Factors determining tropical upper-level cloud radiative effect in the radiative-convective equilibrium framework.

Area of Science:

• Climate Science
• Atmospheric Physics

Background:

• Understanding tropical upper-level cloud radiative effect (TUCRE) is crucial for cloud feedback mechanisms in climate models.
• Previous studies have focused on various factors influencing TUCRE, but a simplified RCE approach offers new insights.

Purpose of the Study:

• To identify the major factors determining tropical upper-level cloud radiative effect (TUCRE).
• To assess the influence of emission temperatures and cloud fraction on TUCRE using a simplified radiative-convective equilibrium (RCE) model.

Main Methods:

• Employed a radiative-convective equilibrium (RCE) model incorporating atmospheric dynamics and thermodynamics from CMIP6 models.
• Adjusted global mean surface temperature for energy balance, varying tropical cloud fraction, reflectivity, and emission temperatures.
• Calculated TUCRE as the change in global mean surface temperature (K) per unit increase in tropical upper-level clouds (%)

Main Results:

• Emission temperatures of tropical moist-cloudy and moist-clear regions, along with tropical upper-level cloud fraction, were identified as the primary determinants of TUCRE.
• High determination coefficients were found between TUCRE and emission temperature in tropical moist regions and upper-level cloud fraction.
• These factors influence TUCRE through their role in trapping outgoing longwave radiation.

Conclusions:

• Accurate representation of upper-level cloud fraction and emission temperature in tropical moist regions is essential for improving TUCRE in climate models.
• The study highlights the significance of these factors in the radiative balance of the tropics.
• Findings contribute to a better understanding of cloud feedback processes in climate change.