Meteorology 166Meteorology 166SJSU - 2010SJSU - 2010

North American MonsoonNorth American Monsoon

Outline for TodayOutline for Today

• Goals for forecasting portion of course• Monsoon overview• Geography and differential heating• Assign laptops• Lunch?• Forecasting basics• Monsoon forecasting: the tools• Monsoon forecasting: the contest

Goals for Forecasting Portion of CourseGoals for Forecasting Portion of Course

– Gain an understanding of the general circulation associated with various stages and phases of the Monsoon

(Understand this for example: “upper-level disturbances rotating around the periphery of the time-mean warm season southwestern US subtropical anticyclone”)

– Gain an appreciation for Monsoon variability on various time and space scales

– Learn Monsoon terminology– Learn the basic parameters used to track the Monsoon.– Learn how the unique geography in AZ combined with

differential heating contributes to observed patterns of convection

– Gain competency in basic Monsoon forecasting

MonsoonsMonsoons

• South Asian Monsoon– The big one

• North American Monsoon– Not really recognized until the late 70’s that

this was indeed a monsoon circulation– What causes the Monsoon?

North American Monsoon Overview North American Monsoon Overview

North American Monsoon Overview North American Monsoon Overview

• Large Scale Onset– large scale circulation changes occur in July, which

conspire to allow moisture advection into the Desert Southwest

• Compare June and July– Strong diabatic heating of the elevated terrain of the

Sierra Madre and Colorado Plateau causes the time-mean warm season southwestern US subtropical anticyclone to move north

– This allows southeasterly flow to advect tropical moisture into the Desert Southwest (lots of complications, but this is the first order result)

• Some practical examples– Examine the archive to study the behavior of

onset (June vs July 500 mb & IPW..no July!)– Examine the archive to understand how the

temporal and spatial variability of the Monsoon is modulated by changes in large scale circulation, specifically the position of the time-mean warm season southwestern US subtropical anticyclone

North American Monsoon Overview North American Monsoon Overview

Moisture SourcesMoisture Sources

• Gulf of California

• Eastern Tropical Pacific

• Gulf of Mexico

• Sierra Madre

• Southern Plains of the U.S.

Moisture SourcesMoisture Sources

Focus: Northern AZFocus: Northern AZ

• The Monsoon manifests itself differently all over the southwest because of topography. We are going to focus in on Northern Arizona, because that’s where we’ll be most of the time.

• Geography Review– Topo maps, counties, cross section

Synoptic and Mesoscale Features Synoptic and Mesoscale Features Influencing the MonsoonInfluencing the Monsoon

• Easterly Waves

• Gulf Surges

• MCS Outflows

• Upper Level Lows

ReferencesReferences

• See web page, download PDF’s for when the Internet is down or slow.

ExerciseExercise

• In the absence of other distinguishable Monsoon circulation features, or often in concert with them, differential heating of elevated terrain and subsequent convection is an important modulator of Monsoon behavior. We’ll take a few looks at this, but let’s start with a simple example: