What Is Specific Humidity?

Specific humidity refers to the ratio of the mass of water vapor to the total mass of air (water vapor mass plus dry air mass) in a mass of wet air. If there is no mass exchange between the humid air and the outside world and no phase change, the specific humidity remains unchanged. With g / g or g / kg as unit, usually the specific humidity in the atmosphere is less than 40g / kg, which is an indicator of the atmospheric water vapor condition.

In a ball

The specific humidity calculation formula is as follows:

In the formula, m _w is the mass of water vapor in the wet air mass; m _d is the mass of dry air in the wet air mass. From this formula and the gas state equation can be derived

Note that in the formula

Specific Humidity Global

IPCCAR4 (2007) summarized the research results of global high-altitude water vapor changes, and pointed out that since the 1970s, the global atmospheric water vapor in the lower troposphere has shown an upward trend, but there are obvious regional differences. Among them, the northern hemisphere and the ocean have obvious upward trends; Humidity has no obvious trend, but the rising trend of specific humidity is more obvious, which is consistent with the global increase in tropospheric temperature; stratospheric water vapor has a significant upward trend since the 1950s. The lower layer of the troposphere over the ocean has experienced a large variability in the past 20 years. From 1988 to 2004, the upward trend of water vapor over the ocean was 1.2% (10a) ¹ . ^[2]

Specific wet China

In China, more than 90% of the water vapor in the upper atmosphere concentrates in the middle and lower tropospheres. The specific humidity decreases rapidly with height. The main factor.

From 1958 to 2005, the specific humidity in the lower layer of the troposphere tended to rise, and in the lower layers of the troposphere, the upper layer and the lower stratosphere tended to decrease. From 1958 to 2005, the specific humidity in the lower layer of the troposphere showed an upward trend. Compared with the whole period, the changes in the middle layer of the troposphere show a trend of north-up and south-down. Inter-decadal changes show that the characteristics of the high-altitude atmospheric specific humidity wet, dry, and wet are basically synchronized with the temperature warm, cold, and warm. The high-altitude temperature is an important factor affecting the high-altitude specific humidity .

Regional differences show that the specific humidity rise is most pronounced in the northwest and middle troposphere, and the rise in the Yangtze River Basin and South China is smaller. Seasonal differences show that the increase in specific humidity in the lower troposphere from 1958 to 2005 mainly occurred in summer and winter, and the specific humidity increased in each season from 1979 to 2005, with the most obvious upward trend in summer.

After the strong ENSO warm (cold) event, the troposphere specific humidity in China increased (decreased), and the volcanic eruption caused the troposphere specific humidity in China to decrease. ^[3]