The Aroon indicator attempts to identify starting trends. It is essentially a system that determines whether a stock is trending or not and how strong the trend is. The indicator consists of up and down lines, which measure how long it has been since the highest high/lowest low has occurred in the last n periods.
Up trends are indicated when the Aroon-Up is between 70 and 100. Strong trends are indicated when when the Aroon-Up is above 70 while the Aroon-Down is below 30. Conversely, down trends are indicated when the Aroon-Down is between 70 and 100. Strong trends are indicated when when the Aroon-Down is above 70 while the Aroon-Down is below 30. The Aroon indicators signal a consolidation when both are below 50 and/or both are moving lower with parallel lines.
Simply: a surge in Aroon-Up combined with a decline in Aroon-Down signals the emergence of an uptrend. Conversely, a surge in Aroon-Down combined with a decline in Aroon-Up signals the start of a downtrend.