Below are images of Atmospheric Tests conducted at the NTS and Various Atolls in the Pacific Ocean.

A Nuclear Air burst or Ground burst is of course extremely nasty, depending on how far away you are from GZ(Ground Zero).
The effects are absolutely terrible, again depending on how far away from GZ you are.
The Blast area can cover a few thousand feet in a circular blast wave from a low yield warhead.
From the larger Mega Ton(Mt) warheads the blast wave can extend out many miles.

When a nuclear detonation occurs, the first stage that happens right after the detonation is the extremely bright flash. This flash can burn out your retina instantly if you look at the flash, this can even occur maybe upto 40+ miles away. you will end up permanently blind with severe burns from the flash. When this flash occurs, it can be seen hundreds of miles away but it only lasts one or two seconds.
After the initial flash the fireball occurs. Depending again on how large the Yield is, this fireball can be just a puff or can rise to tens of thousands of feet in the air, tumbling up to form a mushroom cloud together with the smoke and dust caused by the blast.
Most of the damage caused by a nuclear blast is from the radiant heat that forms from the giant flash and bellowing fireball.
As soon as this fireball is seen rising, you will also see the Blast Wave or Shock Wave coming out in a circular pattern around the Blast.
This shock wave travels extremely fast at supersonic speeds and is extremely destructive depending on its size.
The Shock wave travels both along the ground as a seismic wave and as another wave that travels in the air. This is caused by the Blast pushing the air before it outwards at the supersonic speed. This wave will go out for several thousand feet or miles damaging or demolishing everything in its path. After this wave is released, the fireball will be rapidly rising, again, depending on size of yield, the fireball and mushroom cloud can rise at supersonic speeds! When this rises, it causes a vacuum immediately around the blast. This sucks back in the Blast the opposite direction as to what it was travelling. What happens, is that the wave gets pushed outwards, then gets sucked back inwards making a double blast wave effect, so allot of the buildings that survived the initial heat and blast wave will now get punished again a second time. This Vacuum is immense sucking everything way up inside the fireball.
From miles around the air is sucked in.
Similar effects can be made by the second most powerful bomb ever made which is still used today. The Fuel Air explosive is the worlds most powerful weapon , second only to Nuclear weapons.
The effects are devastatingly similar to an Atomic blast.
The initial blast sends out the radiant heat and shock wave, then causes a vacuum and sucks all available air into the fireball creating more fuel for the immense heat and fire. Anyone in bunkers below a nuclear or Fuel air explosive detonation and survives it will now suck their lungs and other organs out of their mouth or any other hole. If this fails, you will just die from lack of oxygen which was sucked up into the fire. The fuel air explosive was used in iraq, a 15,000Ib bomb, the USA's largest ever bomb dropped by aircraft on bunkers and trenches which caused the iraqis to feel the effects described above. An extremely horrible way to die, and this tells on how the people of Hiroshima and Nagasaki actually went through.
From an air burst, that is detonated a few thousand feet above the ground, many buildings directly below the detonation may survive intact but of course severely damaged and crumbling. This was seen in Hiroshima where the only house standing intact for a mile was the house under the detonation.
The Radiant Heat given off from the bomb is so immense it bends and distorts metal instantly from upto several miles away. This also depends on the yield but also depends on whether it is a normal Atomic Blast or a Thermonuclear blast. Most Modern bombs are Thermonuclear and Hydrogen Bombs with the military going for the more 'heat' than radiation.

The Neutron Bomb:

The Dept of Energy and the Military also developed another Atom type bomb.
This time they wanted to develop a bomb that killed everyone in and near the Ground Zero but also to 'leave' the Buildings Alone.
They developed the Neutron bomb. This kills everything living with but leaves all buildings and vital military equipment in one piece and these can then be captured and re-used.
 

Below are images of Nuclear Above Ground Detonations, including the famous Baker test on capital ships after world war two.

