Plot explanations CARIBIC

Some explanations for the use of the CARIBIC meteorological plots.


Trajectories
For every 3 minutes of flight a 5-day backward trajectory has been calculated using the horizontal and vertical wind components from the ECMWF model. The wind fields were given on the hybrid sigma-pressure ECMWF model levels at a 1x1 degree horizontal resolution at time intervals of 6 hours. We use linear interpolation in longitude, latitude and log-pressure and cubic interpolation in time to obtain the wind at the trajectory positions. The trajectory integration scheme is the iterative scheme proposed by Pettersen with a time step of 1 hour. For every flight one plot shows all trajectories. Colouring indicates the instantaneous trajectory pressure. For flights where whole air samples (WAS) were taken subsets of trajectories corresponding to the time interval air was let in for each air sample have been made. There are trajectory plots for all 12 individual air samples as well as all samples together.
The trajectories have been calculated with the KNMI trajectory model TRAJKS (Scheele, et al., Meteorol. Appl. 3, 267-273 (1996).
There is a description of the trajectory file format for CARIBIC.
"Surface" maps

Pressure level maps

Vertical X-sections
These profiles have been interpolated linearly in latitude, longitude and time to the aircraft location. The ECMWF data were available at 6 hour intervals and with a horizontal resolution of 1 degree in longitude and latitude for CARIBIC. I have chosen a time step of 3 minutes between subsequent profiles (aircraft locations). The reason not to have a higher time resolution is that only 360 profiles can be plotted with our current software. A typical CARIBIC flight lasts more than 10 hours. Please note that the ECMWF cloud products have not been as extensively validated as traditional model parameters like wind and temperatures.
Interpolated data
The ECMWF data have been interpolated linearly in latitude, longitude, log-pressure and time to the aircraft location. The ECMWF data were available at 6 hour intervals and with a horizontal resolution of 1 degree in longitude and latitude on hybrid sigma-pressure ECMWF model levels for CARIBIC. I have chosen a time step of 1 minutes between subsequent points (aircraft locations). For most flights measured and model simulated temperatures are within a few K. The measured and model simulated specific humidities do not agree as well as the temperatures. Best agreement is obtained in the middle and lower troposphere where moisture is relatively abundant. In the very dry upper troposphere and lower stratosphere the measured specific humidity is frequently too high. There are well-known problems both with modeling and measuring such low humidities.


CARIBIC participants are welcome to contact Peter van Velthoven if they have any further questions.