How to Make It
Cook sugar and water in a saucepan over medium-high, stirring occasionally, until sugar dissolves and mixture comes to a boil, 2 to 3 minutes. Boil, stirring occasionally, 2 minutes. Remove syrup from heat; let cool about 30 minutes. Stir together cooled syrup, cranberry juice, and grenadine until incorporated. Cover and refrigerate until well chilled, 4 hours or overnight.
Fill 8 tall 12-ounce glasses with ice cubes, and pour 1⁄3 cup cranberry-syrup mixture in each glass. Slowly pour about 1/2 cup tangerine juice over the back side of a spoon into each glass. Do not stir. Slowly pour 1/4 cup chilled sparkling water into each glass. Garnish with tangerine slices.