Image source: Department of Energy

Above is a nuclear test held on Bikini Atoll in the Marshall Islands. This test was the first test to have showed the effects of the devastating shock wave on true military targets. This test however as you can see was an underwater test inside the Atoll.
This test disgrunted me as most of these fabulous Capital ships could have been used in a museum. Every Ship and Submarine here fought in very famous battles.
This test was in 1946.
The Closest ship of which you can hardly see here because it is near enough  'gone' was USS Saratoga, the very famous US Aircraft Carrier from WW2 which was used in alot of famous battles all over the Pacific.
Other ships that sunk were also very famous which included Battleships of the US and Japanese Navies and also a very famous German Heavy Cruiser, the KMS Prinz Eugen, famed in the Bismarck Battles of the Atlantic. Famous US ships include the USS Arkansas and several other Battleships and cruisers, Japanese Nagato and several other Fuso Class Battleships, the Submarines Pilotfish and Apogan and several other Battleships and Heavy Cruisers.
The Dome of Water you see rising above the ships rose up at over MACH 2.5 in speed. The actual water stem is 6,000ft high at this point.
Immediately after the detonation, USS Saratoga rose an estimated 95ft before tipping over and sinking. It is also believed she actually 'rode' the very first initial wave of 43ft. Eventually, the surge of water rushing outwards as a giant blast wave rose to an estimated 900ft above the surface of the sea and outwards at a speed of over 60 mph. In the picture above you can see the second initial wave appearing at 90ft+. By the time the wave hit the shores of the island they were only 6ft high (thank-god the camera-man says).

This enlarged photo shows a better view of the USS Saratoga.
1.  The second wave forming which rose above 100ft.
2.  USS Saratoga behind the Heavy Cruiser after initially riding out the extremely fast shock wave now gets absolutely dwarfed by the large 100ft'er crashing over her aircraft deck.
3.  The Front of USS Saratoga. which is about to capsize and be sunk by this giant Tsunami. This wave as it heads into more shallower water becomes a massive 900ft high. Unlike most Tsunamis, this wave became smaller as it got closer to shore.
Most Tsunami's caused by earthquakes travel at speeds well over 500mph. This one however only travelled below 100mph.
In the foreground also you can see a 'Fuso' Class Japanese Battleship to the right hand side of the huge upwards wall of water.
4.  The innitial shock wave and a 40ft wave spreading outwards but it soon died down as you can see.

Image source: Department of Energy
Forming the classic 'wilson cloud effect'. You can clearly see the shockwave rushing outwards engulfing many battleships and cruisers. by this time, the Saratoga was completely engulfed and on its way to the bottom of the sea. The rush of water can still be seen rising above the cloud that is formed by Nuclear Blasts.

Image source: Department of Energy
The rush of water still making its way upwards, the 'wilson' cloud has deformed from the nice shape it had above. A large mushroom cloud will form above this moments later. This is full photo of the large above, USS Saratoga is about to be sunk.

Image source: Department of Energy
This photo was taken slightly before the one above, USS Saratoga at this point is riding the innitial 43ft wave that spreads out with frightening speed followed by the 100ft wave behind , that finally gets the carrier.(above)

Below is another Photo of an underwater detonation.

Image source: Department of Energy
The Hardtack Oak 1 detonation in the pacific, a very large explosion at Eniwetok Atoll in 1958.
1958 was the record year for nuclear testing in the united states.

Below is of an image taken from Frenchman Flat in the Nevada National Security Site.
The warhead was inside a 280mm shell fired by an Artillery Gun. The test was conducted in 1953 and was the only detonation of a nuclear warhead fired by this type of weapon. The Yield of the warhead was 15Kt (Eq: 15,000 tons of TNT) The test was called Operation Grable.  This paved way for todays Tactical Nuclear Weapons that can be fired from most artillery guns.

Image source: Department of Energy

Below is an image of the Buster Shot Charlie Detonation on Area 7. Dropped from a B-50 Bomber this Nuclear bomb detonated at 1,132 ft above the ground (Airburst). It was conducted in 1951 and had a Yield of 14Kt.
Airbursts are the most devastating when it comes to electrical Equipment.. and can be used as a supreme weapon against the enemy for thousands of miles distant...this will be explained later...

Image source: Department of Energy
In the foreground you can see the bunkers and buildings used by the Desert Rock / Mercury troops who were used for various tests here. Thousands of troops were used at any one time, sometimes up to 10,000.
You can see the immediate shock/blast wave rushing outwards at supersonic speed, stirring up dust. The large cloud of dust and smoke at the bottom of the mushroom stalk has been sucked in and is on its way 'up' as a massive Vacuum. The mushroom then folds over itself to form a 'tumbling' motion.

Below is an image of Buster Shot Easy.  Similar to the one above except this detonation was of 31Kt Yield.

Image source: Department of Energy
Located in Area7 on Frenchman Flat not far from Mercury, Buster shot Easy was again used in the same tests as above, this was bomb was dropped by a B-45 aircraft and detonated 1,314ft above the flat.  Clearly shown here is the Blast wave rushing outwards and the immense heat of the fireball.  this was dropped roughly in the same place as the one above.

