Fundamental questions on the climate system remain unanswered because of our limited understanding of how clouds, atmospheric circulation, and climate interact. From a climate perspective, it is important to understand clouds and their radiative effects. Clouds play a critical role in regulating the Earth’s energy budget by reflecting the incoming solar radiation and trapping the outgoing thermal radiation. The radiative effects of clouds depend on their macrophysical (altitude, temperature, and geometrical thickness) and microphysical (particle phase and size distribution) properties.1–3 Despite their importance, the accurate representation of cloud types in global/regional climate models remains a challenge. The present work focuses on midlevel clouds. According to the World Meteorological Organization, midlevel clouds are those that typically form in the Earth’s atmosphere with their base altitudes at 2 and 7 km above the surface level.4,5 Surface observations and passive satellite measurements show that midlevel clouds cover up to 22% of the Earth’s surface.6–8 Midlevel clouds have been documented by several field campaigns in the tropics (e.g., Refs. 910–11), midlatitudes (e.g., Refs. 1213–14), and polar regions (e.g., Refs. 1516–17). However, our understanding of midlevel cloud processes and their representation in models remains poor. Studies show that almost all operational global climate models underestimate midlevel cloud occurrences.18,19 One of the challenges in observing midlevel clouds is that when observed remotely from the surface or top of the atmosphere, they are often obscured by low- or high-level clouds. Furthermore, the range of temperatures in the middle troposphere (where ice, liquid, or both phases can exist) makes the determination of the cloud properties more difficult. There are commonly two types of midlevel clouds according to the “genera” of cloud classification:5 altostratus and altocumulus. In general, altostratus clouds are ice dominated and altocumulus clouds are water dominated.20 Altostratus clouds form as thick and dark layers, sufficient to partially or totally block the disk of sun or moon for a surface observer. Altocumulus clouds form as cellular structures and are relatively thin often with ice virga precipitating from the cloud base. Although these traditional midlevel clouds are optically thick, several studies indicate they can also exist as optically thin clouds.18,20,21 Such optically thin altostratus and altocumulus clouds are least studied because of the detection limitations of both ground-based measurements and satellite passive sensors.