Present weather is the condition of atmospheric phenomena occurring at any given time. All day, every day, various conditions throughout the atmosphere change based on the density of the temperature and moisture. The majority of all present weather takes place in the part of the atmosphere known as the troposphere, the lowest region of of air concentration in the sky. It differs from climate, which is the representation of long-term weather patterns over periods of time.
The main outside stimuli that affect present weather include solar radiation and the tilt of Earth's axis. Sunlight impacts the Earth's atmosphere from space, causing changes in temperatures. This radiation is naturally more heat-intensive on the equator and less on the polar regions. Likewise, the fact that the Earth tilts in a certain way, depending on its position during the year, causes radiation to impact at different angles. This results in slight shifts in temperatures and the creation of moisture throughout the atmosphere, creating different weather patterns.
One of the most prevalent ramifications of the solar radiation is the jet stream. This is the flow of high-pressured air to low-pressure areas caused by temperature changes. Most readily, the jet stream moves from the tropical regions near the equator to the polar regions, bringing with it moisture and higher temperatures. Since the jet stream moves in a general pattern across the planet, different regions become hotter, while others become colder. The present weather conditions can vary depending on the rate and level of this movement of air.
Small changes in certain parts of the atmosphere can have major effects across the planet. For example, when a volcano erupts in the Pacific Ocean, it spews dust and heat into the atmosphere. The combination of particles and hotter temperatures cause a diffusion process into areas of colder temperatures, resulting in the present weather conditions changing from the point of eruption to hundreds of miles away. Sometimes, events such as these are so dramatic that the entire planet's climate is altered for a brief period of time until the Earth can regain its equilibrium.
Although present weather conditions are mostly thought to be a facet of the Earth's atmosphere, other planets also maintain weather as well. Venus has some of the most dramatic present weather patterns known in the solar system, with periods of acid rain and major shifts in heat. Mars also features changes, such as high winds, which kick around dust to produce storms. Perhaps the most notable weather phenomenon of the the solar system is that of Jupiter's Great Red Spot, which is actually a storm three times the size of Earth.