Error while merging data in Pandas

import numpy as np
import pandas aspd

series=pd.Series('1/1', '1/2', '1/3', '1/4', '1/5', '1/6', '1/7',
                '1/8', '1/9', '1/10', '1/11', '1/12', '1/13', '1/14', name = 'date')
df1 = pd.DataFrame({'Date':['1/1', '1/2', '1/3', '1/4', '1/6', '1/7', ],
                    "Weather": ["Clear", "Cloudy", "Cloudy", "Cloudy", "Cloudy", "Cloudy"]})
df2 = pd.DataFrame({ 'Date': ['1/8', '1/14', '1/9', '1/12', '1/11',] ,
                    Weather: ["rain", "clear", "clear", "rain", "clear"]})

# Connecting the two DataFrames vertically
merge_df1 = np.concatenate([df1,df2],axis=0)  
print(f'Connected:\n{merge_df1}\n')

# Left external merge_df1 with date key to series
merge_df2 = pd.merge(series, merge_df1, on = 'date', how = 'left')
print(f'left external connection with date key:\n{merge_df2}\n')