将JavaScript变量分配给同一页面上的PHP变量

我有两个下拉列表，第二个将根据第一个下拉列表中选择的值填充。我能够填充数据库中的第一个下拉列表。为了填充第二个下拉列表，我通过记录集启动了一个选择查询。但我无法实现我的目标。这是我的代码

<?php require_once('../Connections/finalkms.php'); 

mysql_select_db($database_finalkms, $finalkms);
$query_getzones = "SELECT distinct Zone FROM asset";
$getzones = mysql_query($query_getzones, $finalkms) or die(mysql_error());
$row_getzones = mysql_fetch_assoc($getzones);
$totalRows_getzones = mysql_num_rows($getzones);
$zone=$_GET['zonehide'];
$query_getcountry = "SELECT distinct CountryCode FROM asset where Zone='.$zone.'";
$getcountry = mysql_query($query_getcountry, $finalkms) or die(mysql_error());
$row_getcountry = mysql_fetch_assoc($getcountry);
$totalRows_getcountry = mysql_num_rows($getcountry);
?>
<script>
function getgraphs()
{
    var zone=document.getElementById('zone').value;
    document.getElementById('zonehide').value=zone;
    alert(zone);
    if(zone == 'SEA')
    {
        alert("hello");
        document.getElementById('countrysea').display='block';
    }

}
</script>

<input name="hdn" id="zonehide" type="hidden" value="<?php echo "<script>document.getElementById('zonehide').value;</script>";?>"/>
Zone:<select id="zone" onChange="getgraphs()">
<?php do { ?>
<option value="<?php echo $row_getzones['Zone']; ?>"><?php echo $row_getzones['Zone']; ?></option>
 <?php } while ($row_getzones = mysql_fetch_assoc($getzones)); ?>
</select>
Country:<select id="countrysea">
<?php do { ?>
<option value="<?php echo $row_getcountry['CountryCode']; ?>"><?php echo $row_getcountry['CountryCode']; ?></option>
 <?php } while ($row_getcountry = mysql_fetch_assoc($getcountry)); ?>
</select>
</select>

有什么想法吗？