## 4 Results and Discussions
### The Fire Diurnal Cycle Characteristic  
The combustion process of the fire is highly dynamic; the study of the variation in characteristics of fire behavior has great value for the accurate estimation of pollutant emissions and future fire extinguishing management. As mentioned in Section 3.1, the diurnal variation of the fire has an obvious Gaussian law [27]; however, there are a few issues in its accurate estimation [28; 29]. Therefore, we try to describe the variation in characteristics of fire behavior more accurately by using geostationary satellite Himawari-8. The parameters of the fire diurnal cycle have been present in the report. The duration and peak time of fire were estimated based on the hourly Himawari-8 FRP time series. Figure 3 shows an example of a grid cell (2 km) in northeastern New South Wales from 7 November 2019 to 11 November 2019, where the last several days of the fire can be seen. The results shown in Figure 3 show that no matter the intensity of the fire, the  
Figure 2: Spatial distribution map of FRP smaller than 10 MW monitored by VIIIRS and MODIS Aqua during the study period. (**a**) Spatial distribution of VIIIRS FRP smaller than 5 MW. (**b**) Spatial distribution of MODIS Aqua FRP smaller than 5 MW. (**c**) Spatial distribution of VIIIRS FRP between 5 MW and 10 MW. (**d**) Spatial distribution of MODIS Aqua FRP between 5 MW and 10 MW. Gaussian function can describe fire activities well. At the same time, it is also obvious that observations from MODIS sampling intervals did not observe highly dynamic changes in fire well. Based on the method of [PERSON] et al. (2019) described in Section 3.1, we use MODIS data to estimate the duration and peak time of the fire diurnal cycle within five days of the selected grid. Compared with the results obtained from the Gaussian curve fitted with the Himawari-8 data, the method based on MODIS overestimates \(\sigma\), that is, overestimates the fire duration. In this example, \(\sigma\) is overestimated by about 1-2 h. Moreover, the peak time is also greatly different from the results of Himawari-8, in this case, there is a difference of about 0.5-2 h across each of the five days. The time resolution of Himawari-8 is once every 10 min, so the observation of Himawari-8 is more consistent with the actual fire combustion process, which will make the error smaller in the process of integrating FRP into FRE. In addition to an observed variability in the fire diurnal cycle seen on different days, we found an interesting spatial distribution in the duration and peak time of fire (Figure 4). We found that the peak time of fire is usually after 14:00 local time. From November 2019 to January 2020, with the southward movement of the fire, the peak time of the fire is gradually later. In November 2019, the peak time of fire was mostly 15:00. In December 2019, the peak time of fire was mostly 16:00. In January 2020, the peak time of fire mainly occurs after 18:00, and the peak time in the early morning was a higher ratio than that in November and December 2019. According to the research of [PERSON] et al. (2020), fuel moisture, wind and other ambient atmospheric conditions are far less conducive to intense fire activity by night than by day, therefore, the fire activity at night will generally be significantly reduced. The continuous burning at night in Victoria indirectly reflects the fierce fire in Victoria, which is hard to control. In addition, most \(\sigma\) values are between 1-3.5 h. As mentioned in Section 3.1, the value of \(\sigma\) is determined by the duration of the fire. Compared to December 2019, the fire in northeast New South Wales in November 2019 lasted for a shorter period of time. In December 2019, most of the fires occurred in the central--eastern and central-southern areas of New South Wales, with a \(\sigma\) value of 2-3 h. As the fire moves to the south, the 0-2 h \(\sigma\) value of January 2020 is much higher than that of November 2019 and December 2019, indicating that there are more short-duration fires in January 2020.