Weather map motion. Two-dimensional streamlines based on wind speeds at various levels show areas of convergence and divergence in the wind field, which are helpful in determining the location of features within the wind pattern. A popular type of surface weather map is the surface weather analysis, which plots isobars to depict areas of high pressure and low pressure. Cloud codes are translated into symbols and plotted on these maps along with other meteorological data that are included in synoptic reports sent by professionally trained observers. The use of weather charts in a modern sense began in the middle portion of the
Weather radio conditions and forecasts, ZBR (operated by the Bermuda Maritime Operations Centre), at 162.4 MHz. Mexico has since launched its own weather radio system, SARMEX (Sistema De Alerta De Riesgos Mexicano, or Mexican Hazard Warning System) for coverage of its cities, which also implements the Mexican Seismic Warning System. Some Mexican alert radios also support activation by a two-tone alert for another type of risk warning. In Germany, the Deutscher Wetterdienst broadcasts marine weather reports and weather warnings via long and short wave transmissions. The weather radio band is part of the marine VHF radio band reserved for governmental services. However,