| importTraj {openair} | R Documentation |
Import pre-calculated HYSPLIT 96-hour back trajectories
Description
Function to import pre-calculated back trajectories using the NOAA HYSPLIT
model. The trajectories have been calculated for a select range of locations
which will expand in time. They cover the last 20 years or so and can be used
together with other openair functions.
Usage
importTraj(site = "london", year = 2009, local = NA, progress = TRUE)
Arguments
site |
Site code of the network site to import e.g. "london". Only one site can be imported at a time. The following sites are typically available from 2000-2012, although some UK ozone sites go back to 1988 (code, location, lat, lon, year):
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year |
Year or years to import. To import a sequence of years from
1990 to 2000 use | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
local |
File path to .RData trajectory files run by user and
not stored on the Ricardo web server. These files would have been
generated from the Hysplit trajectory code shown in the appendix
of the openair manual. An example would be | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
progress |
Show a progress bar when many receptors/years are being
imported? Defaults to |
Details
This function imports pre-calculated back trajectories using the HYSPLIT trajectory model (Hybrid Single Particle Lagrangian Integrated Trajectory Model. Back trajectories provide some very useful information for air quality data analysis. However, while they are commonly calculated by researchers it is generally difficult for them to be calculated on a routine basis and used easily. In addition, the availability of back trajectories over several years can be very useful, but again difficult to calculate.
Trajectories are run at 3-hour intervals and stored in yearly files (see below). The trajectories are started at ground-level (10m) and propagated backwards in time.
These trajectories have been calculated using the Global NOAA-NCEP/NCAR reanalysis data archives. The global data are on a latitude-longitude grid (2.5 degree). Note that there are many different meteorological data sets that can be used to run HYSPLIT e.g. including ECMWF data. However, in order to make it practicable to run and store trajectories for many years and sites, the NOAA-NCEP/NCAR reanalysis data is most useful. In addition, these archives are available for use widely, which is not the case for many other data sets e.g. ECMWF. HYSPLIT calculated trajectories based on archive data may be distributed without permission. For those wanting, for example, to consider higher resolution meteorological data sets it may be better to run the trajectories separately.
We are extremely grateful to NOAA for making HYSPLIT available to produce back trajectories in an open way. We ask that you cite HYSPLIT if used in published work.
Users can supply their own trajectory files to plot in openair. These files must have the following fields: date, lat, lon and hour.inc (see details below).
The files consist of the following information:
- date
This is the arrival point time and is repeated the number of times equal to the length of the back trajectory — typically 96 hours (except early on in the file). The format is
POSIXct. It is this field that should be used to link with air quality data. See example below.- receptor
Receptor number, currently only 1.
- year
The year
- month
Month 1-12
- day
Day of the month 1-31
- hour
Hour of the day 0-23 GMT
- hour.inc
Number of hours back in time e.g. 0 to -96.
- lat
Latitude in decimal format.
- lon
Longitude in decimal format.
- height
Height of trajectory (m).
- pressure
Pressure of trajectory (kPa).
Value
Returns a data frame with pre-calculated back trajectories.
Note
The trajectories were run using the February 2011 HYSPLIT model. The function is primarily written to investigate a single site at a time for a single year. The trajectory files are quite large and care should be exercised when importing several years and/or sites.
Author(s)
David Carslaw
See Also
Other import functions:
importADMS(),
importAURN(),
importEurope(),
importKCL(),
importMeta(),
importUKAQ()
Other trajectory analysis functions:
trajCluster(),
trajLevel(),
trajPlot()
Examples
## import trajectory data for London in 2009
## Not run: mytraj <- importTraj(site = "london", year = 2009)
## combine with measurements
## Not run: theData <- importAURN(site = "kc1", year = 2009)
mytraj <- merge(mytraj, theData, by = "date")
## End(Not run)