ANALYSIS OF THE CONVECTION NEAR THE ALTIPLANO
FROM SATELLITE IMAGERY

The satellite images that the GOES satellite Channel 4 records detect infrarred radiation in wavelenghts that can be closely related to the temperature of cloud tops and the surface of the earth in cloud free locations. This is why this channel has been chosen as a tool to study the diurnal cycle of the convection in the Altiplano and surrounding areas.

Using the IR4 Channel satellite images recorded during SALLJEX, a climatology of the diurnal evolution of temperatures lower than certain thresholds was prepared. This site contains a table through which you can access to the cloud frequency anmations prepared for different temperature thresholds. A brief explanation of what may be visible in the animation is included in the table. A brief analysis of what the satellite images suggest has also been included right after the table.

17.5°C	15.0°C	Ideal to observe the diurnal cycle of the marine-layer stratocumulus over the Pacific Ocean. Topography adds noise near and inland from the coast.
12.5°C	10.0°C	The stratocumulus are still visible. This temperature threshold is good to observe the convection in the Amazon and Salar de Uyuni's surface temperature, since the salt flat tends to appear cloudless most of the time.
07.5°C	05.0°C	Good to observe the diurnal cycle of the Amazon convection. Good to observe the propagation of middle clouds from the Andes into the Pacific Coast in the afternoon and evenings. The stratus are no longer visible since the temperature of the the cloud tops rarely drops below 10°C during the summer. Andean valleys become visible.
02.5°C	00.0°C	Same as the analyses using 5 and 7.5°C as thresholds. Good to describe the amazon convection. The stratus are totally invisible. At these temperatures the convection over the Andes and in particular over Lake Titicaca start to become apparent. Topography, however, still introduces some noise.
-02.5°C	-05.0°C	This shows the regions in which the cloud tops reach below freezing temperatures with frequencies larger than 15% of the time. Some noise is still introduced by topography, particularly near the terrain above 4500 meters.
-07.5°C	-10.0°C	This level is ideal to analyze the convection in the entire region since the noise introduced by topography is gone. Lake Effect storms over Lake Titicaca are fairly visible since most of the time the clouds are shallow and the most frequent cloud top temperatures oscillate between -5 and -20 °C.
-12.5°C	-15.0°C	Ideal for Lake-effect storms. Very good for convection in general.
-17.5°C	-20.0°C	Good for convection in general.
-22.5°C	-25.0°C	Depicts the areas with the coldest cloud tops or deepest convection.
-27.5°C

Analysis of the diurnal cycle of convection

Amazonia

Convection in the Amazonia has a pronounced diurnal cycle in particular towards Brazil (northeast side of the image) and towards the eastern slopes of the Andes. Towards Brazil, the strongest convection occurs during the afternoon with frequencies of temperatures below 0°C as high as 60% of the time, and 35% of the time below -20°C. The Peruvian Amazonia near Puerto Maldonado also shows plenty of convection with an afternoon maximum. In the slopes of the Andes, in contrast, the deepest generally occurs during the night (11pm-4am) with cloud tops below 0°C 70 to 90% of the days near midnight. These cloud tops reach -20°C more than 40% of the time near midnight as well, especially just east of Cuzco (Peru) and cochabamba (Bolivia). Within this belt of frequent convection, a region of less convection can be found just north and near Apolo, Bolivia. The Bolivian low level corridor (San Borja, Trinidad, Santa Cruz) show less convection and a weaker diurnal cycle since this is a region of transition between the nocturnal storms in the eastern slopes and the afternoon storms in the Amazon.

Altiplano

With the exception of Lake Titicaca, the strongest and most frequent convection develops in the afternoon wit a maximum betweeh 5 and 6pm local peruvian time. The development of 5-6pm deep convection (temperatures below -20°C) is more common in the northern two thirds of the Altiplano with frequencies that oscillate between 55 and 65% in the western mountain ranges of the Peruvian Altiplano, to 40-55% in the northern-western and central-western Altiplano, to 20-40% in the rest of the Altiplano located north of Salar de Coipasa and Salar de Uyuni. The convection then fades and migrates towards the northeast generally dissipating by 3am (local peruvian time) with the exception of Lake Titicaca, where nocturnal convection persists. The convection over the lake is particularly visible at thresholds -f -12.5 and -15.0°C, but also visible at thresholds of -27.5°C with frequencies as large as 20% of the days.