Hodograf atmosferdeki rüzgar şiiri ve buna bağlı bazı indeksleri hesaplamak için kullanılan bir grafik ürünüdür. Rüzgar şiiri konvektif hücrelerin oluşumunda oldukça önemli rol oynar. Hodograf konvektif fırtına hücrelerinin cinsinin önceden tahmin edilmesinde oldukça faydalıdır.
Cold Pool/Shear Interactions Vertical wind shear influences storm organization by enhancing the ability of a thunderstorm outflow (or cold pool) to trigger new storms Vertical wind shear is necessary in the creation of organized long-lived convection When low-level wind shear is strong, new cell develop is favored downshear of the low-level shear vector When low-level wind shear is weak, the lifting created by cold pool circulation alone may be insufficient to allow a surface parcel to reach the LFC (unless the LFC is quite low) The deepest lifting occurs when the horizontal vorticity generated along the cold pool’s leading edge is nearly equal in magnitude to, and has opposite sense of rotation as, the horizontal vorticity associated with the low-level vertical wind shear In midlatitudes, 0 to 2.5 km (0-8 kft) shear values of 10-20 m/s are generally sufficient to promote lifting deep enough to favor new cell development along the downshear portion of a gust front. In tropical environments 5 m/s can be sufficient. Additional shear above this layer can also enhance lifting Updraft/Shear Interactions Vertical wind shear acts to tilt an updraft When the vertical wind shear is strong, it initially has a detrimental effect on a developing updraft, especially when the updraft is weak (it can tear the cloud apart) The magnitude of the storm tilt depends on both the updraft strength and the strength of the vertical wind shear Buoyancy gradients on the sides of a towering cumulus create horizontal vorticity on both sides of the rising updraft When there is no wind shear, the horizontal vorticity on either side is in balance and the updraft rises vertically When the shear is stronger, the updraft will tilt toward the side of the storm that is generating the same sign of vorticity as that associated with the environmental wind shear. In other words, the updraft tilts downshear
When the updraft column blocks the environmental flow, it creates a dynamic affect of relative high pressure upshear and low pressure downshear of the updraft. This makes the rising air parcels turn downshear Shear’s Impact on Isolated Storms Vertical wind shear combined with sufficient buoyancy can lead to supercell formation The shape of the shear profile, as depicted on a hodograph, strongly influences the motion and structure of a supercell, leading to splitting cells and curved paths Total vertical wind shear magnitudes of 25 m/s or more over the lowest 4-6 km (13-20 kft) AGL are sufficient to generate supercells. Vertical wind shear < 15 m/s is generally insufficient to produce supercells Shear’s Impact on Storm Systems For a given CAPE, the strength and longevity of an MCS increase with increasing depth and strength of the vertical wind shear It is the component of low-level environmental shear perpendicular to the line orientation that is most critical for controlling squall line structure and evolution Bow echo and supercell environments overlap, with bow echoes often characterizing the later stages of a supercell event Severe bow echoes are most often observed in environments with moderate-to-strong low-level shear and very high CAPE