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Convective organization at the largest scales: ITCZ, monsoonal - - PowerPoint PPT Presentation
Convective organization at the largest scales: ITCZ, monsoonal - - PowerPoint PPT Presentation
Convective organization at the largest scales: ITCZ, monsoonal precipitation zones and their link to the large-scale tropical circulation Simona Bordoni Environmental Science and Engineering California Institute of Technology July 5 2019
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Observed distribution of precipitation
Data source: GPCP
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Observed distribution of precipitation
Data source: GPCP
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Observed distribution of precipitation
Data source: GPCP
Why is the maximum precipitation (ITCZ) north of the equator?
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Precipitation is tied to the atmospheric circulation
Data source: ERA40
m s-1
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Ferrel cells
Precipitation is tied to the atmospheric circulation
Data source: ERA40
Hadley cell Easterlies Westerlies Westerlies
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Ferrel cells
Precipitation is tied to the atmospheric circulation
Hadley cell Easterlies Westerlies Westerlies
Maximum precipitation is co-located with ascending motion in the Hadley cells
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Large-scale circulations and clouds
Hadley/Walker Circulation
EQ Cloud Clusters trade winds stratocumulus cold, eastern subtropical ocean warm, western tropical oceans
Land/Sea Circulation
tradewinds Courtesy: Bjorn Stevens
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What drives the Hadley circulation
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Implied poleward energy transport
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Atmospheric and oceanic energy transport
The general circulation of the atmosphere exists to transport energy from regions with net energy gain to regions of net energy loss
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The energy budget for a moist atmosphere
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The energy budget for a moist atmosphere
h = CpT + Lvq + gz
Relates the circulation to energy sources and sinks, without explicit consideration of latent heating
e.g., Neelin and Held (1987), Held (2001), Merlis, Eisenman, Bordoni and Schneider (2013 a,b,c)
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Because MSE is positively stratified, the Hadley cell usually transports energy in the direction of the upper-level flow
Energetic constraint on Hadley cell
ITCZ δ δ ϕ ϕ
Eq
Adapted from Schneider et al. 2014
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ITCZ position is anti-correlated with the cross-equatorial energy transport
Energetic constraint on Hadley cell
ITCZ δ δ ϕ ϕ
Eq
Adapted from Schneider et al. 2014
hvhi0
e.g., Kang et al. 2008, Hwang and Frierson 2012, Donohoe et al. 2013, Bischoff and Schneider 2014
hvhi0
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What drives hemispheric asymmetry?
Marshall et al. (2013)
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Role of ocean heat transport
Marshall et al. (2013), Frierson et al. (2013)
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Mechanisms of northward shifted position of the ITCZ
Frierson et al. (2013)
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ITCZ position is anti-correlated with the cross-equatorial energy transport
Energetic constraint on Hadley cell
ITCZ δ δ ϕ ϕ
Eq
Adapted from Schneider et al. 2014
hvhi0
e.g., Kang et al. 2008, Hwang and Frierson 2012, Donohoe et al. 2013, Bischoff and Schneider 2014
hvhi0
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ITCZ and EFE
ITCZ δ δ ϕ ϕ
Eq S N
Height Net energy input Net energy deficit
hvhi0
Energy Flux Equator
e.g., Kang et al. 2008, Hwang and Frierson 2012, Donohoe et al. 2013, Bischoff and Schneider 2014
hvhi
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ITCZ and cross-equatorial energy transport
Donohoe et al. 2013
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Tropical rainbelts in climate models
IPCC Assessment Report 5 (2013)
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