Final answer:
In January, the Northern Hemisphere experiences winter due to the tilt of Earth's axis away from the Sun, which leads to less direct sunlight and shorter days. High pressure systems are more common over land in the Northern Hemisphere during winter, while lower pressure tends to prevail over the warmer oceans.
Step-by-step explanation:
On average in January, the Northern Hemisphere is in the winter season because of the tilt of Earth's axis. During this time, the Northern Hemisphere is leaning away from the Sun, resulting in shorter days and less direct sunlight, which leads to colder temperatures. High pressure systems are generally associated with colder, denser air masses and, thus, can be more prevalent over land masses in the Northern Hemisphere during winter. Conversely, areas of lower pressure are commonly found over oceans, which tend to be warmer and can be attributed to heat transfer from the warmer water to the air above.
The seasons and Earth's weather patterns, such as pressure systems, are not significantly influenced by the slight change in Earth's distance from the Sun throughout its elliptical orbit, which varies by only about 3%. Instead, the seasons result from the 23.5° tilt of Earth's axis, which affects the angle at which sunlight hits the surface and the duration of daylight across different times of the year.
Differences in the orientation of the Northern and Southern Hemispheres relative to the Sun during various points in Earth's annual orbit produce the varied seasonal conditions. While January brings winter to the Northern Hemisphere, the Southern Hemisphere experiences summer, with notably warmer temperatures, especially since most of the Southern Hemisphere is covered by oceans that moderate its climate.