# Presentation: 388137

## Climate and the Global Water Cycle Using Satellite Data

**John Bates, Chief**
**Remote Sensing Applications Division**
**National Climatic Data Center**
**NOAA NESDIS**

## Outline

**What is Climate?**
**The Global Water Cycle**
**Remote Sensing of Atmospheric Water Variables**
**Scales of Water Cycle Variability**
**Climate Feedbacks**
**Conclusions**

## 1.  What is Climate?

**WMO Climate Defined as 30-year average on 10 year boundaries**
**‘****Climate is what you expect, weather is what you get’**
**Climate scales of variability include:**
- Intraseasonal
- Seasonal
- Interannual
- Decadal

## 2.  The Water Cycle

## 3.  Remote Sensing of Atmospheric Water

**Water Vapor**
**Clouds**
**Precipitation**

## Atmospheric Water Vapor

**The most important greenhouse gas**
**Lower tropospheric water vapor – flux is responsible for precipitation; strongly interacts with aerosol particles; strongly interacts with stratus clouds**
**Upper tropospheric water vapor – feedback may significantly increase warming; strongly interacts with cirrus clouds**
**Lower stratospheric water vapor – large chemical and radiative impacts**

## Satellite Remote Sensing of Water Vapor

**One of many water vapor absorption bands are sensed in the visible, infrared, or microwave portion of the spectrum**
**Looking down from space, the center of the bands are opaque – hence we can sense a layer of water vapor high in the atmosphere**
**Conversely, low absorption at the edge, or wing, of a band allows us to sense a layer lower in the atmosphere**

## Upper Troposphere Water Vapor Image from GOES Shows Circulation Features

## Satellite Remote Sensing of Clouds

**In the visible portion of the spectrum, clouds reflect sunlight.  The amount reflected is proportional to the optical depth of the cloud**
**In the infrared portion of the spectrum, clouds emit at the cloud top temperature.  This is usually colder than the surface.**
**In the microwave portion of the spectrum, liquid clouds emit relative the background and ice clouds scatter**

## Remote Sensing of Precipitation

**Using infrared data, cold (high) cloud tops are used in the tropics and summer hemisphere as a proxy for instantaneous rain rate**
**Microwave data penetrate the clouds to observe the emission from raindrops and, hence, are a more direct measure of rain rate**

## 4.  Scales of Water Cycle Variability

**Diurnal – the daily cycle**
**Intraseasonal – 10 days to 6 weeks**
**Seasonal – the four seasons**
**Interannual – Year-to-year variability usually associated with extremes in temperature and precipitation (e.g., El Ni****ño)**
**Decadal – Multiyear variability of extremes in temperature and precipitation**

## Diurnal Changes in Visible Cloud Cover 

## Intraseasonal Variability in Tropical Deep Convection

**Identify only the coldest infrared cloud tops in the tropics associated with thunderstorms**
**Reduce 3 dimensions to 2 by averaging latitudes from 7N-7S to obtain a time-space diagram**
**The resulting diagram shows tropical wave modes of characteristic speeds and directions: Madden-Julian oscillations (blue), Kelvin waves (green), and equatorial Rossby waves (black)**

## Seasonal Cycle of Upper Level Water Vapor and Clouds (Outgoing Longwave Radiation-OLR) Shows March of Monsoon-Desert System

## Annual Mean of Global Precipitation

**Highest values are found in the tropical monsoons, inter-tropical convergence zones, and mid-latitude storm tracks**
**Lowest values are found in the subtropical deserts**

## Interannual Variability – El Niño

**El Ni****ño is a coupled ocean-atmosphere phenomena**
**Sea surface temperatures warm in the central Pacific**
**Deep convection and precipitation moves from the western Pacific to the central Pacific**
**Upper level water vapor shows that the shift in convection is accompanied by a global teleconnection pattern**

## Interannual Variability – El NiñoImpacts in North America

**The shift of deep convection to the central Pacific (shaded region on equator) is accompanied by a wavetrain to the northeast**
**An alternating pattern of Hi’s and Low’s results**
**The polar jet stream (arrows) is amplified bringing warm air north into western North America and cold air into eastern North America**
**A strong subtropical jet stream brings moisture-laden storms into the southeastern U.S. and eastern seaboard**

## 5.  Climate Feedbacks and Climate Change

**In an attempt to separate the natural and anthropogenic effects of climate change, the concept of a feedback mechanism has arisen.  For example, given the magnitude of a man-made greenhouse gas such as CO2, the relationship between the magnitude of this anthropogenic climate forcing and the magnitude of the climate change response in a general circulation model, perhaps a global warming of 2********C, defines the climate sensitivity.  Any process that changes the sensitivity of the climate response to the imposed anthropogenic forcing is called a feedback mechanism **

## Water Vapor Feedback

**Assume (most models work this way) that the relative humidity remains constant as man-made greenhouse gasses initially warm the atmosphere and ocean**
**More moisture is evaporated from the surface and the total amount of water in the atmosphere increases**
**The increased water vapor traps more outgoing radiation thereby further increasing global temperatures**
**This is a huge effect – increasing the man-made warming by 2-3 times**

## Expected Decadal Scale Variations of Water Vapor Due to Anthropogenic Influences – Boundary Layer

**Boundary layer water vapor responds to surface temperature with fixed relative humidity and thus follows Clausius-Clapeyron equation**
**There is good agreement between observations and models**
**Radiative effect is small, but effect on precipitation and circulation is uncertain**
**Model estimate increase of 1%/decade from 1965-2000**

## Upper Troposphere Water Vapor Feedback – Satellite Observations

**Retrieve upper tropospheric humidity (UTH) or layer specific humidity (gm/km)**
**Issues with cloud and intercalibration of many instruments over time**
**Global trends small but significant regional trends related to circulation changes not simply thermodynamics**

## Cloud Feedbacks – Stratus Clouds

**In the visible, stratus clouds are highly reflective of incoming solar radiation**
**In the infrared, stratus clouds are low level clouds that emit energy to space at nearly the same temperature as the surface**
**If stratus clouds increase, more incoming solar radiation is reflected back into space with no change in Earth emitted energy**
**The net result is a negative feedback or cooling**

## Why do extreme rain events increase in the models?

## Slide 24