METR112- Earth Hydrological Cycle Professor Menglin Jin Department of Meteorology, San Jose State University

Definitions Insolation – Solstice – Equinox –

Definitions Insolation – Solstice – Equinox – Incoming solar radiation day of the year when the sun shines directly over 23.5°S or 23.5°N the time of the sun's passing a solstice which occurs about June 22 to begin summer in the northern hemisphere and about December 22 to begin winter in the northern hemisphere days of the year when the sun shines directly over the equator either of the two times each year (as about March 21 and September 23) when the sun crosses the equator and day and night are everywhere on earth of approximately equal length

A diagram shows the position of Earth at the beginning of each season in the Northern Hemisphere.

The seasons are marked by solstices and equinoxes — astronomical terms that relate to Earth’s tilt.

Sun angle

Sun angle (2)

High sun Low sun

What influences incoming solar energy? The Sun’s angle of incidence: – Lower sun angle, – Higher sun angle, Length of time the Sun shines each day: – Summer season, – Winter season,

What influences incoming solar energy? The Sun’s angle of incidence: – Lower sun angle, – Higher sun angle, Length of time the Sun shines each day: – Summer season, – Winter season, more incoming energy less incoming energy less sun hours more sun hours

Why do we have seasons?

The major climatic groups are based on patterns of average precipitation, average temperature, and the natural vegetation found on Earth. This map depicts the world distribution of climate types based on the classification originally invented by Wladimir (Peter) Köppen in 1900.

What is hydrological cycle The hydrological cycle. Estimates of the main water reservoirs, given in plain font in 103 km3, and the flow of moisture through the system, given in slant font in103 km3/yr, equivalent to Exagrams (1018 g) per year. (Trenberth et al. 2006a). Major components of hydrological cycle Precipitation Evaporation & evapotranspiration Atmospheric transport Runoff and ground water flow Water reservoir (ocean, lake, glacier, soil water, etc.)

Precipitation: Rain gauge Standard rain gauge used in observing precipitation

Precipitation: Radar & satellite Radar detecting the cloud by collecting reflected microwaves Satellite observe earth in microwave or infrared channels from space and estimate precipitation using retrieval techniques

Precipitation: Observations show great spatial variation Unit: in centimeter (cm)

Precipitation: Observations show decadal variation of precipitation change

Precipitation: Observations show decadal variation of precipitation change alternative

World patterns of thunderstorm frequency Thunderstorms occur most often in the tropical latitudes over land, where the air is most likely to heat quickly and form strong updrafts. Encyclopædia Britannica, Inc.

Precipitation: IPCC AR4 Changes are not spatially uniform General increase of precipitation in most areas in mid- and high latitude, Decreased precipitation in the Western, Southern Africa and Sahel With mixed signs in Eurasia Precipitation increases in Northwest India

Source: IPCC AR4 - Chapter 3, Adopted from: Richard CJ Somerville, APRU World Institute Workshop, 2007 Precipitation variation is complex over the land Increases Decreases

Precipitation: Changes in zonal averaged precipitation Positive anomalies in tropics, negative anomalies in extra-tropics

Precipitation: Changes in seasonal variations vary spatially (Chen et al. 2002)

Precipitation: Intensified extreme precipitation in mid-latitudes More wet days (upper 5%) and heavy precipitation (upper 5% percentile) in US and most Europe Increased possibility of intense precipitation in most extratropical regions Decrease of heavy precipitation in central Africa, south east Asia, west Europe and west Australia IPCC AR4

Average date of onset of the summer monsoon across different regions of Asia

Figure Annual values of the East Asia summer monsoon index derived from MSLP gradients between land and ocean in the East Asia region. The definition of the index is based on Guo et al. (2003) but was recalculated based on the HadSLP2 (Allan and Ansell, 2006) data set. The smooth black curve shows decadal variations. Significant decrease in East Asian Monsoon index since 1976/77 climate shift East Asian summer monsoon index: Sum of mean sea level pressure differences between 110 o and 160 o E for 20 o to 50 o N with 5 o difference.

