The role of dust on cloud-precipitation cycle

Transcription

1 UNIVERSITY OF ATHENS SCHOOL OF PHYSICS, DIVISION OF ENVIRONMENT AND METEOROLOGY ATMOSPHERIC MODELING AND WEATHER FORECASTING GROUP The role of dust on cloud-precipitation cycle Stavros Solomos, George Kallos 6th INTERNATIONAL WORKSHOP ON SAND/ DUSTSTORMS AND ASSOCIATED DUSTFALL 7-9 SEPTEMBER 2011, ATHENS, GREECE

2 Climate indirect effects (Rosenfeld, Science, 2008)

3 Outline Dust particles in the atmosphere Interactions between particles and clouds Implications on regional weather

4 Natural & anthropogenic aerosols emissions a. b. Distribution of dust sources Sea salt production c. Emissions distribution (μg m -2 per hour) at the first free model level of a) CO, b) SO 2, c) NOx and d) NH 3 on 01 July 2005 at 12:00 UTC including domestic and international shipping and aviation. d.

5 Production of dust by density currents Left column: MSG/SEVIRI dust indicator satellite images over North West Africa. Dark red colors indicate clouds and purple colors indicate desert dust. Right column: Corresponding model cloud fraction (grayscale) and dust production flux (colour palette in μg m -2 ). The leading edge of the propagating density current is denoted with black dashed lines. The system originated south of the Atlas Mountains and propagated towards Algeria. Solomos et al., 2011 (in review, JGR)

6 Dust production along the propagating front (18:50 UTC) Potential temperature (red contour lines in K) and dust concentration (color palette in μg m -3 ) at 18:50 UTC for a front-relative frame of reference. S lon = 4.4, lat= N This stationary approach is useful for revealing small scale vortices within the propagating system. The relative wind speed is near zero at the head of the system, and an anticlockwise vortex is forming at the lower model layers due to reversal of flow behind the leading edge and surface friction. This flow pattern is responsible for the suspension of bigger particles (i.e. sand) and for the production of smaller dust particles through the saltation and bombardment mechanism.

7 The integrated model RAMS / ICLAMS The development is carried out on RAMS ver. 6 in the framework of CIRCE project It has two-way interactive nesting capabilities Explicit cloud microphysical scheme It can be nested inside of global systems It can run with configurations from a few meters horizontal resolution up to hemispheric It also includes: Detailed soil surface and water interaction processes Detailed dust cycle description Detailed sea salt cycle Gas phase chemistry module with photochemical processes Aqueous phase chemistry Gas to particle conversion and heterogeneous chemical reactions Dry and wet deposition modules Aerosol-cloud-radiative transfer interaction module Explicit cloud nucleation scheme based on atmospheric composition It can be used mainly for case studies and scenario development related to aerosol processes and feedbacks in the atmosphere

8 CCN properties and an isolated cloud formation Particle distribution Model setup: 2D domain, dx=300m, 35 vertical layers Duration of runs: 6 hours Horizontally uniform initialization with a convectively-unstable profile The number of cloud droplets is explicitly calculated from the aerosol properties and the atmospheric conditions two distributions of initial CN: A. Pristine (100 cm -3 ) B. Hazy (1500 cm -3 ) Pristine - After 80 min Hazy - After 80 min After 80 min run Pristine - After 100 min Hazy - After 100 min Pristine - After 170 min Hazy - After 170 min Total condensates mixing ratio (g kg -1 ) for the pristine and the hazy scenarios (g Kg -1 )

9 Effects of CCN on precipitation Maximum precipitation rate (mm h -1 ) for the pristine and hazy air mass scenarios. Values are taken every 10 minutes. Hourly accumulated precipitation (mm) over the domain, for the pristine and hazy CCN scenarios. Accumulated precipitation over the entire domain was 286 mm for the pristine and 215 mm for the hazy case. Most of this difference can be attributed to the inhibition of precipitation during the early stages of cloud development.

