Assimilation of EOS-Aura Data in GEOS-5:

Evaluation of ozone in the Upper Troposphere -

Lower StratosphereK. Wargan, S. Pawson, M. Olsen,

J. Witte, A. Douglass

Global Modeling and Assimilation Office (GMAO)Chemistry and Dynamics BranchNASA GSFC

A question

How much of the ozone that we see in the troposphere is of stratospheric origin?

Models disagree on this quite dramatically

Plan of Talk

• Motivation – quantifying sources of tropospheric ozone

• Ozone data and GEOS-5 Data Assimilation System

• Results– Evaluation against ozonesonde data– Vertical structure of UTLS ozone fields

We look at the lower stratosphere but the goal is to derive some information on tropospheric ozone as well

Tropospheric Ozone

2010 boreal summer mean tropospheric ozone column [Dobson Units]

Tropospheric Ozone

2010 boreal summer mean tropospheric ozone column [Dobson Units]

Maxima along the subtropical jet streams.Summer, Northern Hemisphere higher

Tropospheric Ozone

2010 boreal summer mean tropospheric ozone column [Dobson Units]

Wave one pattern in the tropics

ConvectionLightning

Tropospheric Ozone

2010 boreal summer mean tropospheric ozone column [Dobson Units]

Tropical Pacific controlled by ENSO and MJO

Tropospheric Ozone

2010 boreal summer mean tropospheric ozone column [Dobson Units]

Very low over snow-covered Greenland and Antarctica

Tropospheric Ozone - Sources• NOx / CO / Volatile Organic Compounds chemistry– Biomass burning– Fossil fuel burning– Lightning

• Transport from the stratosphere• Spatial distribution closely tied to meteorology

These mechanisms are well understood but quantitative attribution is not precise

Constrain ozone in the Upper Troposphere – Lower Stratosphere (abundance, structure, variability)– Stratosphere-Troposphere Exchange

Separate tropospheric and stratospheric ozone columns

Accurate tropospheric ozone budget based on global observations

Assimilation can help achieve this• Model supplies information on dynamics• Vertical grid of a DAS can resolve features that data cannot

GEOS-5 Data Assimilation System• Atmospheric General Circulation Model: • Horizontal resolution: flexible - 2.5° to ¼°• 72 layers from the surface to 0.01 hPa• Parameterized ozone chemistry (stratospheric P&L; dry

deposition)• No representation of tropospheric ozone sources in the model

• 3D-Var analysis: Gridpoint Statistical Interpolation • Observations: • Conventional (surface, sondes, radar, aircraft, MODIS-derived

winds,…)• Satellite radiance data (TOVS/ATOVS, AIRS, IASI, SSM/I, GOES,

GPS-RO)• Ozone data (OMI, MLS retrievals)

Microwave Limb Sounder (MLS) on EOS Aura

• Measures temperature and composition of the atmosphere from microwave emissions

• Limb scanner• Vertical range: We assimilate profiles between

~260 hPa – 0.14 hPa• Vertical resolution: 2.5 – 6 km • 9 years and counting

Ozone Monitoring Instrument (OMI)• Total ozone information derived from observations of

backscattered UV radiation• Observes sun-lit atmosphere• Total Ozone Monitoring Instrument (TOMS) legacy• Operational 2004 - present• Sensitivity varies with altitude and local meteorology (no signal

from below clouds). This is taken into account by weighting the signal by OMI’s efficiency factors (averaging kernels), ε

We have 8 year long, 2°×2.5° assimilation run with this configuration, 2005 - 2008

Results in the stratosphere

60N -90N

10S -10N

90S -60S

Year

Time series of integrated stratospheric ozone column in three latitude bands

• 60N – 90N: Winter-Spring maximum, interannual variability; “Arctic ozone hole” in 2011

• Tropics: Ozone controlled by the QBO

• 90S – 60S: Austral Spring ozone holes

Realistic representation of temporal variability

Vertically integrated Observation – Forecast statistics

• Assimilation significantly reduces the O-Fs for both instruments• Negligible bias between analysis total ozone and OMI data• Stratospheric column biased low w.r.t. MLS observations but MLS

likely overestimates ozone below 200 hPa

Total ozone O-Fs and tropospheric response, June - August

2009

2010

O-F Analysis tendency in troposphere

• Analysis tendencies/increments in the troposphere have similar pattern to total ozone O-Fs: OMI supplies tropospheric ozone information

• O-Fs and increments positive over land and negative in regions of strong convection

Total ozone O-Fs and tropospheric response, June - August

2009

2010

O-F Analysis tendency in troposphere

Biomass burning signal over the Amazon varies from year to year.

Very low fire counts in 2009 result in lower ozone production

Here, OMI makes up for the lack of explicit chemistry in the model

• Analysis tendencies/increments in the troposphere have similar pattern to total ozone O-Fs: OMI supplies tropospheric ozone information

• O-Fs and increments positive over land and negative in regions of strong convection

Lower Stratosphere and Upper Troposphere; Comparison with ozonesondes

Lower Stratosphere, tropopause – 50 hPa

Upper Troposphere, 500 hPa - tropopause

• Excellent agreement of lower stratospheric ozone with sonde data• Good agreement in the upper troposphere; assimilation is biased low by 1.4

Dobson Units – missing NOx chemistry in the model?

Sonde data are from the WOUDC, NDACC, and SHADOZ databases, 2005 - 2012

Ozone in the lower stratosphere – assimilation vs. sondes

Sonde dataAssimilation

Hohenpeissenberg (47.8N, 11E)

Assimilation faithfully reproduces the annual cycle as well as day-to-day variability of ozone in the lower stratosphere at this location.

Vertical structure – an example

Sonde dataAssimilation

High and low ozone layers in the UTLS often form as a result of transport of ozone poor air from low latitudes.

Assimilation reproduces layered structure of this ozone profile as permitted by the vertical resolution of the DASHohenpeissenberg

(47.8N, 11E) on May 4th 2005

Capturing fine structures in the UTLS

Latitude Latitude

Thet

a [°

K]Th

eta

[°K]

Satellite data Assimilation

Combining observations with assimilated dynamics allows accurate representation of small-scale features unresolved by the data.

We use along-track ozone profiles from High Resolution Dynamics Limb Sounder (HIRDLS)Vertical resolution is ~1 km for HIRDLS and ~2.5 – 3 km for MLS

Summary• Eight year long record of global ozone was obtained

by assimilating OMI and MLS observations into GEOS-5

• Very good agreement with ozonesondes in terms of vertically integrated ozone in the lower stratosphere

• Good agreement in the upper troposphere as well. Low bias needs fixing – representation of sources in the model?

• Good representation of shallow vertical structures in the UTLS

• The product can be used to quantify stratosphere – troposphere exchange of ozone