Surface weather analysis United States, temperature and dewpoint are plotted in degrees Celsius. The wind barb points in the direction from which the wind is coming. Each full flag on the wind barb represents of wind, each half flag represents . When winds reach , a filled in triangle is used for each of wind. In the United States, rainfall plotted in the corner of the station model are in inches. The international standard rainfall measurement unit is the millimeter. Once a map has a field of station models plotted, the analyzing isobars (lines of equal pressure), isallobars (lines of equal pressure change),
Atmospheric-pressure laser ionization combined energy of the absorbed photons in this process must be above the ionization potential of the atom or molecule. In the simplest case, a single photon has sufficient energy to overcome the ionization potential. This process is therefore called single photon ionization, it is the basic principle of atmospheric pressure photoionization (APPI). For sufficiently high power densities of the incident light also nonlinear absorption processes like the absorption of at least two photons in a rapid sequence via virtual or real states can occur. If the combined energy of the absorbed photons is higher than the ionization potential, this