# Presentation: 153137

## NAME 2004 Preliminary Scientific Results

- An Assessment Based on Analysis of Field Observations

## General Considerations, Caveats

- Some results are confirmatory of previous studies, but provide greater detail and better insight into physical processes

- Some results are genuinely new

- This is a review of status as of Fall 2005; some datasets are still coming out, much more work yet to be done

- Full impact of NAME 2004 will not be realized until *integration* of analysis and modeling studies

- SWG should promote collaborative studies among groups through workshops and small meetings

- SWG should identify and promote advertisement of key, new scientific findings (e.g., CLIVAR Exchanges, etc.)

## NAME IOPs, P-3 Missions

- 1

- 10

- 20

- 30

***July***

- ●

- ●

- ●

- ●

- ●

- ●

- ●

***August***

- 1

- 10

- 20

- ●

- ●

**TC, Gulf Surge**

**Monsoon Onset**

**Normal Monsoon**

**Suppressed Monsoon**

**Moisture Flux, Tropical Jet, MCS**

**Tropical Wave, MCS**

**Inverted Trough, MCS, Gulf Surge**

**Tropical Wave, Backdoor Cold Front**

**IOPs**

**● ****Moisture Flux**

**● ****Surge Genesis**

**● ****LLJ**

- ●

**● ****Sea Breeze/Moisture Flux**

**P-3 Missions**

## Precipitation Characteristics

-   Two prominent precipitation regimes observed in vicinity of S-Pol radar: “undisturbed” – convection forms over high terrain of SMO and moves westward at ~7 m s-1, large CIN; “disturbed” – convection is longer-lived, extends farther west, is more organized, and moves from S to N along SMO at ~10 m s-1; CIN is reduced (Ahijevych, Carbone, Lang, Nesbitt et al.)
-   MCSs are a dominant mode of convection with respect to rainfall production; they develop in the evening from smaller, afternoon convective cells; a secondary MCS peak occurs along the coast due to the land breeze; MCSs are favored in the northerly phase of easterly waves (Lang et al.)
-   MCSs have complicated organizational structure; convective cores often have large hail (~2 cm) (Lang et al.)

-   Gulf surges do not significantly modulate convection in the S-Pol radar domain (at least for NAME 2004), but this result may be a consequence of a limited-domain analysis

## Precipitation Characteristics (cont.)

-   Coastal 0-500 m elevation band west of SMO has greatest precipitation intensities as systems propagate westward from SMO (87-station NERN network; Gochis et al.)
-    Lower elevations have greater amplitude in the rainfall intensity over diurnal cycle than high elevations
-    Similar diurnal cycle of precipitation frequency E and W of SMO, although afternoon maximum in E is slightly less
-   During NAME, values of short duration, heavy precipitation amounts are typical of those found in tropical environments (> 100 mm h-1)
-   Heaviest rainfall at longer time scales concentrated near GoC coastline; frequency of light-rain days highest over crest of SMO
-   Rainfall peak shifts westward with time west of SMO crest (westward propagation, consistent with radar results)
-   Impact of NERN on 0.25o CPC gridded analysis is substantial

## Precipitation Characteristics (cont.)

-   CMORPH shows westward movement of precipitation ~5 m s-1 near 28oN; westward motion is most prominent in band from 25-29oN (Becker, Berberry)

## Marine Boundary-Layer/Ocean Characteristics

-   R/V *Altair* results (Fairall)
-   *R/V Ulloa* results (Lavin, Cavazos, M. Douglas)

- Top of MBL grew in afternoon (~500 to 800 m); diurnal cycle of 2-cm T ~2-3oC; multiple inversion layers above MBL
- Maximum precipitation typically at ~07-08 L; cloud fraction greatest at night
- SST cooling after TS Blas
- Strong sea breeze effects observed (80 km from land)
- Ocean is saltier near surface (little precipitation)

- Much of the heating of the GoC occurs via advection of warmer water from the south
- During 5-21 June cruise, MBL was very shallow (~300 m), with multiple inversions above; MBL deeper during 2nd cruise (August)

## Monsoon Onset, Advance

-   Earliest onset (7-10 July, IOP1) over northern Tier 1 associated with weak upper-level vortex (best seen in water vapor imagery) passing across region and to west of Baja; minor surge developed in northern GoC
-   Primary monsoon onset in SW US associated with passage of Tropical Storm Blas to south of Tier 1; strong surge developed over northern GoC

-   Dramatic surface dew point rises over Sonora accompanying onset (A. Douglas, Cortez)
-   Negative correlation between surface T and day of year at low elevations on west slope of SMO (influence of vegetation “green-up”) (A. Douglas, Cortez); fluxes associated with green-up documented at 8 flux sites (Watts et al.)
-   Rainfall at inland sites (west of SMO) peaks in July, at coastal sites in August (M. Douglas)

