Let us assume that in a healthy body, there is proportionate amount of kinetic energy, heat and inertia or mass. It is true that energy cannot be destroyed so due to external stimuli the energy is forced to convert from one form to the other, making an excess of one and deficiency of the other form at the same time, as compared to the balanced state. This can be conveniently compared to the oscillation of a pendulum, where the negative kinetic energy gets stored as the pendulum moves up, because of momentum, and swings back in the opposite direction in order to restore the balance
The concept of accumulation (Sanchay), vitiation (Prakop) and balance or restoration (Shaman) is similar to the example of pendulum. We can compare it to the pendulum taken to one extreme end (Sanchay or accumulation of energy), then swinging to the other extreme end as a reaction (Prakop) and gradually coming to standstill (Shaman)
Each season has a unique temperament. Seasons either support a tendency or diminish it. They work as the hand which takes the pendulum to the extreme end. Rest of the process continues as a natural sequence.
Therefore we can also understand Dosha like 3 pendulums which strikes and misbalance each other in a regular frequency, by exchange of energy, prompted by the external conditions like seasons or diseases.
In summer, there is more heat in the external environment, so the body changes the internal heat to kinetic energy in order to maintain a balance. Therefore there are less chemical reactions; less digestive juices are made, less hunger, less food intake and therefore less digestion, which helps to prevent extra heat generation through digestion. Instead there is more water intake and the glands like sweat glands are working faster across the surface of the skin. Skin is the largest organ and it adjusts the excess kinetic energy to continuously sweat and maintain the temperature all over the body. The inertia of this cooling mechanism is the accumulation of Vata.
As the earth gradually starts to moves away from sun, the heat reduces, the climate is not warm enough to hold the built-up vapour (clouds) and it starts pouring as rains. The extra Vata (Kinetic energy) used for maintaining the cooling system of the body in summer, is no longer required due to sudden fall in temperature and causes excess in the body in the rainy season. Vitiation of Vata is compared to the steam that rises when a hot pan (Body in summer) is sprinkled with water.
But this mechanism is not suddenly switched off with the sudden drop in temperatures after the rains. In fact, when there is first rain after lots of summer heat, the rain evaporates and causes a humid environment and the sweat does not get evaporated easily. Also the digestion power, which was appropriate for summer, is comparatively weak in the rainy season to support the heat generation (through digestion) required to combat the sudden drop in temperatures after rains. This gives a minor shock to the temperature regulation system of the body and is the time for start of Vata vitiation.
Gradually, brain starts to make necessary modifications in body physiology. In summer, the body is in the mode of heat loss to preserve the temperature balance. In rainy season, temperatures come down so the body switches off the heat loss mode of the summer automatically, initiated by the heat sensors of the skin. Also the rains reduces the intensity of sunlight due to clouds and a big source of heat is lost. This triggers the process of constriction of the blood vessels and other modes of heat conservation.
Digestion is the most unstable factor in the rainy season, which needs active external help to quickly find balance. Finally, with the approach of winter (Sharad), Vata finds its balance (appropriate amount) in the body in the same way as vapour cools down in a lower temperature.
The longer the body takes to adjust to these changes, the longer is the duration of susceptibility to seasonal diseases or Vata vitiation.
It is said in Charak Samhita that the body that is accustomed of being wet (or stay in humid climate) in rainy season, is exposed to bright sun rays in Sharad. It is interesting that the temperature preservation methods of the body are different in rains than in winter. The blood vessels and sweat glands are not constricted fully, like in the winter because temperatures are higher than the winter and rainy season is humid and ideal climate for micro-organisms to flourish, which is not the case in winter. Secretions from skin glands keep the skin supple and protect from infections or damages. But the heat loss due to cool climate has to be compensated by extra heat, by conversion from extra kinetic energy or Vata.
Temperature balance is crucial for survival and cannot be jeopardized. During transition from rains to winter, the temperatures fall further and the humidity reduces. The microbe growth in environment diminishes and so the skin protection is not as aggressive as in the rains. The blood vessels constrict and more heat is preserved, in addition to the increased internal production of heat by digestion. Also now sun’s heat is available. Therefore during the transition from rains to winter, there is a temporary system producing excess amount of heat. Inertia of this system is the accumulation of Pitta.
The more suddenly these seasonal changes set in, more is the effect of Pitta prakop.
Now in fall (Hemant), the earth moves further away from sun and the environment gets colder. Body gets adjusted to the climate and the Pitta achieves its balance. Now the excess heat is adjusted in the process of digestion. Therefore, person has better appetite in winter as compared to any other season. This is the time when the digestion power and stamina or immunity (Bal) of all the creatures are at its best. Also, no other dosha gets imbalanced because of good digestion and increased metabolism. The time of rains, Sharad and Hemant together is called Adan kal, since it imparts Ras(life juice) to the creatures.
Then the cycle gets back to Visarg kal (First half of the year, when the Bal (strength) is extracted from the creatures. The earth starts moving towards the sun and Shishir(Late Autumn) sets in. This season is more vivid in areas where the ice starts melting. The body is still in the heat preservation mode whereas the environment is gradually getting hotter.
In Vasant (spring), the climate is pleasant; neither too hot nor too cold. The body is gradually changing from heat preservation mode to normal mode. This is the time of Kapha vitiation. This change is described in Charak Samhita as the process of butter melting when placed from a cold place to a hotter one. Various systems undergo changes to maintain the homeostasis of the body. The ways of fluid retention and excretion change. For example, the sweating, which was minimized during winter, starts increasing according to the temperature. One hypothesis can be that an extra mucous lining is formed all over the body in the sebaceous glands or similar organs, which is helpful in insulation during the winter and is contained by the cold temperature, but as the body, in the heat preservation mode is subjected to growing external heat, there is excess heat in the body which dissolves this lining and there is excess of Kapha in the body.
As summer sets in, the body gets accustomed to hotter climate and the Kapha gets balanced. Now Vata starts accumulation and the cycle continues.
This cycle continues throughout the life. Gradually as the ability to quickly adjust to these changes decreases, wear and tear starts accumulating and the damages become more permanent. Here the aging starts. The negative spiral continues to the point when finally the changes become completely unmanageable and the body gives up.
Importance of Ritucharya is in keeping the body almost untouched by these changes for years, by helping it to generate the ability of making rapid adjustments and to quickly repair the wear and tear.