BADC Trajectories

BADC Trajectories - Help

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Data Source Type:: The data sources that are available to you are determined by the data sets you have access to at the BADC. The data source determines which wind and temperatures are used to derive the trajectories. The files needed for forecast trajectories will not always be available on line. You must contact the BADC User Support before you will be able to use this facility.
Start Date:: This is the date you want the trajectory integration to start on. The format shoud be [yy]yymmdd. For example 990101 or 19990101 are valid representations of the 1st of January 1999. At present the model is set up to use the ECMWF operational data and ECMWF reanalysis data that is stored at the BADC. These two data sets together cover the period from January 1979 to almost the current day. The data has been interpolated from model levels onto pressure levels. This adds some additional error to the trajectory calculation. Trajectories run using higher resolution model level data will be availiable soon.
Start Time:: Time from which you want to start the integration. At present the trajectory runs are limited to start at the times the ECMWF data are availiable. These are 0, 6, 12, 18 GMT.
Length of run:: The length of the trajectory run you want to do in a whole number of days. The maximum length allowed is 10 days. If no length of run is given then the default of 5 days will be used.
Trajectory direction:: Use this to specify whether you need trajectories runing forward in time or trajectories running backward in time.
Output Frequency:: The frequency at which you want output, in hours. The default is half an hour, which is the time step of the model. For many purposes this is more frequent than necessary.
Vertical Advection Type:: The vertical advection can either be done isentropically or using the pressure vertical velocity, omega (3D). If you use 3D advection then specify the initial levels as pressure. If you use isentropic advection them specify the initial levels as potential temperature.
Longitudes:: The longitudes of the parcel positions for the trajectory integration in degrees. Positive numbers will be taken as degrees east; negative numbers will be taken as degrees west. For forward trajectories these will be the initial longitudes. For Backwards trajectories these will be the final longitudes. If you want more than one parcel then simply supply a comma seperated list of positions. The number of longitudes should be the same as the number of latitudes.
Latitudes:: The latitudes of the parcel positions for the trajectory integration in degrees. Positive numbers will be taken at degrees north; negative numbers will be taken as degrees south. For forward trajectories these will be the initial latitudes. For Backwards trajectories these will be the final latitudes. If you want more than one parcel then simply supply a comma seperated list of positions. The number of latitudes should be the same as the number of longitudes.
Levels:: The levels of the parcel positions for the trajectory integration. If you use 3D advection then specify the initial levels as pressure in hPa (mb). If you use isentropic advection then specify the initial levels as potential temperature in K. For 3D advection the suggested pressure range for the initial levels is between 950hPa and 10hPa. 10hPa is the upper level for the ECMWF data used. Using pressures less than 950hPa often results in parcels going into the ground. For isentropic advection use levels between about 320 and 700K. Isentropic levels less than 320K often intersect the ground in the tropics and so can result in parcels going into the ground. Any parcels that go off the top or bottom of the data domain will disappear. For forward trajectories these will be the initial levels. For Backwards trajectories these will be the final levels. If you want more than one level then simply supply a comma seperated list of positions. If you want a profile of parcels then simply specify the levels you want to represent the profiles with. If you are not using profiles then the number of levels should be the same as the number of longitudes and latitudes.
Use Profile:: Tick this box if you want a verticle profile. If you choose profile then the list of levels you specify will be used as starting points for each latitude-longitude pair.
Use Cluster:: Tick this box if you want a cluster of points to be run around each of the points you have chosen in the longitudes and latitudes. The cluster consists of four points, one directly north of the central parcel, one directly east of the central parcel, one directly south of the central parcel and one directly west of the central parcel. The distance of the cluster points from the central point is determined by the cluster radius.
Cluster Radius:: This determines the distance of points in a cluster from the central point of each cluster. The distance can be given in either degrees or km.
Number of releases:: If you are running a number of trajectory integrations from the same initial positions, but different start times you can submit them all as one integration using the multiple release options. The number of releases gives the number of releases you want. If you are running backtrajectories then the releases will go backwards in time. This means you should specify the initial time as the last time for which you want a release.
Frequency of release:: The frequency of release determines how often parcels are released if you are using the multiple release option. The release frequency is in hours. If you choose a release frequency that is not a whole number of time steps then the release frequency will be rounded down to a whole number of time steps. The release frequency should be greater than one hour.

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