かこう下降kakou
1.

The act or process of moving downward, often used to describe a reduction in level or position.

2.

A transition to a lower state or condition, commonly associated with a decrease in performance or popularity.

3.

A downwards movement, particularly in relation to air currents, indicating a specific type of airflow that typically accompanies rising temperatures and fair weather.

かこうせん下降線kakousen
1.

A line that trends downward, often used in graphs to indicate a decrease in value or performance over time.

2.

A visual representation in charts signifying a decline or deterioration in a given metric or data set.

Example:

彼の人気は下降線をたどっている。