DVORAK TECHNIQUE

CONTEXT

American meteorologist Vernon Dvorak passed away he was best known for the Dvorak technique which is named after him. The technique is for cyclone forecasting.

VERNON DVORAK

• The National Hurricane Centre of the National Oceanic and Atmospheric Administration named the technique as Advanced Dvorak Technique after updating the software; this technique was developed by Dvorak in the early 1970s.
• The latest update in technique will improve tropical storm forecasts with access to sharper and more detailed images.

LACK OF OCEANIC OBSERVATION MECHANISM

• Ocean observations are limited as compared to land observations
• Vast regions across the oceans have not been fully examined.
• Most observations are taken by deploying buoys or ships, but it is insufficient
• Thus meteorologists depend more on satellite-based imagery.

DVORAK TECHNIQUE

• Forecasters used the available satellite images obtained from polar-orbiting satellites to examine features of developing tropical storms.
• During day time, images in the visible spectrum were used while at night, the ocean was observed using infrared images.
• From the satellite images thus obtained, the Dvorak technique helps forecasters to do a pattern recognition from the observed structure of the storm, locate its eye and estimate the intensity of the storm
• The technique gives the best estimates of cyclone intensity, a vital component of weather warnings.
• Experts claim it cannot help make any predictions or measure wind pressure.
• But it is a guide to estimating the storm's possible intensification which is crucial for local administration in planning evacuation measures.

TROPICAL CYCLONES

Tropical cyclones originate and intensify over warm tropical oceans. The conditions favourable for the formation and intensification of tropical storms are-

• Large sea surface with a temperature higher than 27° C;
• Presence of the Coriolis force;
• Small variations in the vertical wind speed
• A pre-existing weak low-pressure area or low-level-cyclonic circulation
• Upper divergence above the sea level system.

 The energy that intensifies the storm comes from the condensation process in the towering cumulonimbus clouds, surrounding the center of the storm. With a continuous supply of moisture from the sea, the storm is further strengthened. On reaching the land the moisture supply is cut off and the storm dissipates. The place where a tropical cyclone crosses the coast is called the landfall of the cyclone.

The cyclones, which cross 20 N latitude generally, recurve and they are more destructive.

A mature tropical cyclone is characterized by the strong spirally circulating wind around the center, called the eye.

 The diameter of the circulating system can vary between 150 and 250 km. The eye is a region of calm with subsiding air.

 Around the eye is the eye wall, where there is a strong spiraling ascent of air to a greater height reaching the tropopause. The wind reaches maximum velocity in this region, reaching as high as 250 km per hour. Torrential rain occurs here.

 From the eye wall, rain bands may radiate and trains of cumulus and cumulonimbus clouds may drift into the outer region.

POLAR ORBITS

Almost all the satellites that are in a polar orbit are at lower altitudes. This is because we use them for applications such as monitoring crops, forests, and even global security.

A polar orbit travels north-south over the poles and takes approximately an hour and a half for a full rotation. As the satellite is in orbit, the Earth is rotating beneath it. As a result, a satellite can observe the entire Earth's surface (off-nadir) in a time of 24 hours