WEBVTT FILE

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Our lives are in sync with Earth's rotation.

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As our planet rotates on its axis,

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we shift from day to night and warm to cool. 

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As a response, our weather follows a daily cycle.

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Now, the most detailed view of our daily weather has been created

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using a new NASA record that combines almost 20 years of rain and snow.

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By combining these two satellites,

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scientists calculated the changes in precipitation every 30 minutes for two decades.

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This is part of NASA's newest extended precipitation record

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known as the Integrated Multi-satellitE Retrievals for GPM, or IMERG analysis.

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From the vantage of space,

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IMERG shows the 24-hour pulse in weather known as the diurnal cycle.

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This cycle helps shape how and when our weather develops

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and is fundamental to regulating our climate.

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In the case of precipitation, one of the main questions is — the different main modes of variability.


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One main mode of variability is the seasonal variation.

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But on a much shorter time scale, the main mode of variability is the so-called diurnal cycle.

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That is the variation in precipitation over the day.

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IMERG not only shows us how much the rainfall shifts,

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it tells us what time it shifts and peaks.

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Over the U.S. we see a variety of patterns.

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This shows the average amount of rainfall every 30 minutes during the summer months of June, July, and August.

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In Florida, heat from the Sun builds up over the course of the day,

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driving rainfall over land.

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Sea breezes from the Gulf of Mexico and Atlantic Ocean

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feed the storms over land driving storms to peak in the afternoon.

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At night, rainfall moves over the ocean.

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Storms intensify offshore only to move inland during the day again.

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Over the midwest and the Great Plains,

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heating over the Rocky mountains forms storm systems during the day,

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which then roll eastward overnight.

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In the U.S. Northeast, heating over land causes rainfall during the day

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that moves over the ocean at night,

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because the water doesn’t cool down as quickly as over land.

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Due to this, you can clearly see the warm Gulf Stream water

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moving past the East Coast, on its way to the North Atlantic. 

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During the winter months of December, January, and February along the West Coast,

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the daily patterns of rainfall every 30 minutes

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how how the coastal regions generally receive similar amounts of precipitation throughout the day.

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In the winter, precipitation is driven less from the daily heating of the Sun

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and more from the Pacific Ocean bringing in atmospheric rivers —

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corridors of intense water vapor in the atmosphere.

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By studying the diurnal variation,

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this gives us basic scientific understanding of what the atmosphere is doing, 

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and it prepares us to look at models and understand what the relationship is

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between rainfall and these other variables, like air quality.

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Current climate models have difficulty accounting for the diurnal cycle,

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but the improved detail in IMERG could help fill in the gaps

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to create a more complete and accurate picture of daily precipitation,

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not just in the U.S. but around the world.

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