Virendra Prakash Ghate — Argonne National Laboratory
Pavlos Kollias — Stony Brook University
Category
GoAmazon – Clouds and aerosols in Amazonia
Description
Time-height mapping of the diurnal cycle of cloud fraction during cumulus only days (top) and daytime precipitation days (bottom). The Ceilometer detected first cloud base height is shown in black and the Lifting Condensation Level (LCL) is shown in magenta. The vertical bars indicate the one standard deviation values of the parameters. Notice higher nighttime low-cloud coverage during daytime precipitation days than during cumulus only days.
The Amazon rainforest is a crucial sink of carbon and thus, a key regulator of Earth’s climate. Previous studies have shown that the Amazonian biomass critically depends on the precipitation during the dry season. Hence, it is crucial for the Earth System Models (ESMs) to accurately represent the precipitation during the dry season in the simulation aimed at predicting the future climate and energy needs. Although acknowledged to be important, even the most sophisticated ESMs fail to accurately represent precipitation in that region due to various processes that occur on different temporal and spatial scales affecting it.
In this study, data collected by the first Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF-1) during its deployment at Manacapuru, Brazil as a part of the Green Ocean Amazon (GOAmazon) field campaign are used to study the controls of dry season precipitation in that region. Two years (2014 and 2015) of observations collected by various instruments including the vertically pointing Doppler cloud radar, lidars, radiosonde, radiometer and others, during the dry season (June-September) are analyzed. First, the mean diurnal cycle of surface meteorology, surface radiation, clouds, precipitation, and the thermodynamic structure during the dry season are characterized. Individual days are classified as cumulus only (no precipitation) and daytime precipitation based on the presence and timing of the precipitation event. Careful analysis of the diurnal cycles between these two categories suggests that boundary layer water vapor (WV), surface sensible heat flux (SHF), lifting condensation level (LCL), and moisture advection above the boundary layer (Qadv) are key parameters responsible for precipitation. As the frequency of precipitation decreases progressively in the dry season, we further analyzed the daily averaged values of the variables listed above for the 2 dry seasons. The conclusions from this analysis were largely consistent with those from the diurnal cycle analysis, however highlighted the year-to-year variations exhibited by them. Our analyses collectively suggest WV, SHF, LCL, and Qadv to be primary factors in determining precipitation in the Amazonian dry season with the relative contribution of these factors in determining precipitation fluctuating between the two years.
