Many of our most elaborate models cannot simulate it.

Issues What is the basic physical mechanism of the MJO? Why do most current GCMs fail to make an MJO?

(mm day-1)2 6204 Yes, there is still a problem. JOURNAL OF MJO variance of the precipitation rate, CMIP5 models, in (mm/day)2 Only one of the 20 models is able to simulate a realistic eastward propagation of the MJO. Hung et al., JCLI 2013 t e ( m ( C C G s a o m i

In the beginning was Matsuno Where s the MJO? Matsuno 1966

However. X Gill 1980 Given the heating, GCMs can respond with the right wind field.

a) b) c)

Eastward movement Moistening on the east side, partly due to advection Drying on the west side, entirely due to advection GCMs know how to advect moisture.

Moisture Advection Slide from Jim Benedict

Longwave feedback The radiative effects of high clouds promote the MJO. Raymond Grabowski & Moncrieff Bony & Emanuel Andersen & Kuang Arnold GCMs are good at making clouds that block outgoing longwave radiation.

Longwave feedback Radiative heating + Moist static energy anomaly

Radiative heating anomalies

Surface precipitation rate TWP-ICE

Longwave heating rate K/day 1.5 10 4 Height (meters) 1.0 10 4 5.0 10 3 0 38 40 42 44 46 48 50 52 54 56 Elapsed Time (hours) -8-7 -5-4 -2-1 0 2 3 5 6

Wait, radiation moistens? Tropical temperature gradients must remain weak. Radiative heating + Water vapor anomaly The hard part How does radiative heating promote moistening?

Sensitivity to entrainment With stronger entrainment, convection is more sensitive to moisture above the sub cloud layer.

Sensitivity to entrainment With stronger entrainment, convection is more sensitive to moisture above the sub cloud layer. This will only matter if the tropospheric water vapor actually changes.

Sensitivity to entrainment With stronger entrainment, convection is more sensitive to moisture above the sub cloud layer. This will only matter if the tropospheric water vapor actually changes. Moisture anomalies are strongest in the lower middle troposphere. How is water vapor lifted to that level? Parameterized processes are key for the lifting. Holloway and Neelin 2009

Stronger entrainment higher humidity

Why very wet matters (Ref Emanuel 1989, Bony & Emanuel 2005) West East 200 [hpa] 500 Cool & dry Cool & dry p 700 850 SST Lag Day +20 +15 +10 +5 0-5 -10-15 -20 ~20 days ~10 days ~10-15 days -25 Normal Humidity Very Wet Updrafts Downdrafts Held back by entrainment Reduce the CAPE Immune to entrainment Inactive and ineffective

How much radiative heating per unit moistening or How much moistening per unit radiative heating? Radiative heating + Moist static energy anomaly Fig.*3.20* Average*MSE*budg Figure from Walter Hannah

Sensitivity of water vapor to convection Tropical Pacific observations analyzed by Holloway and Neelin 2009 FIG. 4. Composite profiles of relative humidity binned by daily average rain rate in the MF 70% contour is darkened for clarity. Lots of GCMs fail to moisten the lower troposphere during heavy rain. Thayer-Calder & Randall 2009

Smoking gun MJO goodness Lower tropospheric RH during heavy rain!! Kim et al. 2014

Water vapor budget Contour interval = [10-7 g kg-1 s-1]/[mm day-1] Parameterized physics 2 3 q anomaly, g kg-1 DeMott et al., 2014

So, what moistens the air at 700 hpa? ρ q v t = ρv q v M! q v z ρc! + D ( q ) v c q v Environmental vertical advection? Detrained vapor? Evaporation of falling rain? Evaporation of detrained cloud water?!m ρw M c Environmental vertical velocity Chikira, Minoru, 2014: Eastward-Propagating Intraseasonal Oscillation Represented by Chikira Sugiyama Cumulus Parameterization. Part II: Understanding Moisture Variation under Weak Temperature Gradient Balance. J. Atmos. Sci., 71, 615 639.

Chikira s theory ρ s t ρ q v t = ρv s M! s z + Q R + ρlc! + D s c s ( ) = ρv q v M! q v z ρc! + D ( q v ) c q v Environmental vertical motion!m ρw M c

Chikira s theory ρ s t ρ q v t = ρv s M! s z + Q R + ρlc! + D s c s ( ) = ρv q v M! q v z ρc! + D ( q v ) c q v Environmental vertical motion!m ρw M c 0 M! s z + Q R + ρl!c + D s c s ( ) ( ) M! Q R + ρl!c + D s c s s z 1 Weak temperature gradient ρ q v t ( ) = ρv q v + α L Q R + ρl!c + D s c s α L q v z 1 α = h z s z s z 1 1 ρc! + D ( q v ) c q v Radiative moistening

How can we test these ideas? Field data (e.g., DYNAMO) Simulation of field data with cloud-resolving model Look at covariance of radiative heating and alpha during MJO cycle Compare with results from GCMs that do and/or don t simulate the MJO

Why do GCMs have trouble with the MJO? Because they fail to moisten the lower troposphere during heavy rain.