You are a second year student, so I imagine you have some experience with GMAW. As a student you should be able to figure this out.
1) Will the pipe be help stationary or rotated as it is welded?
2) If the pipe is stationary, what positions would the welder have to weld in?
3) What transfer modes allow GMAW in all positions?
4) What is the disadvantage of the transfer modes used for all positions?
5) You probably have your answer by now.
The WPS you reference- GTAW root/hot pass- SMAW fill and cap- is a regularly used procedure in many industrial applications from refineries, to offshore oil rigs, pulp mills, refrigeration, boilers and many others. One of the reasons for it's use is that with a GTAW root the inside of the pipe is kept cleaner by the absence of slag that would need to be cleaned out from a 6010 root. Also with a GTAW ER 70S2 root you have a higher tensile strength from the get go. For these reasons [and others I think some of the smarter folks here will be able to provide] it is not just a commonly used procedure, it is also a technique most industrial mechanical contractors will expect their pipe welders to be able to perform proficiently, not just in carbon steel but numerous alloys. Your question assumes this procedure can only be performed indoors because of the need for gas coverage on the root. Not meaning to be insulting, but the assumption is based on your as yet limited experience and it's understandable. The procedure and techniques to accomplish the weld are difficult and take a great deal of practice- they are challenging- and at your point of development as a welder might seem impractical if not impossible but believe me they are accomplished successfully every day. One of the things you will learn when you get out in the field working is that welders are often expected to accomplish things just short of a miracle or pure magic, and we do which is the reason those skills pay so well. Failure [busted X-Ray] is simply not an option. It will become one of your obligations to construct or use protective coverage in the form of wind protection for the work. Tarps, plywood "hooches", a helper holding a piece of cardboard even a set of leathers hung from a rod have all been deployed to keep the argon from being lost and ruining the weld. You will learn to be clever, resourceful, self reliant, adaptive, determined and indomitable. In short you will perform a kind of magic that will astound the lesser mortals around you and earn you huge piles of negotiable revenues. In short, you will then be a Welder worthy of the name. You will learn patience, perseverance, humility and a level of determination not yet conceivable to you. But it will take more than just practice, it will take a kind of devotion to excellence and a refusal to fail. If this trade is really for you, you will enjoy the setbacks as learning experiences as much as you will enjoy your progress and final successes. Watch and learn and pay attention to the best welders you meet, keep your eyes open to see what it is they are doing, their methodologies, adapt them for your own uses, be prepared to fail and try again until you succeed. Never quit. Now get back in the booth and start burning some rod.