⠺ Charles E. Robert * | Christian von Savigny | Heinrich Bovensmann | John P. Burrows ⠗ Institute of Environmental Physics, Bremen University

Evidence of a

27-day signature in noctilucent cloud occurrence frequency

⠺ Matthew T. DeLand ⠗ Science Systems and Applications Inc. (SSAI), USA

❶Noctilucent Clouds?

H2O T CN✖ ✖

Noctilucent clouds (NLC)

=~135 K3-6 ppmv ???

⠺ www.spaceweather.com/nlcs | Gerd Baumgarten (IAP) ⠗

1.0

0.8

0.6

0.4

0.2

0.0

Frequency of Occurrence

⠺ Robert et al | JASTP | 2009 ⠗

Global Change

Radiative cooling of the upper atmosphere

CO2

CH4

H2O H2O

Increased water vaporin the mesosphere

Ω

⠺ DeLand et al | JASTP | 2006 ⠗

Solar Activity

NH

SH

Evidence of a

27-day signature in noctilucent cloud occurrence frequency

‣ Important to understand WHICH processes affect NLC and HOW

‣ Already evidence of a connection between solar activity (11-year) and NLC properties

‣ Challenges of the task:

‣ Signal buried within other variability

‣ Few 27-day periods in a 90 days season

Is there a 27-day signal in NLC ?

❷Instruments & Data Sets

Limb

7 years

NadirSBUV

28 years

Composite Lyman-alpha

Solar proxy

State of the atmosphere

H2O + Temperature

+Superposed EpochsCross-correlation ❷❶

+

Analysis tools

❸27-day signal in NLC⠺ Cross-Correlation ⠗

Cross-Correlation

NH

SCIAMACHY

NLC

occu

rren

ce ra

te a

nom

alie

s

Lyman-alpha anom

alies

Cross-Correlation

LagTime

2003

2004

2005

2006

2007

2008

NLC

occu

rren

ce ra

te a

nom

alie

s

Lyman-alpha anom

alies

Cross-Correlation

LagTime

SH

Cross-Correlation SCIAMACHY2002/3

2003/4

2004/5

2005/6

2006/7

2007/8

2008/9

Time

NH

Anom

alie

s

SH

One Long Record...SCIAMACHY

NH

α=5% α=5%

α=23.0%

α=0.29%

SH

One Long Record...SCIAMACHY

Corr

elat

ion

Coef

ficie

nt

Lag Lag

SBUV

Time

NH

Anom

alie

s

SH

One Long Record...SBUV

NH

α=5%α=5%

SH

One Long Record...SBUV

Corr

elat

ion

Coef

ficie

nt

Lag

α=4.9%α=0.13%

Lag

❹27-day signal in NLCSuperposed

Epochs ⠺ ⠗

Time

ForcingSignal

Superposed Epochs

Time

Forcing

Superposed Epochs

ForcingForcing

Forcing

Time

Superposed Epochs

Time

Superposed Epochs

Forcing

N�

i=1N

N�

i=1N

N�

i=1N

N�

i=1N

-5 -3 0 3 5 7

Superposed Epochs

Superposed EpochsSCIAMACHY

NH

Lag

Superposed EpochsSCIAMACHY

NH27-day27-day

Lag =0 day

α=0.1%

Superposed EpochsSCIAMACHY

NH SH27-day27-day 26-day

Lag =0 day Lag =? 4 day

α=0.1%

SBUV

NH

Lag

SH

Lag

Superposed EpochsSBUV

α=0.1% α=0.7%

=0 day =0 day

28-day 27-day 25-day25-day

SensitivitySBUV

★ Nice feature of this approach: sensitivity of NLC property on 27-day solar forcing

SensitivitySBUV

Albe

do a

nom

aly

[10-

6 ]

Lyman-α anomaly [1011 photons s-1 cm-2] Lyman-α anomaly [1011 photons s-1 cm-2]

★ Nice feature of this approach: sensitivity of NLC property on 27-day solar forcing

NH SH

27-day

SensitivitySBUV

11-year VS

Sensitivity Comparison11-year VS 27-day

11-year* 27-day

NH

SH

-0.706 ± 0.022 -0.61 ± 0.1

-0.406 ± 0.026 -0.46 ± 0.1

*Deland et al., 2007

❺Temperature & H2O

Lag [days] Lag [days]

Altit

ude

[km

]

NH SH

Temperature Responselatitude: 60°- 80°

[K] [K]

★ Amplitude of SH is 3 times larger than NH★ Maximum occurs at different altitudes

★ The lag response is NOT the same.

Lag [days] Lag [days]

Altit

ude

[km

]

NH SH

H2O Responselatitude: 60°- 80°

[ppm] [ppm]

★ Amplitude of SH and NH are about the same: 0.1ppm★ The maximum response is at different altitudes★ The lag response is unexpected: OPPOSITE in both hemispheres

Lag [days] Lag [days]

Altit

ude

[km

]

NH SH

H2O Responselatitude: 60°- 80°

[ppm] [ppm]

★ Amplitude of SH and NH are about the same: 0.1ppm★ The maximum response is at different altitudes★ The lag response is unexpected: OPPOSITE in both hemispheres

❻Conclusions

Noctilucent cloud properties sensitivity to the 11-year and 27-day solar forcing are in very good agreement, suggesting that the mechanisms responsible for the response could be the same.

❷

Temperature response, NOT water vapor, can explain the noctilucent cloud variation with solar activity

❸

❶ Evidence of a ~27-day modulation in NLC occurrence rates anti-correlated with lyman-alpha solar irradiance using 2 different approaches

Conclusions

Thank you