A new metric to help understand Amazon rainforest precipitation

Aug 14, 2013

In the Amazon rainforest, the chain of events that turns a small-scale process like a localized increase in evaporation into a towering storm cloud is long and twisted. To understand the complex dynamics that lead to precipitation, and to identify the relative importance of various processes, researchers need high temporal resolution, all-weather observations over many years. Such observations have traditionally been scarce for tropical continental environments, such as the Amazon, where logistics are difficult.

In recent years, however, Global Navigational Satellite System (GNSS) stations have provided a way to gather these measurements of . In their study, Adams et al. use 3.5 years of observations from a GNSS meteorological station in Manaus, Brazil, to analyze the processes that turn localized dynamics into deep convective rainfall.

To identify which physical processes are most important in contributing to cloud formation, growth, and precipitation, the authors developed a new metric called the "water vapor convergence time scale." Moist air is more buoyant than dry, so understanding water vapor convergence is important to understanding the development of deep convective . Using their metric derived from GNSS water vapor observations, the authors identify two main time scales relevant to Amazon convective .

Starting about 12 hours before precipitation onset, the authors find that localized evaporation is the most likely dominant factor in moistening the atmosphere. Then, about 4 hours before the onset of deep convective precipitation, water vapor convergence becomes dominant. This 4-hour period of strong water vapor convergence before heavy rainfall encompasses the transition from shallow to deep convection. This transition is a process during which small, scattered cumulus clouds grow into deep convective towers. The authors find that this 4-hour shallow-to-deep convection transition time scale is not dependent on the season, the intensity of the convective precipitation, or the time of day.

Explore further: Atmospheric rivers linked to severe precipitation in Western Europe

More information: GNSS Observations of Deep Convective Time Scales in the Amazon, Geophysical Research Letters, DOI: 10.1002/grl.50573, 2013 http://onlinelibrary.wiley.com/doi/10.1002/grl.50573/abstract

add to favorites email to friend print save as pdf

Related Stories

Oxygen isotopes improve weather predictability in Niger

May 17, 2012

For the African nation of Niger, the effect of seasonal atmospheric variability on the weather is poorly understood. Because most residents rely on local agriculture, improving the predictability of seasonal weather and precipitation ...

Recommended for you

Fires in Central Africa During July 2014

10 hours ago

Hundreds of fires covered central Africa in mid-July 2014, as the annual fire season continues across the region. Multiple red hotspots, which indicate areas of increased temperatures, are heavily sprinkled ...

NASA's HS3 mission spotlight: The HIRAD instrument

21 hours ago

The Hurricane Imaging Radiometer, known as HIRAD, will fly aboard one of two unmanned Global Hawk aircraft during NASA's Hurricane Severe Storm Sentinel or HS3 mission from Wallops beginning August 26 through ...

Fires in the Northern Territories July 2014

Jul 23, 2014

Environment Canada has issued a high health risk warning for Yellowknife and surrounding area because of heavy smoke in the region due to forest fires. In the image taken by the Aqua satellite, the smoke ...

User comments : 0