From AMS Glossary
A mesoscale wind maximum.
It typically may have an along-flow length scale of tens to hundreds of kilometers and a cross- flow length scale of < 100 km. Mesojets differ from planetary-scale jets, which can have length scales of several thousand kilometers, and synoptic-scale jets, which may have length scales of 1000– 2000 km and are commonly found in association with progressive synoptic-scale troughs and ridges. Larger mesojets may also sometimes be known as jet streaks. Mesojets can form adjacent to prominent orographic features in association with terrain-channeled flow. Mesojets are also seen in association with organized mesocale convective systems as typified by the evaporatively driven rear-inflow jet commonly found behind active squall lines lines. Mesojets may also be found in conjunction with prominent lower-tropospheric stable layers where the airflow can become decoupled from the planetary boundary layer, especially at night. An exceptionally well organized lower-tropospheric mesojet extending over hundreds of kilometers might be known as a low-level jet.