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All atmospheric circulation models that accurately predict jet stream anomalies incorporate data on sudden stratospheric warmings (SSWs). Furthermore, any circulation model that incorporates data on SSWs must account for mesospheric wind shear, unless it relies strictly on historical tropospheric temperature gradients. Interestingly, while most atmospheric circulation models developed by the Coriolis Institute incorporate data on SSWs, none of the models developed by the Coriolis Institute account for mesospheric wind shear.

Based on the statements above, which one of the following must also be true?

  1. A
    The total number of atmospheric circulation models that rely strictly on historical tropospheric temperature gradients is greater than the number that account for mesospheric wind shear.
  2. B
    Any atmospheric circulation model that accounts for mesospheric wind shear can accurately predict jet stream anomalies.
  3. Most atmospheric circulation models developed by the Coriolis Institute rely strictly on historical tropospheric temperature gradients.Answer
  4. D
    If an atmospheric circulation model does not accurately predict jet stream anomalies, it does not incorporate data on sudden stratospheric warmings.
  5. E
    Most atmospheric circulation models that incorporate data on sudden stratospheric warmings were developed by the Coriolis Institute.

Answer

Most atmospheric circulation models developed by the Coriolis Institute rely strictly on historical tropospheric temperature gradients.
The stimulus establishes that if a model incorporates SSW data, it must do at least one of two things: account for mesospheric wind shear or rely strictly on historical tropospheric temperature gradients. We are told that most Coriolis Institute models incorporate SSW data, which means this 'majority group' of models is subject to the rule. Since we are also told that NO Coriolis models account for mesospheric wind shear, this majority group cannot fulfill that half of the requirement. Therefore, to satisfy the rule, every model in this majority group must rely strictly on historical tropospheric temperature gradients. Thus, it must be true that most Coriolis models rely strictly on historical gradients.

Step-by-Step Solution

1
Translate the first premise into formal logic.
Accurately predict jet stream -> Incorporate SSW data.
This establishes the necessary condition for accurate jet stream prediction.
2
Translate the second premise (the 'unless' statement) into formal logic.
Incorporate SSW data -> Account for mesospheric wind shear OR Rely strictly on historical gradients.
In conditional logic, 'unless' indicates a necessary alternative; if the first condition isn't met, the second must be.
3
Map the specific characteristics of Coriolis Institute models.
Most Coriolis models -> Incorporate SSW data. No Coriolis models -> Account for mesospheric wind shear.
This applies the general rules to a specific subset of models mentioned in the stimulus.
4
Synthesize the rules to deduce the inevitable conclusion.
The majority of Coriolis models that incorporate SSW data MUST rely strictly on historical gradients, because they cannot fulfill the other half of the 'unless' condition.
Combining a disjunctive necessary condition (A or B) with the negation of one element (not A) forces the remaining element (must be B) to be true.

Key Concept

Conditional Logic with Quantifiers and 'Unless' Formulation
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