10 Effects of GCCN on precipitation A third - GCCN - aerosol mode with a median diameter of 10μm, σ=2, and total concentration=5 cm -3 has been added Adding GCCN to a hazy environment resulted in the reduction of the number of cloud droplets that nucleated. Bigger droplets were allowed to form and the rainfall during the early stages of cloud development was increased. b In contrary, GCCN did not change significantly the warm stage precipitation for the pristine environment. Adding a few GCCN for this case did not significantly change the cloud droplet spectrum because these clouds already contained a limited number of droplets which allowed them to grow fast to rain droplets. Solomos et al., ACP, a

11 Effects of aerosol chemical composition on precipitation Assuming dust particles coated with soluble material (NaCl or (NH 4 ) 2 SO 4 ) and changing the soluble fraction of these particles resulted in significant variations in precipitation. The differences are more evident when the cloud system is well developed after 120 min run. The totally soluble NaCl particles produced overall more precipitation. The dust particles coated with (NH 4 ) 2 SO 4 were more efficient in rain formation when assuming small soluble fractions (0.2 and 0.5) domain total accumulated precipitation (mm) domain total accumulated precipitation (mm) NaCl_frsol1.0 NaCl_frsol0.7 NaCl_frsol0.5 NaCl_frsol run time (min) (NH4)2SO4_frsol1.0 (NH4)2SO4_frsol0.7 (NH4)2SO4_frsol0.5 (NH4)2SO4_frsol run time (min)

12 Effects of topography on precipitation Pristine + flat terrain Pristine + idealized hill Pristine + complex topography Hazy + flat terrain Hazy + idealized hill Hazy + complex topography (mm) 4h accumulated precipitation (mm) and topography (dark contours) The pristine cases generally (but not always) produced more precipitation than the hazy ones and the distribution of precipitation was found to be much more sensitive to terrain variability than to any of the variations in aerosol properties

13 Aerosols & clouds (Case study) b a MODIS Aqua visible channel, 28JAN UTC Cloud fraction (gray) Dust concentration (red) The case study combines a low pressure system and a dust storm over the eastern Mediterranean. A detailed analysis and airborne measurements of this episode were obtained during the Mediterranean Israeli Dust Experiment (MEIDEX) as described in Levin et al., 2005.

14 Model setup and origin of natural particles Dust flux (color palette) in μg m -2 on 27 January :00 UTC. The model was configured with three nested grids (15km, 3km and 750m) that are indicated with dashed rectangles. Initial and boundary conditions were taken from CIRCE LAPS km reanalysis. SST is the NCEP analysis The main sources of dust particles during this particular event were identified over Northeast Africa.

15 Comparison of modeled aerosol with ground measurements Afule Modiin Beer Sheva Comparison of modeled dust and salt particles concentration with PM10 measurements from 3 rural stations imply that almost 90% of the aerosol load during the case study period can be attributed to transportation of dust particles.

16 Comparison of modeled aerosol with airborne measurements CYPRUS MEDITERRANEAN SEA LEBANON Modeled dust number concentration (cm -3 ) at 538 m height on 28 January 2003, 09:20 UTC. Dots indicate the locations of the aircraft measurements. ISRAEL Comparison of aircraft measurements of natural particles with modeled dust and salt concentrations at various heights inside the dust layer.

17 Effects of airborne particles on cloud dynamics 5% hygroscopic dust 20% hygroscopic dust 5% hygroscopic dust + INx10 W-E cross-section of rain mixing ratio (colour palette in g/kg) and ice mixing ratio (black line contours in g/kg) over Haifa. Dust may act both as CCN and IN. By Increasing the percentage of hygroscopic mineral dust or increasing the ice condensation nuclei (IN) concentration by an order of magnitude, both resulted into the freezing of more particles and to the release of latent heat at higher levels. The clouds exhibited stronger updrafts reached higher tops and produced more rain.

