# Numerical Fit Modeling for Temperature Mitigation in
## 1 Introduction
### Interaction of Aerosols with Clouds  
Calcite will be used for the purpose of reducing solar radiation, but it will cause other unintentional effects in the atmosphere. It is well established that aerosols, including dust and mineral particles, interact with the atmosphere. It has been seen that precipitation increases downwind of cities because they are sources of aerosols [15]. Water vapor in clouds usually forms on cloud condensation nuclei (CCN) because water droplets that form from chains of water molecules are more likely to evaporate than grow. However, water is more likely to remain saturated on a surface. Thus, under most conditions, adding aerosols to the air encourages droplet formation. An example of using this phenomenon for SRM is marine cloud brightening [16]. Adding particles to the air provides more CCN where droplets can form, and in marine clouds, the result is often that their optical depth is increased.  
A second form of interaction is that heat fluxes are reduced with high aerosol loads [17]. This is due to two effects. First, evaporation rates on the ground are reduced when solar radiation and temperatures are lower. Second, adding aerosols to the atmosphere can increase temperatures at higher altitudes because they absorb solar radiation. Black carbon is an example of an aerosol that significantly warms the air [18]. When either of these effects occur, heat fluxes are reduced. The result is that there is a lower thermal difference between levels of the air, and so there is less convective cloud formation.  
The two interactions, CCN action and reduced heat flux, have opposing effects, but they operate at different scales. The result is that low levels of aerosol loading may increase cloud formation, but high levels may decrease it [19]. Higher levels are expected in calcite plumes over cities, so reduction of cloud formation is expected. This reduces the benefit from local solar radiation management because clouds have a cooling effect from blocking ground radiation [20].  
The proposed mitigation of high temperatures with calcite is more effective in arid regions [6]. Mitigation will occur mostly on cloudless days with low humidity, so there will be relatively fewer modes of atmospheric interactions. Feedback to convective clouds is an important consideration in humid regions, but less so in arid regions. Therefore, heat mitigation in arid regions should be more effective.  
Previous work used the National Center for Atmospheric Research (NCAR) single-column atmospheric model version 6 (SCAM6), which is based on the community atmospheric model (CAM) [6]. The SCAM6 model provides 15 cases to choose from, and none of the cases are in arid regions [21]. The Atmospheric Radiation Measurement 97 (ARM) case is in the southern Great Plains of the US. [PERSON] modified ARM-97 so that the low altitude air was more typical of Las Vegas, NV [6]. The result was that as humidity decreased, cloud cover was reduced, and the net effect of the calcite on the clouds was reduced. The mitigation effort was much more effective in arid regions. The previous work found that when the relative humidity reached 40% near the ground, the losses to cloud interaction would become insignificant.  
A new method is necessary to apply this information to new locations. Since the SCAM6 data is only available for 15 locations, it is not generalizable. Arid regions are expected to be the most effective location for this type of mitigation, but cases are not available in SCAM6 to analyze them.