Ok, here's the scenario. You're playing a half-orc barbarian whose only weapon is a greatsword (I know, a crime to not have a backup or a ranged weapon). You are fighting a strix fighter who uses his natural flight to stay 10' above you and poke you with a polearm. Question is: Are you completely boned? The only thing I can think of to deal with him is to try and take the polearm away, but I'm not sure if you are allowed to make a disarm against somebody that is 10' away when you don't have a reach weapon even if you are trying to disarm a reach weapon. Love to have some rules clarification with this.
What the others said, mostly. However, a half-orc barbarian with even 1 point in acrobatics is likely to have a jump check of, say...
+4 from 18 strength
+2 from raging
+4 from +10ft speed
+1 from skill point
+3 from class skill
...for a bonus of +14 or better. A vertical jump of 5 feet with a running start is only DC 20. Therefore a roll of 6 or more gets you within attack distance of Mr. (or Ms.) Strix, and even better, within grapple range - and due to that polearm that can't hit adjacent enemies, you aren't going to be eating an attack of opportunity when you try it!
@FarmerGiles - A lenient or merciful DM might allow that with some good reasoning, I can see the argument there.
@wraithstrike - Ah that makes sense. Since it's a type of attack you need to be actually able to reach them. Thanks for the clarification!
@bodhranist - I think for various reasons that would be hard to pull off in this particular situation (mostly because the strix would either stay above you or fly up, but also because the strix in question has improved trip and combat reflexes) but this is about the situation in general and you make a good point! He's not completely boned against a flying opponent as long as he can make a jump check, thanks!
You can ready an attack to disarm when he attacks you, since it will then be within your reach.
Strikeback feat was one of this greatest nerfs to martials in all of Pathfinder, it should be ignored with extreme vengeance.
The fact that there's a specific part of RAW mentioned in your second paragraph that completely invalidates your first paragraph makes it an ... interesting ... interpretation.
By RAW, there's nothing the barbarian can do except throw a rock.
You are a barbarian, you have a full BAB, and a whole bunch of Str.
Just throw the damn greatsword in the Strix face, that's how badass you are.
Just because you're not good at it (as in: you do not possess the Throw Anything feat) doesn't mean you cannot do it.
The greatsword becomes an improvised ranged weapon at -4 penalty. It is up to your GM what kind of damage it deals. (either use the greatswords damage or a Medium-sized improvised weapon damage)
You could also attempt to jump and grab the Strix if he's only 10 ft. above you. You'll need to roll high on your Acrobatics to jump that high, but at least your grapple CMB should be high enough. If he has Spring attack and stays out of reach then you could indeed attempt a ready-action.
EDIT: Oops, just realised this was suggested earlier.
The rules for throwing melee weapons that don't have a range are in the book:-
It is possible to throw a weapon that isn't designed to be thrown (that is, a melee weapon that doesn't have a numeric entry in the Range column on Table: Weapons), and a character who does so takes a –4 penalty on the attack roll. Throwing a light or one-handed weapon is a standard action, while throwing a two-handed weapon is a full-round action. Regardless of the type of weapon, such an attack scores a threat only on a natural roll of 20 and deals double damage on a critical hit. Such a weapon has a range increment of 10 feet.
So, full round action to throw at -4. Range increment 10-feet, 2d6 damage, (20/x2).
Next round, jump to grapple, use acrobatics to avoid the tripping AoO.
Not easy though. This is why we have ranged weapons. : )