institute for climate and atmospheric science balloons, waves and cirrus in the tropics steven...

Institute for Climate and Atmospheric Science

Balloons, waves and cirrus in the tropics

Steven Dobbie

Institute for Climate and Atmospheric ScienceUniversity of Leeds

Sardar Al-Jumur

Benjamin Murray, Theodore Wilson, Zhiqiang Cui

Ottmar Möhler, Martin Schnaiter, Robert Wagner, Stefan Benz, Monika Niemand, Harald Saathoff, Volker Ebert, Steven Wagner and

Bernd Kärcher

Neil Gordon

MOGUL Meeting – Feb 28, 2013

Balloons, waves and cirrus in the tropics

What is interesting about TTL region?

Ice supersaturations frequently exceed 100% Rhi

(Jensen et al, 2005; Peter et al., 2006).

Is something inhibiting the formation of cirrus?

What is interesting about thin TTL cirrus?

High in-cloud supersaturations and low ice number concentrations

(Kramer et al., 2009)

Why aren’t high supersaturations in cloud being quenched?

“Supersaturation puzzle”

Source of supersaturation

- As air rises the air cools and RHice rises

Sink of supersaturation

- As RHice rises vapour deposits on ice crystals present

- Homogeneous nucleation results in numerous crystals of small size so RHice is quenched quickly

- Heterogeneous nucleation results in few crystals of larger size and RHice is slower to quench.

- Numbers of traditional IN are too few

What is up there?

Froyd et al 2010:

Candidates?

-Mineral dust?

- Low numbers

“Even if all mineral dust nucleated they couldn’t explain the ice numbers” (Froyd et al 2010)

What if?

What if some of the numerous solution aerosols were nucleating at lower super-saturations—below water saturation?

Candidates?

Sulphates crystallise in low relative humidity conditions.

- numbers are high

- solid so could act as an ice nuclei?

Candidates?

- Sulphates are too viscous at TTL conditions to crystallise (Bodsworth et al., 2010)

Candidates?

-Very low accommodation coefficient (0.0075) and so slow uptake of water vapour? (Magee et al., 2006)

-Recent work by Skrotzki (2012) shows it is > 0.1

Candidates?

What else could be solid and act as an IN at low temperatures?

Glassy aerosols

”Temperature at which materials change from hard and brittle to soft and pliable”

“The temperature below which an amorphous material is a glassy solid and above which it is a viscous liquid“

Murray et al., 2008 and Zobrist et al., 2008

Previously not thought to be applicable to troposphere but is relevant for TTL.

Thought to potentially inhibit nucleation

Brittle glassy aerosol

T / RHi decreasing

Laboratory glassy aerosols

Brittle glassy aerosol Liquid solution aerosol

T / RHi increasing

AIDA Chamber, Karlsruhe Aqueous citric acid,

Raffinose/M5AS,

Levoglucosan,

i) it has similar functionality to oxygenated organic

compounds known to exist in atmospheric aerosols;

ii) its glass forming properties are similar to a range of other atmospherically relevant aqueous organic solutions and aqueous organic-sulphate mixtures; and

iii) Representative of products found in the atmosphere.

What did the AIDA results show for glassy behaviour during nucleation?

AIDA results:

Above 212K

(non-glassy regime)

Below 212K

(glassy regime)

AIDA results:

Above 212K

(non-glassy regime)

Below 212K

(glassy regime)

Modelling results

1-D APSC (Karcher, DLR) runs:

185 190 195

80 90 100 0 20 40 60 80 100 0 1 2 3 4

Temperature / K Pressure / mBar RHi (%)

H2O mixing ratio

0 100 200 300100

0 100 200 300

b) HET

(%)RHi

Time / minutes

a) HOM

e / cm

(%)RHi

Time / minutes

APSC results: Constant uplift

b) Glassy

0 100 200 300 400100

0 100 200 300 400

1HOM, 0.76 K hr-1

3.8 K hr-1

2.5 K hr-1

1.26 K hr-1

0.25 K hr-1

0.76 K hr-1

0.50 K hr-1

HOM, 0.76 K hr-1

Time / minutes

0.25 K hr-1

0.50 K hr-10.76 K hr-1 1.26 K hr-1

2.5 K hr-1

Time / minutes

APSC results: Citric acid/constant uplift

APSC results: Raffinose/M5AS

IN indirect response

Glassy indirect effect

Forced by single waves: het/glassy

Forced by observed

superposition of waves:

(Jensen and Pfister, 2004)

Deposition coefficient sensitivity

High altitude balloon observations (Hertzog et al., LMD)

- 2-3 months floating around in the tropics

advected on constant density surfaces

- measuring temperature and pressure

High altitude balloon (LMD; Hertzog et al)- 2-3 months floating around in the tropics

advected on constant density surfaces

- measuring temperature and pressure

Hertzog et al

Balloon trajectory

Temperature variations

Het (glassy) model run

Hom activated

Optical depth

Cloud lifetime

Hom Glassy

Radiative properties

Satellite observations

Can we obtain remote sensing at the location of the balloon?

Satellite observations

MLS – AURA CALIPSO - Lidar

Conclusions

Experiments:

- A range of common organics and organic/sulphate mixtures become glassy and nucleate ice heterogeneously

Modelling:

- Modelling results using glassy aerosols are consistent with observed high in-cloud super-saturations and low ice number concentrations

- Modelling agree for ice number, RHi, optical depth, heating rates, etc.

Conclusions

Modelling:

- Consistency for both constant lifting and gravity waves forcings

- Strong potential indirect response with glassy nucleation

- Suppression of ice number

- Shorter lifetime

- Heterogeneous nucleation mechanism is needed to explain observations.

Next steps

Remote sensing:

- Frequency of cloud: average the cloud occurrence from Calipso that are detached, at TTL heights, and close to balloon.

- Launch a balloon with humidity, particle counters, etc.

Challenges

-Need an instrument to measure glassy particles.

-Understand aerosol spatial variations in the TTL and transport mechanisms.

-Assessing potential anthropogenic influences/indirect effects.

-Looking at warmer temperature glassy particles. Are they playing a role outside the tropics?

- Thank you -

Radiative heating rates Optical depth

Forced by single waves: hom

Radiative heating rates

institute for climate and atmospheric science balloons, waves and cirrus in the tropics steven...

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