Climatology of icing conditions over Colombia based on ERA5 reanalysis and in situ observations

This study shows vertical profiles and spatial distribution of upper-air icing frequency over the tropical Americas. We estimated the in-flight icing (IFI) over Colombia using the Current Icing Product-sonde-A algorithm over two data sets: (1) vertical soundings of temperature and relative humidity and surface station data taken at 12 Coordinated Universal Time or UTC (07 Local Time or LT) on five sites and (2) ERA5 at 00, 06, 12 and 18 UTC (19, 01, 07 and 13 LT). In either case, icing was defined for IFI values exceeding 0.01. Results show that icing tends to occur between 550 and 300 hPa (4.5 and 8.6 km altitude), with a maximum at 500-550 hPa and monotonically decreasing to zero until reaching 300 hPa. Aeronautic reports were used to evaluate the total column IFI and a layer-based IFI detection with a probability of detection of 87% and 71%, respectively. The annual cycle of IFI is modulated by the meridional migration of the Intertropical Convergence Zone (ITCZ) with a bimodal distribution with peaks during the rainiest seasons. Spatially, IFI hotspots are found in the Pacific, the Andes Mountains and the Amazonia regions of Colombia; the northern Colombia Caribbean region show lower IFI frequency with a relative maximum collocated over the Sierra Nevada de Santa Marta mountains. The IFI exhibits a strong diurnal cycle with a high between night-time to early morning and a low around noon.