1. ABOUT THE DATASET ------------ Title: Back trajectories released from ocean catchment boundaries Creator(s): Philip Craig (https://orcid.org/0000-0001-9213-4599) Organisation(s): University of Reading Rights-holder(s): Philip Craig Publication Year: 2023 Description: This dataset contains a subset from a dataset of 14-day back trajectories released from points along the ocean drainage basin catchment boundaries used in Craig, Ferreira & Methven (2023), 'A Lagrangian perspective on the Atlantic and Pacific Precipitation-Evaporation asymmetry' (to be submitted to JGR Atmospheres). Six-hourly data from the ERA-Interim re-analysis from the European Centre for Medium Range Weather Forecasts (Dee et al., 2011) and the ROTRAJ model code (https://www.met.reading.ac.uk/~swrmethn/ROTRAJ/) were used to generate the back trajectories. Data were released every 12 hours on 17 vertical levels. The full dataset covers the years 2010-14 and contains 20.3 million trajectories per year. The dataset defining the ocean catchment boundaries is available from the University of Reading Research Data Archive (https://doi.org/10.17864/1947.195). The back trajectories can be read using the Python code readtraj_example.py provided here. Cite as: Craig, P. (2023) Back trajectories released from ocean catchment boundaries. University of Reading. Dataset. https://doi.org/10.17864/1947.000461 Related publication: Craig (2018) The Atlantic/Pacific atmospheric moisture budget asymmetry: the role of atmospheric moisture transport. PhD Thesis, University of Reading (https://doi.org/10.48683/1926.00084855) Craig, Ferreira & Methven (2023) A Lagrangian perspective on the Atlantic and Pacific Precipitation-Evaporation asymmetry. Journal of Geophysical Research: Atmospheres, 128 (24). e2023JD039087 (https://doi.org/10.1029/2023JD039087) Acknowledgements: David Ferreira & John Methven also contributed to this dataset as PhD supervisors. 2. TERMS OF USE ------------ Copyright Philip Craig 2023. This dataset is licensed by the rights-holder(s) under a Creative Commons Attribution 4.0 International Licence: https://creativecommons.org/licenses/by/4.0/. 3. PROJECT AND FUNDING INFORMATION ------------ Title: The Atlantic/Pacific Atmospheric Moisture Budget Asymmetry: The Role of Atmospheric Moisture Transport Dates: September 2014 to April 2018 Funding organisation: NERC Grant no.: NE/L002566/1 4. CONTENTS ------------ File listing utraj-df_afr2010073112 utraj-df_amr2010073112 utraj-df_ara2010073112 utraj-df_ari2010073112 utraj-df_arp2010073112 utraj-df_eaa2010073112 utraj-df_soa2010073112 utraj-df_soi2010073112 utraj-df_sop2010073112 utraj-tr_afr2010073112 utraj-tr_amr2010073112 utraj-tr_ara2010073112 utraj-tr_ari2010073112 utraj-tr_arp2010073112 utraj-tr_eaa2010073112 utraj-tr_soa2010073112 utraj-tr_soi2010073112 utraj-tr_sop2010073112 The file naming convention of the trajectory output files (utraj-df) is: utraj-df_YYYYMMDDhh The trajectory output files are human-readable text files & contain data at timesteps every 6 hours along each trajectory. The metadata header contains the following information: TRAJECTORY BASE TIME (time of trajectories initialization) DATA BASE TIME (only relevant when using forecast data) DATA INTERVAL (size of timestep) TOTAL NUMBER OF TRAJECTORIES (number of trajectories contained in file) NUMBER OF ATTRIBUTES (number of variables interpolated along trajectory) ATTRIBUTE TYPES (variables interpolated along trajectory - represented by integers linked to ECMWF convention) NUMBER OF CLUSTERS (number of clusters, vertical levels in this case) CLUSTER POINTERS (trajectory numbers where each cluster begins) 3D TRAJECTORY (T or F) FORECAST DATA (T or F) FORWARD TRAJECTORY (T or F) The trajectory data are presented as follows: TRAJECTORY NUMBER 1 COMPRISES 56 INTERVALS STEP HOURS LAT LON P (MB) ATTRIBUTES 0 0.00 0.40080E+02 0.41980E+02 0.76041E+03 0.29303E+03 -0.37576E-01 0.54442E-02 0.41508E+03 0.20706E+04 6 -6.00 0.40090E+02 0.43210E+02 0.76268E+03 0.28571E+03 0.30831E+00 0.57332E-02 0.48562E+03 0.95496E+03 12 -12.00 0.39938E+02 0.44454E+02 0.77076E+03 0.28728E+03 0.19342E+00 0.55529E-02 0.62563E+03 0.21712E+02 Header definitions: STEP (timestep along trajectory in hours) HOURS (time along trajectory, negative for back trajectory) LAT (latitude) LON (longitude) P (MB) (pressure in millibars) ATTRIBUTES (other variables interpolated along trajectory) The file naming convention of the trajectory initialization files (utraj-tr) is: utraj-tr_YYYYMMDDhh The trajectory initialization files are human-readable text files & contain data at the trajectory initialization time. The metadata headers are the same as the trajectory output files but without the DATA INTERVAL header. The trajectory initialization data are presented in the same manner as the output files but only at the initialization time (STEP 0). The in the filenames is the catchment boundary of an ocean drainage basin along which trajectories are initialized. These boundaries are: afr (Africa) amr (Americas) ara (Arctic Atlantic) ari (Arctic Indian) arp (Arctic Pacific) eaa (East Asia Australia*) soa (Southern Ocean Atlantic) soi (Southern Ocean Indian) sop (Southern Ocean Pacific) *this boundary is referred to as "South-East Asia" in publications The YYYYMMDDhh timestamp refers to the date and time at which the trajectories were initialized. YYYY (year) MM (month) DD (day) hh (hour) The Python script is a small example of how to read the data. 5. METHODS ----------- This dataset was generated using the ROTRAJ model (Methven, 1997; Methven et al., 2001; de Leeuw et al, 2017) and the ERA-Interim reanalysis (Dee et al, 2011) to calculate trajectories released from catchment boundaries surrounding ocean drainage basins (Craig, 2019; https://doi.org/10.17864/1947.195). Back trajectories were released from points ~70 km apart along the ocean drainage basin catchment boundaries on 17 vertical levels. Each back trajectory is 14 days long and data are output every 6 hours. Extensive information is included in chapter 2 of Philip Craig's PhD thesis (https://doi.org/10.48683/1926.00084855) and in Craig et al (2023, ). References: Craig, P. (2018) The Atlantic/Pacific atmospheric moisture budget asymmetry: the role of atmospheric moisture transport. PhD Thesis, University of Reading (https://doi.org/10.48683/1926.00084855) Craig, P. (2019) Catchment boundaries of ocean drainage basins. University of Reading. Dataset. https://doi.org/10.17864/1947.195 Craig, P. et al. (2023) Dee, D. et al. (2011) The ERA-Interim Reanalysis: configuration and performance of the data assimilation system. Quarterly Journal of the Royal Meteorological Society, 137, 553-597 de Leeuw, J. et al. (2017) Physical Factors Influencing Regional Precipitation Variability Attributed Using an Airmass Trajectory Method. Journal of Climate, 30, 7359-7378 Methven, J. (1997) Offline trajectories: Calculation and accuracy (Tech. Rep. No. 44). Dept. of Meteorol., Univ. of Reading, U.K.: U.K. Univ. Global Atmos. Modelling Prog. Methven, J. et al. (2001) Estimating relationships between air mass origin and chemical composition. Journal of Geophysical Research: Atmospheres, 106, 5005-5019