Presentation on theme: "Cirrus cloud evolution and radiative characteristics By Sardar AL-Jumur Supervisor Steven Dobbie."— Presentation transcript:
Cirrus cloud evolution and radiative characteristics By Sardar AL-Jumur Supervisor Steven Dobbie
Aims and objectives Study the lifetime and evolution of tropical thin cirrus formed on glassy and non-glassy particles. Address the following question and find a reasonable answer: Do we need glassy particles to justify TTL Cirrus cloud observation with: Synoptic scale Gravity wave (GW) The impact of thin and sub-visual cirrus cloud on earth’s radiation balance.
Cirrus cloud -definition Detached clouds in the form of white, delicate filaments, white or mostly white patches with fibrous appearance or silky sheen or both. Cirrus cloud forms below -30 0 C
Tropical tropopause layer (TTL) the tropical transition layer between the troposphere and the stratosphere. 10-18km height and < 215 K.
Glassy aerosols Droplets rich in organic material, ubiquitous in the TTL, may become glassy (amorphous, non-crystalline solid) under TTL conditions. The glass transition temperature (Tg) is the temperature below which the viscosity of a liquid reaches such extreme values that it becomes a brittle solid.
Why do we care about tropical cirrus cloud? In general cirrus cloud often covers more than 70% of the globe with a high frequency in the tropics. There is uncertainty about the microphysics and radiative properties of cirrus and the role of cirrus cloud in radiation budget and earth’s climate It plays an important role in regulating the water budget of the atmosphere.
(Whlie et al, 1994) The frequency of light cirrus The frequency of light cirrus ( τ < 0.7) over land and ocean
TTL Cirrus observation Very low ice number density (0.005-0.2) cm -3 has been observed frequently in TTL at temperatures below 205 K (Kramer, 2009). High in cloud relative humidity (RHi). Report an N ice range of 0.002 – 0.19 cm -3 at 188 to 198K from 2.4 h of observation time in subvisible cirrus during the CR-AVE field campaign Lawson et al. (2008). Flight measurement showed ice concentration as low as (0.001-0.07) cm -3 with mean ice crystal size (1-20 μ m) during (CRAVE) IN 2006.
Input parameters in addition to the AIDA chamber data for the 1-dimensional Advanced Particle Simulation Code(APSCm) used for the model runs
Murray et al,2010 Hetrogeneous nucleation on glassy particles (50% glassy particles) and homogeneous freezing on liquid particles (100 % liquid particles) with deposition coefficient of water vapour on ice α=0.5.
APSC run’s result of the ice number concentration for two vertical profile of temperature the initial Rhi=120%, α=1.0. (Non-glassy case).
In order to have a realistic cirrus scenarios and not just perform an academic exercise, we used observations of gravity waves and vary the key unknown parameters of this problem ( glassy particles concentration, deposition coefficient and cooling rates, amplitude and frequency of gravity wave) in order to explore the possible range of cirrus changes induced by such changes in aerosol and dynamical properties. Gravity waves (GW)
Exists every were in the atmosphere. Transfer the energy from lower to upper atmosphere. Recent studies show that GWs in the upper troposphere and lower stratosphere were found to considerably influence the formation of high and cold cirrus clouds (Jensen et al., 2001; Jensen and Pfister, 2004; Haag and Kärcher,, 2004; Jensen et al., 2005). Why do we care about GW
The corresponding of amplitude and time period and its efficiency to nucleate ice in different mechanisms: heterogeneous and homogeneous RHi = 100% and aerosols number 100 cm -3, 300 cm -3. Deposition coefficient α =(0.5 ) Time period(sec) Amplitude(cm/sec) 90012001500 20--- 50-glassy (equilibrium) 90glassy (equilibrium) glassy/non-glassy (pulse decay) 100glassy (equilibrium)glassy/non-glassyglassy/non-glassy(pulse decay)
gravity waves of amplitude 50 cm/sec and time period 1200 sec, T+5,RHi=100%,IN=50cm -3 (dynamic equilibriume).
gravity waves of amplitude 50 cm/sec and time period 1500 sec, T+5,RHi=100%,IN=50cm -3 (dynamic equilibriume).
gravity wave with amplitude 90 cm/sec and time period 1500,RHi=100%,T+5, IN=50 cm -3 (pulse decay).
imposed a set of seven single gravity waves on constant uplift of 3cm/sec with RH=100%,T+5, glassy particles =50cm -3, deposition coefficient α =0.5.
imposed a set of seven single gravity waves on constant uplift of 3cm/sec with RH=100%,T=T+5,liquid particles =100 cm -3, deposition coefficient α =0.5.
imposed waves (kelvin+RGR+IG) on synoptic cooling scale with glassy particles at 15 0 altitude, other conditions as the same as fig the data has been taken from Jensen & pfister(2004).
Model runs with glassy and non-glassy particles for a wide range of α
The radiative heating and forcing of cirrus cloud have been performed by using 1D – radiative transfer model (Jiangnan code) through calculating the net impact of cirrus on both solar and IR.
The maximum radiative heating of cirrus forming on glassy and liquid particle compared to clear sky for for T+5, IN=50cm -3, aerosols=100cm -3, cloud fraction=100%. Updraft=3 cm/sec. α=0.5
The maximum radiative heating of cirrus forming on glassy particle by superimposed gravity wave on synoptic scale for T+5, IN=50cm-3, total aerosols=100cm -3, cloud fraction=100%.(glassy case)
The impact of deposition factor on cirrus microphysics and radiative properties.
The net flux at the top of the atmosphere (TOA) can be found by using following concept: C ir,s =F cl ir,s - F ov ir,s F cl ir,s the upward flux of infrared or solar for clear sky. F ov ir,s flux of upward infrared or solar for cloudy sky. Then, the net radiative forcing of cirrus cloud for solar and IR radiation computed from: C = C ir + C S (Qiang and Liou, 1993)
The variation of optical depth with time for homogenous nucleation (liquid particle), heterogeneous particles (glassy particles) and with 10% glassy particles. α =0.5
Conclusion Run the model with glassy particles show an agreement with TTL cirrus observation with both constant uplift and gravity waves. Homogeneous freezing with weak updraft could show observation with specific deposition coefficient. Higher amplitude gravity waves produce higher ice number densities and smaller crystals. Higher frequency gravity wave produces higher ice number densities and smaller crystals. The small scale gravity waves have the potential to produce ice with glassy particles within the range of observation in TTL. (dynamical equilibrium) Cirrus cloud forming on glassy particles shows dynamic equilibrium up to amplitude of 90 cm/sec and frequency (1200s) -1 of gravity wave. Cirrus cloud forming on glassy and non glassy particles shows pulse decay with vertical velocity(the amplitude of gravity wave) with 90 and 100 cm/sec and frequency (1500s) -1
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