Sensitivity of satellite observations for freshly produced lightning NOx

Steffen Beirle, MPI Mainz

M. Salzmann, M. G. Lawrence,

U. Platt, and T. Wagner

Lightning NOx...

... is important:• Dominating source in tropical UT• Released in the UT: long lifetime, low background

levels

→ strong impact on tropospheric O3 and OH

... is uncertain:• „Magic number“ 5 Tg [N]/yr• uncertainty still 1order of magnitude• besides total number:

– regional variations– Intracloud flashes versus Cloud to ground– ...

Satellite observations...

... provide new independent measurements

... have high potential:• time series• global cover

→ analysis of temporal & spatial patterns on different scales and for different conditions

→ use them to constrain LNOx estimates!

Different approaches:1. mean NO2 enhancement due to lightning activity

Different approaches:1. mean NO2 enhancement due to lightning activity

Disadvantages:

Observed NO2 (~10 a.m.) is aged LNO2

Dillution Transport Lifetime

1. mean NO2 enhancement due to lightning activity

2. direct observation of freshly produced LNOx

Different approaches: 2. direct obs

Beirle et al., ACP 6, 2006

1.7 (0.6-4.7) Tg [N]/year

Different approaches: 2. direct obs

Direct observation of fresh LNOx

Satellite observations over active thunderstorm

+ confined region of interest

+ negligible chemical loss / dilution

(within satellite pixel, 30 min.)

- highly complex observation conditions (cumulonimbus clouds)

→ what do we actually "see"?

Satellite sensitivity for (L)NOx

• Measured: Slant column density S• Wanted: Vertical column density V• S = V * A A: Air Mass

Factor

• S = V * ai * pi ai: box-AMF

pi: profile (norm.)

• SNO2 = VNOx * ai * li * pi li := [NO2] / [NOx]

• SNO2 = VNOx * ei * pi = VNOx * E

Visibility ei = ai * li "box-AMF for NOx"

Sensitivity E = ai *li * pi = ei * pi = SNO2 / VNOx

Satellite sensitivity for (L)NOx

SNO2 = VNOx * ei * pi = VNOx * E

Visibility ei = ai * liSensitivity E = ei * pi

E = ai * li * pi

Idea: Use cloud resolving model results for a thunderstorm simulation to investigate temporal and spatial variability/evolution of ei and E!

Satellite sensitivity for (L)NOx

SNO2 = VNOx * ei * pi = VNOx * E

Visibility ei = ai * liSensitivity E = ei * pi

E = ai * li * pi

Cloud resolving model

Radiativetransfer modelMCArtim

Hydrometeors

CSRMC (Marc Salzmann)(Cloud system resolving model including photochemistry)

• 3d cloud resolving model ((photo)chemistry+dynamics)

• One week of thunderstorms in the TOGA COARE/CEPEX region (Pacific)

• Output grid: dt=30 min, dx=dy=2km, dz=500m

• Output: NOx, NO2, O3, T, J ...

• Extinction simply parameterized from cloud water&ice (literature)

• Snow, graupel and rain neglected (few large particles)

McArtim: Box-AMFs for all locations at all timesteps

Salzmann et al.,ACP, 2008

NOx volume mixing ratios and qtotm = 0.01g/kg contourduring the developmentof a mesoscale convective system from 24 December1992, 10:00 UTC to 24 December 1992, 12:30 UTC from the LTN1 run.

LNOx Profile NOx partitioning Box-AMF Visibility ~pi li ai ei

Modelled sensitivitiesSensitivity E = ai * li * pi = ei * pi = SNO2 / VNOx

COT=

E=Two examples

LNOx Profile NOx partitioning Box-AMF Visibility ~pi li ai ei

Modelled sensitivitiesSensitivity E = ai * li * pi = ei * pi = SNO2 / VNOx

COT=

E=EnsembleMeans

Modelled sensitivitiesSensitivity E = ai * li * pi = ei * pi = SNO2 / VNOx

... show small dependence on COT

... show small variability

Spatial patterns

• Spatial mean sensitity (relevant for applications): E=0.46 (0.37-0.55)

For more details...

... see Beirle et al., Sensitivity of satellite observations for freshly produced lightning NOx, ACPD (“in print”), 2008.

In addition: – Error discussion– Impact of RTM settings (negligible!)– Impact of satellite resolution (does not change

results)

– Impact of background NOx: critical! (shielding!)

Visibility & sensitivity for LNOx: results

• Satellites "look" deep inside the cloud• But at the cloud top, there is nothing to see

– Cloud top: ei~0 (due to low li)

– Ground: ei~0 (due to low ai)

– Cloud middle: ei maximum (1-2)

• We find low variability of E over one week of thunderstorm simulations!

• On average, E is lowest over anvils• Mean E=0.46 (0.37-0.55)

• Sat. meas. are sensitive for LNOx!

Beirle et al., ACP 6, 2006

1.7 (0.6-4.7) Tg [N]/year

Gulf of Mexico revisited

E0.25 (inconsistent literature sources for pi, li, ai)

0.9 Tg [N]/year

E=0.46 (this study)

Outlook• One model study: How representative?

– Repeat study for other thunderstorms (using other models)

• One empirical study: find more!– Systematic search for coincidences of flashes (WWLLN)

during SCIAMACHY / GOME-2 overpass: High variability!

• Possible reasons:– regional differences of LNOx production efficiency

(Huntrieser et al., 2008)

– general high variability of LNOx production/flash?

– need of higher moments / pdfs instead of means?

• Satellite observations have the potential to improve our knowledge on LNOx!

Thanks for your attention

Sensitivity results

• Single sensitivities vary (~0.1-1)

• Mean sensitivity (~0.3-0.7) always higher than in Mexico-Study (0.25) !

→ is the modelled storm representative?

• With these sensitivities, every active thunderstorm (>500 flashes per SCIAMACHY pixel 30x60km2)should be clearly visible from space (SNO2>2.5e15 molec/cm2)

→ what do we see?

Observations of fresh LNOx

• GOME-event in Gulf of Mexico:– perfect spatial/temporal matching– lightning information (NLDN)

• Meanwhile:– 4 years of SCIAMACHY data– 3 years of WWLLN data (global continuous ground

based lightning counts)

• Automated search for „lightning events“ prior SCIAMACHY overpass: 1680 matches!!!

• keep in mind: 10:00 local time!

→ Coincidences almost all over oceans

Some examples...

Flash time CloudsNO2

Australia

Red: <30 minBlue: 90-120 minGrey: 2-24 h

Tropospheric Slant Column

SNO2

FRESCO CF&CTHBlack: cloud freeColoured: cloudyRed: high cloudBlue: low cloud

1015

Some examples...

In the middle of nowhere...

Pacific

1015

Flash time CloudsNO2

Some examples...

Maximum > 2e16!

USA

1015

Flash time CloudsNO2

What happens here???

Korea

1015

Flash time CloudsNO2

What happens here???

China

Hong Kong

1015

Flash time CloudsNO2

What happens here???

Australia

1015

Flash time CloudsNO2

What is different???

1015

Flash time CloudsNO2

Australia

Global pattern

SNO2Regional differences:• Higher values over land • Higher values close to strong ground sources, indicating deep convection• Higher values east from Australia???

Statistics: SNO2 for coinciding lightning events

Every dot: SCIA-Pixel withmore than 5 WWLLN flashesand cf>0.5

SNO2

log10(flashes)

Statistics: S NO2 for coinciding lightning events

More than

0

10

100

1000

Flashes within the last hour

SNO2Every dot: SCIA-Pixel withmore than 5 WWLLN flashesand cf>0.5

CTH

Some open questions

• Where is the LNOx?

– observed SNO2 enhancement for SCIA-pixels with >1000 flashes (corrected for WWLLN sensitivity):1.6*1015 molec/cm2 on average

– expected:5*1016 molec/cm2 !!!

• How to hide LNOx completely?

– in no simulation run E<0.1

• What makes the differencebetween good and no signal?

30* higher !!!

E = 0.25 (0.14-0.5)

LNOx profile:

Cloud resolving modelsPickering et al. 1998

Fehr et al. 2004

fraction of total

NOx partitioning:

In-situ measurements in New Mexico for cb conditionsRidley et al. 1994, 1996

[NO2]/[NOx]

Box AMFs: (sensitivity)

RTM, cb conditionsHild et al. 2002

Box AMF

Problem: different, possibly inconsistent sources→ use one source: cloud resolving model

SNO2 = VNOx * ai * li * pi

li

piai

LNOx Profile NOx partitioning Box-AMF Visibility ~pi li ai ei

Modelled sensitivitiesSensitivity E = ai * li * pi = ei * pi = SNO2 / VNOx

COT=

E=EnsembleMeans

Lowest sens.