A bewildering variety of eruptive and ejective phenomena continually take place in the solar atmosphere on a wide range of space and time scales. Even though observationally known for many decades now, among those dynamic phenomena there is one whose understanding has progressed very slowly: the surges.
In this colloquium we address the surge phenomenon under a fourfold perspective.
From the theoretical point of view, we show that surges are composed by different populations with distinct evolutionary patterns that are directly related to heating/cooling processes. Concerning observations, although surges are traditionally related to chromospheric lines, we have found that they can exhibit enhanced UV emission in transition region (TR) lines of Si IV with brighter and broader spectral profiles than the average TR. Through forward modeling, we show that surges are strongly affected by non-equilibrium ionization effects, noticeably increasing the number of emitters of the main lines of Si IV and O IV, and that the departure from statistical equilibrium is due to the short characteristic times of the optically-thin losses and heat conduction during the surge evolution.
Moreover, from the code development perspective, we present the most recent results related to surges using the new Generalized Ohm's Law module implemented in the Bifrost code.