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The El Nino-Southern Oscillation Quasi-periodic variation in tropical Eastern Pacific SSTs and the associated atmospheric circulation.

Climatological conditions L H

El Nino conditions L H Southern Oscillation Index: pressure difference between Tahiti and Darwin. DarwinTahiti Southern Oscillation Index is negative for an El Nino

La Nina conditions LH Southern Oscillation Index is positive for an La Nina

Why do we care?

ENSO Indices  Nino 3.4 SSTs 5 month running means of monthly SST anomalies are 0.5C or more for at least 6 consecutive months  Southern Oscillation Index Darwin Tahiti Opposite sign to the Nino 3.4 SST index. Often used together with SSTs e.g. Japanese Met service

ENSO Indices  Precipitation in the tropical Pacific  OLR anomalies  Multi-variate ENSO index uses 6 of the main observed variables over the tropical Pacific: SLP, U, V, SST, SAT, Cloud fraction.

ENSO Indices Why do we need more? Motivation 1: All these ENSO indices rely on measurements of absolute fields at any point in time…instrument drift and calibration between different instruments could be a problem. Motivation 2: Devise a metric that could be used to test GCMs that are aiming to simulate variability and change in tropospheric ozone.

JANJUL Climatological Ozone UV + O 2  O, O + O 2  O 3 NO x from lightening. NO x and CO from biomass burning, soil. Strat-trop exchange. Anthropogenic NO x, CO and VOC emissions

Climatological tropospheric ozone from OMI AURA/MLS from 2004 to 2009 Wavenumber 1 structure: more ozone in the Atlantic than the Pacific. Martin et al (2001) – Atlantic enhancement primarily due to combination of lightening NO x and dynamics. Climatological Tropospheric Ozone

Influence of Convection on tropospheric ozone Possibilities:  Mixing of ozone poor/rich air by the convective updrafts and downdrafts  Uplift of ozone precursors into the free troposphere.  Uplift of things that destroy ozone precursors into the free troposphere.

Influence of Convection on tropospheric ozone  Lelieveld and Crutzen (1994) – Suggest that globally convection reduces tropospheric ozone concentrations by 20%. Convective updrafts transport boundary layer air into the upper troposphere where O3 production is higher and destruction is lower. But, compensating down drafts transport ozone rich air downward to the surface where it can be more effectively removed. Balance between these two effects.  Lawrence et al (2003) – Globally convection increases tropospheric ozone concentrations by 12%. Convection lifting surface NOx emissions into the upper troposphere  more ozone production.  Doherty et al (2005) – Different chemistry scheme. Convection  lifts isoprene  reacts with NOx  less NOx BUT oxidation of isoprene  more HOx  more O3 production.  Argument used for the wave 1 in the climatology and the ENSO changes in these papers is that convective updrafts lift low ozone air from the boundary layer up into the free troposphere   Convection  Less ozone

ENSO Influence on Tropospheric Ozone Tropospheric TOC differences between October 1997 (big El Nino) and October 1996 (neutral conditions)  Drier Indonesia  more biomass burning  more NO x, CO  more O 3  Reduced convection  more total column ozone  Enhanced convection  less total column ozone Chandra et al (1998) DecreaseIncrease

They want to look at variability in tropospheric column ozone with ENSO from total column ozone measurements. Get the tropospheric ozone out from the measurements and derive the ENSO index and show that it works. Demonstrate that actually using total column ozone also works quite well given the zonal invariance of stratospheric column ozone  somewhat easier to calculate. Demonstrate their method for deriving tropospheric column ozone from total column ozone works well. Demonstrating that stratospheric column ozone is quite zonally invariant.

Satellite observations of Ozone  Nimbus 7 TOMS (Total Ozone Mapping Spectrometer)  SBUV/2 (Solar Backscatter Ultraviolet)  Earth Probe TOMS  OMI (Ozone Monitoring Instrument) and MLS (Microwave Limb Sounder) Polar Orbitting, Measures vertical profiles of stratospheric ozone as well as total column ozone using a variety of UV wavelengths. Daily global coverage. Using back-scattered UV in 6 wavelength bands. Like TOMS but on a different satellite Backscattered UV and Visible. Measures more constituents than TOMS. OMI MLS Limb sounding measurements of microwave emissions for vertical profiles

