These features are internal gravity waves (IGW) and are characterized by alternating areas of upwards and downwards movement of air parcels. They propagate on a sharp density interface between a relatively dry layer ambient air above and a layer of sea water laden air below. When the moist air rises the cloud is formed above the condensation level and eventually evaporates at the trailing edge of the wave. In other words, the cloud regions in the photograph represent the wave crest and the "empty space" in between is the wave trough.
An important requirement for IGWs is a stably stratified atmosphere, and specifically for these waves shown in the photograph, a relatively sharp interface. If the interface thickness is larger the continuous variation of density with height adds the possibility of vertical propagation.
IGWs can be generated by a variety of phenomena, ranging from orographic to non-orographic mechanisms. The former is mentioned in the comments and is relatively intuitive and easy to understand. In the latter case it is not so clear, there are several proposed mechanisms that may contribute to the generation of IGWs, for example, Bühler et al (1999) considered the generation of internal waves by an localized unstable shear layer at the top of the jet stream.
In general, three convective generation mechanisms are typically considered (Song et al, 2003):
- Thermal Forcing:
convective clouds are regarded as thermal forcings that generate
gravity waves (nonstationary or stationary waves relative to the
thermal forcing) in a stably stratified environment.
convective clouds are considered obstacles to the flow, and gravity
waves are generated when the flow is subsequently blocked.
- Mechanical oscillator:
strong convective updrafts in convective storms stimulate the stable
stratosphere and generate gravity waves above clouds. Convective cells
acting as mechanical oscillators, as well as a nonsteady diabatic
forcing, can generate gravity waves even under zero background wind
relative to the convective cells
Oliver Bühler, Michael E. McIntyre, and John F. Scinocca, 1999: On Shear-Generated Gravity Waves that Reach the Mesosphere. Part I: Wave Generation. J. Atmos. Sci., 56, 3749–3763.
In-Sun Song, Hye-Yeong Chun, and Todd P. Lane, 2003: Generation Mechanisms of Convectively Forced Internal Gravity Waves and Their Propagation to the Stratosphere. J. Atmos. Sci., 60, 1960–1980.