Зимой сухость воздуха мешает мне спокойно спать.

Зимой is the instrumental singular form of зима.

In Russian, some time expressions use the instrumental case to mean in/during a season:

• зимой = in winter
• летом = in summer
• осенью = in autumn
• весной = in spring

So Зимой here means in winter or during the winter.

Сухость воздуха literally means the dryness of the air.

This uses:

• сухость = dryness
• воздуха = of the air

A learner may expect сухой воздух = dry air, and that is also correct Russian. But the sentence chooses the noun сухость to focus on the condition/quality itself, not just the air as an object.

So:

• сухой воздух мешает мне спать = dry air prevents me from sleeping / interferes with my sleep
• сухость воздуха мешает мне спать = the dryness of the air interferes with my sleep

The second sounds a bit more abstract and emphasizes dryness as the problem.

Because сухость is a noun meaning dryness, and Russian often uses the genitive after nouns to show what something is a quality/state/property of.

So:

• сухость воздуха = dryness of the air
• цвет дома = color of the house
• шум города = noise of the city

The dictionary form is воздух, but after сухость it becomes воздуха.

The verb мешать means to hinder, disturb, get in the way, interfere.

Its common pattern is:

• что/кто мешает кому (делать что-то)
  = something/someone prevents or interferes with someone (from doing something)

In this sentence:

• сухость воздуха = the thing causing the problem
• мешает = interferes / prevents
• мне = to me
• спокойно спать = sleep peacefully

So мне is in the dative case, because мешать takes the person affected in the dative.

Compare:

• Шум мешает мне работать. = Noise interferes with my working.
• Ты мне мешаешь. = You’re disturbing me / getting in my way.

Because мешать does not take a direct object here. It takes the affected person in the dative case.

So:

• мне = to me
• тебе = to you
• ему/ей = to him/her

This is just part of the verb’s grammar:

• Это мешает мне спать. = This prevents me from sleeping.
• Свет мешает ребёнку спать. = The light prevents the child from sleeping.

Using меня would be incorrect in this structure.

Because it describes how the person sleeps.

• спокойный = calm, peaceful, quiet (adjective)
• спокойно = calmly, peacefully (adverb)

Since it modifies the verb спать (to sleep), Russian uses the adverb:

• спокойно спать = to sleep peacefully / to sleep soundly

Compare:

• спокойный ребёнок = a calm child
• ребёнок спокойно спит = the child is sleeping peacefully

Because Russian infinitives do not need a separate word like English to. The infinitive form itself already includes that meaning.

So:

• спать = to sleep
• работать = to work
• читать = to read

After мешать, Russian often uses an infinitive directly:

• мешает мне спать = prevents me from sleeping / interferes with my sleeping
• мешает ему работать = prevents him from working

There is no extra word needed before спать.

It can suggest either, depending on context.

Мешать often means:

• to interfere with
• to disturb
• to get in the way of
• to make difficult

So in this sentence, it does not necessarily mean total impossibility. It often means that the dryness disturbs sleep or makes peaceful sleep difficult.

That is why translations might vary:

• The dryness of the air prevents me from sleeping peacefully
• The dry air makes it hard for me to sleep peacefully
• The dryness of the air interferes with my sleep

Yes, Russian word order is flexible.

This order is natural because it starts with the time setting:

• Зимой = in winter

Then it gives the subject:

• сухость воздуха = the dryness of the air

Then the verb and the rest:

• мешает мне спокойно спать = interferes with my sleeping peacefully

You could also say:

• Сухость воздуха зимой мешает мне спокойно спать.
• Мне зимой мешает спокойно спать сухость воздуха.

But these versions shift emphasis slightly. The original is straightforward and neutral: first the season, then the problem.

Yes, that is grammatical.

That version puts мне earlier and leaves сухость воздуха for the end, which can make the cause sound more emphasized or more like new information.

Compare:

• Зимой сухость воздуха мешает мне спокойно спать.
  Neutral, clear statement.

• Зимой мне мешает спокойно спать сухость воздуха.
  More emphasis on what it is that interferes with me.

Russian often moves words around for emphasis, theme-rheme structure, or style.

Yes, it is very natural.

Спокойно спать means:

• to sleep peacefully
• to sleep calmly
• to sleep without disturbance

It is common both literally and sometimes figuratively.

Examples:

• Я хочу спокойно спать. = I want to sleep peacefully.
• Ребёнок всю ночь спокойно спал. = The child slept peacefully all night.
• После этого я не могу спокойно спать. = After that, I can’t sleep peacefully.

So in your sentence, this phrase sounds normal and idiomatic.

Yes, it would work, but the tone is a little different.

• мешает мне спокойно спать = interferes with my peaceful sleep / makes it hard for me to sleep peacefully
• не даёт мне спокойно спать = literally doesn’t let me sleep peacefully

The second version often sounds a bit stronger or more vivid.

Compare:

• Зимой сухость воздуха мешает мне спокойно спать.
  More neutral.

• Зимой сухость воздуха не даёт мне спокойно спать.
  More emphatic: the dryness really won’t let me sleep.

Both are correct.

Yes. Мешает is present tense, 3rd person singular, from мешать.

Russian present tense is often used for:

• something happening now
• a general fact
• a habitual/repeated situation

Here it expresses a general recurring fact:

• In winter, the dryness of the air interferes with my sleep.

So even though it is present tense grammatically, in English it may sound like a habitual statement rather than something happening only at this exact moment.