php阵列到json编码不起作用

I have a ajax connection to my json.php file and its not working... do you have any idea what is going on? is it my $output variable is it not convertible to json can it be my ajax?! any help will be greatly appreciated. PS: when i click on a city that does not exist.. it does output the $output variable.When i click on a city that doe exist I get nothing. It`s killing me. var_dump($output) {if it is not encoded} is:

    array (size=1)
  0 => 
    array (size=4)
      0 => 
        object(SimpleXMLElement)[9]
      1 => 
        object(SimpleXMLElement)[8]
      2 => 
        object(SimpleXMLElement)[7]
      3 => 
        object(SimpleXMLElement)[10]

json.php file:

<?php

if(isset($_POST['city'])){
    $city = $_POST['city']; //checks if variable city is set if not it will be set as default 
    var_dump($city); 
}else{
    $city = 'New York';


}
//loads data as simple xml
$result = "http://api.wunderground.com/api/KEY/geolookup/conditions/q/ro/$city.xml";
$xml = simplexml_load_file($result);
#echo htmlspecialchars($result, ENT_QUOTES, 'UTF-8');
$place = $xml->location->city; //gets the city name
#var_dump($place);
if(!empty($place)){ //checks if city exits
  foreach($xml->current_observation as $item){
    $current = (string)$item->weather;
    $temperature = (string)$item->temp_c;
    $time = (string)$item->local_time_rfc822;
    $wind = (string)$item->wind_string;
    $humidity = (string)$item->relative_humidity;
    $output[] = array($time, $temperature, $current, $wind); 

}

    }
}else{
    $output = 'No results found, please try a different city.';  //if variable $place is empty it will print this
}

header('Content-Type: application/json; charset=utf-8');
echo json_encode(array('data' => $output),true);
?>

And jQuery file:

 $(document).ready(function() {
    $('li').click(function(){
            var city = $(this).text(); //get the li content as variable city
            $.ajax({

                type : 'POST',      //sending data method
                url : 'json.php',
                data : {city:city}, //data to be sent
                dataType: 'json',
                success : function(data){
                $("#result").html(data);
            }
            });

    });
});

EDIT 1: I have updated my code in such a way that my output is json encoded and equal to

{"data":[["Thu, 24 Sep 2015 02:00:58 +0300","19.3","Clear","From the West at 1.6 MPH Gusting to 2.5 MPH"]]}

I think the problem now is in my AJAX(I am a new user of jQuery) I get no info printed when I Click on a city.

Take a look at the following tutorial: https://lostechies.com/seanbiefeld/2011/10/21/simple-xml-to-json-with-php/

You'll do str_replace and trim then encode the data for the web.

Many Times it occurs when our content of the array is not Encoded. Generally we use UTF-8 Encoding.

So, To Solve this issue you need to add this,

mysqli_set_charset($con, 'utf8');

Just after the connection.