The HAP chart is a guide to frequency selection for HF communications between mobiles and a specified base station, in this case Paris. The recommended frequency for communications with the base at a given hour is read off from the point in the map corresponding to the mobile's location.The predictions are made from real time data which are updated each hour.'dash lines' - If present, these delineate areas of unlikely communication. Poor communication areas which can result from one or more of the following conditions:- the Absorption Limiting Frequency (ALF) is higher than the Optimum Working Frequency (OWF).- the ALF exceeds the highest frequency in the user's frequency set. - there is no suitable frequency from the user's set that is between the OWF and ALF.

Solar X-rays:
Geomag Field: