Long-Term Measurements of the Atmospheric Boundary Layer Height in Central Amazonia Using Remote Sensing Instruments

The height (zi) of the Atmospheric Boundary Layer (ABL) is a fundamental parameter for several areas of knowledge, especially for weather and climate forecasting, pollutant dispersion and air quality. In this work, we used data from a remote sensing instrument (ceilometer), located at the experimental site of the Amazon Tall Tower Observatory (ATTO) in the Central Amazonia rainforest, in order to obtain the height of the ABL. Data used were obtained from 2014 to 2020, with the exception of the year 2017. The results showed that the zi average varies from year to year (interannual variability) and the average of the maximum zi values (zi_max) was approximately 1400 +/- 277 m, occurring at 15:00 local time. In addition, it was found that these maximum heights are higher in the dry season and during El Nino years (about 1741 +/- 242 m) and they are lower during the wet period and in La Nina years (1263 +/- 229 m). Taking into account all the years investigated, the month with the highest zi_max value is September (1710 +/- 253 m), and the month with the lowest value is May (1108 +/- 152 m). Finally, it was observed that the growth rate of the ABL during the early hours after sunrise varies from month to month (intraseasonal variability), reaching its maximum values in September and October (about 210 +/- 53 mh(-1) and 217 +/- 59 m h(-1), respectively) and minimum values in April and July (approximately 159 +/- 48 m h(-1) and 159 +/- 50 m h(-1), respectively). It is concluded that the values of zi in Central Amazonia are influenced by several seasonal factors (temperature, cloud cover, turbulent heat flux, etc.) which gives it a wide variability in terms of heights and growth rates. Additionally, a linear regression was proposed in order to model the maximum zi value as a function of its growth rate from 08:00 LT (Local Time) up to 10:00 LT. The results showed a good correlation compared with the experimental values.