Below is the Project 'Seminole' detonation at Eniwetok Atoll, near Kwajalein Atoll, todays ICBM testing ground.
This was detonated on 1956 and its Yield was 13.7Kt.

Image source: Department of Energy
The classic 'wilson cloud' effect in full swing on this detonation....with the shock wave about to hit the sides of the atoll. Cooked fish ready to serve complete with 25 heads and 5 tails on each!

Below is the IVY MIKE Detonations....conducted in 1952 at Eniwetok Atoll, this was the very first Experimental Thermo Nuclear Device. Like most ThermoNukes, this was very large. Thermo Nuclear Devices detonate with more Radiant Heat than Radiation itself. The Heat kills and destroys faster than Radiation does and of course does maximum damage.
IVY MIKE was the 4th largest bomb to explode from the DoE Testing. Its Yield was a massive 10.4Mt(Eq: 10.4 million tons of TNT) Makes you think how big it was compared with the 31KT yield detonated above!!
If a thermonuclear device was detonated on Frenchman Flat in Nevada, Las Vegas you might aswell say goodbye too, and its population not to mention Mercury!
The Mushroom cloud rose to 60,000ft in 95 seconds and up to 108,000ft  60 seconds later!!
It finaly came to a halt in the stratosphere 120,000ft high and spread out over 60 miles of Ocean. This created massive fallout over the Atolls but not as bad as to what is coming below these IVY images..!

Image source: Department of Energy
IVY MIKE rising up into the Stratosphere....talk about Global Warming, this literally heated up the surrounding area several thousand degrees!
Making its own weather this was truly a massive explosive. The mushroom is over 60 miles wide and 120,000ft high. The tops of the cloud are 'pushing' against the stratosphere.

Image source: Department of Energy
The absolute giant of a fireball rising extremely fast up to the stratosphere. Its own weather being made around it in circles. Taken from many many miles away possible over 100

Image source: Department of Energy
Last photo of Ive Mike, the cloud is more than 60 miles wide reminiscent of a huge Volcano Exploding such as Pinatubo.

Image source: Department of Energy
This is the Atoll IVY MIKE was situated on. Before the detonation of the 10.4Mt warhead

Below is a picture of the same area AFTER the detonation...oh dear!

Image source: Department of Energy
 

BELOW - AMERICA'S LARGEST EVER EXPLOSION!

Below is the Castle Bravo Detonation.
This is a very very controversial test in several ways.
The Castle Bravo was Detonated on Eniwetok Atoll in 1954.
The result was a truly massive explosion, the biggest the DoE every managed, and it was all by accident!!!
The Bomb was only to have a predicted Yield of 6Mt, much smaller than Ivy Mike above.  The resulting chain reaction managed to cunjure up a whopping 15Mt Yield(15,000,000 tons of TNT equilivent)
This massive detonation blew half of the Atoll away.
Although it made the biggest ever explosion in America's history(albeit by accident) it also produced the worlds first and very devastating Nuclear disaster. This was because the fact it was all done by accident. The Predicted 6MT explosion would of been 'within limits' but the whopping 15MT explosion that occurred caused extreme amounts of Nuclear fall-out and the whole area for hundreds of miles was completely contaminated. This mushroom cloud loomed over hundreds of miles and fell down on many Atolls and Islands with thousands of local inhabitants of Marshall Islander's and Japanese. The result was many hundreds killed. Most of the Islanders got effected with 100-200R of fall-out and died of a horrible and painful death, some very slowly.  Japanese fisherman were also caught in the fall-out well outside the exclusion zone like the islanders were. The japanese fisherman, although miles and miles outside the 'zone of danger' were contaminated with over 300R of fall-out and some of the crew died within a few days of exposure.
Many of the islander's children were born with serious deformalities that are reminiscent to todays Chernobyl nuclear disaster.
After this 'accidental' over-rated explosion, the DoE expanded its safe-zone to over 1% of the World's Surface around this Atoll incase other experiments went drastically wrong making it the largest military testing ground on earth.

Image source: Department of Energy
The Resulting absolutely massive Fireball rising up into a dome shape with a hollow middle. burning its way through the atmosphere. The Radiant heat was so much that it would of melted steel in seconds on the Atoll.

This however was not the largest ever Nuclear Detonation...
The Russians also did a large explosion, but this time it was predicted to be as large as it was. Well over 15MT this Giant was detonated on a large island. The resulting effect was the island 'disappeared'.
 

