ATMO.4350.5350 Hydrology of the Atmosphere Spring 2025 Final Exam Study Guide

Atmospheric Factors Impacting Warm Season Precipitation

  • Atmospheric factors influencing excessive warm season precipitation include:

    • Water vapor

    • Precipitable water

    • Precipitation intensity

    • Precipitation duration

Evaporation, Atmospheric Rivers, and Warm Season Precipitation

  • Examine the connections between evaporation, atmospheric rivers, and their influence on warm season precipitation.

Mesoscale Convective Systems (MCSs)

  • Definition of a mesoscale convective system (MCS): refer to all organized convective systems larger than supercells

    • includes squall lines (line of convective cells), bow echoes

    • supercell: individual thunderstorm with a rotating updraft

  • Methods for identifying MCSs using radar products.

  • Importance of MCSs for precipitation at both weather and climate scales, as discussed in student presentations.

Surface Characteristics and Flooding

  • Discussion of how surface characteristics can potentially contribute to flooding: Low elevation, presence of mountainous topography

  • Soil characteristics

    • persistently dry soil cannot uptake water efficiently

    • Cla heavy soil have low permeability

    • Already waterlogged soils cannot uptake any more water, leading to runoff

    • Snowmelt can exacerbate flooding

Climate vs. Weather

  • Distinguish between climate and weather: Weather is short term patterns in atmospheric, temporal, and precipitation conditions. Climate is long term typical weather patterns of a given area, at least 30 years.

  • Define a climate "normal" versus a climate mean/average:

Tools for Defining Hydroclimate Base State and Variability

  • Identify tools used to define the base state and variability of the hydroclimate.

Drought

  • Definition of drought: A period of abdormally dry weather that lasts long enough to cause hydrological impacts

  • How drought is defined.

  • Drivers of drought: Telecommunications (ENSO), atmo rivers, atmo blocks (Omega, High over Low, Blocking High), synoptic conditions, land atmo interactions, human impacts

    • dry soil reduces evap → less local precip → intensifies drought

  • Changes in drought patterns in a changing climate system, as covered in student presentations.

Pluvial

  • Definition of a pluvial: Period of abnormally high precipitation. Can cause flooding but not all pluvials are floods

  • How a pluvial is defined: On annual scale, 10% greater than annual mean. Monthly scale, 40% greater than monthly mean

    • Can use drought indices to identify pluvial periods

  • Drivers of pluvials

    • Blocking patterns: cause persistent weather conditions. Induces ascent, increase moisture transport, cloud cover, enhances precip

    • Land atmo coupling: Precip recycling and drought intensification/perpetuation

  • Changes in pluvial patterns in a changing climate system.

Precipitation Variability

  • Precipitation variability:

    • Spatially

    • Temporally

  • Impact of features like the Hadley Cell and the Walker Circulation on precipitation variability.

Teleconnections

  • Definition of teleconnections: Casual connection or correlation b/w meteorological or other environmental phenomena which occur a long distance apart - Sir Gilbert Walker

  • Types of teleconnections that occur in the hydroclimate system

    • Pacific Decadal Oscillation (PDO): El Nino like pattern, warm and cool phases based on SST anomalies in the Northeast and tropical Pacific Ocean. Phases last 20-30 eyars

      • Positive: cool SST in interior North Pacific. Warm SST along Pacific coast. Below avg sea level pressure over North Pacific

      • Negative: warm SST anomalies interior North Pacific. Cool SST anomalies along NA coast. Above avg sea level pressure over North Pacific. Currently in neg phase

    • North Atlantic Oscillation (NAO): Based on surface sea level pressure diffs b/w Subtropical High and Subpolar low

      • Positive: reflects below normal heights and pressure across high lats of North Atlantic, central North Atlantic, eastern US and western Europe

      • Negative: opposite pattern of height and pressure anomalies over these regions

      • Both phases associated w/basin wide changes in the intensity and location of North Atlantic jet stream and storm track and precip extending from eastern NA to western and central Europe

    • Arctic Oscillation (AO): Charac by winds circulating counterclockwise around the Arctic around 55 N latitude

      • Positive: ring of strong winds circulating around North Pole confines colder air across polar regions. Stronger jet streams, brings storms to Europe. Stronger tradewinds

      • Negative: Belt of winds becomes weaker and more distorted, allowing more southward penetration of cold arctic airmasses + increased storminess of mid lats. Weaker jet streams

    • Pacific-North American Index (PNA): Appears in all months except June and July, assoc w/Rossby Wave dynamics

    • Atlantic Multidecadal Oscillation (AMO): Long term mode of nat’l variability occurring in NA ocean , 60-80 yrs. Based on avg SST anoms in NA basin, over 0-80N

      • Positive: corresponds w/pos SST anoms over NA, strong anoms in subpolar region and weaker in tropics

    • At times teleconnections can aplify or dampen reach other

      • Example: ENSO and PDO

El Nino, La Nina, and the Southern Oscillation

  • Relationship between El Nino and La Nina and the Southern Oscillation:

    • El Nino is warm phase of ENSO, La Nina cold phase

    • Southern Oscillation Index (SOI) = (stdized pressure Tahiti - stdized pressure Darwin) / monthly stdev

      • Corresponds very well w/changes in ocean temps across eastern tropical Pacific

      • El Nino, air pressure higher in Darwin, Aus = neg SOI

      • La Nina, air pressure lower in Darwin, Aus = pos SOI

  • Identification of El Nino and La Nina on maps or graphs:

    • El Nino: positive SST anomalies along equitorial Pacific, especially central and east Pacific. Heavy rising over Pacific. Sinking motion over Maritime cont and Atlantic. Weak trade winds

    • La Nina: neg SST anomalies along eq Pacific. Heavy rising motion over Maritime and Atlantic. Sinking over east Pacific. Strong trade winds

  • Impact of El Nino and La Nina on precipitation distribution and the reasons behind this impact.

    • El Nino: Warmer in Canada, wetter along Jet stream (in a lower position than normal) passing over southern US, dry in SA, drier in Ohio river valley. More hurricanes in Pacific due to less vertical wind shear. Less hurricanes in Atlantic due to stronger vertical wind shear and trade winds

    • La Nina: Colder in Canada, wetter in NW US and Ohio river valley, drier in southern US. Fewer hurricanes in Pacific due stronger vertical wind shear. More hurricanes in Atlantic due to weaker vertical wind shear and trade winds

    • Wind shear: Difference in wind speed and/or direction over a relatively short distance in the atmosphere

Madden-Julien Oscillation and Monsoons

  • Definition of the Madden-Julien Oscillation: 30-60 day oscillation of eastward moving tropical rainfall. Most active over Indian and Pacific oceans. A[[ears 40-50% of the time

    • Influences monsoons

  • Definition of a monsoon: As ITCZ swings north during summer, brings monsoon rains to Kozhikode India. As ITCZ swings south during winter, brings monsoons to Darwin Aus.

    • Monsons occur b/w seasonal ITCZ positions

Climate Change Impacts on the Hydroclimate

  • Types of impacts a changing climate can have on the hydroclimate from local to global scales and the underlying reasons.

    • Oceans will warm, increased precip variability and increased precip extremes.