Changes in daily temperature anomalies and winds:

file:///home/coupe/Documents/main/public_html/NuclearNino/nino/sam_mechanisms/curl/plots/daily_T/nw_ur_150_07

Changes in the daily surface winds of the Pacific Ocean:

file:///home/coupe/Documents/main/public_html/NuclearNino/nino/sam_mechanisms/curl/plots/daily_U/nw_ur_150_07





Changes in the monthly surface winds of the Pacific Ocean:

file:///home/coupe/Documents/main/public_html/NuclearNino/nino/sam_mechanisms/curl/plots/monthly_U/nw_ur_150_07

Changes in monthly wind stress and curl:

file:///home/coupe/Documents/main/public_html/NuclearNino/nino/sam_mechanisms/curl/plots/monthly_TAUX

Changes in the monthly Hadley circulation over the Pacific Ocean:

file:///home/coupe/Documents/main/public_html/NuclearNino/nino/sam_mechanisms/ITCZ/OMEGA/PAC

* southward shift in ITCZ present in: JJA precipitation anomaly, ITCZ identification algorithm,



SSH Anomaly in nw_ur_150_07 and nw_cntrl_03













































Eastward propagation of oceanic kelvin wave here.

Changes in Walker Circulation here.









Summary of Mechanisms From Book Chapter:


(1) Dynamical thermostat mechanism: warming in tropical Eastern Pacific occurs in response to a uniform reduction of surface heat fluxes, because eastern Pacific SSTs are less sensitive to radiative forcing. Eastern Pacific SSTs are partly controlled by water upwelled from below the surface, which is not subject to the volcanically induced cooling.


This is not at play initially in nw_ur_150_07. Upwelling is enhanced during the first 60 days as the South American continent cools, increasing the trade winds over the eastern Pacific and causing anomalous cooling. Below is a plot of temperature anomaly (colors) and zonal wind anomalies (dashed lines are easterly wind anomalies) during 0005-06 (left). Strong cooling of South America is responsible for the anomalously strong trade winds, which enhances upwelling and leads to an increase in the west-east SST gradient across the Pacific (plot below on the right, opposite to what the dynamical thermostat mechanism suggests).




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(2) Subtropical wind stress curl: initial eastern Pacific cooling acts to generate a delayed ocean dynamical response. An easterly wind anomaly and associated negative wind stress curl acts to drive convergence of relatively warm subtropical waters onto the equator – similar to recharge oscillator paradigm for ENSO.


This is absolutely occurring. All that's left to decide is what is causing it.

a) Ocean mixed layer depth: McGregor and Timmerman (2011) suggested that areas with a shallower mean mixed layer depth will display a stronger cooling due to lower heat capacity. This contradicts the dynamical thermostat mechanism.


b) Newtonian damping: Temperature changes in regions with cooler mean states are less damped by latent heating (equatorial cool tongue) which allows them to produce stronger cooling relative to regions with warmerm ean states. Introduced by Xie et al. (2010).


c) Cloud albedo impacts: Areas with high cloud cover and albedo (western Pacific warm pool) will display smaller sfc solar radiation changes and surface cooling. Proposed by McGregor and Timmerman (2011) and first suggested to be of importance by Stevenson et al., (2017).


(3) Changes in Land Precipitation

a) Source of westerly wind anomalies in western Pacific may be caused by volcanically induced intense cooling of Maritime Continent (Ohba et al., 2013). Anomalous land-sea temperature gradient between Maritime Continent and western Pacific induces westerly wind anomalies.

b) Khodri et al., (2017) suggested cooling of the African landmass is responsible for initiating westerly wind anomalies.


ITCZ Changes from Extra-Tropical Eruptions

NH eruptions tended to favor a El Nino response while SH eruptions tended to favor a La Nina response, due to changes in the ITCZ. El Nino-like anomalies influenced by pre-existing ENSO state: a stronger El Nino-like response seems to develop under La Nina compared with El Nino preexisting conditions. Asymmetry of the response can easily be understood since radiative-convective equilibrium imposes an upper limit on absolute intensity that an El Nino can reach (Jim et al., 2003). During an incipient La Nina or neutral conditions, the ITCZ is already further north and the trades are strong on the equator. A nominal zonal wind anomaly along the equator will trigger a larger change in wind stress under incipient La Nina than incipient El Nino conditions.