Figure Time series of northern Australian (north of 26°S) wet season (October–April) rainfall (mm) from 1900/1901 to 2004/2005. The individual bar corresponds to the January of the summer season (e.g., 1990 is the summer of 1989/1990). The smooth black curve shows decadal variations. Data from the Australian Bureau of Meteorology. Current global climate a boon for Australian Monsoon? Statistically significant rainfall show up in predominantly northern parts of Australia Primarily due to additional southern Australian land heat up while no/cold Anomalous changes in oceans

Figure Time series of Sahel (10ºN –20ºN, 18ºW–20ºE) regional rainfall (April–October) from 1920 to 2003 derived from gridding normalised station anomalies and then averaging using area weighting (adapted from Dai et al., 2004a). The smooth black curve shows decadal variations. African Monsoon shows clear signal due to changes in ENSO Both tropical Pacific and Atlantic SSTs have effects on African Monsoon Many studies show deforestation would amplify draught signals

Evaporation (evapotranspiration) observations are limited Pan evaporation observes the potential evaporation Bowen ratio system observes evapotranspiration using energy balance

Global distribution of mean annual evaporation (in centimetres)

(Trenberth and Stepaniak 2003) Would distribution of annual averaged Latent heat flux from 1979 to 2001 from reanalysis

Trend of pan evaporation in US from 1950 to 2001 annual Warm season Blue (red) is decrease (increase), circle is sig at 90% Hobbins and Ramirez 2004

ERA15 (solid curve), COADS (dashed), CE91-95 (dotted curve) Zonally-averaged annual evaporation shows an M- shaped distribution 15-year ECMWF reanalysis Garnier et al. 2000

One way of measuring soil moisture: gravimetric method Two types of augers used for gravimetric soil moisture observations, sitting on a neutron probe. The one on the left is pounded into the ground and used when the ground is frozen. The one on the right is twisted into the ground Robot et al. 1999

soils.usda.gov/use/worldsoils/mapindex/smr.html Major soil moisture climate regimes

Seasonal cycles of soil moisture for various areas Robot et al. 1999

The most recent monthly averaged soil moisture for US

Decreased spring snow covered area in Northern America Statistically significant decline in annual SCA for 2.7x10^4 km^2 SCA maximum shift from February to January and earlier snow melt Melting season shift two weeks earlier from 1972 to 2002 Snow:

Snow cover anomalies in from 1966 to 2006 for northern America

Snow cover anomalies in from 1966 to 2006 for Eurasia

Arctic sea ice extent decreases in the last 20 years annual: -2.7%/dec Sea ice: The annual sea ice extent decrease steadily from 1980

summer: -7.4%/dec Most remarkable change is the summer sea ice diminish, in which the interannual to decadal variability is associated with the variability of atmospheric circulation Summer sea ice decrease in tremendous in the last 20 years

Glacier and ice cap mass loss in response to 1970 warming (Science basis, Chap.4, Fig.4.15) Strong negative specific mess balances in Patagonia, Alaska after mid 90s, cumulative balance equivalent to 10m of water (11m of ice) Total mass loss are contributed mainly from Alaska (0.24 mm/yr of SLE), Arctic (0.19 mm/yr of SLE) and Asia high mountains (0.1 mm/yr of SLE) Glacier:

Muir glacier ， Alaska

Decreased ice extent in Kilimanjaro

Increasing melting near the coast overwrites the thickening in the central during the last 10 years and a recent acceleration in overall shrinkage Ice sheet mass loss explains the sea level rise over the last 10 years: Antarctica to 0.55 mm/yr from 1993 to 2003 Melting of ice sheets in Greenland and Antarctic Ice sheet:

Aggressive retreat of Antarctica peninsula ice shelf

Melting of ice sheets in Greenland and Antarctic Ice sheet: Ice sheet mass loss explains the sea level rise over the last 10 years: Greenland: 0.14 to 0.28 mm/yr SLE from 1993 to 2003

Greenland melt extent seeing from satellite 2005 summer ice extent set a record during 27-year period also shows a especially long melting season (until late Sep) compared to previous years according to Steffen et al. 2004, Hanna et al. 2005

Greenland melt area during summer time increases from 1979 to 2005

What could happen in future: IPCC 21 century model projections

Continuous sea ice decrease in 20 th and 21 st centuries in multi-model simulation

Intensified precipitation intensity in 21 st century

Shrinking of Greenland ice-sheet in a warmer climate Evolution of Greenland surface elevation and ice sheet volume versus time in the experiment of Ridley et al. (2005) with the UKMO-HadCM3 AOGCM coupled to the Greenland Ice Sheet model of Huybrechts and De Wolde (1999) under a climate of constant quadrupled pre-industrial atmospheric CO 2.