The characteristic climate of the Tropical Savannah Region is option 'D', which refers to a definite dry and wet season. Let's understand the reasons behind this characteristic climate in detail:

Factors influencing the climate:
1. Latitude: The Tropical Savannah Region is located in the low latitudes, typically between 10° and 20° north and south of the equator.
2. Air masses: The region is influenced by the trade winds which blow from the northeast in the northern hemisphere and southeast in the southern hemisphere. These winds bring warm and moist air from the oceans.
3. Topography: The presence of mountains or highlands can affect the distribution of rainfall and create microclimates within the region.

Definite dry and wet season:
1. Rainfall distribution: The Tropical Savannah Region experiences a distinct pattern of rainfall distribution throughout the year. It is characterized by a prolonged dry season followed by a shorter wet season.
2. Dry season: During the dry season, which typically lasts for several months, there is little to no rainfall. This is due to the dominance of high-pressure systems, which inhibit the formation of clouds and precipitation.
3. Wet season: The wet season occurs when the region experiences a shift in wind patterns. The trade winds bring warm and moist air from the oceans, which rises, cools, and condenses to form clouds. This leads to increased rainfall during this period.

Impact on vegetation and wildlife:
1. Vegetation: The Tropical Savannah Region is known for its savannah grasslands, characterized by scattered trees and grasses. The dry season limits the growth of vegetation, while the wet season provides ample moisture for plant growth.
2. Wildlife: The distinct seasons in the Tropical Savannah Region affect the movement and behavior of wildlife. During the dry season, animals may migrate in search of water and resources. The wet season brings an abundance of water, leading to the flourishing of plant and animal life.

Conclusion:
The characteristic climate of the Tropical Savannah Region is defined by a definite dry and wet season. This pattern of rainfall distribution influences the vegetation and wildlife found in the region.