1. Evolution of tropical cirrus clouds.
Clare Allen.
Supervisor: Dr Steven Dobbie.
Co-supervisor: Dr Alan Blyth.
RSG: Dr Ken Carslaw.

2. Importance of cirrus clouds:
Cirrus are high altitude clouds consisting mainly of ice.
Globally cirrus covers approximately 20% of the Earth’s surface (Luo et al 2002).
Cirrus clouds have a significant role in regulating the radiation balance of the earth-atmosphere system.

3. Tropical cirrus clouds.
Majority of tropical cirrus forms as result of anvil outflow from the convective processes within cumulonimbus towers.
The convective core dissipates leaving a remaining background cirrus cloud.

4. Example of tropical cirrus anvil.

5. Ice nucleation mechanisms.
Homogeneous ice nucleation:
Spontaneous freezing of supercooled water or solution droplets.
Temperatures < -35oC and RH > 100%.
Heterogeneous ice nucleation:
Freezing of supercooled water or solution droplet aided by a foreign body known as an ice nuclei.
Temperatures between 0oC and -35oC.

6. Aim:
“To understand the influence of dust aerosol of the evolution of microphysical and radiative properties of tropical cirrus clouds.”

7. Dust altering anvil properties:

9. CRYSTAL-FACE location:
Southern Florida was chosen as deep convection frequently occur in July in the surrounding waters.
The aircraft based at Key-West Naval Station.
Ground based instruments were based on the southwest coast of Florida.

10. Flight plans:

11. Model used: Large Eddy Model
Using anelastic approach, allowing reference states of pressure, temperature and density to vary with height.
Using double moment scheme to represent IN:
Mass
Number

12. Current work:
Integrating the influence of gravity waves in the cirrus anvil region.
Increase cirrus cloud lifetime?

13. Gravity waves: Large scale upper tropospheric wave.
Initialized by the convective cloud.
Starr et al (2004).
IR GOES-8 satellite image 23/07/02

14. Preliminary results.

15. Future work: