Why is it winter in early spring in the northern hemisphere?

"beginning of spring" is an important solar term in China lunar calendar, usually on February 4th or 5th every year, marking the beginning of spring. According to the traditional division of solar terms in China, a year is divided into 24 solar terms, which are evenly distributed in period of revolution, reflecting the laws of seasonal changes and agricultural activities. However, this day in beginning of spring does not mean that the climate in the northern hemisphere will enter spring immediately. In fact, it's still winter in the northern hemisphere at this time, and the temperature is low, and there will be cold weather such as snowfall in many areas. The main reasons for this phenomenon are as follows: 1, tilt axis of the earth: when the earth orbits the sun, its axis keeps an inclination of about 23.5 degrees relative to the orbital plane. This means that at different times, the direct position of the sun will move south or north along the latitude. When I was in beginning of spring, although the direct point of the sun began to move to the northern hemisphere, it still didn't reach enough latitude to make the northern hemisphere get a warm climate like spring. 2. Delay effect of heat accumulation: The atmosphere, ocean and land all have certain heat capacity, which can absorb and store heat energy. Even if the solar radiation increases gradually, these environmental factors need time to cope with this change, which leads to a certain lag in climate warming. 3. Complexity of climate system: Climate is influenced by many factors, including atmospheric circulation patterns, ocean currents and storm activities. Beginning of spring is only one of the 24 solar terms, and it cannot decide the climate alone. Therefore, although beginning of spring represents the beginning of the Lunar New Year and the revival of everything, from the climatological point of view, the real spring in the northern hemisphere will not come until March 2 1 day, the so-called "vernal equinox". By then, the sun will shine directly at the equator, and the world will be almost equal day and night.