THE EFFECTS OF AIRBURST DETONATIONS ON ELECTRICAL EQUIPMENT:

If a nuclear bomb is detonated it creates a very destructive power. This power is referred to as Electro Magnetic Pulse (EMP)If they are dropped by a bomber or delivered by missile and is 'airburst' like the Nagasaki and Hiroshima bombs this EMP becomes extremely effective depending on how high the bomb is detonated.
On Christmas Island in the Pacific, the British were conducting nuclear tests, for exchange , the US asked to use this site, and let the British use Nevada for their further underground tests (the above ground British tests were at Woomera, Australia).
Above Christmas Island, DoE detonated a Nuclear bomb. The result was devastating to Hawaii.
Hawaii lies over 700 miles away from christmas Island and the EMP given off by this bomb wrecked electrical equipment in Hawaii, cutting off street lights, house power, everything.
The result was outstanding, a brand new destructive weapon that 'comes with' a nuclear detonation but could knock out the enemies ability to move thousands of miles away.
Figures suggest that detonating a nuclear bomb at 70,000ft above the centre of the USA will cut power to the whole country including canada.
EMP will destroy everything electrical that is not specially 'hardened' to withstand it. Most things flying can be severely effected as EMP can knock out the Avionics.

OVER-PRESSURE:

Another knock out effect of any nuclear explosion is the pressure it causes. A nuclear detonation creates 'over-pressure' and depending how large, the over-pressure can be several thousand PSi(pounds per Square Inch).  NORAD, ICBM Silos, and Command Bunkers are hardened to withstand an Over-pressure of several thousand 'psi'.
Over-Pressure implodes buildings. It generates so much pressure in the air that it causes buildings to just 'implode' under the tremendous 'weight' exceeding outside. This shatters any building and structure to pieces.
Most US ICBM Silo's are hardened to withstand approximately 2000psi. Command bunkers are more than 2000psi.
When launching a missile at a target, you have to consider how hardened that target is to know what MIRV(Multiple-re-entry Vehicle) to fire.
For a city as a target, the accuracy does not matter for a nuclear warhead, no building in the city is hardened to withstand a certain over-pressure so the MIRV does not have to be accurate as to where it hits....no matter where it hits, aslong as its on the city, its going to cause maximum damage and death.
For Target's such as Silo's or Bunkers, the Accuracy of the MIRV becomes very important. It needs to be 'on' target to make sure the over-pressure exeeds the hardened target's overpressure limit.
ICBM Silo's hardened to 2000psi cannot withstand a direct hit from a nuclear warhead, nor can a command bunker hardened to withstand maybe perhaps 4000psi. The Bunker or Silo is only hardened to withstand a semi-accurate weapon, maybe to within a few hundred metres.
This is where the term 'CEP' comes into the situation.  MIRV's(warheads) have a certain CEP. this stands for Circular Error Probable.
This denotes Accuracy.
In the 60's Russian and American MIRV's had a CEP of a few thousand meters. this means the Warhead would touch down anywhere around the target(in a circle) over thousands of meters away, meaning it was NOT be very accurate and was ONLY good enough for City strikes. This also meant that both the US or Russia could not counter-attack each other's ICBM Silos to stop each other launching more attacks.
Today, the CEP of both countries has come down to a few hundred feet, the American Peacekeeper and Russian SS-20 have a CEP of a few meters!!!!.  Although Russia can counter strike america to stop more warheads being dropped on its soil. America has only 'limited' counter-strike capability for several reasons.
1. The USA has much less Nuclear ICBM's available than that of Russia, even today Russia's Nuclear arsenal is fully ready and has not changed in size.
2. American ICBMs are launched from Silos fixed into the ground. Its bombers can be destroyed either on ground or in the air.
3. A Vast Majority of Russian ICBM's are located on 'relocatable' Trains on a massive rail network with each Train having its own Tunnel as a bunker inside a mountain. Each Train can launch several missiles then relocate to a different position so it can't be counter-attacked.
This, plus the overwhelming amount of warheads russia still has available in a state of readiness(Funds do not matter in russia with ICBM's and money has not effected its ability) is a massive fright to American commanders.
America on the other hand has many SSBN's to launch SLBM . Russia had by far the largest force of SSBNs but sadly, the funds have run out to keep them operational and they have gone 'rusty' in the Naval bases aswell as many of the fleet of surface ships.