Aerosol Microphysics 2 Flashcards
what is the sectional approach in GCMs?
-the size distribution is descretised into sections and the particles properties are assumed to be constant over particle size sections
what is the modal approach in GCMs?
the size distribution is approximated by several log-normal modes and particle properties are assumed to be uniform in each mode
what is more costly and complex? Sectional or modal?
sectional is most costly and complex
what is the GDE?
mathematical formulation of all the processes which act to change the atmospheric particle size distribution
is there a general solution to the GDE?
no it must be solved numerically
how does nucleation affect particle number, particle mass, and particle SA
increases particle number, increases particle mass, increases particle SA
how does coagulation affect particle number and particle mass and particle SA
decreases particle number, no effect on particle mass, decrease in particle SA
how does condensation affect particle number and particle mass and particle SA
no effect on particle number, increase in particle SA, increase in particle mass
how does deposition affect particle number and particle mass and particle SA
decreases particle number, SA, and mass
what is time splitting and operator splitting?
-they’re discretisation techniques
-assume independence of the evolutions of the different processes during a time delta t
-they consecutively apply suitable methods to each physical processing during each time delta t
what do bulk aerosol models measure/track?
-only track total mass of aerosol components
-assume typical size distributions
what are some benefits of bulk aerosol models?
-computationally most efficient
-ok to use for air quality models that only require PM10 or PM25
what are some drawbacks for bulk aerosol models?
-cant be used if they require aerosol number concs e.g. climate studies
-cant be used for modelling that requires accurate size dependent aerosol processes e.g. growth
In sectional models, for m chemical compounds, how many equations must be solved?
n x m
what does the accuracy of sectional models depend on?
the number of sections
what can we assume about the particle size distribution within a size bin?
particle size distribution is continuous and monodisperse
name 4 sectional model algorithms
-fixed size sections
-modified fixed method: hybrid approach
-moving size sections
-moving centre method
what are 4 transformation processes?
-nucleation
-coagulation
-condensation
-deposition
what do sectional schemes represent well?
complex aerosol dynamics
what is the most commonly used approach in GCMs?
modal aerosol microphyics schemes
what are some disadvantages of modal schemes?
-cannot capture all the potential detail in the distribution
-simplifications can cause biases in simulated growth rates
what is GLOMAP?
a sectional aerosol microphysics model
why was GLOMAP developed?
-it is able to calculate the details of the aerosol size distribution on a global scale
when can sectional models only be used in GCMs?
-when the bin resolution is reduced significantly
why might data sets from observations not be continuous?
instrument malfunction, maintenance etc
why don’t most GCMs not use regular lat-lon grids?
to overcome difficulties with the grid spacing at poles
describe what GCM grids are like vertically
-terrain following
-based on pressure as verticle coordinate system
do GCM grids follow orography?
-not really, the grid box-resolution is too low to resolve all features
what is the CIS schematic?
collocation of gridded data onto an ungridded sampling where the altitude component of the data if defined on a hybrid height grid
what is nudging?
additional terms are introduced to equations that govern the evolution of temp and winds and nudges them towards observed values from reanalysis data
what is lagrangian measurements?
takes measurements with balloon moving with flow
what is eularian measurements?
takes measurements at surface as flow passes by
how might we identify underlying weaknesses driving descrepencies between simulated and observed data
-improve understanding of the underlying physical processes in the real world
-use more advanced methodologies to model aerosol microphysics
-identify GCM structural and parametric uncertainties
how do single particle back-trajectory models work?
-3 individual trajectories calculated
-initiated 1 hr apart
-each trajectory steps backwards in time through the wind field in hourly steps
what is back-trajectory analysis good for?
the quantification of the source influence distribution on receptor station
why was HYSPLIT developed?
during the arms race we needed to determine where nuclear tests were conducted using global measurements of nuclear fallout
what does cluster analysis allow?
large quantities of data to be divided into distinct aerosol size distributions
what is good about eularian GCMs?
-easy interpretation
-evaluation of model aerosol climatology
-hilights regions of major discrepancy for model improvement
-efficient to produce
what is bad about eularian GCMs?
does not tell us what model or process is causing the observed difference compared to measurements from the arctic
what does potential source regions mean in practice?
-strong sources may be masked by strong sinks during transport
-less than average sink strength during transport may result in opposite relation
why is antarctica good for studying pre-industrial atmosphere?
-antarctica is cleanest part of earths troposphere
what are some benefits to langrangian data?
-allows us to understand where model underperform and why