## Gulf of California Surges

-   Two strong gulf surges during early period of monsoon (12-13, 22-23 July)  [Rogers, Novella, A. Douglas, M. Douglas, Johnson)
-   P-3 observations of surges indicate maximum winds and moisture transport over gulf waters; peak winds near 925 hPa (M. Douglas)
-   Additional weaker surges occurred, typically over the northern gulf in association with convective outflows
-   Surges minimally detectable at Los Mochis, but are sharp features in northern GoC (at Bahia Kino and Puerto Peñasco)

-   Nocturnal in character (amplified by nocturnal LLJ)
-   Triggered by convective outflows from MCSs
-   Associated with tropical cyclone, upper-level trough passage
-   Wind speeds strongest in northern gulf (up to 20 m s-1)
-   Rapid propagation of leading edge (~20 m s-1), surface pressure jumps suggest atmospheric Kelvin wave/bore dynamics, but results are preliminary

## Gulf of California Surges

-   Precipitation over Arizona region is strongly correlated with surges in 2004 based on CMORPH and Eta model (Becker, Berberry)
-   Effect of surges on total precipitation is greater in AZ than in core NAME region over Mexico
-   Additional findings from P-3 flights?

## Mesoscale Circulations, Diurnal Cycle 

-   Land/sea breeze circulation documented by 915-MHz wind profiler at Estacion Obispo, Sinaloa (25 km inland); sea breeze: onshore flow to 1 km, winds aloft more southerly; land breeze: weak at low levels, upper levels show more transience (Hartten)
-   Prominent nocturnal low-level jet over northern GoC; jet weakens toward the south and is virtually absent at Los Mochis (Johnson et al.; M. Douglas)

-   LLJ winds appear to be strongest over the center of the GoC away from topography indicating that the jet does not appear to be generated by classical ‘terrain slope-jet’ dynamics (M. Douglas)
-   QuikSCAT winds show bifurcation of northwesterly flow around southern Baja, with frequent pattern of cold advection at mouth of GoC
-   Depth of coastal sea breeze return flow aloft to the west of SMO is deeper than normal sea breeze over flat terrain

## Synoptic Circulations

-   Synoptic circulations (easterly waves, upper-level inverted troughs, midlatitude troughs, cut-off lows, tropical cyclones, etc.) affect rainfall in NAME region (A. Douglas et al.; 1967-2001 study; Higgins; Stensrud; many others)
-   During NAME 2004, cold fronts affecting the region were well above normal (twice as frequent as 35-year mean); inverted troughs were below normal
-   Inverted troughs (upper troposphere) contribute to 20-30% of total rainfall for 35-year mean; 10-25% for the 2004 year
-   Rainfall peaks 3-4o to the west of axis of inverted trough
-   Cut-off lows in 2004 were near long-term mean; open troughs were above normal

## Other Topic Areas

-   Synoptic circulations (easterly waves, upper-level inverted troughs, midlatitude troughs, tropical cyclones, etc.)
-   Surface-atmosphere exchanges (fluxes over land, ocean; evapotranspiration)

## Specific Objectives1.  Core monsoon region

-   How are low-level circulations along the Gulf of California / west slopes of the Sierra Madre Occidental related to the diurnal cycle of moisture and convection?
-   What is the relationship between moisture transport and rainfall variability (e.g. forcing of surge events; onset of monsoon details)?
-   What is the typical life cycle of diurnal convective rainfall?  Where along the western slope of the Sierra Madre Occidental is convective development preferred?
-   What are the dominant sources of precipitable moisture for monsoon precipitation over southwestern North America?
-   What are the fluxes of energy and water from the land surface to the atmosphere across the core monsoon region, and how do these fluxes evolve in time during the warm season?

- What is the structure and diurnal variation of the PBL, land/ocean?

## Specific Objectives2.  Regional scale

-   How important are interactions between Tropical Easterly Waves, upper-level inverted troughs, cold fronts, cut-off lows, open troughs, and Gulf of California moisture surges in the prediction of  monsoon precipitation?
-   What is the nature of the relationship between the MJO, tropical cyclone activity and monsoon precipitation?
-   What portion of the skill of summer precipitation forecasts, in addition to that already harvested from ENSO, will arise from an ability to forecast MJO activity over a season?
-   What is the physical setting for the bimodal distribution (i.e. wet-dry-wet) in warm season precipitation over Mexico and Central America and what factors influence its interannual variability?

## Specific Objectives3.  Continental scale

-   How is the evolution of the warm season precipitation regime over North America related to the seasonal evolution of the boundary conditions?
-   What are the interrelationships between year-to-year variations in the boundary conditions (both land surface and adjacent sea surface), the atmospheric circulation and  the continental hydrologic regime?** **
-   What are the links, if any, between the strength of the summer monsoon in southwestern North America and summertime precipitation over the central United States?
-   Can numerical models reproduce the observed summer precipitation in average years and years with ENSO/PDO influence?
-   How much of the seasonal predictability of large-scale warm season precipitation anomalies can be downscaled to local precipitation variability?

-   What are the relationships between extreme weather events (e.g. floods, droughts, heat waves, hurricanes), climate variability and long-term trends?