slide1 n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
monsoons: a brief introduction PowerPoint Presentation
Download Presentation
monsoons: a brief introduction

Loading in 2 Seconds...

play fullscreen
1 / 50

monsoons: a brief introduction - PowerPoint PPT Presentation


  • 136 Views
  • Uploaded on

monsoons: a brief introduction. Not quite an ordinary day in monsoon land!. A. C. D. B. what is a monsoon. Monsoon is a climatological feature covering roughly half the tropics (1/4 of the global surface)

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'monsoons: a brief introduction' - daniel_millan


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

monsoons:

a brief introduction

what is a monsoon
what is a monsoon
  • Monsoon is a climatological feature covering roughly half the tropics (1/4 of the global surface)
  • Strictly, a system where the winds and precipitation reverses (summer rain, winter dry)
  • Sufficiently reproducible to host the most successful agricultural system (5000 years of success)
  • Host 65% of the world’s population
  • Small changes in year-to-year climate can be catastrophic
slide7

a description of the

south asian

monsoon

slide8

Halley (of comet fame) was the first to describe monsoon

and attribute differential heating between

land and ocean as the cause

slide9

mean august and january precipitation

from MSU satellite (mm/day)

slide10

Monsoon regions are the

largest region where precipitation exceeds evaporation.

This excess water must come from somewhere …

slide11

…….which defines the scale of the monsoon.

The monsoon is intrinsically inter-hemispheric with the

winter hemisphere being the source of moisture

slide12

monsoon of the americas

  • There are three major
  • monsoon systems:
  • Asian-Australian
  • African
  • Americas
  • Each has its own
  • characteristics and
  • differences but each is
  • characterized by summer
  • rains and seasonal wind-
  • reversals

Rainfall

Surface pressure

trough

slide14

Annual cycle of radiative temperature

“Cold” areas denote

Cloudiness and precipit-

ation. “Warm” areas

show clear regions.

Note that there are

large gradients both

east-west and north-

south indicating that

the monsoon is driven

by heating gradients

in both directions.

slide18

Climatological precipitation over South-Asia/Indian Ocean

  • Three maxima (Bay of Bengal, east coast India, and south of equator)
  • Equatorial maximum indicates importance of intraseasonal oscillations
slide20

variability of the

south asian monsoon

time scales of monsoon variability
Time Scales of Monsoon Variability
  • Interannual variability: Variations on the annual cycle of the monsoon producing anomalously wet or dry years. Generally influenced by sea-surface temperature variations associated with ENSO or inherent variability in the Indian Ocean.
  • Monsoon Weather: Weather events such as monsoon lows and depressions, tropical cyclones (hurricanes) and etc. Produce short-lived local flooding (or drought), erosion, high winds and etc.
  • Intraseasonal Variability: “Envelopes”: or clusters of weather events leading to 20-40 day droughts or flood periods. Most difficult to forecast but perhaps the most important of all time scales for economic and agricultural sectors.
slide22

El Nino influences Indian Ocean

Changes SST, sea surface slope and regions of maximum precipitation

However, other factors are also important …..

slide23

Indian Ocean Zonal Mode:

Inherent mode of Indian Ocean invoked by outside

perturbations including ENSO

Time series of E-W

SST gradient

frequency

spectra

slide24

Sea-level variations associated with IOZM:

Positive phase: warm SST WIO, low SSH EIO

Negative phase: warm SST EIO, high SSH EIO

slide25

Intraseasonal variability of the monsoon:

Active and break periods of the Summer South Asian Monsoon

The summer monsoon is divided into distinct periods of wet and dry.

When it is dry on the plains, it is wet in the foothills of the Himalaya, just as

occurred this year. The result was Nepal, Assam and Bangladesh floods, the latter due to

strong Brahmaputra discharge.

slide26

Intraseasonal Modes: Impact on Rainfall

  • Intraseasonal variability imposes a distinct form to precipitation.
  • Histograms of precipitation, shown for 9 years show distinct wet periods with lulls in between.
  • Lower diagram shows the distinct spatial character

Precipitation histograms in

central India

slide27

Forecasting monsoon variability

on 20-30 day time scales:

Taking advantage of a new

understanding of monsoon dynamics

Peter J. Webster

Georgia Institute of Technology

slide30

Differences between active and break periods of the monsoon

Note distinct bands of precipitation excess or deficit. During breaks, there is a 20-40 day drought across plains of India and excess rain over southern, northern and north-eastern regions

slide31

Latitude-time section of OLR along 90E: 1995

Active phases of the monsoon commence near the equator and

propagate northward (and southward) across South Asia.

Active

phase

northward

propagation

commence

active phase

physical ingredients for a monsoon
Physical Ingredients for a Monsoon
  • Land-Sea differences: land and water have different heating capacities & water can store more heat because it is a fluid and can mix heat down for future release
  • Planetary rotation: introduces swirl and much stronger winds
  • Moisture: water vapor, collected over oceans through evaporation, condenses over land and marginal seas releasing vast quantities of heat
  • Orography: acts as elevated heat source which intensifies flow & also ducts flow.
slide39

Impacts of Elevated Heat Sources

Note the dominating effect of the Himalayas

slide40

Changes in Tropospheric Temperature in Monsoon Region

Temperature changes much larger over Himalayas than elsewhere.

slide41

Impact of East African Highlands

Arguably, without the Himalayas & the East African

Highlands, South Asia would be a desert like North Africa

slide42

Impact of Rotation:

increases in intensity and scale

slide43

Impact of anomalous monsoon seasons

Strong and weak monsoons invoke different

upwelling effects creating SST gradients. Then …….

slide44

Explanation of why there is an IOZM with

approximately biennial period

Atmosphere responds

to SST anomaly associated

with strong/weak

monsoon

Ocean responds to

anomalous winds producing

ocean dynamic modes

Anomalous SST produces

a monsoon of opposite

anomaly which wipes out

IOZM

slide48

predictability of the

south asian monsoon