# Spatio-Temporal Distribution of Deep Convection Observed along the Trans-Mexican Volcanic Belt
## 4 Results and Discussion
### Spatio-Temporal Distribution of Deep Convective Clouds and Severe Weather Events
The similarity between the spatial-temporal distributions of heavy precipitation days (from CHIRPS, Figure 4) and convective frequency (from MODIS, Figure 3) is evident. Between June and September, the wet phase is identified, with the higher values (i.e., the most days) also located over the higher elevations. The mountainous areas at the west of the Gulf of Mexico, the central part of the TMVB and the Pacific Ocean hold the highest values, with a maximum of 175 heavy rainy days in August. Taking into account the fact that the total number of days analyzed is 3653 for 10 years, the wet areas have about a 5% occurrence (using all the days available). Concerning the precipitation thresholds obtained from the 90 th percentile (Figure 5) the Gulf of Mexico stands out with more than 75 mm of daily precipitation in the summertime. The average of the wet phase (June to September) ranges higher than 40 mm/day over the regions identified with more intense rainfall activity. Again, higher values are associated with higher elevations, but in this case, the area of the Gulf of Mexico is dominant. This situation can be associated with moisture fluxes and their interaction with the local topography, as suggested by [PERSON] and [PERSON] (2018), and the possible contribution of the sea breeze. For the area of the central part of the TMVB, the threshold values range between 20-25 mm/day. One of the most important findings here is the exceptional variety of the behavior of the extreme precipitation events in a relatively small geographical area. Whereas the precipitation thresholds in the mountains near the Gulf of Mexico reach 50 mm/day or more, just a few kilometers to the west, the thresholds decrease to values close to 10 mm/day, indicating the great importance of local conditions. Figure 4: Monthly distribution of the total number of days with daily precipitation exceeding 10 mm based on Climate Hazards Group Infrared Precipitation with Station (CHIRPS) data (2008–2017) with a horizontal resolution of 0.05 degrees. In Figure 6 the time series of the tropical cyclone activity, the total observed DCC and precipitation rates over the study area are shown. For the deep convective clouds and precipitation, the active season starts in June, with the first peak in July. Then, in August, the frequency of these two parameters has a relative minimum. The second observed peak in precipitation and deep convection activity in September indicates the influence of the passage of tropical cyclones over the study area. This time series was assessed using the analysis of the International Best Track Archive for Climate Stewardship dataset [59]. To this end, tropical cyclone tracks (2008-2017) that affected the study zone were extracted. Only systems classified as tropical depressions, tropical storms and hurricanes of categories 1-5 were used in this analysis. The results show that the maximum tropical-cyclone activity is in September, which is consistent with Jauregui [60]. Such results relate well to the observed behavior of precipitation and deep convective cloud frequencies in the second part of the active phase. The rest of the months are identified as the transition phase (April-May and October-November), and the passive phase (December-March). Taking into account all monthly means of DCC frequency and accumulated precipitation (i.e., 120-time steps), the domain-averaged temporal correlation coefficient is 0.84, which demonstrates the strong correlation between the two observational datasets. Per season, correlation coefficients are found to be 0.79, 0.77, 0.81 and 0.93 for December-February, March-May, June-August and September-November, respectively. The variation indicates the impact of seasonal changes in weather patterns and associated phenomena (e.g., tropical cyclones, easterly waves and cold fronts) affecting the study area on the relationship between the MODIS-based DCC frequencies and CHIRPS observed precipitation.