EARTH SURFACE Absorption/ scattering by Earth surface and atmosphere Observation by solar backscatter Total ozone column and surface reflectivity is derived by measuring the backscattered light from two wavelengths, one that is strongly absorbed by ozone and one that is absorbed very little. Radiative transfer calculation based on conditions of measurement e.g. viewing angle, latitude, surface reflectance with various different total ozone columns. Figure out which one gives you the reflectance you measure.  Gridded: they’ve already done all the calculation of total column ozone. Got rid of pixels where clouds are interfering etc.  Level 2 footprint measurements (nasa term). Levels describing how processed the data is. Level 2 has been processed to give you the ozone that the satellite sees. But they haven’t taken out e.g. measurements affected by clouds or put it on a uniform grid.

The Convective Cloud Differential (CCD) method Used to derive tropospheric ozone column under the assumptions….. (1) Deep convective clouds in the tropical pacific have physical cloud tops which often lie at or near the tropopause. (2) Zonal variability of stratospheric column ozone in these latitudes is small to within a few DU. Ziemke et al 1998

Testing the zonally invariance of stratospheric ozone using MLS ozone MLS provides vertical profiles of stratospheric ozone  can measure stratospheric ozone column directly. Using monthly means.

Testing the zonally invariance of stratospheric ozone using MLS ozone MLS provides vertical profiles of stratospheric ozone  can measure stratospheric ozone column directly Quite zonally invariant. At most 4DU (<2%).

Testing the zonally invariance of stratospheric ozone using MLS ozone MLS provides vertical profiles of stratospheric ozone  can measure stratospheric ozone column directly Quite zonally invariant. At most 4DU (<2%). Only small deviations from the zonal mean when you de- seasonalise.

Testing the zonally invariance of stratospheric ozone using MLS ozone Even zonally invariant using daily data. When there are sufficient numbers of deep convective clouds in the Pacific, the CCD method can be used to derive SCO and subsequently TCO on short timescales, even daily, to an accuracy of +/- 2DU.

Testing the zonally invariance of stratospheric ozone using GEOS-CCM GCM with interactive stratospheric Chemistry. Internally generated QBO.

MODEL MLS Why?  Strong zonal winds compared to meridional winds.  Weak meridional gradients of ozone in the tropics.  Very small zonal variations in the production and destruction of ozone in the tropics.

If you use the Convective Cloud Differential method to get stratospheric column ozone over regions with high cloud  you can get tropospheric column ozone at other longitudes.

MLS SCO and CCD derived SCO agree well  can use CCD derived TCO measurements to obtain a long term record of TCO

Zonal dipole anomalies in tropospheric column ozone associated with El Nino and La Nina events.

Deriving the Ozone ENSO Index  Temporal cross correlations of Nino3.4 and SOI ENSO indices Averaged TCO over these areas. Use West –East, monthly

Agrees well with Nino3.4 and SOI Index

Could also just use total column ozone measurements

Error associated with assumption of stratospheric zonal invariance

The Ozone ENSO Index Motivation 1: All these ENSO indices rely on measurements of absolute fields at any point in time…instrument drift and calibration between different instruments could be a problem. Motivation 2: Devise a metric that could be used to test GCMs that are aiming to simulate variability and change in tropospheric ozone.

 Goddard Earth Observing System (GEOS-5) GCM  Coupled to the Global GMI stratosphere-troposphere chemical mechanism (interactive chemistry in both troposphere and stratosphere).  117 chemical species, 322 chemical reactions, 81 photolysis reactions.  Includes the O 3 -NO x -Hydrocarbon chemistry necessary for the simulation of tropospheric ozone.  Simulation forced with observed SSTs. ( )

Obs Model

Model (25y)

Comparing the Ozone ENSO Index

Looking at the vertical structure of ozone anomalies using the model Regressed the de- seasonalised ozone onto the Nino 3.4 index averaged between 15S and 15N

The Latitudinal Structure

Comparing vertical profiles with ozonesondes The SHADOZ network.

 They used this to test whether a CCM can reproduce the observed tropospheric ozone variability  it does.  They plan to do a full budget analysis of the ozone changes in the future. Conclusions  A new ENSO index has been derived based on satellite measurements of total column ozone.  Because they are looking at differences between western and eastern Pacific it is self calibrating.  Further examination of the vertical, longitudinal and latitudinal variations in the ozone response demonstrate a relationship with changes in the atmospheric circulation.

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