METEO 820
Time Series Analytics for Meteorological Data

Lesson 2: Autocorrelation and ARIMA

Motivate...

Click for a transcript of Remarkable Rice: How Does Rice Grow?

PRESENTER: How does rice grow? Rice is a grain. It looks like grass when it's fully grown. Most of the rice we eat in the UK comes from India, Thailand, Cambodia, Vietnam, Pakistan, and Italy. People in these countries have grown rice for thousands of years. Actually, you can grow rice in most places as long as the plants aren't exposed to the cold.

Rice grows in a paddy field. It's different from a field you might see in this country because it's usually flooded with water, which is just how the rice plants like it. The water protects the rice plants from extreme heat and cold and stops the weeds from growing by making the ground too waterlogged for them to take hold.

Some rice fields are irrigated with water from nearby rivers. Others are rain-fed areas containing water that falls during the monsoon season. The rice plants start their growing cycle in a nursery paddy field.

After one month, the seedling plants are put into small bunches and transplanted to a larger field to allow them to grow to their full size. The ground in the larger paddy field is prepared for the seedling rice plants by plowing. They use oxen to pull the plow through the waterlogged field.

The small bunches of rice seedlings are then planted in the main field by hand. The seedlings are given plenty of space in the ground because the rice plants will grow to be around a meter tall. It takes three months for the grains of rice to develop at the top of the plants' stalks. When the grains turn yellow and hard, it's time for them to be harvested.

In this field, the rice has to be harvested by hand. So during the harvest, the paddy field is drained to make it easier for the workers. The farmers harvest the rice by cutting the stalks with a sickle. Next, they separate the grain from the stalks by threshing it. This is usually done by hand.

In some places, the rice is spread out like this, and the heat of the sunshine dries it out. But often, the rice is stored in large silos, and using dryers, they heat up the air to dry out the rice. Once the rice is dry, the rice grain is separated from the outer husk using this machine. Now, it's ready to be placed into these one-ton bags and transported to rice mills in Europe.

Rice is an important crop in Thailand and represents a significant portion of the Thai economy and the labor force. As the video discussed, the rice grows in a flooded area, and farmers either rely on irrigation from rivers or rainfall. This rainfall, in Thailand and many other countries, comes from the monsoon. Monsoons are seasonal reversals, in this case from dry to wet. Since farmers in Thailand rely on the wet monsoon season to grow crops, variations in the monsoon season have severe implications for the economy. Being able to predict the wet season of the monsoon is imperative. Because of the general periodicity of the monsoon, we can utilize a time series to predict the coming and going of the wet season.

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Lesson Objectives

  1. Define, compute, and interpret autocorrelation in a dataset.
  2. Create an autoregressive model for a dataset.
  3. Create a moving average model for a dataset.
  4. Create an ARMA or ARIMA model for a dataset.
  5. Explain the differences between models, the strengths and weakness of each, as well as when to use each one.

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