Udaan mudra is one of the variations of Vata-Karak mudra. It helps to manage Udaan Prana Vayu.
Vata Governs
According to Ayurveda Vata has five major functions. The following are;
Prana Vata: The senses, creative thinking, reasoning, enthusiasm, leader of all 15 categories of Vata, Pitta and Kapha.
Udana Vata: Quality of voice, memory, movements of thought.
Samana Vata: Movement of food through the digestive tract.
Apana Vata: Elimination of wastes, sexual function, menstrual cycle.
Vyana Vata: Blood flow, heart rhythm, perspiration, sense of touch.
The practice of Udan mudra is very effective to balance and strengthen Udana Vata. It is essential to lead a healthy life. Udana governs memory, therefore, the practice of this mudra enhance memory, also helps to get fresh and creative thoughts.
Vata out of Balance
Prana Vata: Worries, overactive mind, sleep problems, difficulty breathing.
Udana Vata: Dry coughs, sore throats, earaches, general fatigue.
Samana Vata: Slow or rapid digestion, gas, intestinal cramps, poor assimilation, weak tissues.
Apana Vata: Intestinal cramps, menstrual problems, lower back pain, irregularity, diarrhoea, constipation, gas.
Vyana Vata: Dry or rough skin, nervousness, shakiness, poor blood flow, stress-related problems.

How to do
Join the tips of the middle finger and thumb finger now place the tips of index finger above it like in the picture.
Benefits of Udaan mudra
The practice of Udaan mudra strengthen the vocal cords(voice), the respiratory system and the thyroid-parathyroid glands.
Duration
30 to 45 minutes of practice is enough to get good results.
Precautions:
If you are a Vata Dosha person do this mudra in moderation only.