18 Effects of airborne particles on cloud dynamics When CAPE is large enough, some amount of liquid condensates may thrust into the upper levels of a cloud and eventually freeze in higher altitudes. The released latent heat invigorates convection at higher levels. W-E cross-section over Haifa, 29 January :20 UTC 08:20 UTC 08:20 UTC 08:30 UTC CAPE = 1027 J/kg a b c d a) Vertical structure of the atmosphere over Haifa b) Liquid water mixing ratio (colour palette in g/kg) and ambient temperature (red contours in C o ) c) Θe (colour palette in K) and updrafts (black contours in m/s) d) Θe (colour palette in K) and updrafts (black contours in m/s)

19 Effects of airborne particles on precipitation Aerosol Cases Aerosolcloud interaction Case1 (control run) NO NO Case2 (only radiation interaction) NO YES Case3 (constant aerosol : pristine ) YES NO Aerosolradiation interaction RAMS/ICLAMS model configuration for nine aerosol scenarios Case4 (constant aerosol : hazy ) YES NO Case5 (prognostic aerosol :1% hygroscopic dust) YES YES Case6 (prognostic aerosol :5% hygroscopic dust) YES YES Case7 (prognostic aerosol :10% hygroscopic dust) YES YES Case8 (prognostic aerosol :30% hygroscopic dust) YES YES Case9 (prognostic aerosol :5% hygroscopic dust + IN 10) YES YES Case 1 (0.83) Case 2 (0.82) Case 3 (0.81) Case 4 (0.76) Bias of the 24 h accumulated precipitation for 86 stations in Israel and for nine scenarios of aerosol composition. Bias Case 5 (0.84) Case 6 (0.84) Case 7 (0.96) Case 8 (0.71) Case 9 (0.94) Solomos et al., ACP, Precipitation Tresholds (mm)

20 Preliminary results The role of soot and dust as IN The recently developed ice formation parameterization of Barahona and Nenes (ACP, 2009) has been implemented in RAMS/ICLAMS The new formulation includes four different IN spectrums derived from in-situ measurements and field campaigns: MY92 (Meyers et al.,1992), PDG07 (Philips et al., 2007) PDA08 (Philips et al., 2008) and Classical Nucleation Theory CNT (Pruppacher and Klett, 1997; Barahona and Nenes 2008) The formulation has been extended in RAMS/ICLAMS including also the prognostic dust particles in the IN spectrum The new IN scheme in ICLAMS takes into account both homogeneous and heterogeneous ice activation and also the competition between these two mechanisms (Barahona and Nenes, ACP, 2009). Initial conditions for the IN sensitivity tests Various distributions of dust and soot have been tested on their ability to act as IN for a two-layer cloud structure

21 Preliminary results The role of soot and dust as IN The aerosol particles were assumed to be either dust or soot. Increasing the amount of particles in a two-layer cloud system triggered precipitation and heavy rainfall and hailfall was produced. Further increasing the concentration of airborne particles resulted in more but smaller ice particles. The size of those elements was not sufficient to form rain droplets and precipitation was inhibited. Accumulated rainfall (mm) for various dust concentrations (red line in μg m -3 ) and black carbon concentrations (black line in μg m -3 ). Blue labels denote particle concentration in μg m -3. Total condensates mixing ratio (color palette in g Kg -1 ) and hail mixing ratio (red contours in g Kg -1 ) after 4 hours run for the case of 500 μg m -3 soot.

22 General remarks Hazy clouds suspend precipitation while pristine clouds precipitate faster and produce more rain. High concentrations of aerosols result in significant release of latent heat at middle and higher cloud levels, higher updrafts and finally more ice at the upper levels of the clouds. The uncertainties associated with perturbations in aerosol concentrations, size distribution and composition are considerable. If we want to discuss about future climate trends it is better to improve our knowledge on aerosol radiation cloud processes on an integrated way.

23 Preliminary runs on the effects of dust on cloud formation at the eastern Atlantic Dustload (red contours) and verticaly integrated condensates (color scale) August 2005 No dust radiative effects dust radiative effects SST on 24 August 2011 (Irene Huricane) TRMM observations of accumulated precipitation (mm) August 2005

24 Volcanic ash Iceland volcano eruption April 2010

25 Fukushima case Release March 2011 Near surface concentration Column integrated concentration

26 Acknowledgments The present work is supported by: The European Union 6 th Framework Program CIRCE IP, contract #