Model and Satellite data Flashcards
What is a synoptic analysis?
A simple analysis based on the observed synoptic data provides an instantaneous snapshot of the state of the atmosphere
what are the problems with synoptic analysis?
Scattered observations…excessive interpolation in data sparse regions
Bias by individual measurements
Instrument error
Sample unrepresentative of general conditions
what is the solution to problems with synoptic analysis?
use model data to help generate analysis.
What are three advantages of using model data in analysis
Data from past observations affects present analysis (4D variable assimilation)
Regions without observations are handled more realistically because information from past observation upwind propagates into data-sparse region.
Raw observations are smoothed during interpolation onto model grid – helps remove bias from non-representative measurements
what are the limitations of using model data in analysis ?
Generally better than just sparse observations, BUT it is not real data – errors are very hard to assess.
What is the NWP forecast cycle?
The inclusion of observations in the previous forecast is called data assimilation and takes a large part of the time within a forecast cycle of 6 hours.
What is a NWP model?
Global models divide the world into a grid, data is held on the intersections of the grid
what do the met office limited area models give
higher resolution
how does the uk use the NWP
uses the global model to provide intialisation and boundary conditions
how precise is the resolution over the UK
1.5km
how many vertical levels in both the global and limited area models
70
what is model resolution too low to resolve
Individual clouds, even large thunderstorms.
Full details of topography
Details of changes of surface type
what is parameterisation
Parameterisation is the simplification of a complex physical process in terms of parameters that are available to the model, or readily measured.
Models must use parameterisations of processes that ….
Take place on scales smaller than the model grid
Involve parameters that are not explicitly defined in the model
examples of processes that are parameterised
turbulence, convection and cloud microphysics
which companies produce reanalysis
ECMWF and (ECEP in USA)
why is reanalysis done
Not all observations are available in time to be included in regular forecast cycle
Allows time for extra quality control and corrections to be applied
What does reanalysis provide
the best estimate of past atmospheric data given the available observations
Reanalysis data are widely used in research for…..
Climatological studies - reanalysis provides a consistent dataset over decades.
Model initialization fields in data-sparse regions or upper atmosphere.
Providing boundary conditions for regional-scale modelling studies
New reanalyses are produced from time to time to use new assimilation techniques or model, e.g. ECMWF have produced the following reanalysis datasets….
ERA-15: 1978 - 1993
ERA-40: 1958 - 1997
ERA-Interim 1979 - present.
when was ERA-15 created
1978-1993
when was ERA-40 created
1958-1997
when was ERA-interim created
1979 - present
What does TIROS stand for
Television Infrared Observation Satellite
when was the first TIROS launched
April 1960
What is a geostationary satellite
remain in the same spot on earths surface - orbital period =rotation of the earth
How high are geostationary satellites
36000 km above the surface
how many geostationary satellites give the whole coverage of the earth
5/6
what is a polar orbiting satellite
orbit is orientated north/south slightly (often sun syncronus)
what is the orbital period of a polar orbiting satellite
100 mins
do they pass over the same spot at the same time
no, passes over the same spot at irregular intervals and different parts of the surface with every orbit
what altitude is polar orbiting satellites at
700-800km so low altitude but this allows much higher resolution
what is a passive sensor
Passive sensors monitor some form of radiation (visible, infra-red or microwave data) coming from Earth, e.g. images, temperature and humidity observations.
what is an active sensor
Active sensors emit some radiation and monitor the returning signal, e.g. surface winds over water from radar scatterometer.
what are satellite data retrievals also used to make estimates of
sea surface temperature
wind speeds by tracking cloud movements
land use (amount of vegetation)
amounts of various chemicals (e.g. O3, NO2).
